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07:30-08:10 Session 20: Navigation
Location: Main Auditorium
Accuracy of Image-Less Navigation for Functional Cup Positioning in Total Hip Arthroplasty
PRESENTER: Morteza Meftah

ABSTRACT. Introduction: Computer-assisted navigation has the potential to improve the accuracy of cup positioning during total hip arthroplasty (THA) and prevent leg length discrepancy (LLD). The purpose of this study was to compare acetabular cup position and post-operative LLD after primary THA using posterolateral approach.

Methods: Between August 2016 to December 2017, 57 THAs using imageless navigation were matched with 57 THA without navigation, based on age, gender and BMI. Post-operative weight-bearing radiographs were assessed using for anteversion, inclination and LLD. Goal for functional cup placement was 40° inclination and 20° anteversion based on preoperative weigh bearing pelvic images. Functional LLD was measured as compared to pre-operative radiographs and contralateral side. Proportion of cups within Lewinnek’s safe zone, proximity to a pre-operative target of and the LLD >5 mm was assessed.

Results: The mean age was 54.9 ± 9.6 years (30 – 72) and 57.6 ± 12.5 years (20 – 85) in control and navigated groups, respectively. Mean cup orientation in the navigated group was 20.6°± 3.3° (17 - 25) of anteversion and 41.9°± 4.8° (30 - 51) of inclination, vs. 25.0°± 11.1° (10 - 31) and 45.7°± 8.7° (29 – 55) in control group, where were statistically significant (p=0.005 and p=0.0001), respectively. In the navigated group, significantly more acetabular cups were placed within Lewinnek’s safe zone (anteversion: 78% vs. 47%, p=0.005; inclination: 92% vs. 67%, p=0.002). There was no significant difference in mean LLD in navigation and control groups (3.1 ± 1.5 mm vs. 4.6 ± 3.4 mm, p=0.36), although fewer LLDs >5 mm were reported in the navigated group (7.1%) than in controls (31.4%, p=0.007).

Conclusion: The use of this image-less computer-assisted navigation improved the accuracy with which acetabular cup components were placed and may represent an important method for limiting post-operative complications related to cup malpositioning and LLD.

Combined Pre-Operative Planning and Intra-Operative Navigation to Precisely Restore Patient-Specific Anatomy in Total Hip Replacement Procedures
PRESENTER: Juergen Wahrburg

ABSTRACT. The paper presents an approach for computer-assisted implantation of artificial hip joints. It is based on a novel solution combining pre-operative planning and intra-operative navigation in a way that the natural anatomy of the joint before surgery can be restored as close as possible, or with exactly planned modifications. A surgical workflow has been developed which highly focusses on the registration and restoration of patient specific parameters instead of using generalized criteria like the Lewinnek safe zone. The feasibility of the approach has successfully been demonstrated by a laboratory setup of Sawbone models.

What to Expect in Short-Term Outcomes of “Challenging” Patients with Computer-Assisted Total Knee Arthroplasty?

ABSTRACT. This study investigated if CAOS TKA cases in higher risk patients would impact the outcomes of surgery. An average of 14-month postoperative outcomes on 58 TKAs from a prospective multicenter study were analyzed. The patients were grouped into challenging and standard case groups according to the criteria of age, BMI, comorbidities, and alignment deformity. Both groups demonstrated significant postoperative improvement in all outcome measures. Compared to the standard patients, the challenging patients achieved significantly higher improvement after TKA in KSS Knee score, while demonstrating the same level of improvements in all other outcome measures. Similarly, the two groups generally did not exhibit significant differences in the postoperative outcomes. The data demonstrated consistent postoperative results by CAOS TKA irrespective of patient conditions.

Navigation Improves the Ten to Fifteen-Year Survival Rate After Total Knee Arthroplasty for Severe Coronal Deformation. a French Multicentric Nationwide Study
PRESENTER: Jean-Yves Jenny

ABSTRACT. 1 Introduction The primary hypothesis of this study was that the 10-year survival rate of navigated TKAs for severe coronal deformation will be improved in comparison to conventional TKAs 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 in all participating centers for implantation of a TKA (whatever design used) were eligible for this study. All patients were contacted after the 10-year follow-up for repeat clinical and radiological examination (KSS, Oxford knee questionnaire and knee plain X-rays). Conventional and navigated TKAs were paired according to age, gender, body mass index and severity of the coronal deformation (with steps of 5°). Survival curve was plotted according to the actuarial technique, using the revision for mechanical reason as end-point. The influence of the implantation technique was assessed with a logrank test at a 0.05 level of significance.

3 Results 1,604 TKAs were implanted during the study time-frame. 658 cases could be paired in conventional (329 cases) and navigated (329 cases) groups: in each group, 277 cases with a coronal deformation less than 10° and 52 cases with a coronal deformation over 10°. There was no significant difference between the 12-year survival rates of conventional (97%) and navigated (98%) TKAs in cases without severe coronal deformation. There was a significant difference between the survival rates of conventional (93%) and navigated (98%) TKAs in cases with severe coronal deformation.

4 Discussion This study suggests that navigation implantation should be the default technique for pre-operative coronal deformation greater than 10°.

08:30-09:30 Session 22: Knee II
Location: Main Auditorium
Accuracy of Soft Tissue Balancing in Robotic-Assisted Measured-Resection TKA Using a Robotic Distraction Tool

ABSTRACT. Achieving proper soft tissue balance during total knee arthroplasty (TKA) can reduce post-operative instability and stiffness as well as improve patient reported outcomes. The objective of this study was to compare the final intra-operative gap balance throughout the range of flexion in robotic-assisted TKA, when performed with the aid of a robotic ligament tensioning tool versus standard trials and navigation gap and alignment measurements to balance soft-tissues after making bone resections. The study included a prospective cohort of 52 patients undergoing robotic-assisted TKA using a measured resection technique. The cohort was divided into two sequential groups: 1) a first non-sensor-assisted group (n=25) and 2) a subsequent sensor-assisted group (n=27). following the femoral and tibial resections, For the non-sensor group, once the surgeon determined that the knee was balanced, the final tibiofemoral gaps throughout the range of flexion were measured using a robotic-assisted tensioner with the surgeon blinded to the measurements. For the sensor-cohort, the surgeon preformed soft-tissue releases or re-cuts in order to balance the knee using the gap measurement from the robotic tensioner . The robotic-assisted tensioner was then used to measure the final medial and lateral gap measurements. The average mediolateral gap difference throughout the range of flexion was 1.9±.7mm with maximum difference of 7.8mm for the non-sensor cohort. On the other hand, the sensor-group had an average mediolateral difference of 1.5±.6mm and a maximum difference of 3.8mm. The difference between the two groups was statistically significant from 60 to 90 degrees of flexion. The percentage of knees balanced to within 1mm mediolaterally ranged from 38-41%, for the non-sensor group compared to 48-70% for the sensor group. The percentage range increased to 65-76% for the non-sensor group compared to 78-86% for the sensor-assisted group when comparing mediolateral balance to within 2mm. The number of knees requiring subsequent soft tissue releases was similar in each group, with 0, 1, 2, and 3 releases required in 40%, 48%, 12%, and 0% vs 37%, 44%, 15%, and 4% in the non-sensor vs sensor-assisted groups, respectively. Soft tissue balancing with the aid of a robotic tensioning tool resulted in significantly more accurate soft tissue balance than when using navigation measurements and standard trials alone in this single surgeon study.

Improved Patient Satisfaction Following TKA Using Intraoperative Computer Technology to Obtain Accurate Gap Balancing
PRESENTER: Austin Smith

ABSTRACT. Aims: Approximately 20% of patients are dissatisfied with their total knee arthroplasty (TKA). Computer technology has been introduced for TKA to provide real time intraoperative information on limb alignment and exact flexion/extension gap measurements. Purpose of this study was to determine if patient satisfaction could be improved following TKA using computer technology to obtain the target alignment and precisely balanced gaps.

Patients & Methods: 75 consecutive patients undergoing TKA using computer technology (CT) with real time intraoperative alignment and gap balancing information were compared with a prospective cohort of 75 consecutive patients undergoing TKA with manual jig based instruments during the same time period. There were no differences between groups with age, gender, BMI, and ASA scores. TKA’s were performed by a single surgeon using same implant design, anesthesia and surgical protocols. Patient satisfaction survey using Knee Society (KSS) and Likert scoring system was obtained at 1year follow-up.

Results: Likert scoring system demonstrated 95% of patients in the computer technology group were either very satisfied or satisfied versus 75% in the manual instruments TKA group (p=0.005). Second question of the KSS which deals with pain at rest was significantly better in CT-TKA group (p=0.04). Fifth question which deals with recreational activities was also significantly improved in the CT-TKA group, p=0.02. CT-TKA group had a better average overall satisfaction score of 7.1 versus 6.4 in the manual instrument group, p=0.03.

Conclusion: There are multiple reasons for patient dissatisfaction following primary TKA. Using intraoperative computer technology to achieve the target alignment with flexion/extension gap balancing to within 1mm, a significant improvement in patient satisfaction was demonstrated compared to TKA using conventional manual jig based instruments. Intraoperative computer technology provides real time information in millimeters to help obtain balanced gaps which may minimize the risk of instability and patient dissatisfaction.

Early Clinical Outcomes of a Novel Predictive Ligament Balancing Technique for Total Knee Arthroplasty

ABSTRACT. This study reports on the early clinical results and patient reported outcomes (PROMs) associated with a new tibia-cut first technique that uses a robotic ligament tensioner. PROMs are compared to registry data and historical results in the literature. Two hundred twenty-three patients were prospectively enrolled and underwent robotic TKA (mean age: 66.2 ±8.1; females: 123; BMI: 31.3 ±5.3). Three-month and six-month WOMAC, UCLA activity scale, and HSS-Patient satisfaction assessments were completed by 157 and 92 patients, respectively, and compared to Womac registry data from the Shared Ortech Aggregated Repository (SOAR), and to historical satisfaction reports in the literature. When comparing the baseline PROM scores between the robotic balancing and SOAR groups, robotic patients had equivalent womac knee stiffness (p=0.847) and UCLA activity scale (p=0.775) scores but slightly higher womac knee pain (p=0.038) and functional scores (p=0.018). While all scores improved over time, the rate of improvement was generally greater at 6 months than at three months when comparing the two groups, with statistically higher womac and UCLA scores in the robotic group for all categories at the six-month timepoint (p<0.001). Overall patient satisfaction in the Robotic Balancing cohort was 92.6% and 94.4% at 3M and 6M. Average length of stay was 1.6 days (±0.8). Surgical complications in this cohort included one infection four months post-op, 5 post-operative knee manipulations, one pulmonary embolism and one would dehiscence from a fall. Limitations to this study include the small number of patients and the lack of a closely matched control group. Nonetheless, early results are promising with improved objective measures and subjective outcomes especially in the 3M to 6M period compared to a large registry database and recently reported patient satisfaction measures.

