ABSTRACT. The Coronal Plane Alignment of the Knee (CPAK) is a recent method for classifying knees using the hip-knee-ankle angle and joint line obliquity to assist surgeons in selection of an optimal alignment philosophy in total knee arthroplasty (TKA). Our objective was to characterize the joint imbalance and identify differences between CPAK categories. A retrospective review of TKA’s performed using the OMNIBotics platform and BalanceBot for measuring joint balance using a tibia first workflow were included. Lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were defined by landmarking after exposure. Joint gaps were measured under tension after the tibial resection throughout flexion. Resection thicknesses were validated to recreate the pre-tibial resection joint balance. Knees were subdivided into 9 categories based on the arithmetic hip-knee-ankle angle and the joint line orientation. Differences in balance at 10°, 40° and 90° were determined using a one-way 2-tailed ANOVA test. 1124 knees satisfied inclusion criteria. The highest proportion of knees (60.7%) are CPAK I with a varus aHKA and Distal Apex JLO, 79.8% report a Distal Apex JLO and 69.3% report a varus aHKA. Greater medial gaps are observed in varus knees compared to neutral and valgus knees (p<0.05 in all cases) as well as in the Distal Apex groups compared to the Neutral groups (p<0.05 in all cases). Significant differences in joint balance were observed between CPAK groups. When pre-operatively planning component alignment or selecting alignment strategy hip-knee-ankle angle, joint line orientation and joint balance should be considered.

ABSTRACT. Introduction The purpose of this study was to evaluate 10 year(9-12 Yr) implant survival, functional patient reported outcome measures (PROMs) and radiological outcomes using two different surgical methods Navigated (NTKR) and conventional (CTKR) Materials and Methods The case control study is a retrospective analysis of prospectively collected clinical data, national registry data and radiological analysis. All patients get similar pre and post op management with standaradised practice irrespective of consultant or method of surgery. Statistical Analysis and Results A total of 4050 replacements done between 2008-2011 for mainly primary osteoarthritis by 55 lead surgeons were included. 2247 replacements NTKR, 1803 CTKR. The pre-operative demographics (Gender, BMI and side) were similar apart from age with navigated being younger(p-value=0.000,) Results and conclusion No statistical difference in the satisfaction scores and oxford scores between the two groups. Mechanical axis within ±3 degrees is significantly better for NTKR. Pulmonary Embolism (PE) in NTKR was significantly lower(p-value=0.004). DVT, CVA, IHD and AKI were not significantly different. 114 (2.81%) revisions were done. The revision rate is increased with BMI more than 40(p-value=0.019), younger than 65(p-value=0.000) and post-operative coronal alignment beyond ±3 degrees (p-value=0.046). The revision rates between both methods were not significantly different (p-value=0.089, 2 Proportions test). Conclusion: Excellent results with NTKR and CTKR method at 9-12 years, can be achieved in an elective high volume arthroplasty unit. Navigation results in significantly better alignment. Revision rates were higher in younger patient, higher BMI and alignment outside 3 degrees.

ABSTRACT. INTRODUCTION A key goal of all TKA alignment strategies is to achieve joint balance. This study aims to compare the alignments achieved by preoperatively planning to a novel distracted joint gap protocol to common alignment strategies as well as to the alignment of a healthy non-arthritic population[1].

METHODS A retrospective study comprised of 145 knees was performed. A long-leg supine CT scan, weightbearing AP knee X-ray and two distracted knee X-rays (one each in extension and flexion, making use of an ankle weight to open the joint) were taken pre-operatively. This imaging was used to perform segmentation, landmarking and 3D-to-2D registration. The medial and lateral joint gaps were determined in extension and flexion.

RESULTS The mean weightbearing, KA planned and distracted joint planned HKA were 4.7° (±5.9°) varus, 0.3° (±3.2°) varus, and 2.2° (±3.5°) varus. This compares to a healthy adult HKA of 1.3° (±2.3°) varus. A patient level comparison between the planned KA and distracted joint HKA found that the coronal angles of the two alignments are within 3° of each other for 64% patients, within 3-5° for 26% of patients and greater than 5° for the remaining 10% of patients.

DISCUSSION Of those compared, the planned distracted HKA was the closest to the constitutional varus HKA of a healthy population. Patient level analysis highlighted the fundamental differences between the planned KA and joint distracted alignments. By considering both hard and soft tissue, the planned joint distracted alignment allows for a more holistic foundation for pre-operative surgical planning for a given patient.

REFERENCES 1. Bellemans J, Colyn W, Vandenneucker H, Victor J. The Chitranjan Ranawat award: is neutral mechanical alignment normal for all patients? The concept of constitutional varus. Clin Orthop Relat Res. 2012 Jan;470(1):45-53.

ABSTRACT. Appropriate management of the soft tissue envelope at the time of the surgery is critical to the long-term success of total knee arthroplasty (TKA). In this regard, this study evaluated the ability to achieve the targeted ML gap balance when using a computer-assisted orthopedic surgery (CAOS) system featuring a force-controlled intraarticular distractor. The first 150 cases performed by 16 surgeons were reported without any exclusions, and for each of these cases, the final mediolateral (ML) laxity was compared to the predicted ML laxity. The average signed ML laxity was well aligned with a neutral differential throughout the full arc of motion and ranged from -0.05mm at 35° of flexion to 0.37mm at 85° of flexion. The signed ML laxity curves tend to be surgeon-specific. The average unsigned ML laxity was linear throughout the full arc motion and ranged from 1.14mm at 85° of flexion to 1.27mm at 30° of flexion. Despite data from all the users (not only design surgeons) involved with this pilot release were considered and the learning curve cases were not excluded, it was observed a high ability to achieve the targeted ML laxity using the proposed method.

