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07:40-08:30 Session 8: Biomechanics I
Location: Main Auditorium
No Changes in Bone Mineral Density Following Total Knee Arthroplasty Using an All Polyethylene Tibial Component
PRESENTER: Alistair Ewen

ABSTRACT. Polyethylene particles produced in metal backed tibias (MBT) are understood to contribute to bone loss and component loosening. This, and better surgical techniques (including computer navigation) and increasing costs have renewed interest in all poly tibias (APT). We investigated peri-APT bone mineral density (BMD) in patients; expecting to find no differences between two post-operative values. Patients over 65 years, with BMI ≤ 37.5 and no previous joint replacements were recruited to have TKA using the Columbus APT with computer navigation (OrthoPilot). The study cohort (n=26) had a mean age of 71.9 (sd 4.35), a BMI of 31.2 (sd 3.8). The BMD examinations were performed six weeks and 18 months post-operatively. Six regions-of-interest (ROI) were identified on anterior/posterior and lateral scans. For each ROI at each time point, relative BMD differences (RDs) were determined between limbs and RDs at the two time points were compared. No differences were found between the two RDs for any ROI. No revisions or complications were reported. At 18 months post-operatively, 78.3% of the cohort were “very satisfied” with the outcome of their surgery and Oxford Knee Scores improved significantly compared to pre-operatively (p<0.005). Mean knee range of motion was 102° (sd 10.7◦) and mean leg alignment was 2.0° valgus (1°varus-6°valgus). Results from BMD suggest that implants were well fixated. Patients reported excellent satisfaction and function. We believe that using APTs and computer navigation is a viable and cheaper option to MBT for patients who are less active, have lower BMI and good bone quality.

Metal Artifact Reduction for Orthopaedic Implants of Known Design

ABSTRACT. This work reports and evaluates a method for metal artifact reduction (MAR) in intraoperative cone-beam CT that exercises prior information on surgical instrumentation, such as spine pedicle screws and deformable fixation rods. The known-component MAR (KC-MAR) approach achieves precise localization of instrumentation in projection images using rigid or deformable 3D-2D registration of component models, thereby overcoming residual errors associated with conventional segmentation-based methods. Cadaver studies emulating screw and rod placement in spinal deformity correction were conducted to evaluate performance under realistic imaging conditions. Metal artifacts (standard deviation in voxel values) associated with spine screws and rods were reduced by 40–80%, and the resulting images demonstrated markedly improved visualization of instrumentation (e.g., screw threads) within cortical margins. A single-pixel dilation of the projected components was found to compensate for partial-volume effects. The approach is compatible with a variety of 3D image reconstruction, including filtered back-projection (maintaining speed and simplicity) or more advanced model-based iterative reconstruction methods that could further improve image quality and reduce radiation dose.

Statistical Shape Modeling Approach to Predict Missing Scapular Bone: Applications in Pre-Surgery Planning and Modeling

ABSTRACT. Shoulder joint replacement is regarded as a safe and effective procedure to relieve pain and help resume daily activities. However, successful surgical outcome relies on understanding subject-specific pre-morbid scapular shape as well as pre-morbid shoulder biomechanics. Current pre-planning tools lack the ability to reconstruct pre-morbid scapular shape whereas shoulder models often cannot use the missing information in clinical images. Thus, the aim of this study was to predict the pre-morbid and complete shape of the scapula bone by building a probabilistic principal component analysis based statistical shape models (SSM) of scapular bone and by using a reconstruction algorithm developed specifically for this SSM. Scapula SSM was developed using 66 dry bone shapes. An SSM-based reconstruction algorithm was developed to predict complete scapular shape from a virtually created partial shape information on ten scapular bone shapes. Partial shapes represented defects in the glenoid region (group-1), superior (group-2), and inferior (group-3) region of the scapula. Predicted shape was evaluated for its accuracy for anatomical, distance and similarity measures. Evaluation of predicted shapes revealed moderate to excellent outcomes. RMS distances ranged between 1.21 to 1.29, mean distances ranged between 0.91 mm to 0.96 mm in all groups. Anatomical angle errors ranged from 1.20° (Glenoid version, group-2) to 2.73° (Glenoid version, group-2). Similarity index was also found excellent (≥0.80) in all the groups. Results in predicting anatomical measures were encouraging and better than recently reported predictions for Wallace type I defect in the glenoid region. Further, accurate critical shoulder angle predictions and higher similarity coefficients would lead to better subject-specific prediction of muscle origins and insertions in shoulder modeling studies. In conclusion, this study illustrated that predicting missing scapular shape employing SSM tools can be used in clinical settings and can have strong applications in surgery pre-planning as well as shoulder biomechanics modeling.

The Best Bone of Acetabulum for Cup Component Placement in Total Hip Arthroplasty in Patients with Crowe Type I-III Dysplastic Hips: a Computer Simulation Study

ABSTRACT. For cup implantation in dysplastic acetabulum, the vertical height of the cup center (V-HCC) should be carefully and precisely controlled in order to achieve sufficient host bone-cup coverage (BCC), but excessively superior placement of the cup should be avoided. Using computer software, pelvis models were separately reconstructed in 51 patients (61 hips) with severe osteoarthritis secondary to Crowe type I-III hips. Acetabular height and doom thickness were measured on the mid-acetabular coronal cross section. V-HCC was defined as the vertical distance from the cup center to the interteardrop line (ITL).  In the cup implantation simulation, the cup was placed at the initial preset position, with a V-HCC of 15 mm, and moved proximally by 3-mm increments. At each level, the BCC was automatically calculated by computer. There were no significant between-group differences in maximum thickness of the acetabular doom; however peak bone stock values were obtained at heights of 41.63 mm ± 5.14 mm (Crowe type I), 47.58 mm ± 4.10 mm (Crowe type II), and 55.78 mm ± 3.64 mm (Crowe type III) above the ITL. At 15 mm of HCC, BCC was 79%±7% (Crowe type I), 74%±9% (Crowe type II), and 61%±6% (Crowe type III). In order to achieve 80% of the BCC, the evaluation distance was 1.33 ± 1.62 mm (95% CI 0.67–2.01), 3.32 ± 2.94 mm (95% CI 1.94–4.69), and 9.68 ± 3.91 mm (95% CI 7.60–11.77) for Crowe type I, II, and III hips, respectively. Acetabular bone stock for cup placement correlates with the degree of hip dysplasia in patients. During acetabular reconstruction in Crowe type I, II, or III hips, slightly superior placements, <25 mm from the ITL, retained sufficient bone coverage.

Improved Preservation of Posterior Cruciate Ligament Function with Robotic-Arm Assisted Total Knee Arthroplasty
PRESENTER: Ormonde Mahoney

ABSTRACT. Robotic-arm assisted (RA) total knee arthroplasty (TKA) offers protection of peri-articular tissues. We asked whether the (PCL) would be effectively preserved in knees using a robot to establish a safe boundary around the ligament. 77 patients were enrolled into a prospective multi-center study of conventional instrumentation (33) vs. RA (44) for TKA from July 2016 to Feb 2018. Rollback was measured radiographically at 6 weeks and using intra-op robotic 3D modeling at 90 degrees. Passive knee flexion was also measured. We hypothesized that: knees with well-preserved PCL would demonstrate increased rollback and flexion. We used linear correlation (Pearson’s) to characterize bivariate correlations, two-sample t-tests to test for between-group differences of means, and ordinary least squares regression with an interaction term to compare regression lines between groups. The RA group showed strong correlation of flexion with rollback (r=0.63, p<0.001) while the conventional group showed none (r=0.00, p=0.998). The regression lines were different (slope, p=0.004; intercept, p=0.005). Within the RA group, linear correlation of femoral rollback with intra-operative maximum flexion was seen (r=0.35, p=0.037). The RA group showed 8 deg greater mean flexion 6 weeks after surgery (p=0.031). This is the first study to demonstrate the ability of RA surgery to improve resulting kinematics in TKA. The RA group showed a pattern consistent with physiologic rollback while the conventional instrument group did not. Increased femoral rollback was associated with greater knee flexion after implantation. The RA group showed greater average knee flexion at short-term follow-up.

08:30-09:30 Session 9: Hip I
Location: Main Auditorium
The Uncertainty of Planning Revision Hip Surgery in the Presence of Metal Artefacts
PRESENTER: Alister Hart

ABSTRACT. CT image quality is affected by metal artefacts deriving from orthopaedic implants. We aimed to better understand the impact of retained metal implants on bone image quality in CT-based planning of revision hip surgery. This was a pilot study involving eight patients requiring acetabular reconstruction surgery (beyond Paprosky 3B). Patients underwent two-stage revision surgery to allow imaging of the pelvis following the removal of the failed conventional implants for the design of a bespoke 3D-printed titanium implant. CT scans of their pelvises were taken pre- and post-implant removal. Comparisons of the reconstructed hemi-pelvises were made by assessing differences in bone morphology and stock. The virtual 3D-CT bony models changed in all cases between the initial CT (with implant) and that taken following the first stage scan (without implant). Three cases (37.5%) showed a remarkable difference in the remaining bone that led to a change in implant design. We noted a prevalence of areas of the medial acetabular wall missing from the interval 3D reconstruction (post-implant removal) whereas acetabular rim definition was not clear on the 3D reconstructions derived from pre-implant removal scans. The volume of the innominate bone (at the defect size) on pre-implant removal and on post-implant removal CT reconstructed virtual models did not differ significantly, (p=0.93). The bony anatomy seen on imaging of patients with an implant in situ is affected by metal artefacts. This, together with the bone excised at surgery, can have a direct impact on the design of custom revision implants.

The Accuracy of Pre-Operative 3D-CT Planning and Its Impact on Hip Implant Inventory Size: a Prospective Study.
PRESENTER: Johann Henckel

ABSTRACT. Modern designs of joint replacements require a large inventory of components to be available during surgery. Pre-operative CT imaging aids three dimensional (3D) surgical planning and implant sizing, which should reduce the inventory size. We aimed to better understand the impact of 3D surgical planning on hip implant inventory. An initial feasibility study (25 consecutive cases) was undertaken to assess the discrepancy between the planned component sizes and those implanted to determine whether it was possible to reduce the inventory for future cases. Following this, we performed a pilot study to investigate the effect of an optimized inventory stock on the surgical outcome: we compared a group of 20 consecutive cases (experimental) with the 25 cases in the feasibility study (control). Outcome measures were: (1) accuracy of the 3D-CT planning system in predicting size (%); (2) inventory size changes (%); (3) intra and post-operative complications. The feasibility study showed variability within 1 size range, enabling us to safely optimize inventory size for the pilot study. (1) 3D-CT planning correctly predicted sizes in 93% of the femoral and 89% of the acetabular cup components; (2) there was a 61% reduction in the implant inventory size; (3) we recorded good surgical outcomes with no difference between the 2 groups, and all patients had appropriately sized implants. 3D planning was accurate in >80% of cases; greater than that reported for 2D templating. 3D-CT planning can safely reduce inventory size by up to 61%, leading to a reduction in costs.

Total Hip Arthroplasty Training in Virtual Reality Transfers to the Real-World a Randomized Blinded Study

ABSTRACT. Background Virtual Reality (VR) uses headsets and motion-tracked controllers so surgeons can perform simulated total hip arthroplasty (THA) in a fully-immersive, interactive 3D operating theatre. The aim of this study was to investigate the effect of laboratory-based VR training on the ability of surgical trainees to perform direct anterior approach THA on cadavers.

Methods Twenty-four surgical trainees (PGY1-4) with no prior experience of anterior approach (AA) THA completed an intensive 1-day course (lectures, dry-bone workshops and technique demonstrations). They were randomized to either a 5-week protocol of VR simulator training or conventional preparation (operation manuals and observation of real surgery). Trainees performed DAA-THA on cadaveric. Performance was measured on a nationally validated procedure-based assessment (PBA) of THA, on a 9-point global rating score. Trainees were independently assessed by 2 hip surgeons blinded to group allocation. The secondary outcome measure was error in cup orientation from a predefined target (40° inclination and 20° anteversion).

Results Surgeons trained using VR performed a cadaveric DAA-THA significantly better than those using conventional preparation, as assessed by acetabular cup orientation (p<0.001) and using the PBA. Three VR surgeons achieved Level 3b (performed competently without guidance or intervention but lacked fluency), 7 were graded at Level 3a, and 2 was graded at Level 2b. Seven non-VR surgeons achieved Level 2a (Guidance required for most/all of the procedure) and 5 were graded at Level 1b.

Discussion These data demonstrate transfer of procedural knowledge and psychomotor skills learnt from VR to a real-world setting. Conventional preparation had limited value for novice surgeons learning arthroplasty. VR can augment surgical training for open procedures in orthopedics, so opportunities in real surgery can be maximized. This has implications for how surgical training is delivered for surgeons learning a new, complex procedure.

Pelvic Incidence Cannot Be Used to Predict Pelvic Sagittal Tilt in the Supine and Upright Positions
PRESENTER: Makoto Iwasa

ABSTRACT. Background Pelvic incidence (PI) is a morphological parameter that is specific to each subject. The purposes of this study were to: 1) quantify PI in a large cohort and to investigate the factors that relate to PI, and 2) investigate the relationship between PI and the pelvic sagittal tilt (PST) in the supine and upright position Materials and methods A total of 461 patients who underwent hip surgery were the subjects of this study. PI was measured using preoperative computed tomography (CT) images. Factors such as sex, age, and hip diseases were analyzed if they were related to PI. Pelvic tilt (PT) and sacral slope (SS) in the supine position were also correlated to PI. To investigate the relationship between PI and PST, PST was defined as the tilt of the anterior pelvic plane. Anterior tilt of the pelvis was set as a positive angle. After the PST in the supine and upright position was quantified, PST was correlated to PI to analyze the relationship. The correlation between PI and the change in PST from supine to upright position was also assessed. All statistical analysis was performed using JMPR 14 (SAS Institute Inc., Cary, NC, USA). P values of <0.05 were considered to be statistically significant. Results The mean±standard deviation (SD) of the PI for all patients was 53.0±10.8°. When compared between sex, age groups, and hip diseases, there were no significant differences (p=0.15, 0.22, and 0.81, respectively). PT and SS in the supine position was 9.9±7.5° and 43.1±8.7°, respectively. Both were significantly correlated with PI (PT: r=0.60, p<0.01 and SS: r=0.73, p<0.01). PST changed from 4.6±6.9° (supine) to -1.7±9.3° (upright) when changing positions, and the amount of change was -6.2±5.2°. When PST in the supine and upright position was correlated to PI, no significant correlation was found (p=0.20 and 0.35, respectively). Change in PST from supine to upright position was also not correlated with PI (p=0.96). Conclusions PI was not correlated with sex, age and hip diseases. Further, PI was not correlated with PST in the supine and the upright position. Change in PST from supine to upright position was also not correlated with PI. Collectively, these results indicate that PI is a parameter that is independent of sex, age, and hip diseases and has no effect on PST. Thus, the clinical relevance to correlate PI with PST seems unclear.

Mobile-Based Cognitive Training for Direct Anterior Approach Total Hip Arthroplasty: a Randomised Controlled Study

ABSTRACT. Background Total hip arthroplasty (THA) is a complex skill; cognitive training prior to performing real surgery may be shorten its learning curve. This study sought to create a cognitive training mobile app to perform direct anterior approach THA; and test its use as a training tool compared to conventional material.

Methods Four experts were independently observed performing THA before undergoing semi-structured cognitive task analysis (CTA) before completing successive rounds of electronic surveys until Delphi consensus. The agreed CTA was incorporated into a mobile app (Touch Surgery). Thirty-six surgical trainees (PGY3-6) were randomised to CTA-training or a standard op-techs with surgical video, before performing a simulated DAA THA.

Results Experts reached 100% consensus after five rounds. They defined THA 11 phases, each comprising basic steps, cognitive demands, and critical errors and strategies. This CTA was mapped onto an open-access mobile app.

Trainees who prepared with CTA performed a simulated THA more efficiently (Time: 26 vs. 36 minutes), with fewer errors in instrument selection (29 vs 49 instances) and help required (13 vs. 25 instances), and with more accuracy (acetabular inclination error: 10° vs. 8°, anteversion error: 14° vs 22°) than those who prepared with conventional material.

Discussion This is the first validated CTA tool for arthroplasty, combining education on decision making, knowledge and technical skill in an open-access app. It is more effective at preparing orthopaedic trainees for a new procedure than conventional materials. It should be used as an adjunct alongside simulation for preparing trainees for real surgery.