Femoral Trochlear Groove Recreation Following TKA Correlates with Improved Patient Reported Outcome

ABSTRACT. Femoral component positioning and recreation of the trochlear groove post- total knee arthroplasty (TKA) impacts patello-femoral tracking. The effect on outcome related to the variation in recreation of the trochlear groove using a standardised implant design and variable patient anatomy is not well understood. This study sought to analyse the role of recreation of the trochlear groove in driving outcome post TKA. A database of TKA patients operated on by 6 surgeons from 1-Jan-2014 with pre-operative and post-operative CT scan and 6-month postoperative Knee Injury & Osteoarthritis Outcome score (KOOS) were assessed. All knee operations were performed with the Omni Apex (Raynham, MA) implant range using CR or PS components and a dome patella button. Post-operative component positioning was determined by registering 3D implant and bone models from the preoperative CT to the postoperative CT. The difference in trochlear recreation was calculated. The offset at the medial and lateral peaks and the trough was measured at 10° intervals from full extension to 90° flexion. Trochlear groove measurements were then compared to patient KOOS scores. A total of 396 patients were included. 59% (235) were female and the average age was 69.2 years (+/-8.1). Implant-bone offsets were small for the lateral apex of the implant trochlea groove (-0.36±2.43 mm) and the trough (-0.31±2.18 mm). The medial apex however, significantly increased post-implantation to 3.65±2.63mm, driven primarily by the most proximal measurement (6.08±2.19 mm). A weak but significant correlation was found between the trochlear lateral apex in early flexion and KOOS Pain score, finding that increased implant build-up correlated with worse outcomes (r = -0.2, p = 0.03). Impairment when straightening and pain while bending were the primary drivers, with patients more than twice as likely to report difficulty straightening (p = 0.037) with an increased lateral apex. The results indicate that a target femoral component flexion to achieve improved post-operative outcomes is patient specific and dependent upon trochlear geometry. The difference between the anterior thickness of the implant relative to the anterior resection therefore, should be considered. This work suggests that reducing the proximal lateral apex of the trochlear groove post-implantation leads to improved patient outcomes when straightening the knee. This work has implications for both implant design and target component placement.

Posterior Cruciate Ligament Resection in Total Knee Arthroplasty: Effect on Flexion-Extension Gaps, Mediolateral Laxity, and Fixed Flexion Deformity
PRESENTER: Babar Kayani

ABSTRACT. Purpose: The objective of this study was to assess the effect of posterior cruciate ligament (PCL) resection on flexion-extension gaps, mediolateral soft tissue laxity, fixed flexion deformity (FFD), and limb alignment during posterior-stabilised total knee arthroplasty (TKA).

Methods: This prospective study included 110 patients with symptomatic knee osteoarthritis undergoing primary robotic-arm assisted posterior-stabilised TKA. All operative procedures were performed by a single surgeon using a standard medial parapatellar approach. Optical motion capture technology with fixed femoral and tibial registration pins was used to assess gaps pre- and post-PCL resection in knee extension and 90 degrees knee flexion.

Results: PCL resection increased the flexion gap more than the extension gap in the medial (2.4 ± 1.5mm vs 1.3 ± 1.0mm respectively, p<0.001) and lateral (3.3 ± 1.6mm vs 1.2 ± 0.9mm respectively, p<0.01) compartments. The gap differences following PCL resection created mediolateral laxity in flexion (gap difference: 1.1 2.5mm, p<0.001) but not in extension (gap difference: 0.1 2.1mm, p=0.51). There was a strong positive correlation between preoperative FFD and change in FFD following PCL resection (Pearson correlation coefficient=0.81, p<0.001). PCL resection did not affect limb alignment (change in alignment: 0.2 1.2 valgus, p=0.60).

Conclusion: PCL resection creates flexion-extension mismatch by increasing the flexion gap proportionally more than the extension gap. The increase in the lateral flexion gap is greater than the increase in the medial flexion gap, which creates mediolateral laxity in flexion. Improvements in FFD following PCL resection are dependent on degree of deformity pre-PCL resection.

Robotic Total Knee Arthroplasty Has a Learning Curve of Seven Cases for Integration into the Surgical Workflow but No Learning Curve Effect for Accuracy of Implant Positioning
PRESENTER: Babar Kayani

ABSTRACT. Purpose: The primary objective of this study was to determine the surgical team’s learning curve for robotic TKA through assessments of operative times, surgical team comfort levels, accuracy of implant positioning, limb alignment, and postoperative complications. Secondary objectives were to compare accuracy of implant positioning and limb alignment in conventional jig-based TKA versus robotic TKA.

Methods: This prospective cohort study included 60 consecutive conventional jig-based TKAs followed by 60 consecutive robotic TKAs performed by a single surgeon. Independent observers recorded surrogate markers of the learning curve including operative times, stress levels amongst the surgical team using the state-trait anxiety inventory (STAI) questionnaire, accuracy of implant positioning, limb alignment, and complications within 30 days of surgery. Cumulative summation (CUSUM) analyses were used to assess learning curves for operative time and STAI scores in robotic TKA.

Results: Robotic TKA was associated with a learning curve of seven cases for operative times (p=0.01) and surgical team anxiety levels (p=0.02). Cumulative robotic experience did not affect accuracy of femoral (0.90) or tibial implant (p=68) positioning, limb alignment (p=0.61), posterior condylar offset ratio (p=0.87), posterior tibial slope (p=0.79), and joint line restoration (p=0.76). Robotic TKA improved accuracy of implant positioning (p<0.001) and limb alignment (p<0.001) with no additional risk of postoperative complications compared to conventional manual TKA.

Conclusion: Implementation of robotic TKA led to increased operative times and heightened levels of anxiety amongst the surgical team for the initial seven cases but there was no learning curve for achieving the planned implant positioning.

09:30-10:30 Session 23: Hip II
Location: Main Auditorium
Computer Navigation for Revision Total Hip Arthroplasty Reduces Dislocation Rates

ABSTRACT. INTRODUCTION: Computer-assisted hip navigation offers more accurate placement of hip components, potentially avoiding impingement, edge-loading, and dislocation; major causes of failure leading to revision THA. As such, the use of computer navigation may be particularly beneficial in the revision THA population. The purpose of this study was to determine if the use of computer-assisted hip navigation reduced the rate of dislocation in patients undergoing revision THA.

METHODS: A retrospective review of 72 patients undergoing computer-navigated revision THA between February 2016 and May 2017 was performed. Demographics, indications for revision, type of procedure performed, and postoperative complications were collected for all patients. Clinical follow-up was recorded at 3-months, 1-year and 2-years.

RESULTS: All 72 patients (48% female; 52% male) were included in the final analysis. Mean age of patients was 70.4 ± 11.2 years. Mean BMI was 26.4 ± 5.2 kg/m2. The most common indications for revision THA were instability (31%), aseptic loosening (29%), osteolysis/eccentric wear (18%), infection (11%), and miscellaneous (11%). At 3-months, 1-year, and 2-years there were no dislocations in any patients (0%). Compared to preoperative dislocation values, there was a significant reduction in the rate of dislocation with the use of computer-assisted hip navigation (31% vs. 0%; p<0.05).

DISCUSSION: Our study demonstrates a significant reduction in the rate of dislocation following revision THA with the use of computer navigation. Although the cause of postoperative dislocation is often multifactorial, the use of computer-assisted surgery may help to curtail femoral and acetabular malalignment in revision THA.

A Comparison of Supercapsular Percutaneously Assisted Total Hip Arthroplasty with Smart Mechanical Nagivation Versus Robotic-Arm Assisted Direct Superior THA

ABSTRACT. Introduction:

One of the potential advantages of computer-assisted surgery is to facilitate minimally invasive total hip arthroplasty (THA). Both the supercapsular percutaneously assisted total hip arthroplasty (SuperPath) and Direct Superior (DS) approaches seek to preserve capsule, short external rotators, and avoid IT band dissection, but limited exposure of anatomic landmarks may increase the risk of acetabular component malpositioning. The purpose of this study was to evaluate patient reported outcome measures, adverse events, cost, and radiographic parameters of robotic-arm assisted DS THR compared to SuperPath with smart mechanical navigation.


This is a case control cohort study comparing robotic assisted Direct Superior THA versus Superpath with smart mechanical navigation. 228 consecutive patients were identified from a single surgeon practice, and enrolled consecutively. The first 114 SuperPath hips were matched to robotic assisted DS group from the same study period. Reduced WOMAC scores as well as surgical complications were prospectively collected. Patient demographics, length of stay (LOS), discharge disposition, visual analog pain scores, and opioid consumption were retrieved from the hospital EMR. Acetabular component positioning was measured using previously validated 2d-3d matching software (HipMatch).

Results: The Superpath group also had a lower mean BMI, age and ASA scores, but pre-operative reduced WOMAC scores were similar. There were no significant differences in pain scores, narcotic consumption, or surgical times between groups. Likewise, there were no significant differences in reduced WOMAC scores at two or six weeks. LOS was less in the Superpath mechanical navigation group (1.14 +/-0.39 days vs 1.43 +/-0.48 days, P<.001). 10 DS patients went to rehab, while only one Superpath patient went to an inpatient facility p=.01. Hospital costs were less for the Superpath ($17,088 +/-4064 vs $18,956 +/-1947, P<.001). There were two dislocations within the first 34 Superpath hips, but none in the next 80 cases. The overall dislocation rate for the DS cohort was 5.2% (N=6).


Despite promises of greater precision, safety, and value, we could not identify a clinical benefit to robotic-arm assisted minimally invasive THA at short-term follow-op. Randomized studies with long-term follow-up will be needed to fully evaluate these surgical approaches with computer navigation.