ABSTRACT. Purpose: The aim of this study was to validate navigation in the measurement of knee kinematics.

Method: 10 e.Motion® total knee prosthesis (BBraun-Aesculap) FP were implanted, using the OrthoPilot TKA Version 4.3 Kobe version navigation system. The kinematic recording by the navigation system was then performed simultaneously with the recording of a series of fluoroscopies during a continuous passive flexion movement of the prosthetic knee, twice. The kinematic parameters were extracted from the fluoroscopic recordings by image processing using JointTrack Auto® software. The main criteria were knee axis, femoral rotation, femoral translation relative to the tibia, and medial and lateral femoro-tibial decaptation. Data analysis was performed using a Kappa correlation test. The concordance of the measurements was assessed using the intraclass correlation coefficient (ICC) and its 95% confidence interval.

Results: For the 20 kinematics studied, the ICC of the HKA angle was 0.839 [0.820; 0.856], femoral translation 0.560 [0.517; 0.600], femoral rotation 0.652 [0.616; 0.686], medial femoro-tibial decoaptation 0.905 [0.894; 0.916] and lateral 0.767 [0.740; 0.791].

Discussion: OrthoPilot system cannot, at the end of this work, be considered as a reliable instrument for measuring the kinematics of the prosthetic knee.

ABSTRACT. Introduction Computer-assisted navigation systems (CAS) are increasingly being integrated into total knee arthroplasty (TKA) procedures, but perceptions of associated learning curve and increased operative time continue to curtail uptake. Newer-generation navigational systems aim to streamline integration into surgical workflow to mitigate increases in operative time. Here, we assess the impact of a novel imageless CAS on operative time for TKA.

Methods A retrospective analysis of prospectively collected data of a cohort of patients undergoing primary unilateral TKA with one of three surgeons between October 2019 and March 2020 was conducted. Consecutive cases using a novel imageless CAS were included in analysis. For each surgeon, average operative time was recorded and compared in sequential five-case cohorts to average operative time for the same procedure performed conventionally using a two-tailed t-test.

Results Average conventional operative times were 95.9±15.0, 86.6±13.7, and 116.9±25.1 min. for the three surgeons. Initial CAS-assisted operative times increased to 107.0±9.8 (p=0.07) and 102.4±13.2 (p=0.06) min. for Surgeons 1 and 2 and decreased to 113.2±9.8 min (p=0.52) for Surgeon 3. Most recent CAS-assisted operative times were 94.8±13.9 (p=0.88), 88.7±15.3 (p=0.84), and 104.8±13.2 (p=0.12) min. as compared to pre-CAS. Absolute differences for the most recent navigated procedures ranged from 12.1 min. faster to 2.0 min. slower.

Conclusion The learning curve for TKA navigation may be as few as 10 cases, and any associated increases in operative time may be transient and non-significant. Moreover, navigation may ultimately speed operative time, perhaps as the result of enhanced intraoperative assessment of alignment.

ABSTRACT. Sensor augmented robotic assisted surgical platforms can quantitatively achieve a balanced joint in total knee arthroplasty (TKA). The impact of balance on 2-year outcomes has not been investigated. In this study we investigate if intra-operative joint balance is associated with midterm outcomes and aim to define optimal balance targets for KOOS pain scores 2 years post-TKA.

TKAs were performed using a robot assisted TKA platform with a joint tensioning device. Joint gaps were recorded throughout flexion during trialing. Demographics were recorded pre-operatively and Knee Injury and Osteoarthritis Outcome Score (KOOS) was collected at 2-year post-op. Correlations between joint gaps and KOOS outcome were investigated.

Demographics of the population are: 58%F, 67±8 years, BMI of 32±5 kg/m2, coronal deformity of 5.2°±6.2° varus. Balance and laxity targets with maximum and minimum thresholds for improved pain scores were identified throughout flexion. When all targets were satisfied the highest KOOS pain score was achieved (93.8) and a gain of 26% of patients who achieved the Patient Acceptable Symptom State was realized (p = 0.008). No associations were identified between femoral or tibio-femoral component alignment and outcome.

Intra-operative joint gaps correlated with 2-year KOOS Pain scores across all flexion angles investigated. Combining joint gap windows, subgroups of patients were found with further improved outcomes. No association was found between alignment and outcome, indicating joint balance may have a greater impact on outcome than alignment.

ABSTRACT. Objectives: This study aimed to assess if multiplayer training was superior to single player training for acquisition of both technical and non-technical skills in learning anterior approach total hip arthroplasty Methods: 40 participants (20 novice surgeons and 20 novice scrub nurses) were enrolled in this study and randomised to solo or team immersive virtual reality training learning anterior approach total hip arthroplasty. Solo participants trained with virtual avatar counterparts, whilst teams trained in pairs (surgeon and scrub nurse). Both groups underwent 5 VR training sessions over 6 weeks. Subsequently, they underwent a real-life assessment in which they performed AA-THA on a high-fidelity model with real equipment in a simulated operating theatre. Teams performed together and solo participants were randomly paired up with a solo player of the opposite role. Videos of the assessment were marked by two blinded expert assessors. The primary outcome was team performance as graded by the NOTECHS II. Secondary outcomes were procedure time and procedural errors from an expert pre-defined protocol Results: Teams outperformed solo-trained participants for non-technical skills in the real-world assessment (NOTECHS-II score 50.3 ± 6.04 vs 43.90 ± 5.90, p=0.0275). They completed the assessment 28.1% faster (31.22 minutes ±2.02 vs 43.43 ±2.71, p=0.01), and made close to half the number of technical errors when compared to the individual group (12.9 ± 8.3 vs 25.6 ± 6.1, p=0.001). Conclusions: Multiplayer training leads to faster surgery with fewer technical errors and the development of superior non-technical skills.