Comparison of Clinical Outcomes After Total Hip Arthroplasty with and Without Computed Tomography-Based Navigation System for Osteonecrosis of the Femoral Head: a Propensity Score Matched Analysis
PRESENTER: Kazuma Takashima

ABSTRACT. Background This study aimed to investigate whether use of a computed tomography (CT)-based navigation system reduce the risk of dislocation after total hip arthroplasty (THA) in patients with osteonecrosis of the femoral head (ONFH). Materials and methods This study included 271 hips from 192 consecutive patients that underwent primary THA for ONFH. There were 110 hips in non-navigation group, and 161 hips in navigation group. After applying exclusion criteria, 209 hips from 149 patients were selected for this study. Clinical outcomes and complication rates were evaluated, and implant alignments were also calculated. To identify whether the navigation system was useful to prevent dislocation, the inverse probability of treatment weighted Cox regression analysis using a propensity score in relationship to sex, age at surgery, body mass index, and femoral head size was performed. Results No significant difference was observed in clinical scores between both groups. Dislocation was significantly lower in the navigation group (3 hips, 2.7%) than in the non-navigation group (11 hips, 11.2%; p = 0.012), whereas periprosthetic joint infection and aseptic loosening did not differ between the groups. Variance of cup anteversion and inclination angles was smaller in the navigation group than in the non-navigation group (anteversion, p < 0.001; inclination, p < 0.001). Use of the CT-based navigation system (HR; 0.26, 95% CI, 0.07–0.98; p = 0.047) turned out to be the predictor for preventing dislocation. Conclusions Use of the CT-based navigation system provided a precise placement of components, and thus help prevent dislocation in patients with ONFH in the propensity score analysis.

09:30-10:30 Session 10: Knee I
Location: Main Auditorium
The Extension Planning Angle in Gap-Balancing Total Knee Arthroplasty Influences Mid-Flexion Laxity
PRESENTER: Sami Shalhoub

ABSTRACT. Gap balancing in full extension versus slight flexion may produce different results due to the varied interaction of the posterior knee structures and posterior capsule. We therefore compared post-operative TKA laxity throughout the flexion range for knees that were gap-balanced at 0 versus 10 degrees of flexion. Forty patients (mean age: 71±10, BMI: 28.6±7.7) undergoing robotic-assisted TKA were retrospectively reviewed. The tibia was resected in neutral alignment and the knee joint was tensioned with 80-100N per side using a computer-controlled ligament tensioning tool. Femoral implant resections were then planned to produce equal and symmetric knee gaps at either 0° (Group-0, 18 knees) or at 10° (Group-10, 22 knees) of flexion, and at 90° flexion. The femur was resected, a femoral trial was inserted, and the postoperative gaps were measured throughout the ROM while the tensioner applied equal tension to the ligaments. Mean and standard deviation of the post-operative gaps were calculated for each group. T-tests were used to identify significant differences between the two groups. In both Group-0 and Group-10, medial and lateral postoperative gaps were balanced within 1 mm of each other throughout the range of flexion (P>0.X). However, postoperative gaps were significantly larger in Group-0 by 1.3 mm to 2.2 mm from 0o to 80o (p<0.03). Gaps at 0o extension were 1.3 mm tighter in Group-B (p=0.03). Final knee extension achieved with the trial component was equivalent Gap planning at 10o of flexion produced equal and symmetric gaps from 10-90o that were similar in patterns to those reported in the native knee. Gap planning at 10o resulted in smaller gaps and increased tension at full extension, however, which may result in a flexion contracture requiring a posterior capsule release or distal femoral recut to achieve full extension. Planning at 0o resulted in larger gaps and lower joint forces at full extension, but increased knee laxity in mid-flexion which may contribute to mid-flexion instability. Depending on the clinical circumstances of the case, the implications of planning at both 0o and 10o in gap balancing TKA should be taken into consideration.

Robotic-Assisted TKA Can Predict and Achieve Accurate Post-Operative Ligament Balance

ABSTRACT. Achieving balanced gaps is a key surgical goal in total knee arthroplasty (TKA), yet most methods rely on subjective surgeon feel and experience to assess and achieve knee balance intra-operatively. Our objective was to evaluate the ability to quantitively plan and achieve a balanced knee throughout the range of motion using robotic-assisted instrumentation. A robotic-assisted gap-balancing technique was utilized in 121 knees. Predicted gap profiles were used to plan the femoral implant position within certain alignment boundaries to achieve a balanced knee throughout the range of flexion. Femoral cuts were then made according to this plan. A computer-controlled tensioning device used to measure the pre-operative gaps used in the prediction algorithm was inserted into the joint to quantify the final gap balance under known tension, and the final gap profiles were compared to the predictive gap plans. The overall RMS error between the predicted and achieved gaps was 1.3mm and 1.5mm for the medial and lateral side, respectively. Use of robotic-assistance resulted in over 90% of knees having mediolateral balance within 2mm across the flexion range. Gaps at 0° flexion were 2mm smaller than the gaps at 90°. This is difference decreased to less than 1mm when comparing the tibiofemoral gaps at 10°, 45° and 90°. Robotic-assisted TKA could accurately predict post-operative gaps prior to femoral resections. This allows surgeons to virtually plan femoral implant alignment to optimize soft-tissue balance throughout a range of motion. The predictive gap capabilities and high bone resection accuracy of robotic-assisted TKA resulted in post-operative balance in most cases.

How Surgeons Perform Total Knee Arthroplasty? a Global Appraisal of Computer-Assisted Surgeries

ABSTRACT. This study investigated global variations in the surgical methods used with a contemporary CAOS system in TKA. Individual surgical profiles were identified from a database of technical reports on all TKA cases performed using a CAOS system. The profiles were divided into groups based on geographic regions (US, EU, and APAC), implant types (CR and PS), and application years. Differences were found in the surgeons’ preferences of surgical parameters and methods, reflecting the existence of variabilities in how surgeons perform TKA.

Can Standard Implants Reproduce the Native Kinematics of a TKA Patient?

ABSTRACT. Total knee arthroplasty (TKA) is a reliable surgical procedure, yet up to a fifth of primary implant patients remains unsatisfied. One of the most common procedures in TKA focuses on achieving good alignment of the mechanical axes, which not always results in the desired functional outcome for the patient. Therefore, new approaches as soft-tissue balancing and kinematics alignment have been emerging. Although pre-operative planning tools were recently introduced to support the surgeon in obtaining mechanical alignment, these planning tools do not support these new approaches yet. A patient-specific musculoskeletal model (MSM) that predicts kinematics and ligament length elongations when squatting, for both pre-TKA and post-TKA knees, was used in this study. Kinematics and ligament elongations were calculated for a combination of implant positions, as well as for the native knee. The results were used to determine the optimal implant position, defined as the positions with the smallest error between the pre-TKA and the post-TKA kinematics and ligament elongations. Then, those results were compared with the results of the mechanical alignment technique. We conclude that the presented modelling approach is a promising candidate for allowing surgeons to evaluate the patient-specific implant alignment and restore the patient-specific biomechanics. The current method provides a solid starting point to enhance the integration of computational models into clinical practice and evolve towards a patient-specific optimized approach.

Improved Bone Preservation with Restoration of Joint Line in Robotic-Arm Assisted Total Knee Arthroplasty
PRESENTER: Ormonde Mahoney

ABSTRACT. Optimal technique should include the smallest tibial resection required to achieve stable fixation without raising the joint line. We asked: does the precision available with robotic-arm assisted (RA) total knee improve the accuracy of restoring the joint line with preservation of tibial bone? 77 patients were enrolled consecutively into a cohort study of conventional (33) vs. RA (44) for TKA from July 2016 to Feb 2018. Resection depth was set 9 mm below the non-deformed side of the tibia. Resections were measured using a caliper. Bone removed included resection thickness plus sawblade width (1.27 mm conventional, 2.00 mm RA). We also calculated bone removed from and net change in extension and 90 deg flexion. We used two-sample t-tests for between-group differences of means, and Wilcoxon Rank-sum and chi-square tests for ordinal and categorical variables with alpha = 0.05. More bone was removed from the medial side of the tibia with conventional instrumentation (1.5 mm difference, p=0.011). Medial bone removed was greater using conventional instrumentation (mean differences, 1.6 mm in extension (p=0.023), and 1.2 mm in 90 deg flexion (p=0.051). Both restored joint lines (mean (range) net change -0.6 (-3, +3) mm and -0.2 (-3, +4) mm p=0.349). Greater tibial thickness was used with conventional instrumentation (mean difference 1.1 mm, p=0.005). This is the first study to describe the ability of RA TKA to improve seating the tibia on stronger proximal bone while restoring the joint line. RA allowed use of the thinnest component the majority of the time (52% vs. 24%, p=0.011).

Robotic Total Knee Arthroplasty Is Associated with Improved Early Functional Recovery and Reduced Time to Hospital Discharge Compared with Conventional Jig-Based Total Knee Arthroplasty: a Prospective Cohort Study
PRESENTER: Babar Kayani

ABSTRACT. Purpose: Robotic assisted surgery enhances postoperative rehabilitation in urology, cardiology, and general surgery, but the effect of this technology on knee arthroplasty has not been previously reported. The objective of this study was to compare early postoperative functional outcomes and time to hospital discharge between conventional jig-based total knee arthroplasty (TKA) and robotic TKA.

Patients and Methods: This prospective cohort study included 40 consecutive patients undergoing conventional jig-based TKA followed by 40 consecutive patients receiving robotic TKA. All surgical procedures were performed by a single surgeon using the medial parapatellar approach with identical implant designs and standardized postoperative inpatient rehabilitation. Inpatient functional outcomes and time to hospital discharge were collected in all study patients.

Results: There were no systematic differences in baseline characteristics between the conventional jig-based TKA and robotic TKA treatment groups with respect to age (p=0.32), gender (p=0.50), body mass index (p=0.17), ASA score (p=0.88), and preoperative haemoglobin level (p=0.82). Robotic TKA was associated with reduced postoperative pain (p<0.001), decreased analgesia requirements (p<0.001), decreased reduction in postoperative haemoglobin levels (p<0.001), shorter time to straight leg raise (p<0.001), decreased number of physiotherapy sessions (p<0.001) and improved maximum knee flexion at discharge (p<0.001) compared with conventional jig-based TKA. Median time to hospital discharge in robotic TKA was 77 hours (IQR 74 to 81) compared with 105 hours (IQR 98 to 126) in conventional jig-based TKA (p<0.001).

Conclusion Robotic TKA was associated with decreased pain, improved early functional recovery and reduced time to hospital discharge compared with conventional jig-based TKA.

11:00-11:30 Session 11: Presidential and Keynote Addresses
  1. 11:00 - 11:10: Inaugural Presidential Address - Patrick Meere
  2. 11:10 - 11:20: Q&A Session on Business Future of Advanced Technology - Ken Langone
  3. 11:20 - 11:30: Keynote Address on Soft Robotics in Medicine: Origins & Future Prospects - Carmel Majidi
Location: Main Auditorium
11:30-12:30 Session 12: Robotics I
Location: Main Auditorium
Robotic-Arm Assisted Unicompartmental Knee Arthroplasty: Mid-Term Survivorship and Patient-Reported Outcomes from a Single Surgeon
PRESENTER: Joost Burger

ABSTRACT. Studies are lacking on mid-term outcomes of robotic-arm assisted (RA) unicompartmental (UKA). Therefore, the aim of this study was to evaluate five-year survivorship, modes of failure and patient-reported outcomes of RA UKA. A retrospective review of RA UKA patients between June 2007 and August 2016 was performed. Patients received a fixed-bearing metal-backed onlay medial or lateral UKA. Patients were contacted and asked to complete a questionnaire regarding revision surgeries, reoperations, level of satisfaction, and the Knee Injury and Osteoarthritis Outcome Score Junior survey (KOOS, JR). Mean follow-up was 4.5 years. Five-year survivorship of medial UKA (n=742) and lateral UKA (n=171) was 98.4% and 97.7%, respectively. Component loosening and progression of OA in the unoperated compartment were the most common reasons for revision (n=8). Average KOOS scores after medial UKA and lateral UKA were 84.6 and 85.6, respectively. The majority of the patients were satisfied with their knee function (medial UKA patients: 91.0% and lateral UKA patients: 92.6%). In addition, 91.9% of the medial and 92.6 % of lateral UKA patients would choose to undergo the surgery again. This study showed excellent mid-term survivorship and patient-reported outcomes in medial and lateral UKA, using robotic-arm assisted surgery. When comparing our survivorship with other recent large studies, reporting outcomes of fixed-bearing UKA, the use of robotic assistance appears to result in higher mid-term survivorship than conventional techniques. However, comparative studies are necessary to further evaluate this.

The Learning Curve and Alignment Assessment of an Image-Free Handheld Robot in TKA: the First Patient Series in Europe
PRESENTER: Peter Bollars

ABSTRACT. BACKGROUND: The typical goal of TKA is to obtain a neutral mechanical axis of the leg. The NAVIO® Surgical System (Smith & Nephew, Pittsburgh, PA, USA) is aimed at reducing technical errors and outliers. The aim of this study is to assess the surgeons’ learning curve and limb alignment in TKA. METHODS: The first sixty-nine patients who underwent TKA with the NAVIO system by two experienced surgeons were included in this study. Pre- and postoperative mechanical limb alignment and balancing was measured by the NAVIO system. Registration time, planning time and cutting time was monitored preoperatively by the NAVIO™ system. All data was analyzed retrospectively. RESULTS: The mean preoperative mechanical limb alignment was 3.18° varus (SD 4.28°, range 15.08° varus to 4.30° of valgus). The mean intraoperative planned angle was 0.59° varus (SD 0.97°, range 2.50° varus to 0.99° valgus). The mean postoperative alignment was 1.17° varus (SD 1.78°, range 4.52° varus to 4.33° valgus. The mean extra surgical time (EST) for registration and planning decreased from 23.4min (SD 3.7min) to 13.2min (SD 2.0) throughout the learning curve with a range of 10min05sec to 28min19sec.CONCLUSION: The NAVIO robotic system is a valuable tool in assisting total knee arthroplasty. It allows the surgeon to accurately determine optimal implant position for each patient and minimize statistical outliers in alignment.

Image-Guided, Calibration-Free Robotic K-Wire Placement for Pelvic Fracture Surgery

ABSTRACT. An x-ray image-guided robotic instrument positioning system is reported for use in K-wire and screw placement in pelvic fracture surgery. The approach uses the known-component registration (KC-Reg) algorithm to register a 3D patient CT and the robotic end effector (a surgical drill guide) to two (AP/LAT) intraoperative 2D radiographs, which can be used to drive the robotically held instrument to target trajectories defined in the CT. Experiments in a pelvis phantom compared an approach that assumes prior geometric calibration and encoded motion of the imaging system against a novel, “calibration-free” workflow that uses the patient anatomy to establish the epipolar geometry necessary to solve for the robot end effector pose. Both workflows were able to deliver trajectories (16 K-wires) without breach of the pelvic cortex, with no statistically significant difference between the two approaches. Accuracy of placement was measured to be ~2 mm and 2° with respect to the planned trajectory, comparable to the accuracy achieved using stereotactic navigation systems. The proposed solution offers to extend robotic assistance to simple imaging systems (e.g., common mobile fluoroscopic C-arms) that lack encoded motion control or do not support reliable geometric calibration. X-ray guidance offered accurate positioning of the robotic drill guide and could fit naturally with clinical workflow of fluoroscopically guided procedures using images already acquired in routine practice.

Learning Curve in Active Robotic Total Knee Arthroplasty
PRESENTER: Siddharth Mahure

ABSTRACT. Background: Total Knee Arthroplasty (TKA) continues to incorporate changes in implant and instrument design to provide optimal outcomes. Surgeons are presented with an additional challenge to adapt modern technology. The Active Robotic TKA (ARoTKA) performs autonomous resections of the tibia and femur in efforts to optimize bone cuts. Evaluating the Learning Curve (LC) is essential in an effort to continually improve instrumented outcomes. The purpose of the study is to assess LC associated with ARoTKA.

Materials and Methods: A prospective FDA case-series was conducted from 2017-2018 including 68 patients that underwent ARoTKA performed by four different surgeons. Operative data recorded included operative time, bone resection time, and bone registration. Operative time is defined from patient preparation to end of tibial resection, this includes a combination of Surgeon and Active Robotic system. T-tests were used for comparisons of the first three surgeries with the following groups of three surgeries.

Results: ARoTKA was associated with a learning curve of 10 cases for operative time (p=0.028). The first 3 cases had an average operative time of 49.1±17 minutes that was compared to cases 10-12 that had 36.5±7.84 minutes (p=0.028). Cumulative experience decreased operative time starting at cases 10-12 having a significant difference in operative time.

Conclusion: Early results demonstrate ARoTKA is associated with a LC of 10 cases during which operative time significantly decreases – thus suggesting an ease of implementation amongst surgeons.

Robot-Assisted Versus Conventional Fluoroscopy-Guided Tas Placement for Atlantoaxial Instability: a Retrospective Cohort Study
PRESENTER: Jingwei Zhao

ABSTRACT. As a treatment of atlantoaxial instability, C1-C2 transarticular articular screw (TAS) technique is effective but very challenging. Robot system was proved capable of improve the accuracy of screw insertion in thoracolumbar spine. However, there is few literatures reporting the use of robotic system in upper cervical spine, and the advantages of robotic system are not known when used in TAS insertion. In this study, 49 patients treated with TAS fixation were included. The robot-assisted group (RG) included 28 patients (54screws inserted) and the fluoroscopy-guided group (FG) included 21 patients (42screws inserted). Screws were graded from Grade A to E: A, perfect intrapedicular localization; B, < 2mm cortex breach; C, < 4mm cortex breach; D, < 6mm cortex breach; and E, ≥ 6mm deviation from the cortex. The deviation from the actual to ideal axis of each screw was measured at the entry point and end point on axial and sagittal views. Consequently, the proportion of clinically acceptable screws in the RG (97.5%) was significantly higher than that in the FG (83.3%) (P=0.039). The deviation was 1.0±0.6 mm in the RG (296.4±147.8 ml) and 2.4±1.3 mm in the FG, and the difference was significant (P< 0.001). The robot-assisted surgery is safe and effective for TAS insertion in patients with atlantoaxial instability.