Patient-Specific ROM and Load-Based Target Zone for Total Hip Arthroplasty and Its Application in a Retrospective Analysis

ABSTRACT. The outcome of total hip arthroplasty (THA) depends on multiple alignment and design parameters. Unsuitable parameter settings could lead to impingement, dislocation, increased wear, and loosening. This work introduces a method for calculating a patient-specific target zone based on range of motion (ROM) related and load related criteria. Possible bone or prosthesis impingement are analyzed. The resulting hip force is calculated and compared to the pre-operative situation. The edge loading risk is analyzed. Pelvic tilt is considered for the calculation of the ROM and the load. THA parameters fulfilling all criteria are included in the target zone. The above described method has been applied to 30 cases retrospectively. All cases had been planned and navigated on the basis of CT data. From each patient, pre- and post-operative CT and EOS data and Harris Scores were acquired. The pre-operative data served as the input data for the target zone calculator. We hypothesized that cases with post-operative THA parameters inside the target zones have higher scores than other cases. The patients whose implants are within the target zones had higher scores than the remaining patients. Especially patients inside both target zones (combined target zone) had higher scores. The results also show that for 19 out of 30 patients, conventional CT-based planning and navigation does not provide optimal placement regarding the combined target zone. A further validation of the method with a larger sample size is part of our ongoing work.

Proximal Femoral Asymmetry in Japanese Patients Before Total Hip Arthroplasty

ABSTRACT. Templating is an important and established step in the preoperative planning process of total hip arthroplasty (THA) in order to select the size and position of the implant. In severely arthritic cases, the unaffected contralateral side is sometimes used as a reference to reconstruct morphological parameters of the planned implantation (ipsilateral) side, for example the femoral offset, the leg length or the antetorsion. Recent studies have shown that a significant side-to-side asymmetry of important proximal femoral parameters already exists in healthy subjects questioning the validity of the contralateral side as a reference. However, if preoperative asymmetry is larger than asymmetry in healthy subjects, preoperative planning can still make use of the contralateral side to target a postoperative result within the range of physiological asymmetry. Therefore, the specific objective of this study was to quantify the preoperative side-to-side asymmetry of five important morphological parameters of the proximal femur. Significant side-to-side differences between the ipsilateral side and the contralateral side were detected for the antetorsion, the offset, the neck length and the femoral length. The antetorsion is significantly higher for the ipsilateral side whereas offset, neck length and femoral length are significantly smaller. Mean and maximum difference in antetorsion is almost twice as high for the THA patients in comparison to healthy subjects. The same trend can be observed for the femoral length, less pronounced also for the caput-collum-diaphyseal angle. The comparison of proximal femoral side-to-side differences for subjects before THA and healthy subjects leads to the conclusion that contralateral templating can be a reasonable basis for THA planning of severely arthritic hips if the contralateral side shows no signs of osteoarthritis or developmental dysplasia.

Improved Accuracy in Restoration of Native Hip Biomechanics Using Robotic-Guided Surgery Compared to Conventional Manual Techniques for Total Hip Arthroplasty: a Prospective Cohort Study
PRESENTER: Babar Kayani

ABSTRACT. Objectives: The primary objective of this study was to compare accuracy in restoring the native centre of hip rotation in patients undergoing conventional manual THA versus robotic THA. Secondary objectives were to determine differences between these treatment techniques for THA in achieving the planned combined offset, cup inclination, cup version, and leg-length correction.

Methods: This prospective cohort study included 50 patients undergoing conventional manual THA and 25 patients receiving robotic THA. Two independent blinded observers recoded all radiological outcomes of interest using plain radiographs. There was no difference between the two treatment groups for age (p=0.25), gender (p=1.00), body mass index (p=0.39), laterality of surgery (p=0.78), and ASA scores (p=0.67).

Results: Correlation coefficient was 0.92 (95%CI:0.84-0.95) for intra-observer agreement and 0.88 (95%CI:0.82-0.94) for inter-observer agreement in all study outcomes. Robotic THA was associated with improved accuracy in restoring the native horizontal (p<0.001) and vertical (p<0.001) centres of rotation, and improved preservation of the patient’s native combined offset (P<0.001) compared to conventional THA. Robotic THA improved accuracy in positioning of the acetabular cup within the combined safe zones of inclination and anteversion described by Lewinnek et al (p=0.02) and Callanan et al (p=0.01) compared to conventional THA. There was no difference between the two treatment groups in achieving the planned leg-length correction (p=0.10).

Conclusion: Robotic THA was associated with improved accuracy in restoring the native centre of rotation, better preservation of the combined offset, and more precise acetabular cup positioning within the safe zones of inclination and anteversion compared to conventional manual THA.

In-Vivo Precision of a Non-Invasive Ultrasound-Based Device to Measure Pelvic Tilt for THA

ABSTRACT. The cup orientation plays a major role in the long-term implant stability following Total Hip Arthroplasty (THA). Because of the patient specific spine-hip kinematics, the safe zone introduced by Lewinnek is more and more controversial. Several solutions have been recently developed to take into account such parameter for THA but are all either invasive, difficult to use or expensive. A non-invasive ultrasound (US) based device has been recently proposed which allows the acquisition of the pelvic tilt in different daily positions. The goal of this study is to analyse the in-vivo intra and inter-observer precision of this device. Measurements were realized by three physicians on three healthy subjects having a low, medium and high Body Mass Index (BMI). Among the three physicians, there were an expert, an intermediate, and a novice user. For each subject, the pelvic tilt was measured ten times by the three physicians in the supine, standing and sitting positions. The inter and intra-observer precisions have been analysed using the intraclass correlation coefficient (ICC) and according to the BMI, the positions and the user expertise level. The inter-observer precision was therefore excellent whatever the BMI. It was also excellent regarding the supine and the sitting positions and good concerning the standing position. The in-vivo intra-observer precision was excellent for all measurements and whatever the user’s expertise, the BMI and the positions. This study shows therefore that the precision of our system meets the clinical requirement.

11:00-11:30 Session 24: Special Tribute for 25th Anniversary and Keynote Addresses
  1. 11:00 - 11:10: Tribute to the Founder of CAOS - Leo Joskowiz
  2. 11:10 - 11:20: CAOS Achievement Award Acceptance - Lutz Nolte
  3. 11:20 - 11:30: Keynote Address on the Future of Robotics in Orthopedic Surgery - Robert Cerfolio
Location: Main Auditorium
11:30-12:05 Session 25: Industry Video Demonstration
  • 11:30 - Introduction by Moderators
  • 11:32 - Smith & Nephew
  • 11:39 - Stryker
  • 11:45 - Zimmer- Biomet
  • 11:50 - Think Surgical
  • 11:55 - OrthoSensor
  • 12:00 - Corin - OMNI
Location: Main Auditorium
12:05-12:30 Session 26: Special Session I – Advanced Technologies in Orthopedic Surgery: Forecasting the Future

Panelists: Robert Cohen, Pierre Couture, Branislav Jaramaz, Stefan Kreuzer, Christopher Plaskos.


  • Why has robotics and CAOS been unable to demonstrate improved functional outcomes?
  • What are the specific industry criteria for robotic designation?
  • Is there a role for predictive algorithms in surgical planning?
  • Should the instrumentation cost be part of the implant purchase?
  • When can we expect an integrated use of enhanced visualization and sensor feedback?
  • What is the value-added that will ensure mass adoption?
Location: Main Auditorium
12:30-13:30 Session 27A: Lunch Symposium

Redefining Robotics - ROSA Knee

Sponsored by Zimmer Biomet.

Location: Main Auditorium
12:30-13:30 Session 27B: Poster Session II
Comparative Analysis of the Surgical Treatment of Giant Cell Tumor of Pelvic Bone Assisted by Computer Navigation and Traditional Surgery

ABSTRACT. Objective: Compared with the traditional surgical methods and surgery assisted by computer navigation for giant cell tumor of pelvic bone in the same period, advantages of the surgical methods and treatment results were discussed. Methods Between January 2008 and December 2016, surgical treatment were performed for 37 patients with giant cell tumor of pelvic bone. There were 20 females and 17 males with an average age of 37.7 years (21 to 79). There are 33 primary cases and 4 recurrence cases. In accordance with the classification system for pelvic tumors by Enneking and Dunham, further modified by Sanjay et al. Tumors were located at zone I in 4 cases, zone III in 2cases, zone I+II in 4 cases, zone I+IV in 9 cases,zone II+III 16 cases zone I+II+III in 2cases.. In the operation for these 14 cases, we carried out the process by the Navigation System software. Another surgical processes for 23 cases were performed by traditional freehand method. Results The mean follow-up was 52 months (24 ~ 108 months). The average operation time was 266 minutes and the blood loss was 1780 ml in 14 patients with computer-assisted navigation, and the average operation time was 305 minutes and the blood loss was 2500 ml in 23 patients with traditional surgery. There were 13 cases of disease-free survival (92.8%) by computer assisted navigation and 22 cases of disease-free survival (95.6%) by traditional surgery. Local recurrence was found in 5 cases (13.5%) in all cases and 4 cases in all primary cases. There were 1 recurrence case (8.3%) by computer-assisted navigational surgery and 3 recurrence cases (14.3%) by traditional surgery. Computer-assisted navigation was performed in 12 patients with primary tumor, extensive resection in 2 patients and marginal resection in 4 cases without recurrence. Intracapsular resection was performed in 6 cases and recurrence in 1 case (16.7%). There were 21 cases of primary tumor by traditional surgery and 1 case of extensive resection and marginal resection in 3 cases without recurrence. Intracapsular resection was performed in 17 cases and recurrence in 3 cases (17.6%). Extensive and marginal excision was achieved under navigation guidance in 6 cases (50%). Extensive and marginal resection was achieved with traditional surgery in 4 cases (19%). Conclusion: The computer navigation-assisted surgery for giant cell tumor of pelvic bone is superior to traditional surgery in local control.