ABSTRACT. Localised treatment of knee osteochondral defects can avoid or delay the need of more invasive procedures such as partial or total knee arthroplasty. Such procedures, however, are relatively uncommon, partly because of the difficulty of ensuring a good match between the shape of the implant and the surrounding bone anatomy. This work presents a prototype workflow to assists clinicians with the selection of an appropriate implant for a given patient and lesion, and the optimisation of its pose. The software was integrated with the NAVIO™ surgical platform and tested on synthetic bone phantoms.

ABSTRACT. INTRODUCTION Native extension and flexion joint gaps are primarily measured intraoperatively using devices such as navigation systems or tensioners, but there are advantages to being able to pre-operatively plan to such gaps. This study aims to validate the ability of a novel distracted joint gap radiology protocol to measure pre-operative extension and flexion joint gaps.

METHODS A retrospective study comprised of 42 knees was performed. Patient imaging was obtained and used to perform segmentation, landmarking and 3D-to-2D registration. The pre-operative medial and lateral joint gaps were determined in extension and flexion. Intraoperatively, a range of motion analysis was conducted using the Brainlab Knee 3 navigation system to measure the joint gaps in extension and flexion.

RESULTS SECTION In extension, both medial and lateral pre-operative radiological and intraoperative navigated gaps displayed moderate and statistically significant correlations (r=0.45; p=0.003 for medial and r=0.4; p=0.01 for lateral). In flexion, only the medial radiological and navigated joint gaps correlated (r=0.54, p<0.001), with a not statistically significant trend for the lateral flexion joint gaps.

DISCUSSION The moderate and statistically significant correlations between these joint gaps to those measured intraoperatively suggests they are reflective of on the table experience with patients. Although further work is required to understand if differences are attributable to variability in the radiological or intra-operative assessments, the pre-operative analysis technique described in this study provides the opportunity to develop a more holistic pre-operative surgical plan which considers the state of both hard and soft tissue within the joint.

ABSTRACT. Abstract Introduction Preoperative planning of total hip arthroplasty (THA) using 2D low-dose full-body imaging (EOS imaging, Paris,France) has gained popularity in recent years. The EOS system purportedly produces a calibrated image with constant magnification. To date no studies using conventional, non-EOS, digital planning software to determine variations in EOS image magnification have been reported. The purpose of our study was to investigate magnification variability in order to assess the need for routine magnification calibration with conventional software for more accurate THA planning with EOS technology. Methods Postoperative EOS images from 137 patients who underwent THA for primary osteoarthritis were retrospectively evaluated. Three prosthesis types were used in the surgeries: (Smith and Nephew-Biolox Delta [N=112], Stryker-Biolox [N=23], and Zimmer-Echo [N=2]). The femoral head diameter was measured by two independent observers using both Orthoview™ and TraumaCad™ software. Actual sizes of the implants were extracted from surgical reports to calculate image magnification. Results Magnification varied among cases (mean 133%, range 129–135%). There was no statistical difference in mean image magnification among the various implant sizes (p=0.8). Mean observer and inter-observer reliability was rated excellent. Conclusion THA planning with 2D EOS imaging is subject to magnification variation as analyzed with conventional planning software in this series. This finding is of paramount importance for surgeons using EOS imaging in preparation for THA since errors in magnification could influence the accuracy of preoperative planning and ultimately the clinical outcome.

ABSTRACT. Purpose Operative management of distal radius fractures (DRF) is increasingly common. As operative indications are controversial, radiographic parameters (RPs), e.g. radial inclination, dorsal tilt, and articular step-off, can provide objective support for effective decision making. However, manual measurement of RPs is time-consuming and may be imprecise and subject to inconsistency. We have developed custom software to automatically compute six common RPs associated with DRF in anteroposterior (AP) and lateral radiographs. This study aims to assess the effect of automatically computed RPs on decision making for treatment of DRFs. Our hypothesis was that precise and consistent measurement of RPs may improve decision making. Methods Thirty-five radiograph series of DRFs were presented to nine fellowship-trained hand and orthopaedic trauma surgeons. Each case consisted of plain AP and lateral radiographs together with basic clinical patient information. One of two possible treatment options was selected: casting, or open reduction with a locking plate. The survey was repeated three weeks later with computer generated RP measurements. Data was analyzed for inter and intraobserver variability with the interclass coefficient (ICC) and Kappa value. Cases were evaluated according to latest DRFs guidelines treatment protocol; the selected treatment was compared to the guidelines recommendation. Results The ICC value for interobserver variability was 0.35 in the first survey, improving to 0.50 when RPs were included (p<0.001). Improved ICC was found in trauma and hand sub-specialties. The mean intraobserver ICC was 0.68 (p<0.001). Correlation to guidelines treatment recommendation was 0.33 (0.18-0.48) without the RPs, and 0.50 (0.38-0.63) with the RPs (p=0.060). Conclusion Providing computed RPs to orthopaedic surgeons improves the consistency of clinical decision and adherence to guidelines for treatment of DRFs.