Robotic-Assisted Total Hip Arthroplasty Yields Enhanced Surgical and Clinical Outcomes Compared to Manual Hip Arthroplasty Using the Same Implant System
PRESENTER: Laura Scholl

ABSTRACT. INTRODUCTION: Several radiographic studies have demonstrated the precision and accuracy of component placement in robotic-assisted total hip arthroplasty1,2 (THA). However no studies have evaluated the intraoperative experience and early clinical outcomes between robotic and manual techniques. This is the first study to compare intraoperative surgical information and early postoperative clinical outcomes between robotic-assisted and manual implantation using the same novel additively manufactured porous3 acetabular shell and a tapered wedge stem. METHODS: In a prospective, non-randomized trial, 105 hips across five centers received the same THA system of a tapered wedge stem and novel additively manufactured titanium porous clusterhole acetabular shell in primary THA. 38 hips were implanted with a robotic-assisted surgical system while 67 hips were implanted manually. Demographic and surgical information were collected, along with 6-week clinical outcomes of the Harris Hip Score (HHS), Lower Extremity Activity Scale (LEAS), EuroQol-5D (EQ-5D) and Veterans Rand 12 (VR12). There were no significant differences in body mass index (BMI), age, or ASA Score between the robotic-assisted and manual cohorts RESULTS: The robotic-assisted cohort yielded a shorter mean skin-to-skin surgical time of 60.4 minutes compared to 85.2 minutes for the manual cohort (p<0.0001), along with a shorter hospital stay of 1.3 days compared to 1.7 days (p=0.0081). The robotic-assisted cohort resulted in a lower blood loss of 155.3 cc compared to 364.9 cc for the manual cohort (p<0.0001). Standard deviation for incision length was half the value in robotic-assisted cases when comparing with manual cases (1.7cm vs. 2.9cm). These trends translated to improved clinical outcomes with the robotic-assisted THA cases demonstrating a significantly higher 6-week postoperative HHS (87.8 vs. 72.6), physical VR-12 (41.75 vs. 32.3), and LEAS (10.0 vs. 7.5). 57.7% of robotic-assisted cases scored an excellent HHS at 6-weeks, compared to only 25.8% of manual cases (Figure 1). Robotic-assisted cases reported a higher preoperative pain score specific to indoor and outdoor housework yet experienced a significantly lower postoperative pain score compared to manual cases. The EQ-5D treatment effect size at 6-weeks postoperative for robotic-assisted cases exceeded a large effect with a value of 1.2, while the effect size for manual cases was 0.4. (Figure 2). DISCUSSION and CONCLUSION: Robotic-assisted 3-D patient specific planning and haptically guided robotic-assisted surgical execution demonstrated an improved operative experience relative to surgical time, blood loss, and incision length. The decrease in surgical time and blood loss may be contributed to the use of a single-ream technique for acetabular preparation. The robotic cohort also yielded improved early clinical and functional outcomes when comparted to manual techniques at six week. These early, enhanced robotic-assisted THA results support surgeons using robotics with the goals of decreased patient pain, greater range of motion, and increased joint stability4. The ability to plan and recreate the desired hip center of rotation, hip length, and offset5 likely contribute to the improved clinical outcomes. Although many confounding variables were controlled for, longer term follow-up with larger numbers and uniform surgical approaches may be required to confirm enhanced outcomes and surgical experiences using the robotic-assisted total hip arthroplasty.

12:30-13:30 Lunch

Sponsored by Stryker

12:30-13:30 Session 13A: Lunch Symposium

Closing the Gap in Patient Satisfaction with Robotics and Kinematic Implants

Sponsored by Smith & Nephew inc.

Location: Main Auditorium
12:30-13:30 Session 13B: Poster Session I
Interesting Cases in Robotic-Arm Assisted Total Knee Arthroplasty
PRESENTER: Joseph Ehiorobo

ABSTRACT. Introduction: Robotic-arm assisted surgery allows for the execution of well-aligned knee arthroplasty regardless of pre-existing deformity. This case series is presented to show the utility of robotic-arm assisted TKA in achieving well-balanced, well-aligned results in a variety of challenging scenarios.

Methods: We present seven challenging cases of robotic-arm assisted total knee arthroplasty. There were two conversion TKAs following a previous surgery. One case featured a previous tibial plateau fracture treated with a plate and screws construct while another featured a prior femoral nail with significant bony overgrowth. Five cases of severe deformity were also identified, with one tibial nonunion, two valgus knees and one patient with two varus knees due psoriatic arthritis treated with staged bilateral TKAs. Patient clinical history, physical examinations, intraoperative surgical techniques and postoperative courses were recorded.

Results: All cases were able to utilize effective preoperative planning to obtain precise intraoperative bone cuts and component positioning. Each of the seven cases achieved well-balanced, well-aligned arthroplasties. There were no intraoperative or postoperative complications. At latest follow up, all patients showed significant improvements in pain and ambulation compared to preoperative exams.

Discussion: Robotic-arm assisted surgery allows for the integration of preoperative CT scans to establish and execute a surgical plan with precision. Despite the complexity of these cases, excellent results were achieved without the need for revision-type components. These cases display the ability of robotic-arm assisted surgery to achieve consistent well-aligned results with minimal bone loss in challenging total knee arthroplasty cases.

Relationship Between Femoral Anteversion and Patellofemoral Joint―Investigation Using 3-Dimentional Computed Tomography

ABSTRACT. [Introduction] Many have reported relationship between abnormal rotation of the leg alignment and patellofemoral joint disorder. Then, the aim of the study is to determine the relationship between femoral anteversion and patellofemoral joint alignment based on computed tomography (CT) findings. [Patients and Methods] In this study, 27 patients with 30 hips that underwent CT scan before femoral head replacement or total hip arthroplasty were included. Underlying diseases included femoral neck fracture, primary hip osteoarthritis, developmental hip dysplasia and femur head necrosis. For femoral neck fracture, the normal legs were measured, and involved legs were measured for the others using 3D template soft (Zed Hip®, Lexi). Items to be measured were femoral anteversion (AV) as well as sulcus angle (SA), congruence angle (CA), and lateral patellofemoral angle (LPA) as measures of the patellofemoral joint alignment. SA, CA, and LPA were measured on slices at the patellar center level. Patients were divided into AV 20° group (LAV group) and AV <20° group (SAV group) to examine the relationship with the patellofemoral joint alignment. [Results] LAV group included 10 hips and SAV groups included 20 hips. Mean in LAV group was 29.1±5.4 for AV, 149.8±14.1 for SA, -1.9±11.4 for CA, and 7.3±4.4 for LPA. Mean in SAV group was 13±5.4 for AV, 149.7±10.2 for SA, 9.1±24.7 for CA, and 4.8±4.9 for LPA . Significant difference in AV was found between 2 groups (p<0.001). However, no significant differences in SA, CA, and LPA were found between 2 groups. [Discussion] Reikerås has reported that no significant differences in SA, CA, and LPA were found between femoral anteversion  20° group and < 20° group as measured by CT scan. This result is similar with that of our study. However, Drew et al. described in the systematic review that CA obtained on CT scan at knee flexion of 15° was likely associated with patellofemoral pain. Lateral deviation of the patella and morphologic abnormality of the femoral condyle may have not been reflected because, in both this study and previous reports, CT scan was performed at hip/knee extension position and patellofemoral joint alignment was measured using one slice. [Conclusion] No relationship between femoral anteversion and morphology of the patellofemoral joint was found. However, caution is required because CT scan obtained at knee extension position may not reflect abnormal alignment.

Change in Pelvic Tilt from Supine to Standing Position Before and After Spinopelvic Fixation
PRESENTER: Hidetoshi Hamada

ABSTRACT. Purpose: The purpose of this study were (1) to measure change in pelvic tilt from supine to standing before and after spinopelvic fixation, and (2) to estimate the risk of edge loading on the cup of a total hip arthroplasty induced by pelvic tilt before and after spinopelvic fixation. Methods: Twenty-two subjects underwent spinopelvic fixation for ASD in our institution were reviewed. Before and after spinopelvic fixation, the pelvic tilt was measured in supine and standing position by using CT image and plane radiographs of hip joint. To estimate the risk of edge loading induced by change of pelvic tilt by spinopelvic fixation, we analyzed the incidence of change of pelvic tilt from supine to standing with backward 15 degrees or more. Results: The mean change of pelvic tilt from supine to standing was backward 12 degrees. After fixation, the mean change of pelvic tilt from supine to standing was backward 3 degrees. The mean change of pelvic tilt from preoperative supine to postoperative standing was backward 5 degrees. In 27% of the subjects, the change in pelvic tilt from supine to the standing before fixation was backward 20 degrees or more, and in 36% that change was backward 15 degrees or more. In no subjects, the change in pelvic tilt from supine before fixation to the standing after fixation was backward 20 degrees or more, and in 5% that was backward 15 degrees or more. Discussion: In conclusion, in case of the cup orientation in supine position with 40 degrees inclination and 15 degrees anteversion, edge loading after the following spinopelvic fixation would not occur.

Navigated LUMiC® Endoprosthetic Reconstruction in Orthopedic Tumor Surgery - Development and Testing on 3D-Printed Pelvic Models

ABSTRACT. Reconstruction of periacetabular defects after pelvic tumor resection is a highly demanding procedure with severe rates of unsatisfactory outcome and a complication rate up to 50% [1,2]. Due to the absence of anatomical landmarks after tumor resection, correct 3D-placement of the prosthesis is very challenging. Compared to biomechanical studies on human bones, 3D-printed anatomical models proved to be a reliable alternative reducing cost and organizational effort [3]. A spine navigation module with surface registration was used to implant guide wires for LUMiC® prostheses on 3D-printed pelvic models (n=36) by three orthopedic consultants and three medical students. 3D-positions of the navigated guide wires were compared to conventional implanted ones in CT-scans. Results: The spine registration module proved to be reliable at the pelvic models. Navigation significantly improved the position of the prostheses compared to the conventional method for experienced surgeons and medical students. 4 (22%) of the conventional and 0 of the navigated implanted LUMiC guide wires put surrounding anatomical structures at risk. Discussion: The new method proved to simplify correct placement and due to the improved position potential complications could be reduced. Medical 3D-printing is rapidly evolving and it is assumed that applications of 3D-printing will be widely utilized in health care [4]. The surgically unexperienced medical students adapted much faster to the new navigation method compared to the orthopedic consultants and had a steeper learning curve. A possible explanation could be their increased childhood video gaming experience [5].

[1] Nieminen J et al.(2013) Orthopaedic Reconstruction of Complex Pelvic Bone Defects. Evaluation of Various Treatment Methods. Scandinavian Journal of Surgery 102(1): 36-41 [2] Brown TS et al. (2018) Reconstruction of the hip after resection of periacetabular oncological lesions: a systematic review. Bone Joint J 100-b(1 Supple A): 22-30 [3] Stirling ER et al. (2014) Surgical skills simulation in trauma and orthopaedic training. J Orthop Surg Res 9: 126 [4] Schubert C et al.( 2014) Innovations in 3D printing: A 3D overview from optics to organs. Br J Ophthalmol 98: 159-161 [5] Rosser JC et al. (2007) The impact of video games on training surgeons in the 21st century. Archives of Surgery 142(2): 181-186

Revision Total Hip Arthroplasty for Recurrent Dislocation
PRESENTER: Ema Nakahara

ABSTRACT. One of the most common reasons for revision surgery after total hip arthroplasty (THA) and revision THA is dislocation. The purpose of this study was to analyse a factor for successful treatment after the revision surgery for unstable THA focusing on the femoral head diameter and the implant alignment based on the combined anteversion theory. Subjects of this study were 19 revision THAs in 19 patients underwent for the treatment of recurrent dislocation following initial THA in our institution from 2007 to 2017. The mean period from the initial THA to revision was 8.9 years and the mean follow up period was 3 years. Both before and after these revision THAs, the alignment of the implant and head diameter were assessed using their CT data in each time, and we categorized their alignment and head diameter in both pre- and post-revision THA according to the previous report. We estimated the prognostic factor to associate with recurrent dislocation. All 19 subjects before revision had implant malalignment or femoral head with 32mm or less. Two cases whose malalignment had been uncorrected and used 36mm femoral head during revision dislocated recurrently after revision. Conversely, there is no recurrent dislocation in subjects where malalignment was corrected or upsizing over 36mm of femoral head was used in the revision THA. Our study indicated that the prognostic factor for recurrent dislocation after revision THA was uncorrected malalignment combined with no use of large femoral head.

Comparison Effect of Anatomical and Conventional Tibial Cut in Post-Operative Radiographic Parameter and Clinical Outcome of Ankle Joint in Computer Assisted TKA

ABSTRACT. Background In Total knee arthroplasty (TKA), not only knee joint affect when we restored limb alignment, but also other joints involved. Ankle joint is one of them. By changing in talar tilt, many studies shown this will lead to increase pain and disturb function of ankle. Patients may end up with unsatisfied result of TKA. Anatomical cut of tibia is use in order to avoid this problem. Object To compare between pre- and post-operative talar tilt angle (TTA) and ankle clinical assessment by foot function index (FFI) and ankle-hindfoot index (AHI) after anatomical tibial cut (varus 3° with anatomical axis) and conventional tibial cut (perpendicular with anatomical axis) in computer-assisted total knee arthroplasty Material and methods This study was retrospective study. We collected data of 70 knees from 54 patients. 32 knees were done by anatomical cut. The rest were conventional cut. We evaluated at pre- and post-operative for TTA. At 12-month follow-up for TTA & ankle clinical assessment. Result In conventional group, TTA was changed 2.33° (p<0.001) then 0.920 (p=0.02) at follow up. In anatomical group, TTA was changed 2° (p=0.037) then 1.38° (p=1.56). Changing of TTA was not significantly different at post-operatively (p=0.76) and follow-up (p=0.98) between 2 groups. FFI& AHI were not significantly different between both groups. Conclusions Ankle joint always involved when restored alignment of knee that underwent TKA. No matter method of tibial cut was use. But this effect will get better over time and not effect to clinical outcome of ankle.

What Is the Factors That Lead to Adduction or Abduction Contracture?
PRESENTER: Tetsuro Tani

ABSTRACT. Various types of contracture are accompanied with hip osteoarthritis (HOA) and they induce pelvic obliquity which can lead to functional leg length discrepancy. The purposes of this study was to evaluate morphological features of HOA that related to contracture using CT images. Two hundred forty-three hips of 231 patients with HOA who underwent primary total hip arthroplasty (THA) were the subjects of this study. Preoperative AP radiographs of the bilateral hips acquired in maximum adduction and maximum abduction were used to quantify contracture. Measuring angle, we classified as abduction contracture (group Abd), adduction contracture (group Add) and non-contracture group (group N).To analyze the predictors for contracture, classification of HOA, anatomical factors, spinal factors, femoral anteversion and the position of the osteophytes (Capital drop: Cd, Double floor: Df) were measured. Eighteen hips (7.6%) were classified into group Add and 23 hips (9.4%) were into group Abd. The remaining 202 hips were classified into group N. Crowe classification, leg length discrepancy and spur showed a significant correlation in group add. A significant correlation in group Abd were offset, pelvic obliquity, functional femoral anteversion and spur. In multivariate logistic regression, the strongest relating factor of group add was CroweⅢ (odds ratio:34.7) and group Abd was osteophyte (odds ratio: 21.5) .  In conclusion, Crowe classification relates to adduction contracture of the hip while osteophyte morphology related to abduction contracture of the hip.

The Effect of the PCL on Kinematics as It Relates to Soft-Tissue Preservation from Robotic-Arm Assisted Surgery

ABSTRACT. The posterior cruciate ligament (PCL) is the primary restraint to posterior translation of the tibia and plays a role in joint compression [2]. Many studies have been done to evaluate the PCL through simulations as well as passive testing which speaks to the importance of the PCL [1, 2, 3]. The use of haptic-based robotic-arm assisted total knee arthroplasty (hRATKA) has demonstrated a decrease in soft tissue damage. Hampp et al. compared the soft tissue damage in a cadaveric study between manual total knee arthroplasty (MTKA) and hRATKA and found that the hRATKA specimens had significantly less damage to the PCL than the MTKA specimens [4]. The purpose of purpose of this study is to look at the effect of the PCL on kinematics, as defined by anterior-posterior (AP) tibial translation, during stair climb. Using a 6 degree-of-freedom (6-DOF) joint motion simulator, the stair climb profile was run on four cadaveric knee specimens with PCL intact and the PCL cut. In the PCL deficient condition, there was more posterior tibial motion and less anterior tibial motion than when the PCL was intact, and this was more noticeable during the high flexion portion of the profile. These findings speak to the importance of soft tissue preservation, and the development of haptic-based robotic-arm assisted TKA can help prevent soft tissue damage to the PCL. Learning more about the effect of the PCL on knee kinematics highlights the advantages of using hRATKA to preserve physiological motion.