Usability and Accuracy Assessment of an Innovative Low Dose C-Arm with 2D Fluoroscopy, 3D Imaging and Real-Time Navigation in a Single Platform for Spine Surgery – a Cadaveric Experimentation

ABSTRACT. Introduction Clinical benefits of intra-operative 3D imaging and surgical navigation are widely described in the literature. However, existing guidance systems are often reported as complex and time consuming1,2,4. The Surgivisio / eCential system is an innovative intra-operative C-arm combining 2D fluoroscopy, 3D imaging and real time navigation capabilities within unified an all-in-one platform3. The aim of this cadaveric experimentation is to evaluate the usability of the system, and to assess pedicle screw placement using this novel device. Material and methods Surgivisio / eCential device offers an all-in-one solution with a unique workflow and user interface. The embodiment used here is dedicated to any spinal procedures requiring insertion of a trocar inside a pedicle. The usability of the system is assessed by measuring the ability of the user to navigate the trocar and place k-wires percutaneously inside a group of pedicles. The accuracy of screw placement is evaluated using post-operative 3D image of the implanted screw exported on an internally developed image visualization tool. The screw placement is assessed according to Gertzbein grading scale by the operator and two other evaluators. Results Usability For each vertebrae group, fixation of the patient reference to the end of 3D reconstruction was done in less than 10 minutes. The percutaneous navigation and placement of 6 k-wires in a vertebrae group could be performed in 28 minutes for the first 2 groups and in 22 minutes for the third group. Pedicle screw implantation 100% of screws was graded 0 on Gertzbein scale by all evaluators.

Trends in Cup Position Utilizing Computer-Assisted Navigation During Total Hip Arthroplasty
PRESENTER: Morteza Meftah

ABSTRACT. Proper positioning of the acetabular cup deters dislocation after total hip arthroplasty (THA). The concept of a safe zone for acetabular component placement was first characterized by Lewinnek et al. and furthered by Callanan et al. The safe zone concept remains widely utilized and accepted in contemporary THA practice; however, components positioned in this safe zone still dislocate. This study sought to characterize current mass trends in cup position identified across a large study sample of THA procedures completed by multiple surgeons. This retrospective, observational study reviewed acetabular cup position in 1,236 patients who underwent THA using computer-assisted navigation between July 2015 and November 2017. The overall mean cup position of all recorded cases was 21.8° (±7.7°, 95% CI = 6.7°, 36.9°) of anteversion and 40.9° (±6.5°, 95% CI = 28.1°, 53.7°) of inclination. For both anteversion and inclination, 65.5% (809/1236) of acetabular cup components were within the Lewinnek safe zone and 58.4% (722/1236) were within the Callanan safe zone. Acetabular cups were placed a mean of 6.8° of anteversion (posterior/lateral approach: 7.0°, anterior approach: 5.6°) higher than the Lewinnek and Callanan safe zones whereas inclination was positioned 0.9° higher than the reported Lewinnek safe zone and 3.4° higher than the Callanan safe zone. Our data shows that while the majority of acetabular cups were placed within the traditional safe zones, the mean anteversion orientation is considerably higher than those suggested by the Lewinnek and Callanan safe zones. The implications of this observation warrant further investigation

Robotic-Assisted Total Hip Arthroplasty May Reduce the Risk of Complications in Patients Younger than 35

ABSTRACT. Purpose: In younger patients during total hip arthroplasty, the presence of morphologic deformities, previous surgeries, and retained hardware, can pose technical challenges making reconstruction difficult. The purpose of our study is to assess the outcome of robotic-assisted THA compared to conventional THA in patients younger than 35 years old.

Methods: A retrospective analysis of 123 patients younger than 35 years old that underwent primary unilateral THA between January 2013 and April 2018 was conducted. Patients were divided into two cohorts: (1) robotic-assisted THA and (2) conventional-THA (c-THA). Demographics, operative details, and postoperative outcomes were carefully studied. Radiographic analysis included measurement of postoperative acetabular anteversion and inclination angles as well as postoperative leg length discrepancies. Chi square and unpaired student t-tests were performed for all categorical and continuous variables, respectively.

Results: Of the total 123 patients, 30 patients (32 hips) were in the robotic-THA cohort, and 93 patients (100 hips) were in the conventional-THA cohort. Patients in the robotic-THA cohort were younger (26.6±6.2 vs. 29.0±5.3; p=0.03), had a higher mean BMI (29.8±8.2 vs. 25.7±5.9; p=0.03) at surgery. The most common indication for THA was DDH and osteonecrosis. The acetabular component was positioned within Lewinnek’s safe zone more often in the robotic-THA cohort compared to the c-THA cohort (94% vs 65%; p<0.01) (Figures 1 and 2). Leg length discrepancies were similar between both cohorts. Patients in the c-THA group were more likely to experience clinically significant higher rates of dislocation (2.9% vs. 0), revision (6.8%), any postoperative complication (7.8%), and 90-day readmission (2.9) following THA.

Conclusion: Robotic THA can help improve outcomes in younger THA recipients. Future studies with larger cohorts and longer follow-up times should evaluate outcomes in this historically technically demanding patient population.

Total Hip Arthroplasty in Patients Younger than 35 Is Effective Regardless of Surgical Approach

ABSTRACT. PURPOSE: Indications for total hip arthroplasty (THA) are expanding to include increasingly younger patients, yet limited outcomes research has focused on this population. This study compares outcomes between the anterior and posterior approach, as well as between conventional and technology-assisted THA in patients under 35-years of age.

METHODS: Retrospective analysis of 139 primary THAs in 135 patients younger than 35-years old was conducted. Patients were divided into two cohorts: (1) anterior-THA and (2) posterior-THA. A posterior-THA sub-group analysis was performed to compare: (1) technology-assisted THA (tech-THA) versus (2) conventional-THA (con-THA). Demographics, perioperative data, radiographic and clinical outcomes were analyzed using Chi squared and unpaired student t-tests for categorical and continuous variables, respectively.

RESULTS: Of the 139 cases performed, 40 were anterior-THA and 99 were posterior-THA. The anterior-THA cohort had shorter mean surgical time (95.0±25.7 vs. 118.3±43.3 minutes; p<0.01), shorter hospital admissions (1.9±1.4 vs. 2.7±1.2 days; p<0.01), and lower estimated blood loss (343.4±164.1 vs. 438.0±272.8 mL; p<0.01) compared to the posterior-THA cohort. There were no significant differences in component positioning, limb length discrepancy, clinical outcomes or postoperative complications between cohorts. In the sub-group analysis, cup placement within Lewinnek’s Safe Zone was achieved in 78% of tech-THA versus 49% of con-THA (p<0.01). Need for revision THA was significantly higher among the con-THA group (9.4% vs. 0%; p<0.01).

CONCLUSION: There is no significant difference in outcomes between anterior- and posterior-THA among patients under 35-years of age, however, the anterior approach may promote earlier hospital discharge. Technological-assistance can improve component positioning and may reduce the rate of revision for posterior-THA in patients under 35-years old.

Mid-Term Patient Reported Outcomes and Survivorship Following Robotic Assisted Total Knee Replacement: a Cohort Study

ABSTRACT. Despite the advantages of real time alignment assessment and visual feedback while balancing offered by robotic assisted total knee arthroplasty, few clinical studies have reported patient outcomes. The purpose of this study is to report the midterm patient reported outcomes and survivorship of a computer-navigated TKA system with a robotic cutting guide. This patient cohort is the first IRB approved series of patients treated in the United States with this robotic knee system. This study serves as a midterm follow-up study on for this cohort, upon which learning curve, intra-operative efficiency, and deformity management were previously reported Recipients of 152 consecutive total knee arthroplasties using a computer-navigated TKA system performed by a single surgeon between June 2010 and January 2012 were surveyed between 5-7 years post-operatively. 94 patients were reachable for outcome measures and survivorship data was obtained in 98 patients. Mean patient age at follow up was 74.6 +/- 8.6 years. Implant survivorship was 99.0% at an average of 6.5 years. Mean patient reported knee outcome scores were 62.7 (KSS-SF) and 79.5 (KOOS-JR). Overall satisfaction rate was reported as “satisfied or very satisfied” in 80.2%, “neutral” in 11.0%, and “dissatisfied or very dissatisfied” in 7.7% of patients. Robotic assisted total knee arthroplasty using a computer-navigated TKA system with a robotic cutting guide appears to provide a durable outcome with sustainable midterm patient reported outcomes and excellent survivorship. Further follow up is required to determine if there are long term outcome and survivorship benefits of robotic assisted total knee arthroplasty.

How Does Robotic Technology Influence TKA Implant Placement for Surgeons in Fellowship Training?
PRESENTER: Laura Scholl

ABSTRACT. Implant malalignment during TKA may lead to suboptimal outcomes. Accuracy studies are typically performed with experienced surgeons; however, it is important to study less experienced surgeons when considering teaching hospitals where younger surgeons are operating. Therefore, the purpose of this study was to assess whether computer assisted TKA (CATKA) allows for more accurate and precise implant position to plan when compared to manual TKA (MTKA) when the surgery is performed by less experienced surgeons. Two surgeons, currently in their fellowship training and having minimal CATKA experience, performed a total six MTKA and six CATKA on paired cadaveric knees. Computed tomography (CT) scans were obtained for each knee pre- and post-operatively. CT scans were analyzed to compare post-operative implant position to the pre-operative planned position. Mean system errors and standard deviations were compared between CATKA and MTKA for the femoral component sagittal, coronal, and axial planes and the tibial component in the sagittal and coronal planes. A 2-Variance testing was performed using an alpha=0.05. CATKA had greater accuracy and precision to plan than MTKA for: femoral axial plane (1.1º±1.1º vs. 1.6º±1.3º), coronal plane (0.9º±0.7º vs. 2.2±1.0º), femoral sagittal plane (1.5º±1.3º vs. 3.1º±2.1º), tibial coronal plane (0.9º±0.5º vs. 1.9º±1.3º) and tibial sagittal plane (1.7º±2.6º vs. 4.7º±4.1º). There was no statistical difference between surgical groups or between the two surgeons performing the cases. With limited CATKA experience, the fellows showed increased accuracy and precision to plan for femoral and tibial implant positions. Furthermore, these results are comparable to what has been reported for an experienced surgeon performing CATKA.

A Robotic Nondestructive Osteochondral Tissue Harvesting for Autograft Transplantation
PRESENTER: Pradipta Biswas

ABSTRACT. Osteoarthritis is the degeneration of bone-cartilage. Healthy cartilage absorbs mechanical stress and provides smooth limb movement. Cartilage has poor healing capabilities due to the absence of blood, lymphoid tissue and nerve that makes treatment of the damaged cartilage difficult, making surgical intervention an inevitable solution. Mosaicplasty is a popular surgical practice involving transplantation of small cylindrical bone-cartilage plugs to refill the lesion. A lack of custom-shaped donor harvesting mechanism makes it impossible to fill the lesion with a single graft. The success of transplanting a customized autograft to replace the osteochondral lesion lies in effective extraction of the autograft from the donor site. Currently, no method exists to harvest such grafts since it requires access to the root side of donor. In this paper, we propose a robotic cartilage-bone removal mechanism to harvest a custom-shaped autograft. Our method involves drilling a profile determined from the lesion to be removed and slicing off the desired cartilage-bone graft from the root. We designed a new graft removal mechanism capable of inserting a thin wire saw and slicing through the root of the prepared profile to extract an intact autograft. The device can be attached to a standard 6-DOF robotic arm that can provide profile drilling and gross positioning of the graft removal device.