ABSTRACT. Although proximal humeral fractures remain a challenging and common clinical issue, there is lack of consensus about their classification and consequently to decide about the most appropriate treatment option. Dedicated software based on three-dimensional (3D) computer tomography (CT) models for quantitative assessment of fragment displacement would potentially allow for a more accurate fracture classification and help to plan the surgical strategy needed to reduce the fracture in the operating theatre. Traditionally, access to computational resource intense 3D-CT data processing software is limited to workstation computers. The aim of this study was to elaborate the feasibility of using state-of-the-art cloud technology to enable access to fracture pattern analysis functionality for humeral head reconstruction in a distributed manner. Therefore, the feasibility of implementation of computational resource intense classification and planning software functionality for proximal humeral fractures using state-of-the-art cloud technology was studied. Software architectural concepts of computational load distribution between client and server were investigated. The implemented solution was tested in a usability study with five biomedical engineers. Implementation of a cloud-based solution was feasible using state-of-the-art technology under application of a specific software architectural approach allowing to distribute computational load between client and server. Mean System Usability Scale (SUS) Score for the developed application was determined to be 63 (StDev 20.4). These results can be interpreted as a medium low usability with high standard deviation of the measured SUS score. We conclude that more test subjects should be included in future studies and the developed application should be evaluated with a representative user group such as orthopaedic shoulder surgeons in a clinical setting.

ABSTRACT. Remote patient monitoring, using wearable devices and connected patient engagement platforms has the potential to improve timely clinical decisions. Data collected from multiple patients, including using the remote engagement platforms themselves, can be used to produce evidence-based reference to support clinical decisions. While some normative references for functional measure currently exist for total knee arthroplasty (TKA), these are still lacking for VAS pain scores. Therefore, VAS pain scores on a 10-point Likert scale were analyzed for 126 patients, each reporting at least five scores in the 180 days following surgery. These were used to produce a normative recovery model for total knee arthroplasty patients. A nonlinear mixed effects model was fitted, whereby the response variable is assumed to be distributed following a beta-binomial distribution. The population mean trend shows an increase in pain in the first few days following surgery, with wide dispersion showing scores ranging throughout the 10-point scale. After the first week, the expected pain score steadily decreases, resulting in a score no higher than one in 50% of the population beyond 90 days after surgery. The fitted model allows referencing individual patient's pain scores at different stages of recovery, against the model’s predicted distribution. This approach can support early detection of patients that significantly deviate from the reference model and be a useful integration into clinical decision support software tools.

ABSTRACT. Soft tissue balance can be achieved by adjusting component position or releasing soft tissues in total knee arthroplasty (TKA). The objective of this study was to investigate the impact of alignment and soft tissue release on patient outcome. In a multicenter study, soft tissue releases during TKA were prospectively documented in 330 robotic-assisted TKAs. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were captured post-operatively. Delphi analysis was used to determine inlier and outlier component alignment boundaries: Tibia Coronal (TC): ±3°, Femur Coronal (FC): ±3°, Femoral Axial (FA): 3°Int-6°Ext, Hip-Knee-Ankle (HKA): 3°Val-4°Var, Tibiofemoral Axial (TFA): 3°Int-6°Ext. Kruskal-Wallis ANOVA tests were used to compare groups. No significant differences were found between any individual or grouped inlier and outlier alignment criterion and KOOS at any time point. Outlier alignment frequencies were: TC:0%, FC:12%, FA:8%, HKA:9%, TFA:8%, any:23%. Soft tissue releases were performed in 18% of cases. Knees with soft tissue releases reported significantly worse KOOS scores at: 6M: Symptoms (80.0 vs 75.3, p=0.03), ADL (86.2 vs 80.8, p=0.030), QOL (70.1 vs 60.9, p=0.008); 12M ADL (90.0 vs 85.1, p=0.023); and 24M ADL (91.9 vs 87.2, p=0.016). A higher proportion of patients achieved Minimally Clinically Important Difference (MCID) for pain at 6 months for those having no releases vs released (92.3% vs 81.0%, p = 0.021). No significant associations were found between pre-operative deformity, pre-operative or post-operative KOOS. These results suggest small deviations in the component alignment to achieve balance are preferable to soft tissue release for improved short-term outcomes.

ABSTRACT. Imperial College London’s first venture into orthopaedic robotic surgery was with a spinoff company called Acrobot Ltd. This was developed over many years, culminating in a series of uni-condylar knee replacement (UKR) surgery operations with excellent results. Much was learned from this experience with many hardware iterations culminating in a trolley based cooperative system with 3 powered axes carrying a cutter that required large arm motions. To exploit the resulting know-how, Signature Robot Ltd, was founded. The Signature Robot is also cooperative, with the cutter motor being held between the fingers while the wrist is supported comfortably on a platform. The Signature Robot overcomes multiple limitations of orthopaedic robots such as the ACROBOT. Firstly, it is significantly smaller due to the implementation of a passive lockable gross positioner rather than a large actively controlled robot arm. The mechanism to allow precise finger motion is also significantly smaller than the devices needed for larger arm movements, this also results in much lower impedance to back-drive each of the axes. The design was optimised to cover the workspace required for UKR resulting in a robot with a 150x140x150mm footprint. The robot was kinematically calibrated to validate its accuracy resulting in end-effector positioning with an average error of 0.82mm.