The Impact of Workflow on Cutting Time for Partial Knee Arthroplasty
PRESENTER: Emily Hampp

ABSTRACT. To date, there are no studies aimed at characterizing the active cutting time for a robotic-assisted PKA procedure and impact of workflow. This study quantified the active cutting time for three medial PKA workflows using the same robotic-assisted system.

Three surgeons each prepared six cadaveric knees for robotic-assisted PKA using workflows: A) burr-only, using a legacy, clinically-successful burr design; B) burr-only, using a new burr design; or C) planar, using a new burr design and saw. For a burr-only workflow, the femur and tibia are prepared with a burr. For a planar workflow, the femur and tibia are prepared with a burr and saw. The total mean trigger time to complete all femoral or tibial bony resections was statistically compared between workflows using ANOVA and Tukey Pairwise Comparison.

There was statistically significant less time required to prepare the femur and tibia in B and C, compared to A (p≤0.05). Less time was required in C than B, but this was not statistically significant (p>0.05). Workflow A took an average of 429±104 seconds (range, 314 to 529 seconds), B took an average of 302±40 seconds (range, 244 to 363 seconds), and C took an average of 236±50 seconds (range, 196 to 332 seconds).

The new burr design, when used with both burr-only and planar workflows, has the potential to be more efficient (30 and 45% faster, respectively) compared to the legacy burr using the burr-only workflow, for a medial PKA. Bone resection time should be investigated in a clinical setting.

Does Workflow Influence Component Accuracy to Plan for Partial Knee Arthroplasty?
PRESENTER: Emily Hampp

ABSTRACT. Accurate component alignment may enhance outcomes for partial knee arthroplasty (PKA). The aim of this study was to determine whether workflow impacts the accuracy of component position to plan for three medial PKA workflows using the same robotic-assisted system.

Three surgeons each prepared 6 cadaveric knees for PKA with robotic-assisted technology using workflows: A) planar, using a new burr design and saw; B) burr-only, using a new burr design; or C) burr-only, using a legacy, clinically successful burr design. All bone resections were executed with the robotic-assisted system and implants were cemented. Computed tomography (CT) scans were obtained for each knee preoperatively and postoperatively. CTs were analyzed to compare postoperative implant position to the preoperative planned position for 3 translations and 3 rotations (6 DOF). Measurements were checked for normality and statistically compared between workflows using ANOVA, Welch’s Test or Kruskal Wallis.

For femur components, median accuracy to plan was ≤2.0 mm or 2.0° for all 6 DOF and all workflows. For tibia components, median accuracy to plan was ≤2.0 mm or ≤2.1° for all 6 DOF and all workflows. For 11/12 measurements, there was no statistical difference in final cemented PKA component accuracy, when comparing three workflows from the same robotic-assisted system.

Final component alignment to plan is critical for achieving desired overall limb alignment. Similar cemented component accuracy to plan was observed in this cadaveric study for different robotic-assisted workflows. For further confirmation, workflow should be investigated in a clinical setting.

CT-Based Navigation THA Using CT-Fluoro Matching Registration

ABSTRACT. CT-fluoro matching (CFM) registration is one of the registrations for CT-based navigation developed by Brainlab company, in which the contours of the intraoperative fluoroscopic 2D X-ray images were matched to the contours of 3D pelvic and femoral models created based on the preoperative CT images. Since Brainlab company stopped to provide CT-based navigation and shifted to imageless navigation for THA, clinical efficacy of this CFM registration is not well known. We analyzed the accuracy of implant position and postoperative complications after CT-based navigation assisted THA of 45 cases (43 females, 2 males, average age: 72.7 y.o.) using CFM registration and cementless implants (SQRUM cups and J-Taper high offset stems [Kyocera, Japan]). The differences (average ± standard deviation of absolute values, [95% confidence interval]) between the pre- and post-operative angles of cup inclination, anteversion, and stem antetorsion were 2.2±1.5⁰, [1.8~2.6⁰], 3.7±3.1⁰, [2.9~4.6⁰], 5.9±4.5⁰, [4.6~7.1⁰], respectively. The differences (average ± standard deviation of absolute values, [95% confidence interval]) between the intra- and post-operative angles of cup inclination, anteversion, and stem antetorsion were 2.2±1.7⁰, [1.7~2.6⁰], 2.3±2.1⁰, [1.7~2.8⁰],4.6±3.0⁰, [3.7~5.4⁰], respectively. These values were clinically acceptable when we compared with the previous accuracy studies of CT-based navigation using surface matching registration. There was no dislocation after THA in this study. From these results, this CFM registration is useful for THA. However, this CFM registration will be discontinued in the near future. We really hope to develop a novel CT-based navigation system based on this CFM registration procedure.

Femoral Component Rotation Angle After Unicompartmental Knee Arthroplasty Using the Anatomical Tibial Component Cutting Technique with Computer-Assisted Surgery by CT-Scan

ABSTRACT. Background: Complication following unicompartmental knee arthroplasty(UKA) in medial compartment osteoarthritis knee often related to rotatory malposition of the femoral component1. The purpose of this study was to study outcome following Femoral component rotation angle after unicompartmental knee arthroplasty using the anatomical tibial component cutting technique with computer-assisted surgery by CT-scan measurement in Rajavithi hospital. Material and Methods: This is a retrospective descriptive study of sixteenth patients performed Unicompartmental knee arthroplasty in Rajavithi Hospital Bangkok Thailand. All patients underwent surgical by a single orthopedic surgeon and using computer-assisted with anatomical tibia cutting technique(tibial resection in 3-degree varus). The femoral component rotation was assessed in an axial cut CT scan. measure angle between Epicondylar axis and Posterior condylar axis

Results: The Femoral component rotation angle in this study was good position Mean is 2.94-degree internal rotation(internal rotation compare with Epicondylar axis). A range of femoral component internal rotation was 0-6 degree .mean varus-valgus angle was 1.81-degree varus and mean flexion-extension angle was 5.56-degree flexion

Conclusion: Femoral component rotation angle in unicompartmental knee arthroplasty(UKA) in medial compartment osteoarthritis knee with using of the computer-assisted with anatomical tibia cutting technique have a favorable result (Mean = 2.94-degree internal rotation 1.81-degree varus and 5.56-degree flexion)

Results of a 10-Year Follow-up Study on Concentrated Autologous Bone Marrow Aspirate Transplantation for Osteonecrosis of the Femoral Head and Proposal of a Method for Quantitative Evaluation of Necrotic Volume
PRESENTER: Yohei Tomaru

ABSTRACT. In 2003, we began conducting concentrated autologous bone marrow aspirate transplantation (CABMAT) to treat osteonecrosis of femoral head (ONFH). In Japan, ONFH is mainly classified by the qualitative Japanese Orthopaedic Association (JOA) system. We aimed to report the long-term results of ONFH treated by CABMAT and to determine whether quantitative evaluation can accurately predict the outcome of ONFH. Between 2003 and 2008, 109 hips with idiopathic ONFH in 69 patients were treated by CABMAT. The necrotic volume was measured by MRI using the OSIRIX software. To detect the predicting factors of conversion to Total Hip Arthroplasty (THA), multivariable logistic analysis was performed. The mean age of the patients was 42 years. Preoperatively, 4, 1, 27, and 48 hips were analyzed as types A, B, C1, and C2, respectively and 12, 31, 14, 18, and 5 as stages 1, 2, 3A, 3B, and 4, respectively, based on the JOA classification. Ten-year follow-ups were conducted for 80 hips in 44 patients (21 men and 23 women). The follow-up rate was 73.4%, and the mean follow-up period was 12.0 years. The overall conversion rate to THA was 34% (27/80 hips). The preoperative and most recent mean necrotic volume ratio in 19 patients were 13.9 % and 9.89 %, respectively. The necrotic volume ratio was significantly reduced after CABMAT. In the multivariate regression analysis, the necrotic volume significantly correlated with conversion to THA. Thus, the necrotic volume method could be valuable in predicting the conversion to THA in cases of ONFH.

Analysis of the Femoral Torsion of 2787 TKA Sample with the Amplivision System Navigation

ABSTRACT. Study: We study the application of the AMPLIVISION infrared system TKA NAVIGATION in combination to the SCORE ultaconcruant TKR posterior référence cut arthroplasty with rotated PE insert. We approuve a retrospective study of the clinical record DATA radioclinical evaluation A first tibial cut on 90 referred the base of the rectangular gap. The extension and flexion gap balancing is adjusted with anteroposterior prosthesis displacement in combination of the femoral implant’s rotation and a strong correlatioship of the preoperative HKA alignement is definited of the isometric collateral ligaments stretching and the condyle hypoplasia in the coronal and sagittal planes.

Results:WE definited positive the externale rotation and negative the internale rotation to the bi-condylar axis. In both series the median femoral implant rotation is above +2 degrees The mean variance is -3 to + 6. Median of knee varus deformation 175 Median of knee valgus déformation 184 Mean one year’s flexion degrees 125 Mean one year’s extension degrees 0

Conclusions: The knee navigated TKR opérative procedure is a very accurate method and the forgotten TKA after 5years follow-up rate is upper to 65% with a no-infection revision rate lesser of 1% The computer assisted orthopedic surgery is a very performance reproductivity technique of the ligament balancing implants adjustment to the personalize and the final implants positioning is definited on the real time per-operative dynamic technique with numerical digitalization of the flexion and extension gaps.

In-Hospital Manufacturing of Patient Specific 3D-Printed Guides

ABSTRACT. Introduction Patient specific instrumentation is a novel aid the industry has been implementing in our hospitals during the last years. However, the cost of the process and the impossibility to discuss face to face with the manufacturer the needs of the particular cases may favor the in-hospital production of these devices.

We present the design and manufacturing process of three patient-specific devices to treat complex common situations in orthopaedic surgery, such as intramedular tumor resections, long bone pseudarthrosis and malunions of articular fractures.

Material and Methods CT scans of the region of interest were performed to all the patients. Horos® software was used to isolate the affected bone region, whereas Meshmixer® software was used to create the patient specific guides. An Ultimaker 2+® 3D printer was used to print the guide, in a biocompatible material (SmartFil® Medical). The printing parameters included a nozzle of 0.6 mm and a layer height of 0.1 mm. There was one case of a low-grade chondrosarcoma in which we created a guide to resect enough cortical bone to make an extended curettage of the lesion. Phenol and PMMA were used as adjuvants after the curettage. We used the same guide to obtain an exact replica of allograft which was later placed in position. We had a femur diaphyseal atrophic pseudarthrosis in a patient with achondroplasia, in which the guide permitted the resection of the affected bone with a saw and posterior osteosynthesis with an anterior LCP plate. Finally, in an intraarticular malunion of a distal radius Die-Punch fracture we used the guide to make an osteotomy of the affected articular portion and correct the articular surface. Bone autograft was added prior to the osteosynthesis with a plate.

Results Mean design time was 6.3 hours. Mean printing time was 5.2 hours. The price of the filament used for each guide was under 10 USD. The mean time from the CT-Scan and the surgery being performed was 2.7 months. In all cases the patient specific guides fitted in the bone and permitted the planned resection/osteotomy. All the surgeries fulfilled their purpose.

Conclusions Patient specific guides are easy to design in a local setting with the aid of free software. Design time still needs dedication although it permits the manufacturing of the guides following surgeon needs. The use of self-designed and printed guides is safe and accurate, with a low cost for the institutions.

Prospective RCT in Patients Who Underwent CAS and Conventional TKA with Simultaneous Bilateral Total Knee Arthroplasty Technique

ABSTRACT. Introduction: At present, it is well known that computer-assisted surgery of TKA can increase the accuracy and precision of implant placement. But there is no clear conclusion regarding the outcome of the surgery that the use of CAS is better than conventional technique. Therefore, it is the source of this research by comparing surgery with the same patient. By one knee surgery using the computer-assisted method and the other knee surgery by conventional methods. Methods : 30 patients underwent simultaneous bilateral TKA in Bhumibol Adulyadej Hospital, from a single surgeon. One knee is operated by CAS-TKA and the other side surgery by conventional technique. Analysis included pre-, intra-, post-operative data, postoperative limb alignment, KSS, WOMAC, and The Oxford Knee Score Survey. Results: The alignments were significantly better in the CAS group. The mechanical axis was within 3 degrees of neutral mechanical alignment in 96.7% of the CAS group and 83.3% in conventional group. KSS in CAS group (at 1,3 months and 1 year follow up) better than conventional group with statistical significance. ROM of the knee is also found to be better as well, and significantly different from 6 months (P= 0.04). CAS group give the smaller in the mean of blood loss than that of the conventional group (210 and 256 ml, p = 0.021). Conclusions: CAS-TKA has clear surgical results that are superior to conventional technique, whether in the alignment of implants or function of the knee. But the operative time is longer when compared to conventional methods.

Effect of Spinal Navigation System on Surgical Outcomes and Operator During Cervical Pedicle Screw Insertion

ABSTRACT. Introduction Spinal navigation system leads safe and accurate pedicle screw placement 1-3). In this study, we reviewed the surgical outcomes with using a 3D navigation system; (1) to check the accuracy, (2) to demonstrate the influence on operators and surgical procedures. Methods Study 1: Early 75 cases were enrolled in this series. (1) We evaluated the accuracy of screw placement. (2) We checked technical modifications according to intraoperative data. Study 2: We surveyed 5 spine specialists (3 surgeons: daily use, 2 surgeons: infrequently use navigation). This survey was composed with questionnaire regarding the need of navigation for screw insertion in 45 / 75 cases. Their judgments were assorted into six grades (from 0 to 100%) according to their confidence to insert screw with or without navigation (table). Results Study 1: We used 44 trans-articular screws (TS) in 26 cases and 206 pedicle screws (PS) in 49. The TS were followed with the preoperative plan and no perforation. 16 PS (7.8%) was perforated. Though 12 PS had been abandoned at preoperative assessment, real time survey with CT and navigation enabled 4 PS insertions. Study 2: We analyzed 41 cases with sufficient questionnaire data. Overall, we had same or similar judgments in 75%. In the rest 1/4 cases their responses were divided into two groups. Three surgeons, daily use, requested the navigation in 6/41 patients for high-risk pedicle. They needed safety in screw placement and relied on spinal navigation system. Discussion Accuracy of screw insertion was 92.2 % and only three screws (1.5%) were perforated in our early phase. Our baseline was similar to previous reports 1,2). Spinal navigation still has some difficulties to gain general acceptance among surgeons. Some surgeons have negative opinions due to lack of necessity and unreliable accuracy 4, 5). We demonstrated the positive feedback of navigation. Though clinical application of spinal navigation has a learning curve 6), the use makes spine surgeon more confident to his procedure especially in a difficult case. High accuracy and better intra-operative control increases surgeon's confidence. Then, they request to use the navigation in their daily use. Conclusions 3D fluoroscopy-assisted spinal navigation has comprehensive effects with not only precise technique but also favorite condition on spine surgeon.

Posterior Decompression Using Navigation System of Far-out Radiculopathy Caused by Lumbosacral Osteophyte or Disc Herniation: a Report of Two Cases

ABSTRACT. Far-out radiculopathy of lumbosacral level is very rare case and difficult to achieve good clinical result by surgical treatment. As far as it's possible, the press factor which exists in the anterior should be removed to decompress a nerve root. Several case reports of decompression by the anterior procedure or posterior have been published. However, it's difficult to grasp the degree of bone excavation correctly during the operation by posterior decompression. < Case 1> The patient was 44 year old man. He had a numbness and a muscle weakness of the right leg. X-ray showed 6 lumber vertebras. MRI showed no appearance of disc herniation, canal and foraminal stenosis. A large osteophyte which protrudes to the anterior in left lumbosacral level was shown in CT images. Posterior decompression using an endoscope was carried out. Navigation system was started at the time of prone position, and the location of the paramedian skin incision was decided referencing the navigation images. After excavating sacral alar using high speed drill, the navigation system was used once again. Excavation of the osteophyte which exists in the anterior has been begun. Accordingly, the excavation situation was confirmed by a navigation pointer. For protection of a nerve root, the cancellous bone was excavated first and a lateral wall was left outside. A cortical bone on a lateral wall was extracted piece by piece. < Case 2> The patient was a 54 year old man. His chief complaints were pain and muscle weakness of right leg. MRI showed a large herniation at the far-out lateral between right L5/S. Posterior surgery using an endoscope is carried out. The navigation was used at the time of prone position. The excavation of sacral alar was carried out confirming the degree of excavation by using a navigation pointer accordingly. The disc herniation was extracted. < Discussion and Conclusions> The advantage of anterior surgery is certain osteophyte removal, but the invasion of surgery is much bigger. On the other hand, the operation is minimally invasive in decompression with an endoscope from posterior approach, but there is apprehension of lack of decompression. The report of lumber operation using intraoperative navigation system has been published. We thought that the advantage of intraoperative navigation images combined to the posterior endscopic surgery. It's useful for confirmation of the bone resection from posterior procedure.