Increasing Patient Empowerment in TKA-Recovery via a Mobile Application: an Observational Study
PRESENTER: Ward Servaes

ABSTRACT. Introduction In the last half-century, total knee arthroplasty (TKA) has evolved tremendously to routine surgery with faster recovery, optimized pain-control, immediate mobilisation, shorter hospital stay and predictable outcome1. Despite, supervised physiotherapy,has remained the gold standard. This observational study assessed the patient acceptance and compliance of a recovery app for remote patient surveillance and care. Patients and Methods: More than 200 patients used the proposed mobile application (moveUP) for their recovery after TKA surgery between June 2017 and October 2018. Through objective and subjective feedback, the app accommodates the rehabilitation program and provides personalised feedback. In addition, the physiotherapist is notified in case of anomalies through a smart filtering system. Every patient was evaluated on usability and digital acceptance.

Results This study depicts the results of the first 185 patients that used the aforementioned application until the end of their rehabilitation. Usability-scores and adherence of the application was found to be very high. Mean adherence (number of daily questionnaires completed on total number of days until the end of rehab) 84% (SD 17%)(Median 90%). 78% percent of the patients were promotors of the system, 8% detractors and 14% undecided.

Conclusions This observational study confirms our hypothesis that reliable compliance is reached, and the technology may permit optimisation of the rehabilitation process. Further research will evaluate if these advancements in rehabilitation, by permitting close patient surveillance and monitoring in an outpatient setting, may provide better outcomes and significant cost savings.

The Influence of Pre-Operative Radiographic Patellofemoral Joint Degeneration and Malalignment on Patient-Reported Outcome Scores Following Fixed-Bearing Medial Unicompartmental Knee Athroplasty
PRESENTER: Joost Burger

ABSTRACT. Controversy still exist as to whether the presence of patellofemoral joint (PFJ) degenerative changes and malalignment is a contraindication for medial unicompartmental knee arthroplasty (UKA). Therefore, the aim of this retrospective study was to examine the influence of preoperative radiologic PFJ osteoarthritis (OA) and alignment on midterm knee and PFJ-specific patient-reported outcomes following fixed-bearing medial UKA. Radiographs of robotic-arm assisted fixed-bearing medial UKA patients from a single surgeon were assessed using the Kellgren-Lawrence (KL), Altman classification and PFJ alignment measurements. Knees with severe bone loss or grooving of the lateral patellar facet were excluded. Outcomes were evaluated at a minimum two-year follow-up with the Kujala (Anterior Knee Pain Scale) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) Junior outcomes. A total of 536 patients (639 knees) were included with a mean follow-up of 4.3 years (SD 1.6, range 2.0 – 9.2). Good-to-excellent Kujala and KOOS scores were reported independent of the presence of PFJ OA. Knees with OA in either the medial or lateral PFJ had similar outcome to those without. Furthermore, both patellar tilt angle and the congruence angle did not influence knee and PFJ-specific patient-reported outcomes. These results show that neither mild to moderate PFJ degeneration nor abnormal patellar tilt or congruence should be considered a contraindication to fixed-bearing medial UKA.

Long Term Patient Outcomes Following Navigated Knee Replacement:a Retrospective Analysis
PRESENTER: Frederic Picard

ABSTRACT. Total knee replacements (TKR) are often deemed successful when patients recover and maintain their functionality both in the short and long term. The other main indicator for success is the revision rate following TKR. This study analyses the long term results of navigated TKR based on patient related outcomes in terms of patient satisfaction, Oxford Knee Score (OKS) and also knee revision rates.

The retrospective data of all patients who underwent navigated Columbus TKR from the author’s institution from 2005 to 2011 was analysed. The overall cohort size was 1679 with a mean age of 68.81yrs (sd 8.46). The OKS, satisfaction scores, complication and revision rates were compiled and evaluated up to ten years post-operatively. The patient reported outcomes were recorded six weeks, one, two, five and ten years post-operatively.

The results from the OKS and satisfaction scores demonstrated marked improvement throughout recovery to the ten year time point. The OKS had a mean improvement of 16.6 from the pre-operative score at the 10 year time point and the satisfaction scores improved at each follow-up and remained high at the 10 year time point. There were a total of 61 complications and 36 revisions recorded, with infection being the major cause for revisions.

This survey has identified and established that for the majority of patients undergoing knee arthoplasty using the Columbus total knee system and computer navigation are functioning reasonably well in the long term and the revision and complication rates in this hospital are within the national levels.

Robotic Use Improves Post-Resection Bone Cuts During Total Knee Arthroplasty
PRESENTER: Laura Scholl

ABSTRACT. The purposes of this study were to assess 1) number of bone recuts with manual TKA (MTKA) vs RATKA and 2) influence of robotics on surgeon’s posture and workload during recutting. Two surgeons each performed three MTKAs and three RATKAs. Occurrence, time and type of post-resection recuts were recorded. Movement sensors were placed on surgeons to measure lower back, shoulder, and cervical movements. Data was analyzed for average angle, percent of time in high-risk range of motion (ROM), number of times in high-risk sustained positions, and repetitions per minute. Surgeons were surveyed to assess physical and mental effort on a 1-10 scale (1 as lowest effort). Six TKAs required recuts, five MTKA and one RATKA. 5 were on tibia and 1 (MTKA) was on femur. Compared to RATKA, MTKA had: increased time to perform recut (4.8-minutes vs. 3.7-minutes), increased occiput and T3 (38.9 vs 17.0° and 16.0 vs 3.0°) average angles, increased lower back ROM, sustained positions, and repetitions (14 vs 0%, 1 vs 0, and 1.9 vs 0), increased non-dominant shoulder ROM and repetitions (22 vs 0% and 2 vs 1), reduced dominant shoulder ROM (56 vs 19%), increased mental (4.2 vs 2.8) efforts and increased physical (3.3 vs 1.7) efforts. Results indicate RATKA may reduce incidence of post-resection bone recuts. Increased time and required efforts for MTKA may be due to setting up surgical cutting instruments. Whereas, for RATKA, recut changes are made on the robotic surgical screen and the robotic-arm is used to help perform the recut.

Does the Use of Robotic Technology Improve Surgeon Ergonomic Safety During TKA?
PRESENTER: Laura Scholl

ABSTRACT. Surgeon physical stress in the operating room is a known potential cause of musculoskeletal overuse injuries, specifically in surgeons who perform total knee arthroplasty (TKA). Injuries have been attributed to ergonomically challenging postures. This study compared surgeon lower back and shoulder posture between manual TKA (MTKA) and robotic assisted TKA (RATKA). Two surgeons performed a total six MTKA and six RATKA on a set of cadaveric knees. Movement and EMG sensors were secured to each surgeon to monitor lower back and shoulder movements, as well as muscle activities. Data was analyzed and activities were assessed as low, medium, or high risk, providing a score between 0-lowest and 16-highest. Risk data was compared between MTKA and RATKA for three separate surgical tasks: 1-bone cut preparation & cutting (MTKA = placement of cutting jigs, bone cutting, RATKA = array placement, bone registration, bone cutting), 2-knee balancing and 3-trialing. Overall, there were more high-risk shoulder than lower back activities in MTKA and RATKA. More high-risk movement and EMG stimulation were measured in the dominant shoulder than the non-dominant. When lower back and shoulder data were combined, highest risk task was bone cut preparation & cutting (MTKA: 13 vs. 6 vs. 6 and RATKA: 11 vs. 8 vs. 6), with a higher risk for MTKA than RATKA. Poor posture can be a potential cause for surgeon work-related injuries. This study evaluated which tasks presented highest risk to surgeon ergonomic safety while performing TKA, and found lower overall ergonomics risk for performing RATKA vs. MTKA. Although this study provides data indicating reduced ergonomic risk with RATKA, additional studies in the operating room need to be performed.

What Factors Influence Surgeon Cervical Posture and Perceived Workload During TKA?
PRESENTER: Laura Scholl

ABSTRACT. Orthopaedic surgery is a mentally and physically demanding procedure for surgeons. Studies reported 44-66% of surgeons surveyed have had a work-related injury attributed to poor surgeon posture. The purpose of this study was to understand how surgical variables may affect a surgeon’s posture and workload when performing TKA. Variables included: influence of level of surgical experience, type of surgical procedure, and specific surgical tasks. Two experienced surgeons, with a median 22-years surgical experience, and 2 surgeons, currently in their fellowship training, each performed 3 manual TKAs (MTKA) and 3 robotic assisted TKAs (RATKA) using a cadaveric setup. Kinematic sensors were placed on the occiput and T3 to measure flexion of the head and neck. Surgeons were surveyed to assess their physical and mental effort using a 1-10 scale (1 being least effort). Compared to the fellows, experienced surgeons had reduced occiput and T3 angles for MTKA (28.0 vs. 38.7°, 4.2 vs. 15.7°) and RATKA (18.0 vs. 29.2°, 4.8 vs. 13.2°) as well as reduced mental and physical effort. Considering surgical procedure, all surgeons had reduced occiput angles for RATKA compared to MTKA. Considering surgical task, surgical application (MTKA vs. RATKA) had greater influence on cervical angles for the fellows group. All three factors influenced the surgeon’s posture and workload. Occiput angle was reduced by approximately 10° during RATKA, which is attributed to the surgeon standing in a more upright position, to visualize the robotic screen during cutting and trialing. Robotics may help newer surgeons better visualize knee balancing during TKA, easing the process of balancing and trialing.

Depth Camera Augmented Fluoroscopy with Video Overlay
PRESENTER: Matthew Hickey

ABSTRACT. In many orthopedic surgeries, the surgeon relies on a C-arm fluoroscopy machine with the images usually displayed on a bedside monitor. The mental effort that surgeons expend transferring information from the imaging display back to the surgical site can lead to distraction causing errors that could directly influence quality of surgery.