ABSTRACT. To determine the extent and frequency of soft tissue releases required to achieve balance in measured resection (MR) vs gap balanced (GB) total knee arthroplasty (TKA), this study compared mediolateral (ML) balance and joint laxity throughout flexion between the two techniques. The precision of predictive GB was also assessed.

Two surgeons performed 95 robotic assisted GB TKA’s using the same implant with a predictive balance algorithm, limiting tibial varus to 3° and adjusting femoral positioning to optimize balance throughout flexion. Final joint laxity was measured using a robotic ligament tensioner. Planned MR (pMR) was simulated on all cases post-hoc by applying neutral tibial and femoral coronal resections, 3° of external femoral rotation, and default resection depths set to the implant thicknesses. Differences in ML balance, joint laxity, component alignment, and resection depths were compared between planned GB (pGB) and pMR. Further analyses compared ML balance and laxity between pGB and final GB (fGB).

pMR resulted in a higher proportion of knees with >3 mm of ML imbalance at 10° (38% vs. 9%), 45° (34% vs. 3%), and 90° (30% vs. 0%), p<0.001 compared to pGB. Mean pMR laxity was 2 mm tighter medially and 1 mm tighter laterally than pGB throughout flexion. RMS errors in laxity between fGB and pGB were between 1.9 and 2.4 mm throughout flexion.

Surgeons should expect to correct a 3 mm gap imbalance in 30% of patients when performing MR.

ABSTRACT. Background: Several studies have been performed that compare the accuracy of Robotic-Assisted Total Knee Arthroplasty (RATKA) to conventional instrumentation as well as Computer Assisted Surgery (CAS) to conventional instrumentation, yet there is a lack of studies comparing RATKA to CAS. The purpose of this study is to evaluate the accuracy of a contemporary image free CAS system for TKA in a cadaveric study using the same methodology as used previously to access the accuracy of a RATKA system and Conventional instrumentation. Methods: Four orthopaedic surgeons performed bi-lateral TKA on 18 pelvis-to-toe cadaveric specimens without implantation using the BrainLab Knee3 CAS system. Pre-operative and post-operative computed tomography scans were taken to access the resection accuracy of the CAS system relative to alignment targets recorded intraoperatively. Results: The mean error in femoral coronal angle was 1.08°±0.87° compared to 1.39°±0.95° conventional and 0.63°±0.50° RATKA; the differences between CAS and RATKA were statistically significant. The mean error in the tibial coronal angle was 1.24°±1.13° compared to 1.65°±1.29° conventional and 0.93°±0.72° RATKA. The mean error in femoral flexion was 2.13°±1.87° compared to 3.27°±2.51° conventional and 1.21°±0.90° RATKA; the differences between CAS and manual and CAS and RATKA were statistically significant. The mean errors in the femoral rotation (CAS 1.30°±1.38°, conventional 1.00°±0.70°, RATKA 1.04°±0.81°) and tibial slope (CAS 1.89°±1.28°, conventional 1.63°±1.39°, RATKA 1.62°±1.13°) were similar between the groups. Conclusion: This study showed that for some metrics CAS improves resection accuracy compared to conventional instrumentation and RATKA further improves resection accuracy compared to CAS.

ABSTRACT. Introduction: Primary robotic total knee arthroplasty (TKA) is associated with favorable outcomes. To further understand robotic TKA learning curve, we evaluated early postoperative outcomes of robotics vs. manual TKA, based on surgeon experience. Methods: Patients (> 64 years) from the Medicare database, with primary, unilateral, elective TKA (“index”) from October 2015 to December 2019 were identified and categorized based on robotic vs. manual surgery, and surgeon experience: low-count surgeons had < 40 cases in the 12-months pre-index; medium-low, medium-high and high count surgeons had 41-80, 81-120 and 121-160 cases, respectively. The low-count robotic cohort (RC) was compared to the low, medium-low, medium-high, and high count manual cohort (MC) for the length of the hospital stay (LOS), and rates of home and skilled nursing facility (SNF) discharge. Descriptive statistics (means and proportion with 95% confidence intervals) were performed. Results: 296 low-count robotic cases were compared to 209,494 low-count manual and 252,905 medium-low, medium-high and high-count manual cases. The low-count RC had an average LOS of 2.03 days (95% confidence intervals (CI): 1.86-2.20) vs. 2.20 days (95%CI: 2.20-2.21) for the low-count MC. 82.4% patients (95%CI: 78.1%-86.8%) from the low-count RC were discharged home vs. 74.2% (95%CI: 74.0%-74.4%) in the low-count MC and 83.6% (95%CI: 83.3%-84.0%) in the high-count MC. Discharge to SNF affected 15.2% (95%CI: 11.1%-19.3%) in the low-count RC vs. 21.0% (95%CI: 20.9%-21.2%) and 15.2% (95%CI: 14.9%-15.4%) in the low-count and medium-high MC, respectively. Conclusion: Patients operated with robotic surgery by surgeons with low yearly volume had a LOS and probability of home discharge similar to that of patients operated with manual surgery by high-volume surgeons. Patients in the robotic group also had a lower rate of SNF discharge compared to the patients in the manual surgery group, with surgeons of similar experience.