Spontaneous Healing of Brown-Sequard Syndrome Caused by Cervical Disc Herniation
PRESENTER: Xiaoyun Liu

ABSTRACT. Brown-Sequard syndrome (BSS) is most commonly seen in patients with spinal trauma and extramedullary spinal neoplasm. Pure BSS caused by cervical disc herniation is extremely rare. Operative treatment is generally recommended those patients with BSS to improve neurological function. Here, we report a rare case of spontaneous healing of BSS caused by cervical disc herniation. Two years follow-up showed complete disappearance of symptoms without recurrence. To our knowledge, no similar cases have been reported before. Therefore, for appropriate patients, conservative treatment can be considered for a few months before deciding on surgical treatment.

Experimental Study on Image Drift Accuracy in Navigation Based Robotic System

ABSTRACT. Recent studies have reported the accuracy of computer assisted surgical systems for performing various spinal surgical procedures. Most studies are related to screw accuracy, while the actual accuracy measurement of intraoperative deviation have not been addressed. In order to explore what causes the deviation in robotic-assisted spinal surgery, the author designed an experiment to find a reasonable range of distance and angle for clinicians to select during spinal surgery. TianJi Robot® was used in this study as a robot-assisted surgical navigation device based on 3D fluoroscopy. Special tools for integrated positioning accuracy detection were also included. We found that the angle of the robot arm tracer was an important factor affecting the accuracy value. In lumber pedicle groups, we analysed the relationship between the accuracy values and the robot arm angle values and concluded the means of appropriate interval angle was 20 degrees. We defined the range of all continuous accuracy values less than 1 mm as the interval value and the two ends of the range as the extremity value. In different subgroups, the overall interval angles were between 15 and 25 degrees. The appropriate horizontal distance between the NDI camera and the tracker was about 1.5m compared with different distances. As a result of our research, near the extremity value, where the NDI camera is hard to capture the tracker stably, the accuracy value and standard deviation are increased; and within the interval value, where the NDI camera is easy to capture the tracker, the accuracy value and the standard deviation will be smaller. So, we suggest that the surgeon should pay attention to the operating parameters of the robot arm to get a more accurate position of the pedicle screw, especially during a cervical vertebra surgery.

Gap Deviation After Cementation in Computer Assisted Navigation TKA

ABSTRACT. INTRODUCTION The outcome of knee replacement depended on alignment, balancing of soft tissue, symmetrical and rectangular gaps adjustment, and accurate implant placement. Many techniques have been used to improve these factors including navigator assisted knee replacement, which has precise bone cut and accurate soft tissue balancing. However, cementation may change gaps and alignment that can affect outcome of knee replacement.

OBJECTIVE To compare gaps and alignment after cementation in computer assisted total knee replacement

MATERIAL AND METHODS Prospective collecting data all cases performed computer assisted total knee replacement with cruciate retaining - mobile bearing implant design. Gaps and mechanical axis was collected and compered between complete trial prosthesis and final cementation.

RESULT Lateral extension gap and flexion contracture significantly increase after cementation when compared with trial implantation [0.6 mm (P = 0.021), 2.7o (P = 0.00)]. The mechanical axis was not deviated after cementation (P = 1.00).

CONCLUSION Cementation is able to influence gap and alignment. It may be useful to control and recheck gap and alignment with navigation system during cementation. Clinical correlation needs further investigation.

13:30-14:20 Session 14: Advanced Technologies
Location: Main Auditorium
A Method for Validation and Error-Quantification of 3D-Printed Models for Acetabulum Fracture Surgery

ABSTRACT. Despite the increasing use of 3D printing in orthopedic surgery, there is no established method for the validation of a printed bone model. A printing error could potentially lead to complications, especially when the model is used for surgery planning. We aimed to validate a series of 33 acetabular fractures with a novel method by detailed analysis of model errors. After applying a surface filter on both the patients model and the 3D printed model, a two-step registration consisting of landmark-based pre-registration and ICP-registration, was slightly varied and conducted 100 times, yielding a mean surface deviation and standard deviation for each model surface point. We furthermore showed that more than 30 random ICP-registration points lead to a sufficiently good registration, and that the variation of the pre-registration is small enough to guarantee a stable ICP registration result. Deviations caused by failed registration are unveiled by a large standard deviation of the 100 registration routines. For the fracture series, the mean surface deviation error between the printed model and the patient model was less than 1 mm (median = 0.7 mm; 95% CI = 0.68-0.72 mm). The largest errors were found in areas with remaining support structure material, on printbed-facing model sides and on abrasive surface regions. By visualizing the residual registration error, it was possible to clearly detect surface deviations and to quantify them.

Validation of Patient Specific Surgical Guide for Curved Periacetabular Osteotomy
PRESENTER: Takashi Sakai

ABSTRACT. INTRODUCTION In order to elucidate the accuracy of pelvis osteotomy patient specific surgical guide (PSG) setting comparing between the preoperative planning and intraoperative computed tomography (CT), and to determine the usefulness of PSG comparing between the preoperative planning and postoperative CT in curved periacetabular osteotomy (CPO), we performed experimental study using 18 hips from 9 fresh cadaver samples. MATERIALS AND METHODS All hips were imaged from the whole pelvis to the femoral condyles using (first-time) helical CT. The osteotomy line of the ilium and ischium was decided using the sphere. And then, the acetabular fragment was rotated laterally to acquire more than 40 in lateral center-edge angle. PSG consisted of osteotomy guide part which had four 2-mm diameter metal sphere markers for the evaluation of PSG setting accuracy on the bone surface, and rotation guide part which regulated rotation angle of the bone fragments. CPO with PSG was performed in 9 hips (PSG group) while CPO without surgical guide was performed in other 9 hips (manual group). After PSG for CPO was fixed screws on the pelvis bone surface, second-time (intraoperative) CT was imaged for validation assessment between the preoperative planning and PSG setting in 9 PSG group hips. After CPO procedure, which included osteotomy, rotational motion, and screw fixation of the acetabular fragment, third-time (postoperative) CT was imaged for validation assessment between the preoperative planning and the surgery in all 18 hips. RESULTS The absolute error between the preoperative planning and PSG setting for CPO was 1.6±0.9mm for the horizontal direction, 1.8±1.5mm for the anteroposterior direction, and 2.7±2.3 mm for the vertical direction, respectively. The absolute errors between the preoperative planning and postoperative CT (PSG / manual) was 2.8±1.8 / 7.9±5.4 (p=0.03) for the flexion angle and 4.6±2.9 mm /11.6±6.8mm (p=0.02) for the anteroposterior direction, respectively. There were no significant differences in osteotomy lines of the ilium and the pubis between PSG group and manual group. DISCUSSION The absolute errors in PSG group between the preoperative planning and the surgery was significantly smaller in the flexion angle and the anteroposterior direction than in manual group. In conclusion, the PSG for CPO is useful for the osteotomy of the pelvis and for the rotation of the acetabular bony fragment.

Development of a Biofeedback Wearable Sensor System to Improve Rehabilitation Following Surgical Repair of Achilles Tendon Tears
PRESENTER: Joshua Giles

ABSTRACT. A novel, wearable biofeedback device has been developed to assist patients recovering from Achilles tendon tears in adhering to prescribed rehabilitation guidelines, and to provide a quantitative assessment of rehabilitation outcomes to clinicians. This device will provide feedback to patients and clinicians alike, ensuring rehabilitation exercises are being performed correctly and routinely thereby safeguarding an effective and controlled recovery process. In addition to aiding individual patients, user biomechanical data can be logged over time to allow clinicians to compile quantitative data to test the efficacy of different rehabilitation guidelines.

This device was designed to be ergonomic and minimally intrusive to allow the system to simply be worn day-to-day as a patient undergoes rehabilitation. The complete system consists of three modules: 1) wearable sensors, 2) a Bluetooth-enabled microcontroller, and 3) a smartphone app. The array of sensors is capable of quantifying muscle activation, foot pressure, and relative ankle angles, which constitutes a unique biofeedback device. The data are computationally analysed to produce meaningful biomechanical measurables such as ankle flexion-extension, ankle inversion-eversion, degree of weight bearing, muscle activity, and basic gait parameters. A companion smartphone app receives data via Bluetooth communication from the microcontroller, providing the user and clinician with access to data that tracks the rehabilitation process. The smartphone app possesses interactive tools such as an “exercise mode” that is tailored by a user’s clinician based on the prescribed protocol. This mode will provide visual, real-time biofeedback to assist patients in conducting rehabilitation exercise correctly. Furthermore, this device can internally log all data and is capable of identifying functional activities performed by a patient through machine learning-based event identification. The data will ultimately be capable of guiding patients through their clinically-prescribed rehabilitation processes and, for the first time, quantitatively validate the efficacy of rehabilitation protocols.

Custom 3D-Printed Stems in Robotically Milled Femurs: Dynamic Load Testing
PRESENTER: Douglas Unis

ABSTRACT. Disclosures: Funding for this project was provided by Monogram Orthopedics, Inc.

INTRODUCTION: Robust long-term fixation of a non-cemented total hip replacement is highly dependent on the strength of the initial fixation. However, with conventional implants, surgeons are limited to a small array of stem sizes and shapes, making it difficult to achieve ideal initial press-fit fixation. Recent advancement in 3D printing technology and deep learning software may make customization of implants to a patient’s unique anatomy more practical and economical than in the past. The objective of the present study was to evaluate and compare the initial stability of a novel, patient matched 3D-printed femoral stem to a commercially available stem with a successful long-term clinical history, under combined dynamic axial and torsional loading.

METHODS: A custom designed 3D-printed short femoral stem and a commercially available non-cemented flat-tapered wedge stem were used. The custom stem was designed and printed according to the dimensions of the femur, in order to achieve maximal cortical contact with the proximal femur, based on the 3D geometry of the composite bones (Sawbone Model number 3406-5), as it has a weaker synthetic cancellous structure, thought to be more representative of poor quality bone. Identical versions of the custom stem were tested as the composite anatomic femurs were uniform. For the non-cemented tapered stem, clinical practices were followed in determining the proper sizing for the composite femur. Loading was applied by an MTS 858 biaxial servohydraulic load frame (MTS, Minneapolis, MN). A combined dynamic axial and torsional load was applied cyclically in increasing increments at a rate of 1 Hz. Loading commenced at 200 N and 1 Nm of external rotation, increasing in amplitude with time until reaching a peak axial load of 2000 N and a peak torque of -5/+20Nm internal/external rotation. At each level of loading, 500 cycles were applied for a total of 5,500 cycles. Micromotion at the bone-stem interface was measured using a highly accurate, minimally invasive system developed by the investigators [1-5]. Interfacial motion was measured by microminiature DVRT motion transducer (MicroStrain, Inc. Williston, VT) with 8-32 threaded bodies and an accuracy ≤ 1.0 µm. Two DVRT transducers were placed to measure proximal anteroposterior and mediolateral motion of the stem relative to the cortical shaft, and two were placed at the distal tip of the stem. MATLAB programs were used to calculate the cyclic amplitudes of motion for each DVRT under maximum loading after each loading step. SPSS Statistical Software (SPSS Inc, Chicago, IL) was used to analyze the data. T tests were conducted to calculated the p-value associated with the difference in the per-cycle motions of the specimens with the standard stem as compared to those with the custom stems, for each of the transducer locations.

RESULTS: The peak per-cycle motion at the implant-bone interface was calculated at each of the four transducer locations, during the 200N compressive loading cycles. During these initial cycles under minimal loads, the micromotion of all specimens with custom stems remained below 3 microns, at all transducer locations. For the specimens with standard stems, the micromotion generally stayed below 5 microns, but distally, one specimen underwent approximately 20 microns of motion, and another, 11 microns. Despite these low values, the standard stems displayed statistically significantly greater motions at the proximal lateral location (p=0.004) and the distal anterior location (p=0.006). Similarly, the peak per-cycle motion at the implant-bone interface was also calculated for the final cycles of compressive loading at 2,000N. During these final cycles of high loads, the micromotion of all specimens with the 3D custom stems remained below 25 microns at all transducer locations. Conversely, for specimens implanted with the standard stems, the micromotion was much higher, remaining below 100 microns in most cases, but exceeding 100 at the distal lateral location in one specimen and the proximal lateral location in another specimen. Accordingly, the standard stems displayed statistically significantly greater motions at all transducer locations than the custom stems (p<0.04 in all cases). DISCUSSION: As expected, micromotion levels at every location increased the end of the cyclic loading. Specifically, at all four transducer locations, with the custom stem, micromotion remained below 30 microns. In contrast, with the standard stems, micromotion increased to above 50 microns in all locations, and above 150 microns in one specimen. The cyclic motions measured for the specimens with the standard stems, were statistically higher in every location compared to the custom stem (p<0.04). Previous studies have established the threshold for implant stability to achieve successful bone ingrowth to range from 28-40 microns and for fibrous ingrowth, as high as 150 microns [6-8]. In light of these thresholds, the custom stem in the present study met or exceeded these standards. On the other hand, the design of the standard stem used in this study has been well established in the literature, with some authors reporting success as high as 100% for aseptic loosening at 29 years [9].

SIGNIFICANCE/CLINICAL RELEVANCE: The findings from the present study are very promising with regard to the custom stem; however, more studies are needed to evaluate the potential and feasibility of this novel custom 3D-printed technology for total hip replacement. Clearly as every stem is intended to be unique for individual patients, a wide array of specifications that vary in proximal anatomy and bone quality will be necessary to evaluate.

REFERENCES: 1. Sangiorgio, S.N., et al., J Appl Biomater Funct Mater, 2013. 11(1): p. e26-34. ; 2. Sangiorgio, S.N., et al., J Bone Joint Surg Am, 2004. 86-A(4): p. 813-20. ;3.Sangiorgio, S.N., et al., J Biomech, 2011. 44(2): p. 235-43.; 4.Sangiorgio, S.N., et al., J Biomech, 2011. 44(1): p. 22-7.; 5. Sangiorgio, S.N., et al., J Appl Biomater Biomech, 2008. 6(2): p. 72-80.; 6.Engh, C.A., et al., J Bone Joint Surg Am, 1992. 74(7): p. 1009-20.; 7.Engh, C.A., et al., Clin Orthop Relat Res, 1992(285): p. 13-29. 8. Pilliar, R.M., J.M. Lee, and C. Maniatopoulos, Clin Orthop Relat Res, 1986(208): p. 108-13. 9. McLaughlin, J.R. and K.R. Lee, J Arthroplasty, 2016. 31(6): p. 1275-8.

Radiographic and Clinical Outcomes in Total Hip Arthroplasty Utilizing a Porous Acetabular Shell Developed with Additive Manufacturing
PRESENTER: Michael Masini

ABSTRACT. INTRODUCTION: Utilizing novel technology to develop an acetabular implant surface is revolutionizing total hip arthroplasty1. Specifically, innovative additive manufacturing has the ability to construct layers of titanium alloy powder for a slim acetabular shell wall, allowing for optimal polyethylene thickness to encourage greater range of joint motion2, along with resulting in a cancellous bone replica. The outcome yields a shell with a roughened surface and high coefficient of friction to promote initial fixation of the implant with native bone3. The purpose of this study was to evaluate outcomes of patients who underwent total hip arthroplasty (THA) using a highly-porous titanium shell produced via additive manufacturing. We assessed radiographic outcomes and patient-reported outcomes at various time points. METHODS: Data was prospectively collected from 191 hips (88 male, 103 female, 7 bilateral) across seven centers in a non-randomized, post-market study where a cementless acetabular shell created with additive manufacturing was used in primary total hip arthroplasty. An independent surgeon, who was not a study Investigator, reviewed the patients’ low anteroposterior (AP) pelvis and Lauenstein lateral x-rays preoperatively and postoperatively at 6-weeks, 3-6 months, and 1-year. Radiographic analysis of the acetabular component employed three zones (Zone 1 – Zone 3) in the AP views. Parameters reviewed included radiolucency and migration, in addition to overall cup stability. Radiolucency in at least 50% of a zone and measuring at least 1 mm in width was defined as radiolucency present. Clinical outcomes such as all-cause survivorship, the Harris Hip Score (HHS), Lower Extremity Activity Scale (LEAS), Veterans Rand 12 (VR-12), and EuroQol 5D Score (EQ-5D) were also collected preoperatively and postoperatively. RESULTS:. The all-cause survivorship of the acetabular shell was 99.48% at 1-year follow-up. One patient suffered a perioperative acetabular fracture resulting in the lone failure of an implant which was successfully revised eight months postoperatively. Of the reviewed radiographs, all cups were reported stable at all time points. Furthermore, no cases of acetabular erosion, stress shielding, or lack of fixation were reported. Table 1 summarizes radiolucency specific to acetabular zones. Of note, there were no reported radiolucencies greater than 2mm for any zone and no findings in any zone for 93.8% of cases at 1-year follow-up, respectively. These trends translated into enhanced clinical outcomes with 84.2% of cases scoring an excellent HHS at 1-year postoperatively. Additionally, from preoperatively to 1-year postoperatively, the VR-12 Physical Component and VR-12 Mental Component increased 17.51 points and 1.12 points, respectively. Table 2 summarizes an increase of all patient-reported outcomes over time.