The Depth Camera Augmented Fluoroscopy (DeCAF) device uses an Intel RealSense depth camera to provide real-time visualization of the surgical site by overlaying x-ray images from the C-arm onto live video of the patient’s surface anatomy. Using geometric data acquired via the depth camera, the device facilitates transforming a real-time video feed aligned with the camera coordinate system to a perspective aligned with the x-ray source. The x-ray overlay is attained while restricting incursion on the surgeon’s work area and allowing the C-arm to be used in its normal position to minimize radiation exposure.

DeCAF successfully facilitates an x-ray video overlay feature while eliminating key limitations such as size, radiation exposure and acquisition time associated with other similar devices. Future work will involve evaluating overlay accuracy, the addition of second depth camera to aid in filling in areas with missing details, and a design iteration involving bagging of the camera with a sterile cover to ensure compliance with asepsis requirements prior to evaluating the system in the operating room.

A 90-Day Episode-of-Care Cost Analysis of Robotic-Arm Assisted Total Knee Arthroplasty
PRESENTER: Christina Cool

ABSTRACT. Introduction One way to potentially help contain the rising healthcare costs is the utilization of technological advances, such as robotic-assistive technology, for total knee arthroplasty (TKA). Therefore, the purpose of this study was to perform a cost analysis between robotic-arm assisted TKA and manual TKA (mTKA) techniques. Specifically, we compared: 1) 90-day EOC costs, as well as several variables within the episode, including 2) index costs; 3) index lengths-of-stay (LOS); 4) discharge disposition; and 5) readmission rates.

Methods A retrospective claims analysis was performed on Medicare FFS beneficiaries who underwent rTKA and mTKA procedures between January 1, 2016 and March 31, 2017. Patients were matched rTKA to mTKA in a 1-to-5 ratio, yielding 519 rTKAs and 2,595 mTKAs. The overall 90-day EOC costs, including the index procedures, LOS, discharge dispositions, and readmissions were compared between cohorts.

Results Overall 90-day EOC costs ($18,568 vs. $20,960) as well as index facility costs ($12,384 vs. $13,024; p=0.0001) were found to be less than that for rTKA vs. mTKA. rTKA also accrued $1,744 fewer costs than mTKA (5,234 vs. $6,978; p=<0.0001) utilized fewer days in inpatient (4 vs. 7; p<0.0001) and SNF care (15 vs. 16; p=0.0642) as well as a 90-day readmission reduction of 33% (p=0.0423).

Discussion The results from this study show rTKA to be associated with significantly lower 90-day EOC costs. These lower rTKA patient costs are likely attributable to the significantly lower index costs, increased likelihood of being discharged to home, shorter LOS, and decreased readmission rates, when compared to mTKA patient costs.

Kinematic Analysis of Total Knee Arthroplasty Using Verasense : Genesis-II Prosthesis Versus Anthem Prosthesis
PRESENTER: Jong-Keun Seon

ABSTRACT. Purpose The aim of this study was to elucidate the kinematic change according to the implant’s specific femoral rotation by evaluating the femoral rollback differences between two total knee arthroplasty (TKA) implants using Verasense. And also we evaluated the clinical and radiological outcomes of the patients between Genesis-II TKA system and Anthem TKA system. Methods We evaluated 44 patients (56 knees) who underwent conventional TKA using two kinds of implants. We evaluated both medial and lateral femoral tracking proportion of Verasense. For clinical evaluation, we used Knee Society Score (pain and function), Western Ontario and McMaster Universities (WOMAC) scoring system, Kujala scores including anterior knee pain and satisfactory level. For radiological evaluation, postoperative patellar tilt angle and amount of lateral shifting were measured using Merchant view. Results Overall femoral tracking proportion regardless of implants was significantly higher on the medial compartment compared to the lateral compartment, with percentage of 13.3±8.4% and 6.3±5.0%, respectively (p<0.001). Genesis-II showed 12.1±8.2% on the medial compartment and 8.0±5.8% on the lateral compartment (p=0.100). Anthem showed significant difference between the compartments with 14.2±8.6% on the medial compartment, and 5.2±4.2% on the lateral compartment (p<0.001). Medio-lateral difference of femoral tracking proportion was 4.1±11.3% on Genesis-II TKA system and 9.0±9.0% on Anthem TKA system (p=0.095). Genesis-II TKA system showed less reverse roll back compared to Anthem. Clinical results showed significant improvement after TKA but, did not showed significant differences between two prosthesis (p>0.05) Conclusion Our study showed reverse femoral roll-back movement with higher tracking distance on the lateral compartment. Genesis-II system with femoral component rebuilt, showed less difference between medial and lateral compartments. Both TKA system showed excellent clinical outcomes without significant difference. With longer follow-up and larger cohort, the advantage and effectiveness of femoral component rotation can be elucidated in the future.

Does the Use of a CT Based 3D Plan Improve Joint Balancing in Total Knee Arthroplasty? a Multi-Center Study
PRESENTER: Jingwei Zhang

ABSTRACT. Studies have shown that dissatisfaction following TKA may stem from poor component placement and iatrogenic factors related to variability in surgical execution. A CT-based robotic assisted system allows surgeons to dynamically balance the joint prior to bone resection. This study aimed to determine if this system could improve TKA planning, reduce soft tissue releases, minimize bone resection, and accurately predict component size. Six hundred and sixty-six cases undergoing primary robotic assisted TKA we enrolled in a prospective, multicenter study. Seven surgeons participated from seven US centers. Patient demographics and intraoperative surgical details were collected. Initial and final 3-dimensional alignment, component position, bone resection depths, use of soft tissue releases, knee balancing gaps, and component size were collected intraoperatively. Descriptive statistics were applied to determine the changes in these parameters between initial and final values. In this study, 513 varus knees, 86 valgus knees, and 26 neutral knees were captured and stratified for analysis. Native deformity ranged from 12 degrees of valgus to 19 degrees of varus. 85% of all patients in this study did not require a soft tissue release. Complex deformities who required a soft tissue release were corrected on average to 3.36 degrees while cases without releases were corrected to 1.1 degree on average. All surgeons achieved their planned sizes on the tibia and femur more than 97.5% of the time within one size, and 100% of the time within two sizes. Flexion and extension gaps during knee balancing were within 2mm (mean 1mm) for all knees. New tools may allow for enhanced execution and predictable balance for TKA, which may improve patient outcomes. In this study, preoperative planning via CT scan allowed surgeons to assess bony deformities and subtly adjust component position to reduce soft tissue trauma. Patient follow up is needed to determine clinical outcomes.

Neuromonitoring to Avoid Euthanasia in a Quadriplegic Patient

ABSTRACT. Background: Under very limited circumstances euthanasia can be performed in Belgium since 2002(1). If a patient has medical condition with no hope on improvement, with physical and/or psychological suffering, he can ask for terminating his life. The written demand is on voluntary bases, well considered, repeated and was not induced due to external pressure from other people. Neuromonitoring has been used in spine surgery during the last four decades.(2-4) With the development of new modalities, new applications were introduced in spine surgery in order to avoid neurological damage during surgical procedures. Method: A patient with a partial recovered ASIA A C7 quadriplegia suffering from wounds caused by his spinal instrumentation had intraoperative neuromonitoring. In case he became dependent for his personal care, he wanted to have euthanasia executed on him. Conclusion: So far there is no literature on the use of neuromonitoring to avoid euthanasia in cases where spinal surgery is needed, but has an inherent risk of causing damage to nerval structures, which can cause loss of recovered nerve function after spinal cord injury. This potential loss of independence was an unbearable physical and psychological suffering the patient would not want to go through again. By using neuromotoring, the key muscles were observed during the surgery. No neurological events were seen during the procedure. He had some general weakness after the surgery but kept his autonomy, so no euthanasia was needed.

Anterior Mechanical Navigation Device Is as Accurate as Lateral Device for Hip Socket Position
PRESENTER: David Freccero

ABSTRACT. In total hip arthroplasty (THA), accurate acetabular component position promotes prosthetic hip joint stability and longevity, and minimizes polyethylene wear. Image-based mechanical navigation is known to improve accuracy and reproducibility of accurate cup position intraoperatively via the posterior approach and the superior capsular approach. The purpose of this study was to assess the accuracy of acetabular component position using image-based mechanical navigation via the direct anterior approach (DAA). We prospectively followed 96 patients who underwent THA with one fellowship-trained arthroplasty surgeon over a nine-month period. Thirty-three patients underwent DAA THA with the anterior HipXpert device (Group 1), and 63 patients underwent posterior approach THA with the lateral HipXpert mechanical navigation device, serving as an operative control group (Group 2). Standard postoperative plain film radiographic measurements of acetabular component inclination and anteversion were assessed. The average inclination angle was 38.6 degrees and 40.6 degrees in Groups 1 and 2, respectively. The average anteversion angle was 27.6 degrees and 30.1 degrees in Groups 1 and 2, respectively. There were no postoperative hip dislocations and no study patients underwent revision THA at an average follow-up of 12 months. There were no patient outliers in Groups I or II with inclination angles or anteversion angles outside 10 degrees of the preoperatively planned values. We conclude that the anterior HipXpert mechanical navigation device enhances accurate acetabular component position and may reduce outlier component placement. Acetabular socket position is as accurate using the anterior device as it is using the lateral device.

Clinical and Functional Outcomes of Robotic Assisted Bicompartmental Knee Arthroplasty

ABSTRACT. This study reports on mid-term survivorship and outcomes of medial bicompartmental robotic assisted primary knee arthroplasty. Forty-six knees in 43 patients with a mean 6 year follow up were consented to participate in this retrospective data collection. All patients received primary treatment for knee osteoarthritis with fixed metal backed medial femoral and patellar implants. Demographic data along with post-operative outcomes were collected including; the KSS patient portion, implant survivorship, and patient satisfaction. All patients were included in the survivorship analysis. 45 knees in 42 patients were available for analysis of KSS and patient satisfaction. The mean follow-up was 6.1 years (range 2.1 - 7.6 years). Sixty-three percent of patients were male and 37% female. Average age at the time of surgery was 67 years and average BMI was 29. There were 3 revisions and 1 arthroscopic surgery resulting in 97.8% all cause survivorship. 86.7% of patients reported walking more than 10 blocks and 95.6% of patients reported walking without the use of assistive devices for support. All patients were able to go up and down stairs, 48.9% required use of a rail. 82.2% of patients reported being satisfied with their knee at 5 years. In this study we found 97.8% survivorship at a mean 6 year follow up with 82.2% of patients being very satisfied or satisfied with the implant. Longitudinal follow up at 7 and 10 years will continue to evaluate long term outcomes on the variations of robotic assisted knee arthroplasty.