ABSTRACT. An image-based guidance system for reduction of the ankle syndesmosis is reported. The approach uses: (1) active shape model (ASM) segmentation to obtain patient-specific surface models of the tibia, fibula, and talus; followed by (2) multi-body 3D-2D registration of the 3D models to 2D fluoroscopic images that are routinely acquired in standard clinical practice. This information, along with a planned target fibula pose, is used as input to a robotic manipulator to assist in performing the reduction. Phantom experiments were performed to evaluate the geometric accuracy and robustness in recovering the displaced fibula pose with respect to the corresponding tibia. The accuracy was measured to be ~2 mm (1.3 mm interquartile range [IQR]) when using the proposed image-based approach, compared to ~7 mm (1.0 mm IQR) when using conventional trackers. Robustness to errors in statistical shape modeling errors was also assessed, demonstrating <5 mm registration error when using models with mean surface distance error of <0.9 mm. The proposed image-guided system is consistent with the workflow requirements of fluoroscopically guided procedures, offers the potential to mitigate radiation exposure to surgical staff using as few as 2 fluoroscopic views for registration and provides quality assurance for accurate joint reduction (essential for long-term clinical outcomes).

ABSTRACT. Technology for balancing gaps has progressed from manual to digital ligament tensioning tools integrated with robot-assisted navigation. However, there has been no comparison between femur-first and tibia-first techniques with this technology. We prospectively investigated joint balance accuracy, precision and early outcomes between a femur-first measured resection and tibia-first gap balancing technique utilizing a digital gap balancing tool. 106 patients were prospectively enrolled (age: 69.0±9.1, BMI: 30.7±3.7kg/m2, gender: 60%F) and underwent PCL sacrificing TKA using a digital gap balancing tool. The cohort was divided into four sequential groups with varying degree of visibility to the gap data generated with the digital ligament tensioning tool: 1) Femur-first blinded to gap data, 2) Femur-first non-blinded to gap data, 3) Tibia-first blinded to gap data, 4) Tibia-first non-blinded to gap data with predictive gap balancing. The mediolateral (ML) gap difference was used to calculate joint balance. KOOS and UCLA scores were obtained up to one year post-operatively. Group 4 reported significantly less midflexion imbalance (40°) compared to groups 2 and 3 (1: 1.5mm, 2: 1.7mm, 3: 1.6mm, 4: 1.0mm, p<0.031) and reduced variance compared to all other groups at 40° and 90° (p<0.012), resulting in an increased frequency of joints balanced within 2 mm throughout flexion in group 4 (1: 69%, 2: 65%, 3: 67%, 4: 91%, p<0.006). No significant differences were found between 3-month, 6-month, or 1-year KOOS and UCLA scores with technique. A tibia-first approach with predictive digital balancing allows surgeons to achieve a target joint balance more accurately in TKA.

ABSTRACT. Introduction Patient recovery from neuromuscular injuries that cause upper limb dysfunction is commonly assessed via manual methods. Manual muscle testing is subjective, time consuming and requires extensive training. Existing dynamometers are more objective, but they are prohibitively expensive and impractically large, making them inaccessible to most clinics and patients with disabilities. Our aim is to develop a table-top upper limb muscle dynamometer that provides standard positioning, ease of use and portability while giving clinicians consistent and reliable quantitative data on a patient’s isotonic and isometric muscle power and strength, respectively.

Methods The device consists of a lever arm, a brushless DC motor, a load sensor and an ergonomic cuff. It outputs analog data via standard BNC connectors. The device can be intuitively controlled by the operator to test various upper limb joints and motions. Isometric measurement repeatability was assessed by recording the maximal voluntary contractions of 18 healthy participants over three trials.

Results The repeatability across 3 trials was 2.70±2.27 Nm (95th percentile: 6.74 Nm) for elbow flexion, and 2.83±2.13 Nm (95th percentile: 5.65 Nm) for elbow extension.

Conclusions The dynamometer demonstrates a marked improvement in repeatability relative to manual muscle testing. Its small footprint and low cost can make it an easily accessible, standardized testing tool that requires little training to use. Future research and development will focus on using field-oriented control to measure isotonic muscle power in addition to isometric strength.

ABSTRACT. Navigated ligament balancing techniques in TKA reference patient soft tissues and bony landmarks to position implants intended for preserving natural kinematics of the knee using stereotaxic instrumentation. An intraarticular device that can maintain a consistent joint tensioning force without eversion of the patella or any adjustment can reduce cognitive burden on the surgeon while continuing to reference the patient soft tissues for making clinical decisions. The objective of this study was to report in-vitro verification testing of the novel device that generates nearly constant condylar forces independently on both medial and lateral compartments at typical tibiofemoral gap thicknesses encountered during TKA.

Using an Instron load frame a tibiofemoral gap was simulated by mounting femoral trials in extension at 9mm, 12mm, and 15mm distances from a flat stainless steel platen representing a tibial resection. At 9mm, 12mm and 15mm gaps, the average force values were 33.5lbf, 36.8lbf and 34.0lbf respectively with standard deviations of 0.57lbf, 0.87lbf, and 0.88lbf respectively.

Balancing the knee joint with a constant force on both medial and lateral compartments allows for obtaining patient specific information about the knee joint, which can be leveraged for setting up femoral cut parameters. While conventional devices have allowed for obtaining the soft tissue information at specific flexion angles, this intraarticular spacer may facilitate the acquisition of patient data without everting the patella or adjustment while automatically applying a consistent force throughout an entire range of motion. Use of a quasi-constant force tensor in surgery could allow for improvement of patient outcomes by providing real time patient data about the knee balance and kinematics during TKA.