Table 1. Percentage of Patients with Radiolucent Findings Across Acetabular Zones 1-3. Radiolucency 6 week 3-6 month 1 year Zone1 >=1 and <2mm 1.44% 4.05% 6.25% >=2mm 0.72% 2.70% 0.00% Zone2 >=1 and <2mm 9.35% 5.41% 0.00% >=2mm 0.72% 0.00% 0.00% Zone3 >=1 and <2mm 0.00% 1.35% 0.00% >=2mm 0.00% 0.00% 0.00%

Findings in All Zones 0.00% 0.00% 0.00% No Findings in any Zones 89.21% 90.54% 93.75% X-rays Reviewed 139 74 32

Table 2. Summary of Mean Patient-Reported Outcome (PROM) Scores at Different Time Intervals

DISCUSSION: Supported by early encouraging clinical findings, we observed that engineering tolerances achieved with additive manufacturing are associated with reduce variation in the implant4. Additionally, an absence of radiolucencies in 93.75% of hips, along with total cup stability at 1-year, is also consistent with early implant fixation5. The patient reported outcomes that correlate with the radiographic findings give further evidence of early bone-to-implant fixation. We believe additive manufacturing coupled with improved understanding of the anatomy of the host bone will allow more predictable surfaces that promise to optimize fixation of orthopedic implants in the future.

14:20-15:00 Session 15: Shoulder
Location: Main Auditorium
Clinical Use of a Computer Assisted Reverse Total Shoulder Arthroplasy System: an Analysis of 1702 Cases
PRESENTER: Alexander Greene

ABSTRACT. INTRODUCTION: Placement of the glenoid implant in reverse total shoulder arthroplasty (rTSA) is of paramount importance and can affect a patient’s range of motion postoperatively. Preoperative planning combined with intraoperative navigation allows a surgeon to more accurately and precisely place a glenoid implant with respect to a preoperative plan. This study examined the clinical use of a computer assisted rTSA system.

METHODS: Postoperative surgical reports from the first 1702 clinical cases of a CT based preoperative planning software and intraoperative rTSA navigation system were collected and analyzed for implant selection, implant placement, and operative time, and compared to similar date cohorts for non-navigated cases.

RESULTS: For operative time, navigated rTSA cases lasted significantly longer than non-navigated cases (p < .05), when compared to a similar date range cohort (Nav: 93 ± 31 minutes; Non-nav: 71 ± 28 minutes). For implant usage in the navigated cohort, standard glenoid components were used 28.7% of the time, compared to total sales data for the same date range of 80.5%. For resulting version and inclination, standard non-augmented glenoid components were implanted in 1.4 ± 3.0° of retroversion and -0.5 ± 1.4° of inclination, extended cage non-augmented glenoid components were implanted in 1.0 ± 3.9° of anteversion and -1.4 ± 3.7° of inclination, 8° posterior augments were implanted in 3.1 ± 3.2° of retroversion and -0.1 ± 1.2° of inclination, 10° superior augments were implanted in 3.4 ± 4.2° of retroversion and 0.1 ± 1.1° of inclination, and 10°/8° superior/posterior augments were implanted in 2.1 ± 3.1° of retroversion and -0.6 ± 2.2° of inclination.

DISCUSSION: Navigated cases took significantly longer than non-navigated cases. Anecdotal individual surgeon time data suggests a learning curve, where the surgeon’s total incision time decreases after a number of cases. The high frequency of augmented glenoid component use in the navigation cohort and inconsistent degree of version correction in each implant category paired with high standard deviations raises questions about how much retroversion for an rTSA is optimal.

SIGNIFICANCE: This navigation system may represent an improvement in implant placement and longevity. Further study is required to see if these improvements in preoperative planning and implant placement are associated with better clinical outcomes in the short and long term.

Clinical Use of a Computer Assisted Anatomic Total Shoulder Arthroplasty System: an Analysis of 574 Cases
PRESENTER: Alexander Greene

ABSTRACT. INTRODUCTION: Accurate reproduction of glenohumeral anatomy during anatomic total shoulder arthroplasty (aTSA) has been shown to correlate with positive clinical outcomes. Preoperative planning combined with intraoperative navigation allows a surgeon to more accurately and precisely place a glenoid component with respect to a preoperative plan. This study examined the clinical use of a computer assisted aTSA system.

METHODS: Postoperative surgical reports from the first 574 clinical cases of a CT based preoperative planning software and intraoperative aTSA navigation system were collected and analyzed for implant selection, implant placement, and incision start to incision close operative time, and compared to similar date cohorts for non-navigated cases.

RESULTS: For operative time, navigated aTSA cases lasted significantly longer than non-navigated cases (p < .05), when compared to a similar date range cohort (Nav: 104 ± 27 minutes; Non-nav: 84 ± 29 minutes). For implant usage, standard non-augmented glenoid components were used 34.5% of the time, compared to non-navigated usage of 80.2%. 8° augmented glenoid components were used 61.0% of the time, compared to non-navigated usage of 19.0%. Lastly, 16° augmented glenoid components were used 4.5% of the time, compared to non-navigated usage of 0.8%. For resulting version and inclination, non-augmented glenoid components were implanted in 3.1 ± 3.2° of retroversion and 1.9 ± 3.2° of inclination, 8° augmented glenoid components were implanted in 4.1 ± 4.1° of retroversion and 1.5 ± 3.1° of inclination, and 16° augmented glenoid components were implanted in 5.8 ± 4.6° of retroversion and 2.0 ± 4.2° of inclination.

DISCUSSION: Navigated cases took significantly longer than non-navigated cases. Anecdotal individual surgeon time data suggests a learning curve, where the surgeon’s total incision time decreases after a number of cases. The high frequency of augmented glenoid component use in the navigation cohort and inconsistent degree of version correction in each implant category paired with high standard deviations raises questions about how much retroversion for an aTSA is optimal.

SIGNIFICANCE: This navigation system may represent an improvement in implant placement and potentially implant longevity. Further study is required to see if these improvements in preoperative planning and implant placement are associated with better clinical outcomes in the short and long term.

Towards a Commercial System for Intraoperative Manufacture of Patient-Specific Guides for Shoulder Arthroplasty
PRESENTER: Alastair Darwood

ABSTRACT. The accurate placement of orthopaedic implants according to a biomechanically derived preoperative plan is an important consideration in the long-term success of these interventions. Guidance technologies are widely described however, high cost, complex theatre integration, intraoperative inefficiency and functional limitations have prevented the widespread use. A novel, intraoperative mechatronics platform is presented, capable of the rapid, intraoperative manufacture of low-cost patient-specific guides. The device consists of a tableside robot with sterile drapes and some low cost, sterile disposable components. The robot comprises a 3D optical scanner, a three-axis sterile computer numerical control (CNC) drill and a two axis receptacle into which the disposable consumables may be inserted. The sterile consumable comprises a region of rapidly setting moldable material and a clip allowing it to be reversibly attached to the tableside robot. In use, patient computed tomography (CT) imaging is obtained at any point prior to surgery and a surgical plan is created on associated software. This plan describes the axis and positioning of one or more guidewires which may, in turn, locate the prosthesis into position. Intraoperatively, osseous anatomy is exposed, and the sterile disposable is used to rapidly create a mould of the joint surface. Once set, the mould is inserted into the robot and an optical scan of the surface is taken followed by automatic surface registration, bringing the optical scan into the same coordinate frame of reference as the CT data and plan. The CNC drill is orientated such that the drill axis and position exactly matches the planned axis and position with respect to the moulded surface. A guide hole is drilled into the mould blank, which is removed from the robot and placed back into the patient with the moulded surface ensuring exact replacement. A wire is subsequently driven through the guide hole into the osseous anatomy in accordance with the preoperative plan. The guide blank may be slid off the wire and discarded allowing the procedure to continue in the normal manner. A Pre-clinical prototype robot was constructed and used to insert guide wires into a cadaveric shoulder arthroplasty model. Initial end to end accuracy achieved was 0.5mm with respect to planned vs achieved glenoid point of entry and 3.0° with respect to planned vs achieved wire angle.

Assessment of Shoulder Mobility and Stability in Reverse Total Shoulder Arthroplasty: a Sensor Perspective

ABSTRACT. In reverse total shoulder arthroplasty stability is primarily controlled by the soft-tissue constraints rather than the congruency of the articulating surfaces. However, assessing the tension in these stabilizing structures currently remains highly subjective intra-operatively. In an attempt to quantify this feel during surgery, an intra-articular load sensor is introduced in this paper.

In an in-vitro setting, the load sensor was used in eight reverse total shoulder arthroplasties on full torso specimens. The specimens were mounted on an inclined chair, such that the scapula could freely move to mimic surgical conditions. The resulting load vectors were captured through the range of motion under three different conditions, subjectively categorized by the surgeon as having a low, normal and high tightness.

In neutral rotation and under a subjectively optimal condition assessed as neither too tight nor too loose, glenohumeral loads in the range of 10-20lbs were observed. For the same subjectively assessed optimal shoulder, loads up to 30lbs were observed under maximum internal/external humeral rotation. This contrasts the subjectively assessed loose and tight conditions, where lower resp. higher loads were observed that additionally affected the range of motion. On the other hand, stability was potentially missing under loose conditions as no increase in load was observed near the limits of the range of motion, indicating the lack of soft tissue restraint.

In conclusion, this series of in-vitro experiments has shown the relevance and potential clinical value of assessing a shoulder’s stability and mobility using intra-articular load measurements during the trialing phase.

15:00-16:00 Session 16: CAOS Executive Board Meeting II

Meeting reserved for CAOS International Executive Board

Location: New York Suite
15:30-17:00 Session 17A: Short Podiums
Location: Main Auditorium
Evaluation of Ligamentous Effects on Compartmental Loads During Total Knee Arthroplasty Using Functional Knee Simulator
PRESENTER: Jackson Wirekoh

ABSTRACT. Despite widespread use of measured resection and soft tissue balancing techniques to balance reconstructed knees during total knee arthroplasty (TKA), there is still a lack of understanding of the relationship between ligamentous tensions, gap distance, and compartmental loads. This study focuses on the establishment of a quantitative relationship between these entities that can be used to measure their effect on patient outcomes and demonstrate that the appearance of gap balance is not sufficient to prevent adverse instabilities post-operatively. A numerical model was developed to approximate the effects of ligamentous tensions and gap distance on measured compartmental loads under average surgical conditions during TKA. Subsequently, a functional knee simulator, with adjustable ligaments, was designed to verify the model. The numerical model and experimental results demonstrated that asymmetrical ligamentous tensions, at full-extension, outside the range of ligament load ratio LLR=F_LCL/(F_LCL+F_MCL )= [28.6%±2.75%-83.3%±2.75%] would result in condylar liftoff. Furthermore, at the LLR bounds, although the gaps appeared to be balanced, condylar liftoff had occurred. The onset of condylar liftoff, in which there is only uni-condylar contact despite the appearance of gap balance, occurs at ligament load ratios (LLR=F_LCL/(F_LCL+F_MCL )) of 28.6%±2.75% or 83.3%±2.75%. Ligamentous tensile asymmetry at full-extension which is equal/outside LLR bounds will lead to condylar liftoff during natural knee flexion/extension. Ultimately, because the preservation of bi-condylar contact relies on the lever arm length about the condyles and ligamentous tensions, symmetrical gap balancing should be conducted with sensing systems to ensure a compartmental load balance that will prevent adverse instabilities.

All-in-One Intraoperative 3D Imaging and Navigation on Percutaneous Vertebroplasty. Preliminary Results on the First 51 Patients
PRESENTER: Jerome Tonetti

ABSTRACT. Vertebroplasty (VP) is the gold standard for vertebral compression fracture (VCF) treatment. VP could be improved by using intra operative cone bean computed tomography (CBCT) although duration is largely increased. We report first series of 51 patients whom underwent VP integrating intraoperative navigation to CBCT, in order to cut down time consumption. During a 8 month period, 51 patients were prospectively enrolled. The mean age was 71 years old (36-94). There were 17 male and 35 female. We stored 65 VP (14 thoracic and 51 lumbar). After percutaneous pins fixation to the spinous process of the “Butterfly” acquisition reference frame, 180° rotation of the C-arm CBCT (Surgivisio®, eCential, Grenoble France) generated a 3D volume. Optically localized, sterile self-calibrated trocar was navigated in order to reach the vertebral body center by an unilateral pedicular approach. Cement (Vertaplex HV®, Stryker) was injected under fluoroscopic lateral view by the same machine, using standard 2D X-ray modes. Considering the 38 patients who underwent 1 level VP, mean time procedure was 00:30:09 [00:21:00 to 00:54:00; SD 00:10:23]. The mean DAP was 5,41318 Gy.cm2 and mean exposure duration 3,68 seconds. The mean efficient dose (E) was 1,32 mSv. In all cases cement placement was classified as excellent or mild, without any leakage. This new C-arm CBCT with integrated navigation is efficient to dramatically decrease operating time in comparison to literature (00:46:00 to 00:52:08). The reduction of radiation dose is already demonstrated in literature for navigated VP.

C-Arm Cone Beam Computed Tomographic Guide-Wire Trajectory Overlay for Fluoroscopic-Guided Placement of Percutaneous Screws in Pelvic Ring and Acetabular Fractures
PRESENTER: Satoshi Nakasone

ABSTRACT. Purpose The purposes of this study were to evaluate the feasibility, accuracy, and complications of real-time 3D fluoroscopy navigation in combination with guide-wire trajectory planning for pelvic percutaneous screw placement.

Patients and methods A total of 44 patients with nondisplaced pelvic ring and acetabular fractures, 20 females and 24 males, mean aged 66 years, were included in this study. After general anesthesia, C-arm cone beam computed tomography (CBCT) images of each patient was acquired with a in the hybrid OR. The guide-wire trajectory was planned on the workstation using software which can create any multiplane reconstructed images. The virtual trajectory was then projected and overlayed on the real-time fluoroscopic images and displayed on a dedicated live monitor. Guide-wire were inserted along the planned trajectory, then cannulated cancellous screw (CCS) were inserted.

Results The average surgical time was 115 minutes (42-277) and external blood loss was 9.2g (5-30). Total 121 CCSs including 52 ilio-sacral screws, 21 trans-iliac trans-sacral screws, 8 antegrade-pubic screws, 22 retrograde-pubic screws, 11acetabular screws and 5 iliac screws were inserted. There were no complications including vascular injury, neural foramen perforations and postoperative infection and hematoma. Bone union were achieved 97.7% (43/ 44pts) with mean 11.7 weeks (8-20).

Discussion Our results showed real-time 3D fluoroscopy navigation in combination with guide-wire trajectory planning enabled percutaneous screw placement accurate, safe and noninvasive manner in pelvic ring and acetabular fracture. For orthopedic surgeons, inserting a guide-wire while watching a fluoroscopic image is a simple and familiar procedure, which seemed to have led to good accuracy and clinical results.

Robotic Assisted Total Knee Arthroplasty in Presence of Extra-Articular Deformity

ABSTRACT. Introduction: There is a lack of data concerning the use of the robotic device for patients with other potentially complex surgical factors. Therefore, the purpose of this series was to present cases in which the robotic-arm assisted TKA (RATKA) application was used in the setting of extra-articular deformities to educate the surgeon community on this potentially useful method to address these complex cases.

Methods: Three cases of patients who underwent RATKA in the setting of pre-operative extra-articular deformities were identified. One had femoral and tibial fracture malunion, another had proximal tibial fracture nonunion, and another with a healed tibial plateau fracture. Patient clinical histories, intra-operative surgical techniques, and post-operative outcomes were obtained. Specific focus was placed on the surgical management of the patient’s pre-existing deformity.

Results: The robotic software was able to appropriately consider the extra-articular deformity in the pre-operative and real-time updated intra-operative plans. Doing so, the surgeon achieved a balanced and aligned TKA. No intra-operative or post-operative complications occurred. Antero-posterior and lateral radiographs demonstrated well fixed and aligned femoral and tibial components with no signs of loosening or osteolysis. On physical exam, all patients had excellent range of motion with mean flexion of 122 degrees (range: 120 to 125 degrees of flexion) at final follow-up.

Discussion: Utilizing pre-operative CT-scans with a 3D plan for robotic-arm assisted surgery allowed for appropriate assessment of the deformity pre-operatively and execution of a plan for a balanced and aligned total knee arthroplasty. We have demonstrated excellent results utilizing robotic-arm assisted TKA in these complex cases.

Component Placement Accuracy Using Active Robotic Total Knee Arthroplasty
PRESENTER: Stefan Kreuzer

ABSTRACT. Introduction: Computer-assisted technologies attempt to reduce patient dissatisfaction by improving cutting accuracy. The THINK active robotic total knee arthroplasty (TKA) system (i.e. software-controlled autonomous milling) aims to prepare the bone cuts such that final component placement accurately matches a pre-operative plan. The purpose of this study was to determine component placement accuracy and early clinical outcomes using TSolution One.

Materials and Methods: Seventy-five subjects were included in this study as part of a US IDE clinical trial. For each case, the surgeon created a pre-operative plan and performed TKA with TSolution One. The 3D differences in planned vs actual component placement were computed by comparing pre-operative and 3-month post-operative CT scans. Post-operative SF-12 PCS and Knee Society scores were compared to baseline scores.