Minimum 5-Year Outcomes of Robotic-Assisted Primary Total Hip Arthroplasty with a Nested Comparison Against Manual Primary Total Hip Arthroplasty: a Propensity Score Matched Study
PRESENTER: Manoshi Stoker

ABSTRACT. Background: Robotic-assisted technology has been a reliable tool in enhancing precision of cup placement in total hip arthroplasty (THA). However, there is a lack of evidence indicating whether benefits in outcomes of robotic-assisted arthroplasty (rTHA) can be expected in comparison to manual THA (mTHA). The present study is among the first to report rTHA outcomes at minimum 5-year follow-up, and to compare them against those of a propensity score matched mTHA group.

Methods: Prospectively collected patient data were retrospectively reviewed for primary THA recipients during June 2008 to July 2013. Patients with minimum 5-year follow-up for Harris Hip Score (HHS), Forgotten Joint Score-12 (FJS-12), Veterans RAND-12 Mental (VR-12 Mental), Veterans RAND-12 Physical (VR-12 Physical), 12-Item Short Form Survey Mental (SF-12 Mental), 12-Item Short Form Survey Physical (SF-12 Physical), Visual Analog Scale (VAS), and satisfaction were included. Patient-reported outcomes, cup placement, and revision rate of the rTHA group were compared against those of a propensity score matched mTHA control group.

Results: Ninety-nine rTHAs performed during the study period reported HHS of 90.92±12.36, FJS-12 of 84.50±19.97, VR-12 Mental of 60.52±7.17, VR-12 Physical of 50.51±8.58, SF-12 Mental of 56.67±5.57, SF-12 Physical of 49.35±8.81, VAS of 1.13±1.98, and satisfaction of 9.07±1.74. Sixty-six rTHAs were matched to 66 mTHAs. The rTHA group reported significantly higher HHS, FJS-12, VR-12-Physical, and SF-12 Physical (P<0.001, P=0.002, P=0.002, P=0.001). While revision rates were similar (P=0.479), the acetabular component placement by rTHA had a reduced risk of placement outside the Lennewick and Callanan Safe-Zones (Relative Risk (RR), 0.11 [95% Confidence Interval (CI), 0.03-0.46]; P=0.002; RR, 0.21 [95% CI, 0.01-0.47]; P=0.001). Additionally, rTHA recipients had smaller absolute values of leg length discrepancy and global offset (P=0.091, P=0.001).

Conclusions: Patients who received rTHA reported favorable outcomes at minimum 5-year follow-up. Furthermore, in comparison to a propensity score pair-matched mTHA group, rTHAs reported higher patient-reported outcome scores and had 89% reduced risk of acetabular component placement beyond the Lennewick Safe-Zone and 79% reduced risk of placement beyond the Callanan Safe-Zone.

Level of Evidence: Level III, Retrospective Group Study.

13:30-15:00 Session 28: Improving Outcomes
Location: Main Auditorium
Data-Driven Design of an Implant Library for Osteochondral Lesion Repair in the Knee Joint
PRESENTER: Fabio Tatti

ABSTRACT. Focal cartilage defects are widespread and a common cause of joint discomfort and pain. Cartilage resurfacing procedures with the use of focal implants are a viable solution for patients who fail or cannot be treated with regenerative approaches. Minimal invasiveness and congruency with the surrounding cartilage are important design criteria in the development of such implants, with the ideal implant being one that perfectly matches the shape and size of the defect. In this study, we present a novel data-driven approach for the design of a library of focal implants the shape of which is based on the statistical modeling of a dataset of real osteochondral defects, identified from MRI images. We demonstrate the possibility of exhaustively modeling the defects’ surface with a limited number of parameters, and then exploiting statistical methods to further reduce the parameters needed and identify the best surfaces to adopt as implants. Compared to the most common solutions currently in use, which typically rely on a limited set of standard shapes, our approach offers a broader set of non-standard surfaces, the selection of which is driven by real patient data. We believe this approach may offer an advantage also in comparison to patient-specific implant solutions such as, as these require a preoperative MRI of the patient, which may not be available.

AMIS Total Hip Arthroplasty Using Traction Table: 5 Years Follow-up
PRESENTER: Thomas Apostolou

ABSTRACT. Background Minimal invasive surgery has gained popularity among hip surgeons and patients. Based on early studies, the method is described as a very promising alternative, with low dislocation rates, resulting in a non-traumatic procedure and early functional return. However, complication rates arising of the recent studies raise concern about the applied technique. Aim The aim of the study is to present the clinical results and intra- and post-operative complications of the AMIS procedure in patients with osteoarthritis of the hip, managed with total hip arthroplasty with positioning table, in a 5 years follow up. Patients and Methods One senior hip arthroplasty surgeon performed all surgeries. Three hundred eighteen consecutive patients (195 females, 123 males) were clinically and radiologically evaluated, postoperatively 2, 6 and 12 months. Mean patient age was 69.7 years (24 to 88). Results There was significant improvement according to Harris-Hip Score. The mean incision length was 7.5cm (6 to 8cm). The mean operating time was calculated at 85 minutes. The patients were discharged on the second post-operative day, able to walk with partial weight bearing. One month post-operative, the patients were advised for full weight bearing walking without crutches. Intraoperative complications included two femoral perforations. Postoperative complications included two patients with femoral fractures; one with dislocation; five with superficial infections; three with femoral stem aseptic loosening; one with ceramic inner fracture and two acetabular component protrusion in the same patient, among which only the last patient had reoperation in both hips. Conclusions Anterior Minimal Invasive Surgery of the hip is a non-traumatic procedure, associated with reduced pain, faster recovery and no major complications, but requires higher experience level from the hip surgeon.

Intra-Operative and Anatomic Verification of a TKA Computational Model for Pre-Operative Surgical Planning

ABSTRACT. Traditional methods for measuring dynamic outcomes in Total Knee Arthroplasty (TKA) are unsuitable for routine preoperative planning. Computer simulations are a promising scalable alternative that allows the impact of patient and surgical factors on joint dynamics following TKA to be studied. Intra-operative validation of simulated joint dynamics and its relation to patient specific anatomy has not been achieved previously. A database of TKA Patients undergoing surgery from 1-Jan-2014 operated on by 9 surgeons, who received a preoperative and post-operative CT and 6-month post-operative Knee Injury and Osteoarthritis Outcome (KOOS) score were assessed. All knees received a CR or PS OMNI (Raynham, MA) APEX prosthesis and a dome patella button. Segmented preoperative bones and component geometries were registered to the post-operative CT to determine the achieved component placement. A subset of these patients had surgery performed with the OMNIbotics navigation system from which the log files were extracted. A musculoskeletal computational model with similar boundary conditions to the Oxford Knee Rig was used to simulate post-TKA knee dynamics. The simulated tibiofemoral contact force and force difference between the medial and lateral condyles was compared to: navigation data; difference femoral collateral ligament offsets; and post-operative KOOS scores. 284 patients were identified in the database, 69 of which had corresponding navigation data. 59.5% (169) were female and the average age was 68.9±11.6 years. A significant moderate-strong correlation was found between the simulated contact force and navigated laxity in mid-flexion (r=-0.452, p<0.0001), and between the medio-lateral contact force difference and difference in distal to posterior femoral collateral ligament offset (r=-0.473, p<0.0001). A significant difference of 5 KOOS pain points (p=0.02) was found between patients dichotomised in to a mid-range simulated contact force (1500-300 N) and those outside this range. This study shows statistically significant correlations between patient specific anatomy, simulated kinematics, and navigation data, indicating the preoperative simulation is capable of distinguishing patient specific kinematics prior to surgery. Furthermore, the simulated forces are shown to significantly correlate with patient reported outcomes, confirming the clinical relevance of such simulations for identifying kinematics which may result in improved patient outcomes.

Conservative Kinematic Alignment Strategies Report Higher Incidence of Mid-Term Pain Following TKA: a Retrospective Study

ABSTRACT. Kinematic Alignment (KA) has emerged as a surgical philosophy to challenge mechanical alignment (MA), with the aim of addressing the high dissatisfaction rate in total knee arthroplasty (TKA). Conservative KA approaches are a means of achieving a compromise between KA and MA philosophies when unusual or outlier anatomy encountered. This study sought to investigate how achieved TKA alignment correlates with short term patient outcomes. A database of TKA patients operated on by nine surgeons from 1-Jan-2014 was accessed. All patients had a pre- and post- operative CT. The achieved alignment was measured and categorised as either KA, MA, or a conservative approach to KA by restricting coronal cuts to <5° deviation from neutral. The relationship between achieved alignment and 12-month postoperative Knee Osteoarthritis & Outcome Score (KOOS) was determined. All TKAs were performed using CR or PS Omni Apex (Raynham) implants. 369 TKA knees were identified in the database. 60% (221) were female, with an average age of 70.1 years (+/-8.2). 21% (76) of the knees were classified as KA, with 10% of the total (37) being conservative rather than fully KA. When dichotomising patients into those with a KOOS Pain score less than or greater than 70, a trend was found, in which 76% (28/37) of the conservative KA group, 88% (257/293) of the MA group and 95% (37/39) of the full KA group reached the threshold low pain. When combining the MA group with the full KA group and comparing the outcome with that of conservative KA, the difference was statistically significant (p = 0.026) and represents a 1.8 times risk ratio. Rather than achieving improved joint stability compared to KA, by limiting the deviance of the resections, and improved native soft tissue balance compared to MA, by reducing the number of releases, conservative KA is reported here to increase the rate of post-operative pain. The origin of the increased rate of pain is currently unknown, but may be due to the compromise on soft tissue and bony resection, leading to instability in both the supporting soft tissue structures and articulating components. This study showed an increase in pain when the achieved alignment formed a compromise between a restorative and a reconstructive approach. This suggests that conservative approaches to kinematic alignment that maximise patient outcome may require selective application of kinematic alignment rather than blanket application of modified anatomical rules.