ABSTRACT. Total knee arthroplasty is a common procedure in the management of knee arthrosis, but up to 30% of patients are still not fully satisfied with the post-operative outcomes. Although custom knee implant could improve prosthesis ‘durability and patient’s comfort, the pre-operative planning for the determination of the prosthetic implant design does not consider the femoral and tibial cartilage thickness. The aim of this study is to map the thickness of healthy femorotibial cartilage from CT arthrograms segmentations and to propose a clinical classification according to the thickness. 20 CT arthrograms of knees of adult patients with no history of chondropathy were included. After a semi-automatic segmentation, 2D cartilage thickness maps were constructed for each patient using a bounding box algorithm for the tibial side and a fitting sphere algorithm for the femoral side. To compare the individual maps, a non-rigid registration was applied by taking an unbiased reference image. Average, maximum, minimum and standard deviation maps were constructed. The thickness of the healthy tibial cartilage is relatively homogenous but a greater variability is observed regarding the healthy femoral cartilage, especially in weight-bearing areas. A patient-specific approach has to be developed to consider tibial and femur cartilages for a better definition of custom knee implants.

ABSTRACT. In reducing the risk of dislocation after total hip arthroplasty (THA), it is ideal to control the cup alignment according to the stem alignment to avoid implant impingement during various activities of daily living. There are many reports of impingement simulation of THA, but the selected activities are different which ended up with different safe zones. The purpose of this study was to assess the effects of internal rotation angle at hip 90° flexion on the size of safe zone according to the stem anteversion. The hip implants used in the simulation were an anatomical short stem with an AP reduced neck design, a hemispherical flat liner, and a 32mm femoral head. Implant impingement was evaluated using collision detection in the 3D CAD software Solid Edge (SIEMENS). The initial position of the stem was set at 5° of flexion and 5° of adduction. The stem anteversion angle was set from -10° to 50° with an increment of 5°. Initially, 14 different activity hip positions reported by Widmer were selected, including 30° internal rotation at 90° flexion. The stem anteversion, which showed the largest safe zone area was 5°. However, when 40° internal rotation at 90° flexion reported by Miki was added, the safe zone area with 5° of stem anteversion became 59% smaller than that in the previous condition. The stem anteversion, which showed the largest safe zone area in the revised condition was 25°. The hip position of 40° internal rotation at 90° flexion is preferred for Japanese women in classic activities of daily living. Caution should be taken that internal rotation angle at 90° flexion has a large impact on impingement simulation for safe zone.

ABSTRACT. The psoas major tendon resides on the articular capsule side within the psoas major muscle and passes just above the anterior articular capsule. It is associated with disorders such as internal snapping hip syndrome and Iliopsoas Impingement after Total Hip Arthroplasty (THA). In both cases, snapping and impingement are likely to occur when the hip is moved from the flexion, abduction, and external rotation (FABER) position to extension. However, there have been few reports on the dynamics of the psoas major tendon around the acetabulum in vivo. The purpose of this study was to analyze the dynamics of the psoas major tendon at the anterior aspect of the hip joint from the flexion, abduction, and external rotation (FABER) position to the extended position using wide-bore Magnetic Resonance Imaging (MRI). The subjects were five healthy males. MRI was performed for hip flexion (°)/abduction (°)/external rotation (°) in the following limb positions: (a) 0/0/0, (b) 0/30/0, (c) 30/0/0, (d) 30/30/30, (e) 60/0/0, and (f) 60/30/30. The images were imported into the free software 3D-Slicer, and the proximity of the psoas tendon to the acetabulum at a distance of 5 mm or less was visualized by mapping and qualitatively evaluated. The most proximal distance between the psoas major tendon and the acetabulum in each position and the nearest point identified by Anterior Pelvic Plane (APP) coordinates with the center of the bone head as the origin were calculated. The dynamics of the psoas major tendon in relation to the acetabulum was close to the psoas valley in all limbs, and its sliding area was localized. The most proximal distance was on average 2.8±0.2 mm, and there was no significant difference between any of the limbs compared to the intermediate position. The nearest point of contact was 8.4±1.6 mm medially, 27.8±1.1 mm anteriorly, and 13.7±2.5 mm superiorly from the origin at the center of the head, and there was no significant difference in any limb position compared to the intermediate position. In conclusion, the sliding portion of the psoas major tendon was localized to the psoas valley area of the acetabulum. Therefore, it was suggested that avoiding interference at this site may be important for the prevention and treatment of snapping and impingement of the psoas major tendon.

ABSTRACT. Aim: Despite the success of total knee arthroplasty (TKA), malalignment continues to be a problem which often leads to post-operative complications. The aim of this study was to investigate the accuracy of a novel, imageless, optical surgical navigation tool to assist with the alignment of femoral and tibial cuts performed during total knee arthroplasty.

Methods: Six board-certified orthopedic surgeons performed TKA procedures on 9 cadavers (17 knees total), using a novel, imageless navigation system (Intellijoint KNEE, Intellijoint Surgical). Varus/valgus, femoral flexion, tibial slope, and rotation measurements from the device were compared with angular measurements calculated from post-operative computed tomography (CT) images.

Results: Navigation measurements were highly correlated with those obtained from CT scan in all three axes. For the femoral cuts, the absolute mean difference in varus/valgus was 0.83° (SD 0.46°, r = 0.76), in flexion was 1.91° (SD 1.16°, r = 0.85), and in rotation was 1.29° (SD 1.01°, r = 0.88) relative to Whiteside’s line and 0.97° (SD 0.56°, r = 0.81) relative to the posterior condylar axis. For the tibia, the absolute mean difference in varus/valgus was 1.08° (SD 0.64°, r = 0.85), anterior/posterior slope was 2.78° (SD 1.40°, r = 0.60), and rotation was 2.98° (SD 2.54°, r = 0.79).