Results: Anterior-posterior, proximal-distal, flexion-extension, varus-valgus, and internal-external positioning of the femoral component had small statistical differences from the pre-operative plan (<1.5 mm/degree, p<0.05). Proximal-distal and varus-valgus positioning of the tibial component had small statistical differences from the pre-operative plan (<0.6 mm/degree, p<0.05), while tibial slope (i.e. flexion-extension) was not statistically different from plan. No medial collateral ligament injuries, extensor mechanism disruptions, neural deficits, periprosthetic fractures, patellofemoral dislocations, tibiofemoral dislocations, or vascular injuries were observed. SF-12 PCS and Knee Society scores improved from baseline to 6 weeks, 3 months, and 6 months post-operatively (p<0.001).

Conclusion: Early clinical findings suggest minimal deviations between planned vs actual component placement when using the TSolution One active robotic TKA system. Patients had significant improvements in clinical outcome scores with no complications after surgery.

Comparison of Surgical Results of C-Arm Versus O-Arm in Transarticular Screw Fixation for Atlantoaxial Instability

ABSTRACT. Objective To compare the accuracy of transarticular screw (TAS) for atlantoaxial instability using O-arm with that using C-arm. Methods The present study was conducted in 71 patients who underwent surgery for upper cervical instability in our hospital between April 2006 and February 2018. The mean age at surgery was 61 (34–82) years. Fifty three patients underwent surgery with C-arm (C-group) and 18 patients with O-arm (O-group). In C-group, C3-7 laminoplasty (LP) was performed in 7 patients and C4-6 anterior spinal fusion in a patient simultaneously. In O-group, LP was performed in 3 patients simultaneously. C-group includes 46 patients with rheumatoid arthritis (RA), 2 with pseudoarthrosis of odontoid fracture, 2 with trauma, 1 with unknown reason. O-group includes 13 patients with RA, 2 with pseudoarthrosis of odontoid fracture, 2 with atlantoaxial rotatory fixation, 1 with os odontoideum. Ninety one TAS were inserted: 62 in C-group, 29 in O-group. Unilateral TAS was performed in 44 patients and bilateral in 9 patients in C-group. Unilateral TAS was performed in 7 patients and bilateral in 11 patients. All patients underwent 3D computed tomography (CT) angiography and the VA course was evaluated. Operative time, intraoperative bleeding, accuracy of screw, perioperative complications and bone union were evaluated. Screw accuracy was assessed using Neo’s classification. Namely, grade (G) 0: no perforation, G1: perforation<2mm, G2: perforation 2-4mm, G3; perforation>4mm. Results The mean operative time was 183 (105–349) min in C-group and 207(116-266) min in O-group. The mean blood loss was 132 (20–382) g in C-group and 360 (20-2684) g in O-group. The operative time without additional surgery was 170 (105-249) min in C-group and 179 (116-266) min in O-group. The mean blood loss without additional surgery was 132(20-382) g in C-group and 163 (20-480) g in O-group. The accuracy of TAS in C-group was G0:39, G1:17, G2: 3, G3:3 and, in O-group that was G0:28, G1:1. Bone union was confirmed in 68 patients. Bone union rate was 84.3% (43/51pts) in C-group, and 93.7% (15/16pts) in O-group. Bone union was completed 100% (20/20pts) with bilateral TAS, though 80.4% (37/46pts) with unilateral TAS. No complication was observed regarding screw insertion. Conclusion O- arm dramatically improved accuracy of TAS. Bone union rate was 100% with bilateral TAS. Therefore, atlantoaxial fixation should be performed with bilateral TAS if O-arm is available.

Accuracy, Inter- and Intra-Observer Reliability of a CT Alignment Measurement Protocol for Robotic-Arm Assisted Total Knee Arthroplasty
PRESENTER: Jingwei Zhang

ABSTRACT. Component position and overall limb alignment following Total Knee Arthroplasty (TKA) have been shown to influence device survivorships and clinical outcomes. However, these parameters are often assessed through 2D radiographs after surgery, which can be prone to inaccuracy. The purpose of this paper is to develop a new method for 3D CT based overall limb alignment and component position measurements. The technique utilizes a new mathematical model to calculate prosthesis alignment from the coordinates of anatomical landmarks used in RATKA. The hypothesis is that the proposed technique demonstrated good accuracy, as well as low intra and inter-observer variability. Two groups of patients (n=120 per group) underwent RATKA and conventional TKA at 4 imaging locations between October 2016 and August 2018, where they were recruited and consented for this prospective, non-randomized, multicenter study. CTs were collected 6 weeks post-operatively and analyzed using RATKA landmarks and the proposed technique. Measurements of 30 randomly selected cases were compared to the surgeons’ operative plan and component target positions for accuracy analysis. Two surgeons performed the same measurements separately for inter-observer variability analysis. One of the two surgeons repeated the measurements 30 days later to assess intra-observer variability. Average measurement error of overall limb alignment, femoral and tibial component positions were less than 1 degree. Bland Altman plots analysis showed great reproducibility between observers. Correlation analysis showed low variability within observer, with slopes between 0.8 to 1.0 and R-squared > 0.8. The proposed method demonstrated great accuracy to plan and low intra and inter-observer variability. This can be a great tool for RATKA studies where component accuracy is assessed using post-operative CTs.

Gap Pattern in Valgus Knee: an Assessment with Computer Navigation

ABSTRACT. Valgus knee is a challenge of ligament balance in total knee arthroplasty. A lateral release is often recommended to achieve symmetric extension gaps in a valgus deformity, due to the traditional requirements of a tight lateral gap. However the gap pattern valgus osteoarthritis knee has not been studied. This was a retrospective study on navigated total knee arthroplasty with 89 valgus- osteoarthritis knees. The gap measurement, bone cut and component rotation values were collected from navigation and the data were analyzed. Only 6.70% of valgus knees in our series had lateral flexion gap that was narrow than the medial flexion gap and 7.90 % had a lateral extension gap that was narrower than the medial extension gap. Conversely, most valgus cases were observed in larger lateral flexion gaps than in medial flexion gaps (76.4%). This finding is consistent with the extension gap patterns (80.9%). Subsequent analysis revealed that the lateral distal femoral condyle hypoplasia might have a more important role in the extension gap than ligament tension. In contrast, lateral ligament might influence the lateral flexion gap more than lateral femoral condyle deficiency. Lateral structural release for correction of valgus deformity during extension could lead to instability in flexion especially for gap patterns with a lateral flexion gap that is wider than the medial flexion gap. Gap measurement are recommended before performing ligament release.

Accuracy of Ratio for Center of the Ankle Method as a Landmark for Proximal Tibial Cutting in Computer Assisted Total Knee Arthroplasty Compared with Extramedullary Method

ABSTRACT. Introduction: Proximal tibial cutting is an important surgical step in total knee arthroplasty (TKA). Normally, an anterior surface of tibia used as anatomical landmark (extramedullary method), this method based on visual judgment. D.C. Marchant et al.¹ calculated ratio for center of the ankle, ratio of lateral distance to total inter-malleolar distance was observed at 0.57 in normal ankle sample. However, there is no study documenting about accuracy of ratio for center of the ankle as a landmark for proximal tibial cutting in computer assisted TKA (CAS TKA).

Methods: 65 patients with osteoarthritis knees scheduled to receive CAS TKA from January to December 2018. Proximal tibial cutting was simulated by extramedullary method and ratio for center of ankle respectively. Tibial cutting alignment was recorded by CAS.

Result: Tibial cutting alignment within 3 degrees was 84.6 and 92.3% for extramedullary and ratio for center of the ankle. The average total tibial cutting alignment was 0.84 and 0.66 degrees of valgus (p = 0.497) and the average tibial cutting alignment more than 3 degrees from mechanical axis was 3.60 and 1.5 degrees of valgus (p = 0.049) for extramedullary method and ratio for center of the ankle method respectively.

Discussion: Ratio for center of the ankle demonstrated result in numeric value and anatomical landmark of lateral and medial malleoli was simple to identified. Our results shown the tibial cutting alignment with ratio for center of the ankle method had higher accuracy and lower average degrees of outlier than extramedullary method.

Patient Specific Surgical Guide Improve the Accuracy of Acetabular Component Placement in Total Hip Arthroplasty with Dysplastic Acetabulum

ABSTRACT. To investigate the accuracy of a novel 3D CT scan-based preoperative planning software linked to patient-specific instrumentation (PSI) for placing acetabular components planning in patients with acetabular dysplasia undergoing total hip arthroplasty (THA). Methods: A total of 30 consecutive patients were prospectively enrolled and the accuracy of placement of the acetabular component was measured using post-operative CT scans.Results: There was good reproducibility of preoperative and postoperative position of reconstructed rotation center. The mean absolute deviation from the planned inclination and anteversion was 6.2°and 4.8°, respectively. In 90% of cases the planned target of +/-5°was achieved for both inclination and anteversion. And 95% of cases of planned target of +/-3mm was achieved for vertical height of rotation center.Conclusions: Accurate placement of the acetabular component can be achieved using patient-specific guides and is superior to free hand techniques.

Combining Multiple Technologies to Achieve Optimized Surgical Outcomes in Total Knee Arthroplasty

ABSTRACT. Purpose Innovative technologies such as robotic assistance and intraoperative load sensors for total knee arthroplasty (TKA) aim to reduce outliers, as well as to address patient dissatisfaction. There is currently no information available that assesses the findings of using these technologies together during TKA. Methods Intraoperative data on alignment, gap spacing, and quantitative balance was prospectively collected in a cohort of 79 consecutive TKAs performed with robotic assistance. An instrumented trial component was utilized that captured medial and lateral tibio-femoral loads, allowing the quantitative assessment balance. Results Of the 79 knees, 58 (73%) had varus alignment and 21 (37%) had valgus. We divided these groups into correctable and fixed deformities. Correctable varus knees: At trial reduction 30% of the knees demonstrated quantitative imbalance at trial reduction. Fixed varus knees. At trial reduction 55% (of knees were deemed imbalanced. Correctable valgus knees: At trial reduction, 35% were imbalanced. Fixed valgus knees: Half of the knees (n=2) were imbalanced at trial reduction. The imbalance in all groups was addressed with combinations of bone and soft tissue adjustments so that at final implantation 99% of cases (n=78) were quantitatively balanced Conclusion While the robot was both precise and accurate with its cuts to create appropriate gap spaces, only 57% were quantitatively balanced. Ultimately, almost all knees were balanced with final implants, but that state required the use of additional techniques, including soft tissue and bony modifications. More data is needed to determine if these technologies will equate to increased clinical success.

Robotic Arm Assisted Total Knee Arthroplasty: Addressing 1-12 Degrees Valgus Knees
PRESENTER: Jingwei Zhang

ABSTRACT. The purpose of this work was to determine the number of soft tissue releases and component orientation of valgus cases performed with Robotic-Arm Assisted total knee arthroplasty (RATKA). This study was a retrospective chart review of cases performed by a single surgeon from July 2016 to December 2017. 72 RATKA cases were defined as having a valgus deformity pre-operatively. Patient demographics and intraoperative surgical details were collected, including initial and final 3D component alignment, knee balancing gaps, full or partial releases. Post-operatively, radiographs, adverse events, and reduced WOMAC pain and KOOS Jr scores were collected at 6 months post-operatively. Pre-operatively, knee deformities ranged from 1o to 12° with fixed flexion contracture. All knees were corrected within 2.5 degrees of mechanical neutral. Medial and lateral gaps were balanced in extension 100% of cases and flexion 93% of cases. Radiographic evidence suggested well seated and well fixed components. No revision and re-operation is reported. Patient reported outcomes measures collected at 6-month follow up indicated an improvement in WOMAC pain score from 9.6 to 3.2 and improvement in KOOS Jr from 44.7 to 74.4 points. In this retrospective case review, soft tissue releases were not needed to address valgus knees ranging from 1-12° of deformity. The surgeon was able to balance the knee with bone resections and avoid disturbing the soft tissue envelope. While this study has a number of limitations, RATKA for valgus knees should continue to be investigated in a multicenter study.

Development and Validation of Image-Based Subject-Specific Skeletal Models of Spinal Deformity Patients for Use in Motion Analysis
PRESENTER: Thomas Overbergh

ABSTRACT. Conventional radiographic analysis in spinal deformity only quantifies the static skeletal body structure and no conclusions can be drawn with respect to functional abilities. The aim of this work was to introduce subject-specific, skeletal full spine multi-body models in a spinal deformity population for quantifying their full dynamic function. To accomplish this, a user-friendly application, based on biplanar radiographic images in an upright, load-bearing position, was developed. In order to quantify the accuracy of this personalization system, it was first applied on a plastinated cadaver. This ensured that the ground truth spinal alignment during a supine CT acquisition was identical to its upright, load-bearing position during radiographic imaging. The second objective was to in vivo quantify the vertebral tracking accuracy of the thus generated model and associated custom marker protocol in spinal deformity patients. In order to obtain 3D information about the spinal alignment, biplanar radiographs were obtained for nine patients in an upright load-bearing position, and a bended position, while wearing the markers. The markers were used as input for an inverse kinematics simulation, which was then compared to the ground truth in the bended image. Low errors in location and orientation of the vertebrae, for both objectives, confirmed the performance of the custom software in personalizing the spinal alignment and the marker-based vertebral tracking capacity, thereby facilitating multi-body analysis of spinal deformities. As such, this work puts within reach the extension of the current state-of-the-art clinical management from static based concepts with concepts that integrate dynamic functional data.

Reliability of Pelvic Parameters Measurement with sterEOS: Preliminary Results

ABSTRACT. SterEOS is a software developed by EOS Imaging® allowing the measurement of 3D orthopaedic parameters on two bi-planar radiographs. The goal of this preliminary study was to assess the reliability of the pelvic measurements. Two observers, a novice and an intermediate user, measured three times these parameters on pre and postoperative EOS images coming from ten patients. Intra- and inter-observer precision have been evaluated with intra-class coefficient (ICC) and Bland-Altman graphs. On preoperative EOS images, a high intra- and inter-observer precision (ICC>0.8) was obtained for the measurement of the femoral head diameter, the femur length, the pelvic version and the pelvic obliquity. The offset, the femoral neck length, the pelvic incidence and the sacral slope measurement had a high intra-observer precision but a lower inter-observer precision. The measurement of the acetabulum inclination and anteversion, the CCD angle, the femur torsion, the pelvic rotation and the anterior pelvic plane inclination had a low intra- and inter-observer precision. Similar results were found on postoperative EOS images. Our results are partially consistent with the literature since authors found high intra- and inter-observer precision for all pelvic parameters. Further studies are therefore needed to evaluate the impact of the observer experience on the reliability of those measurements.

Iatrogenic Bone and Soft Tissue Trauma in Robotic Total Knee Arthroplasty Compared with Conventional Jig-Based Total Knee Arthroplasty: a Prospective Cohort Study and Validation of a New Classification System
PRESENTER: Babar Kayani

ABSTRACT. Background: The objective of this study was to compare macroscopic bone and soft tissue injury between robotic-arm assisted total knee arthroplasty (RA-TKA) and conventional jig-based total knee arthroplasty (CJ-TKA) and create a validated classification system for reporting iatrogenic bone and periarticular soft tissue injury after TKA.

Methods: This study included 30 consecutive CJ-TKAs followed by 30 consecutive RA-TKAs performed by a single surgeon. Intraoperative photographs of the femur, tibia, and periarticular soft tissues were taken before implantation of prostheses. Using these outcomes, the macroscopic soft tissue injury (MASTI) classification system was developed to grade iatrogenic bone and soft tissue injuries. Interobserver and Intraobserver validity of the proposed classification system was assessed.

Results: Patients undergoing RA-TKA had reduced medial soft tissue injury in both passively correctible (P<0.05) and non-correctible varus deformities (P<0.05); more pristine femoral (P<0.05) and tibial (P<0.05) bone resection cuts; and improved MASTI scores compared to CJ-TKA (P<0.05). There was high interobserver (intraclass correlation coefficient 0.92 [95% confidence interval: 0.88-0.96], P<0.05) and intraobserver agreement (intraclass correlation coefficient 0.94 [95% confidence interval: 0.92-0.97], P <0.05) of the proposed MASTI classification system.

Conclusion: There is reduced bone and periarticular soft tissue injury in patients undergoing RA-TKA compared to CJ-TKA. The proposed MASTI classification system is a reproducible grading scheme for describing iatrogenic bone and soft tissue injury in TKA.

Ten to Fifteen-Year Survival of Navigation-Assisted Total Knee Arthroplasty
PRESENTER: Jean-Yves Jenny

ABSTRACT. 1 Introduction The hypothesis of this study was that the 10 to 15-year survival rate of this particular TKA will be improved in comparison to historical papers when analyzing survival rates and knee function as evaluated by the Knee Society Score (KSS).

2 Material and methods All patients operated on between 2001 and 2004 for implantation of a navigated TKA in the two participating centers were eligible for this study. All patients were prospectively followed with clinical and radiological examination. Survival curve was plotted according to Kaplan-Meier, using the occurrence of TKA revision for mechanical reason as end-point.