Conclusions: Intraoperative monitoring with the imageless navigation tool accurately measures femoral and tibial cuts in TKA, and may help to increase component alignment.

ABSTRACT. Custom implants in Total Knee Arthroplasty (TKA) could improve prosthesis’ durability and patient’s comfort, but designing such personalized implants requires a simplified and thus automatic workflow to be easily integrated in the clinical routine. A good knowledge of the shape of the patient's femur and tibia is necessary to design it, but segmentation is still today a key issue. We present here an automatic segmentation approach of the three joints of the lower limb: hip, knee and ankle, using convolutional neural networks (CNNs) on successive transverse views from CT images. Our three 2D CNNs are built on the U-net model, and their specialization each on one joint allowed us to achieve promising results presented here. This could be integrated in a TKA planning software allowing the automatic design of TKA custom implants.

ABSTRACT. Mismatch between the patient’s knee morphology and the implant geometry is linked to poorer clinical outcome after total knee arthroplasty (TKA). Hence, patients whose knee morphology differs strongly from the norm may have a higher risk to be dissatisfied after surgery. Consequently, a preoperative risk assessment regarding differences between individual knee morphology and implant geometry is favorable. For adequate availability and limited radiation dose, this should be based on standard imaging techniques in TKA, being conventional X-rays. We reviewed morphological measures of the knee to be evaluated on X-rays. Only measures of the articulating areas, without connections to pathologies such as patellar instability or pain, were included. In addition, the accuracy of 2D-3D knee reconstruction was reviewed, in order to assess the potential use for 3D X-ray based morphological analysis. Many parameter definitions for the evaluation on anterior-posterior (AP) and lateral X-rays exist in the literature. If given, the inter- and intraobserver reliability can be interpreted as moderate to excellent. Several authors have reported on 2D-3D reconstruction accuracies. For in vivo/ in vitro studies maximum absolute errors of ~5-6 mm are reported. General limitations of the parameter definitions presented are the respective image requirements and the manual identification of relevant landmarks or reference points required. Methods for 2D-3D reconstruction demonstrated potential for enabling 3D X-ray-based morphological analysis, while improvements regarding accuracy and larger in vivo validation studies are pending. Comprehensive preoperative risk assessment using X-rays is possible. Future steps should include analyses on measurement reliability and on automated parameter derivation.

ABSTRACT. Purpose The aim of this study was to analyze the coronal alignment of a large population of patients undergoing total knee arthroplasty using a modern classification of the knee phenotypes found in a population of non-osteoarthritic patients.

Methods Five hundred twenty navigated total knee arthroplasties were analyzed. The following angles were measured with a computer image free navigation system: medial femorotibial mechanical angle without stress and with maximum manual stress to reduce deformation, and medial distal femoral mechanical angle. The native medial distal femoral and medial proximal tibial angles were calculated. These data were then compared with those published in a non-arthritic population, considered as a control group. The main criterion was the percentage of subjects with normal overall coronal alignment, defined by the association of a normal native medial distal femoral angle and a normal native medial proximal tibial angle. The most frequent phenotypes in the study group were identified.

Results Normal overall coronal alignment was found in 66 patients in the study group (12.7%) and 76 patients in the control group (24.7%) (p<0.001). There were fewer normal patients in the study group than in the control group for medial femorotibial mechanical angle, native medial distal femoral angle and native medial proximal tibial angle. There was a wider distribution of the phenotypes in the study group than in the control group.

Conclusion The distribution of functional phenotypes of the knee in patients undergoing total knee arthroplasty are different from those found in a reference non-osteoarthritic population.

ABSTRACT. The impact of patient specific pre-operative factors on optimal post-operative joint balance has not been investigated. This study prospectively investigated the impact of pre-operative patient demographics, pre-operative KOOS pain score and pre-operative joint balance and laxity on optimal post-operative joint balance for improved post-operative pain. 364 patients were enrolled in a prospective cohort investigation and received robot assisted posterior cruciate sacrificing TKA with an ultra-congruent tibial insert. Medial and lateral gaps were measured under a load of 70-90N throughout flexion after all resections immediately prior to closure. All resection thicknesses and angles were validated and recorded. Pre-op gap and balance groups were selected to subdivide the population into approximately equal thirds. Spearman linear correlations were used to identify differences between subgroups and inform optimal balance and gap thresholds. Significant associations were found in demographics and pre-op laxity subgroups between post-op laxity and 1-year pain outcomes (p < 0.05). More loose knees pre-operatively preferred to remain relatively loose post-operatively in extension and midflexion (average gap exceeding -0.5 mm in extension (10°): 92.0vs84.5, p=0.048, average gap exceeding 2mm in mid-flexion (40°): 93.1vs87.5, p=0.039). More elderly knees reported a higher sensitivity to extension imbalance and laxity in which imbalance>1.5mm (93.4vs86.4, p=0.035) and Lateral Laxity>0mm (92.9vs84.6, p=0.016) resulted in worse scores. Pre-operative laxity and patient age impacted the optimal final intra-operative laxity targets for improved 1-year pain outcomes in TKA. With additional data available to surgeons, data driven patient specific soft tissue balance targets may improve patient outcomes compared to generic alignment philosophy approaches.