3 Results 578 TKAs were implanted during the study time-frame. 116 patients deceased prior to the 10-year follow-up (20%). Final follow-up (including death or revision) was obtained for 439 cases (76%). Clinical status after 10 years was obtained for 341 cases (59%) (KSS, 254 cases – Oxford questionnaire, 299 cases – radiologic evaluation, 197 cases). 10 prosthetic revisions were performed for mechanical reasons during the follow-up time (2%). The global 10-year survival rate was 95.5%, and it decreased to 91.5% at 15 years. The 10-year survival rate for mechanical revision only was 98.0%, and decreased to 96.2% at 15 years (figure 1). The mean KSS at the last follow-up was 188 points, and the mean Oxford score was 55 points. No component was considered loose at the final radiographic evaluation. No polyethylene wear was detected at the final radiographic evaluation. No difference was observed between the two participating centers for any baseline or follow-up data. evaluation.

4 Discussion The present study represents the longer follow-up of navigated TKAs published in the literature. This study confirms our initial hypothesis, namely quite satisfactory results of navigated implanted TKA after more than 10 years. Navigation, whose precision is no longer to be demonstrated, probably contributed to the quality of the results. A more consistent anatomical reconstruction and ligamentous balance of the knee should lead to more consistent survival of the TKA. Other authors did observe similar results (Baumbach 2016). However, superiority of navigated TKA in comparison to conventional implanted TKA is difficult to prove because of the subtle differences expected in mostly underpowered studies (D’Amato 2018). Longer term follow-up may be required.

Measuring Prosthesis Migration Using a Novel Ultra-Low Dose CT-Based Algorithm

ABSTRACT. Background Implant migration is a predictor of survival after hip arthroplasty, and thus crucial to introduce and monitor novel prostheses. Roentgen Stereophotogrammetric Analysis (RSA) is the gold standard method, but requires calibrated radiographs using expensive, specialist equipment and significant technical expertise. We aimed to develop an ultra-low dose CT-based spatial analysis (CTSA) method as an alternative.

Method A ceramic hip resurfacing arthroplasty and 20 tantalum beads were implanted into a pelvis model, mounted onto a 6-degree of freedom motion stage. The pelvis was repeatedly scanned with an ultra-low dose CT protocol, with imposed micromovements in translation (T) from 0.1mm to 1mm, and rotation (R) from 0.2° up to 1° in x, y and z axes to enable the accuracy and precision (double measurements) to be determined. Data were interrogated using a semiautomated 3D CT model-based technique with Materialise Mimics and Mathworks MATLAB software. The effective radiation dose <0.15mSv.

Results For the head, the worst accuracy was 0.19mm (Ty) and 0.74°(RZZ); for the cup it was 0.13mm (Ty) and 0.62 (Rxx) For the head, the worst precision was 0.36mm (Tx) and 0.38°(RXX); for the cup, it was 0.12mm (Tz) and 0.51° (RYY).

Conclusion This in vitro study demonstrates that ultra-low dose CTSA is similar in accuracy to standard-dose (~0.30mSv) RSA. CT is ubiquitous, and this method may be a safer and inexpensive alternative to RSA to longitudinally measure prosthesis migration in multicentre studies and clinical practice. Clinical validation studies are required to estimate the effect of patient variability on accuracy.

17:00-18:00 Session 18: Guided Posters I
Patient-Specific “Safe Zones” Reduce the Rate of Dislocation After Total Hip Arthroplasty

ABSTRACT. INTRODUCTION: Most dislocations have been shown to occur within Lewinnek’s proposed safe zone (LSZ) for cup inclination (40°±10°) and anteversion (15°±10°). Using a functional and dynamic simulation that accounts for individual patient anatomy and variations in pelvic tilt, we created a patient-specific target orientation for the acetabular cup. The purposes of this study were to: (1) compare pre-operative acetabular cup parameters using this novel dynamic imaging sequence to the LSZ, and (2) describe rates of dislocation in patients whose pre-operative acetabular cup parameters were determined using dynamic imaging sequences.

METHODS: We retrospectively reviewed 1,500 consecutive, primary THAs that underwent dynamic sitting and standing pre-operative acetabular cup planning. Using these inputs, we modeled an optimal cup position for each patient. Inclination, anteversion, pelvic tilt, pelvic incidence, lumbar flexion angles, and rates of dislocation were analyzed.

RESULTS: Mean age of patients was 63 years. Mean pelvic tilt was 4.7o when supine, -0.3o when standing, and -0.7o when flex-seated. Mean pelvic incidence was 54o and mean lumbar flexion was 43o. Mean inclination was 40° and mean anteversion was 24°. Only 56% of the dynamically planned cups were within the LSZ (p<0.05). Mean inclination and anteversion difference between dynamic and LSZ was 1.3o and 8.9o, respectively. Only 0.5% of dynamically planned cups dislocated post-operatively, all were within LSZ.

DISCUSSION: Acetabular cup positioning in patient-specific safe zones reduces the rate of dislocation after THA. Historical target parameters for cup inclination and anteversion significantly differ to target values obtained with the use of functional imaging.

Handle Navigation for a Smart Handheld Robot
PRESENTER: Ping-Lang Yen

ABSTRACT. We demonstrated a miniature handheld robot in assisting the surgeon to create a tunnel during pedicle screw fixation. The robot is aimed at stabilizing the drill during penetrating the surface of a vertebra and reducing the drill drifting from the entry point caused by involuntary tremor. The handheld robot is consisted of a hexapod platform. The master control was designed to cooperate with the 6-DOF parallel slave robot. The human machine interface has been investigated for the drill to target the planned trajectory with the operator’s handle motion.

Assisted Preoperative Planning in Total Hip Arthroplasty to Reduce Leg Length Discrepancy

ABSTRACT. Preoperative planning is an integral part of total joint arthroplasty, aiming to restore the joint mimicking the native functionality (Choplin 2008).Dimensions of bone and prosthetic implants are usually evaluated by preoperative radiographs to restore leg length discrepancy and femoral offset (Amirouche et al 2015).Nevertheless, even when using dedicated software, the femoral component is precisely selected only in 34% of the cases, resulting in a significant variability in 50% of the patients with 10mm in postoperative leg length discrepancy (Strøm e Reikerås 2018) With the aim of reducing postoperative complications, in this work a computer algorithm has been developed that uses preoperative x-rays and performs automatic extraction of anatomical landmarks together with an automatic selection of the component that closely restore the native hip. In a first phase, the Fuzzy logic based algorithm extracts the axis of the femoral neck, the femoral axis of the middle diaphysis,both the trochanters and the center of the femoral head.Then,by checking the geometrical data of commercially available hardware selects the component closer to the native anatomy. In a second phase,by a kinematic approximation the algorithm uses the segmentation of the intramedullary canal to position the implant,assuming a press-fit insertion and thus anticipating potential contact region and, consequently, leg length discrepancy and offset. The algorithm has been tested on a set of x-ray images. The correlation diagram is used to determine the femur length bt means of the diameter of the femoral head. A sample of 16 femoral radiographs in Antero-posterior view was used to validate the algorithm. The head size was used to evaluate the error between the dimension calculated and the one manually measured on the radiograph, resulting in the order of + 2.00 mm.The prediction of the fixation by means of press-fit technique gives an average contact height of 21.49 mm and an angular deviation of 4.13 ° of the neck axis, applying a force of 9.25 kN (Sakai 2011).Compared to existing methods, the proposed algorithm allows to calculate the femoral sizes necessary for dimensioning the implant from 2D radiographs in the frontal view only and to predict the prosthesis-bone contact in terms of height and interference reached after hammering.It has to be noted that the study, based on coronal x-rays, does not actually account for pelvic tilt (Bono 2018), that will be include in a further research.

Automatic Analysis of Morphological Parameters of the Patella Based on Three-Dimensional (3D) Surface Data

ABSTRACT. Morphological knowledge about the patella is fundamental to understand normal and pathological knee joint mechanics and guide the design of patellar prosthesis. In literature there are a large number of parameters and measurement methods described to characterize the patellar morphology. However, the majority rely on manual measurements, sample sizes are often small and the number of morphological parameters is limited. The goal of this study was to identify morphological parameters of the patella, develop a standardized and fully automatic workflow for their extraction, and to provide accurate statistical numbers for a large number of patients.

An anonymized dataset of 412 knee geometries from consecutively scheduled total knee arthroplasty patients (gender: 248 female, 164 male) were available. A total number of 8 morphological parameters were identified and later used for the calculation of 3 additional aspect ratios. A fully automatic workflow was developed for parameter extraction based on the three-dimensional surface data. The workflow was applied to all datasets and the results were stored in a database for statistical analysis.

The workflow could process all 412 patellar geometries fully automatic without any algorithmic adjustment or user interaction. The processing time was in the range of 30 s per case. The results of the statistical analysis were in very good agreement with the literature. The numbers clearly demonstrated gender-specific differences, however, it is still unknown whether these are sexual dimorphism or can be eliminated by a scaling. Extensive statistical analysis on gender-specific differences and their normalization is part of future work.

Navigational Versus Conventional Primary Unicompartmental Knee Arthroplasty: Clinical and Radiological Long-Term Results with an Average Follow-up of Ten Years
PRESENTER: Jong-Keun Seon

ABSTRACT. Purpose The aim of this study was (1) to compare the clinical and radiological outcomes of robotic and conventional unicompartmental knee arthroplasty (UKA) with a average follow-up of ten years, (2) to evaluate the survival rate, (3) and to estimate the accuracy of the two techniques by analyzing the outliers of the UKA patients. Methods We evaluated 129 patients, 83 patients undergoing navigational UKA, and 46 patients treated with conventional UKA with a mean follow-up of 10.8 years. HSS, KSS, WOMAC, and SF-12 questionnaires were used for clinical evaluation. Mechanical alignment, implant radiological measurements, and outliers were analyzed for radiological results. Kaplan-Meier survival analysis was performed for survival rate. Results All clinical assessments showed excellent improvements in both groups (all p < 0.05), without any significant difference between the groups (p > 0.05). The conventional UKA group showed a significantly higher number of outliers compared with the navigational UKA group (p < 0.05). The cumulative survival rate was 97.2% in the navigational UKA group and 95.4% in the conventional UKA group with excellent survival (p = 0.763). Conclusion Our study showed excellent survival with both navigational and conventional UKA and similar clinical outcomes at long term follow-up. And, in terms of radiological outcome, navigational UKA showed better accuracy and consistency with fewer outliers compared with conventional UKA. With longer follow-up and larger cohort, the accuracy and effectiveness of navigational UKA on implant survival rate can be elucidated in the future.

Preliminary Planning for a Multi-Institutional Database for Ultrasound Bone Segmentation
PRESENTER: Prashant Pandey

ABSTRACT. Ultrasound (US) bone segmentation is a key component in many US-based computer assisted orthopaedic systems. Although numerous US bone segmentations techniques exist, there remains no direct way of comparing their performances. This is primarily due to the lack of an accessible US bone image database, and secondly due to a lack of standard validation practices. To address this issue, we are beginning a multi-institutional international collaboration across multiple research centres with the aim of creating an open database for US bone segmentation consisting of several thousand US images and corresponding bone surface segmentations. Our collaboration also aims to address outstanding issues in US bone segmentation, such as determining the reliability of manual segmentations and establishing a set of evaluation metrics which should be reported in future segmentation studies. Finally, we strongly encourage interested researchers to join and contribute to this project as this will help to create a more diverse database and knowledgeable collaboration.

Automatic Standardized Shape Analysis of the Sagittal Profiles (J-Curves) of the Femoral Condyles Based on Three-Dimensional (3D) Surface Data

ABSTRACT. The sagittal geometry of the articular surfaces of the femoral condyles is one of the main factors affecting knee kinematics. A circular approximation has been often followed in different concepts of knee implant designs. However, the radii are very sensitive regarding the length of the fitting arc and position of the sagittal plane. The goal of this study was to automatically analyse the medial and lateral sagittal profiles of the femoral condyles mathematically in a standardized and robust fashion.

The study was based on bony femoral geometries of 20 male subjects. At first, a standardized anatomical coordinate system was calculated. The posterior cylindrical axis was used to locate the sagittal cuts. Subsequently, a curvature analysis revealed the boundary points of the articulating portion. Finally, the circle least-square method was applied resulting in a posterior and distal circular arc with tangential transition and continuity.

The framework was able to process all datasets without any computational error. The visual inspection revealed an accurate circular fitting. The mean medial and lateral posterior radii were approximately equal.

We presented a standardized approach to describe the medial and lateral sagittal profiles of the femoral condyles mathematically by two-circular arcs. The developed framework is capable of analysing fully automatic the medial and lateral sagittal profiles robustly in a standardized manner, solely based on femoral cutting profiles. The framework may also have the potential in femoral component design optimization and automatic morpho-functional studies of large data bases.

Stress Distribution in the Femur Where Cementless Stems Were Placed with Thermoelastic Stress Analysis and Finite Element Analysis

ABSTRACT. Background: Stress analysis using a distortion gauge is generally used as a mechanical experiment, but can evaluate stress distribution at point level only. Thus, we measured surface stress under actual loads with thermoelastic stress analysis(TSA), which can measure continuous surface stress rather than stress at individual points and visually evaluate overall stress distribution. Objectives: To examine differences between TSA and finite element analysis(FEA) by analyzing surface stress in a synthetic femur where tapered wedge stems are inserted. Methods: In the TSA, the vertical was applied to the bone head. Changes in the temperature of the surface of the samples with thermoelastic effect were obtained using an infrared stress imaging system. In the FEA, Mechanical Finder was used for the analysis. 1800 N was applied downward vertically to the top of the bone head to completely constrain the distal femur and calculate “maximum − minimum principal stress.” Results: Both methods revealed that the minimum principal stress was distributed in the medial side, and the maximum principal stress was distributed on the lateral side. In the TSA, the localized stress distribution gradually decreased toward the surroundings around the sites of contact with the stems. In the FEA, strong stress was found in the middle portion on the lateral side and gradually decreased toward the surroundings. Discussion: TSA can visualize more-localized and diffuse stress distributions in the surroundings, and revealed a gradual decrease in stress concentration toward the surroundings. Although stress distribution was similar for both analyses, TSA can better visualize synthetic bones.

Imageless Computer Assisted Navigation in Ceramic-on-Ceramic Total Hip Arthroplasty Vs. Manual Approach: a Single-Centre Retrospective Study
PRESENTER: John McLoughlin

ABSTRACT. Background: Acetabular cup positioning is vital to the long-term survivorship of total hip arthroplasty (THA). Malalignment has been linked to dislocation, wear and osteolysis. Although there are many studies demonstrating the reduction in variability of cup positioning with computer-assisted techniques, there are relatively few reporting long-term patient reported outcomes and revision rates. Aim: The aim of this study was to review whether those patients who underwent navigated THA had better long-term survivorship or better patient reported outcomes. Methods: We compared revision rates and Oxford hip scores of 152 THAs (47 navigated and 105 non-navigated) performed at a single site between 2003 and 2008, with a minimum follow-up of 10 years. Results: 9 of the non-navigated and none of the navigated hips were revised at 10 year follow-up (p=0.057). There were no observable differences in 10-year Oxford hip scores between the navigated and non-navigated hips, 44.82 and 43.38 respectively. Conclusion: With respect to the rate of revision, although statistical significance was not achieved, it can be shown from our data that there was a clinically significant reduction in revision rates with navigated vs. non-navigated techniques. More data with higher patient numbers in the navigated cohort may be required to validate the results of our study.

Accuracy and a Learning Curve of an Accelerometer-Based Computer Navigation System in Total Knee Arthroplasty
PRESENTER: Hirotake Yo

ABSTRACT. The KneeAlign2 (OrthAlign,Inc., Aliso Viejo, CA) is a portable accelerometer-based navigation device for use in performing the distal femoral resection accurately perpendicular to the mechanical axis in the coronal plane in total knee arthroplasty (TKA).This device works as a computer-assisted surgical system. It does not require the use of a large console for registration and alignment feedback. The aim of this study was to investigate the accuracy in positioning the femoral component and the existence of a learning curve in conducting TKA using this device. A total of 86 patients with primary osteoarthritis of the knee were enrolled in this prospective study. There were 64 women and 22 men . The mean age of the patients was 76.6 years (53 to 89). The KneeAlign2 system was used for distal femoral resection. These patients were divided in two groups. Group1: TKA operated by surgeon of experience using the KneeAlign2 more than 30 cases.(42 knees) Group2:TKA operated by surgeons of experience using the KneeAlign2 less than 30 cases.(44 knees) Standing AP hip-to-ankle radiographs were obtained postoperatively. Positioning of the femoral component was measured by the radiographs.Outlier in coronal alignment were defined as >2°of varus/valgus.The radiographic results and operation time were compared between the groups. Students t-test was performed to assess the statistical analysis (p<0.05) There was no statistical significance between the demographics( age, gender, BMI) of each groups. And radiographic results and operation time have no statistical significance between the groups. Owing to these results, this portable navigation device is highly accurate in positioning the femoral component in TKA. And as the learning curve for using this device does not be observed, this portable navigation is easy to handle even for beginner users.

18:00-22:00 Faculty Dinner

Shuttle for the Boat Tour Dinner will leave at 17:30 from the Conference Venue (Hilton New York Midtown Manhattan Hotel).