Healthcare Utilization and Payer Cost Analysis of Robotic-Arm Assisted Total Knee Arthroplasty at 30-, 60-, and 90-Days

ABSTRACT. Introduction This study performed a healthcare utilization analysis between robotic-arm assisted and manual TKA techniques at three intervals to better understand intra-episode trends that can lead to optimized care pathways. Specifically, we compared: (1) index costs; and (2) discharge dispositions; as well as (3) 30-; (4) 60-; and (5) 90-day: a) total episode-of-care costs, b) post-operative healthcare utilization, and c) readmissions.

Methods The Medicare 100% Standard Analytical Files was queried for robotic and manual TKAs (rTKA and mTKA) performed between January 1, 2016 and March 31, 2017. Based on strict inclusion and exclusion criteria, and 1:5 propensity score matching, 519 robotic and 2,595 manual TKA patients were analyzed. Total episode payments, healthcare utilization, and readmissions, at 30-, 60-, and 90-day time points were compared between cohorts with a generalized Linear Model, Binomial Regression, log link, Mann-Whitney, and Pearson's Chi Squared tests with p<0.05 for statistical significance.

Results The robotic vs. manual cohort average total episode payment was $17,768 vs. $19,899 (p<0.0001) at 30-days; $18,174 vs. $20,492 (p<0.0001) at 60-days; and $18,568 vs. $20,960 (p<0.0001) at 90-days. At 30 days, 47% fewer rTKA patients utilized SNF services (13.5 vs. 25.4%, p<0.0001 and had lower SNF costs at 30- ($6,416 vs. $7,732; p = 0.0040), 60- ($6,678 vs. $7,901, p=0.0072), and 90-days ($7,201 vs. $7,947, p=0.0230). rTKA patients also utilized fewer home-health visits and costs at each time point (p<0.05). Additionally, 31.3% fewer rTKA patients utilized emergency room services at 30-days postoperatively. The robotic cohort had significantly fewer 90-day readmissions (5.20 vs. 7.75%; p=0.0423).

Discussion Robotic TKA is associated with significantly lower 30-, 60-, and 90-day post-operative costs and healthcare utilization. These results are of marked importance given the emphasis to contain and reduce healthcare costs for total joints arthroplasties. This analysis provides initial economic insight into robotic-arm assisted TKA with promising results.

Ten Years Results of Total Hip Arthroplasty Using CT-Based Navigation System
PRESENTER: Nobuo Nakamura

ABSTRACT. The purpose of the study is to investigate minimum ten years clinical results of primary and revision THA using CT-based navigation. Forty-nine primary THAs and 2 revision THAs were performed on 42 patients and followed for at least 10 years. The mean age at surgery was 58 years and the mean follow up was 130 months. During surgery, navigation was used for acetabular reaming and cup implantation in all cases. We evaluated Japanese Orthopaedic Association (JOA) clinical outcome scores, revision surgery and complications. In one primary THA case, navigation procedure was aborted because of registration failure. This case experienced femoral periprosthetic fracture at 4.5 years and dislocation at 8.5 years postoperatively. In another primary THA case, revision THA was performed because of aseptic loosening of cup at 4.5 years postoperatively. Except these two cases, there were no complications such as fracture, dislocation, infection, nerve palsy, deep vein thrombosis or loosening. Preoperatively, mean JOA clinical score was 44 points. Ten years postoperatively, it was improved to 96 points. When the aborted case is eliminated, there were no dislocations at ten years. The survivorship rate at ten years was 98% when revision surgery for any reason was considered as the end point. In conclusion, ten years clinical results of THA using CT-based navigation system were acceptable.

Early Experience with CAOS Enhanced Total Knee Arthroplasty – a Global, Multi-Surgeon Evaluation
PRESENTER: Ian Gradisar

ABSTRACT. This study investigated surgeons’ perceptions of their experience while adopting a novel CAOS enhanced mechanical instrument system for TKA, including ease of usage, task complexity, and demands of surgical time and physical activity. A group of 9 surgeons from multiple countries with no experience in the investigated system used the CAOS enhanced mechanical instrument system during their surgical practice. After performing each TKA case, the surgeon independently completed a 6-section questionnaire formulated to survey his/her experience with the case. The results demonstrated high level of surgeons’ experiences with the adoption of the CAOS enhanced conventional instrumentation, with particularly satisfying experiences in minimum demand of time in landmark acquisition and disruption of the existing surgical process.

Bony Resection Outliers: Insights from 10,144 Clinical Cases Using a Contemporary Computer-Assisted Total Knee Arthroplasty System
PRESENTER: Charlotte Bolch

ABSTRACT. This study accessed the alignment outliers of intraoperatively measured bony resection during total knee arthroplasty on 10,144 cases performed using a modern CAOS system. The impacts from geographic regions, surgeon’s adoption of the technology (learning or proficient phases), and historical progression of the CAOS application (software versions) were evaluated. The comprehensive analysis demonstrated that the CAOS system is a robust and accurate solution to assist the surgeons to achieve his/her surgical resection goals across its application history.

Multilevel Modeling of Resection Accuracy: Insights from 10,144 Clinical Cases Using a Contemporary Computer-Assisted Total Knee Arthroplasty System
PRESENTER: Charlotte Bolch

ABSTRACT. This study applied an advanced statistical tool (multilevel modeling) to assess the accuracy of bony resection during total knee arthroplasty on 10144 cases performed using a modern CAOS system. An extensive list of factors was included for the modeling, including geographic region, inter-surgeon difference, surgeon’s adoption of the technology (learning or proficient phases), and historical progression of the CAOS application (software versions). The comprehensive analysis demonstrated that the CAOS system is an accurate and precise solution to assist the surgeons to achieve his/her surgical resection goals.

15:00-16:00 Session 29: CAOS Advisory Board Committee Meeting

Meeting reserved for members of the CAOS International Advisory Board

Location: New York Suite
15:30-16:10 Session 30A: Spine
Location: Main Auditorium
Safety and Accuracy of Robot-Assisted Versus Fluoroscopy-Assisted Pedicle Screw Insertion in Thoracolumbar Spinal Surgery
PRESENTER: Xiaoguang Han

ABSTRACT. Object: To compare the safety and accuracy of the TiRobot system-assisted with conventional fluoroscopy-assisted pedicle screw placement in thoracolumbar spinal surgery. Methods: 234 patients suffering from thoracolumbar spinal degenerative or traumatic disorders and requiring spinal instrumentation were randomly assigned to TiRobot assisted group (RG) or fluoroscopy assisted group (FG) in a 1:1 ratio. The primary outcome measure was accuracy of screw placement based on the Gertzein-Robbins scale. Grades A and B (<2 mm pedicle breach) were considered clinically acceptable. Further, in RG, the discrepancies between the surgeon’s plan and the actual placements were also measured by merging of postoperative CT images and trajectory planning images. Secondary parameters included proximal facet joint violation, duration of surgery, intraoperative blood loss, postoperative hospital stay and radiation exposure. This study is registered on, number NCT02890043. Results: A total of 1161 pedicle screws were implanted in 234 patients (FG, 119; RG 115). In RG, 95.3% screws had perfect positions (Grade A). The remaining screws were graded B (3.4%), C (0.9%) and D (0.4%). In FG, 86.1% screws had perfect position (Grade A). The remaining screws were graded B (7.3%), C (4.6%), D (1.2%) and E (0.5%). The proportion of acceptable screws was higher in RG compared with FG (P< 0.01). In RG, the mean deviation was 1.5+0.8 mm for each screw. The most common direction of screw deviation in RG, was lateral, where it was medial in FG. Further, two screws misplacement in FG required a second surgery, but no revision was required in RG. None of the screws in RG violated the proximal facet joint, while 12 screws (4.2%) in FG violated the proximal facet joints (P< 0.01). Blood loss was lower in RG (186.0±255.3 mL) than in FG (217.0±174.3 mL) (P< 0.05). There is no different in surgical time and postoperative hospital stay between groups. The mean cumulative radiation time was 81.5±38.6s in RG and 71.5+44.2s in FG, but there is no significant difference (P= 0.07). But the radiation exposure to surgeon is significantly lower in RG (21.7±11.5 μSv) than in FG (70.5±42.0 μSv) (P< 0.01). Conclusion: TiRobot-guided pedicle screw placement is a safe and useful tool for assisting spine surgery in thoracolumbar spinal surgery.

Ultrasound Guided Pedicle Screw Entry Point Identification for Spinal Fusion Surgery

ABSTRACT. Accurate identification of the location the vertebra and corresponding pedicle is critical during pedicle screw insertion for percutaneous spinal fusion surgery. Currently, two dimensional (2D) fluoroscopy based navigation systems have extensive usage in spinal fusion surgery. Relying on 2D projection images for screw guidance results in high misplacement rates. Furthermore, fluoroscopy-based guidance exposes the surgical staff and patient to harmful ionizing radiation. Real-time non-radiation-based ultrasound (US) is a potential alternative to intra-operative fluoroscopy. However, accurate interpretation of noisy US data and manual operation of the transducer during data collection remains a challenge. In this work we investigate the potential of using multi-modal deep convolutional neural network (CNN) architectures for fully automatic identification of vertebra level and pedicle from US data. Our proposed network achieves 93.54% vertebra identification accuracy on in vivo US data collected from 27 subjects.

Robot-Assisted Versus Fluoroscopy-Guided Pedicle Screw Placement in Transforaminal Lumbar Interbody Fusion for Lumbar Degenerative Disease

ABSTRACT. Objective: To compare the clinical accuracy for pedicle screw placement in transforaminal lumbar interbody fusion (TLIF) between robot-assisted (RA) technique and fluoroscopy-guided (FG) technique. Methods: 77 patients scheduled to undergo RA (43 patients) and FG (44 patients) TLIF surgery were included. Radiographic accuracy was compared according to post-operative CT images. The accuracy of pedicle screw placement was according to the Gertzbein and Robbins scale. Results: Of the 176 screws in the RA group, 164 screws were grade A, and 9, 2 and 1 screws were grade B, C and D, respectively. Of the 204 screws in the FG group, 175 screws were grade A, with 16 screws scored as grade B, 8 screws grade C, 3 grade D, and 2 grade E. The rate of perfect screw position (grade A) was greater in the RA group than in FG (93.2% vs. 85.8%; P=0.020). 191 screws (93.6%) in FG group were clinically acceptable (group A + B), whereas more acceptable screw positions were achieved in RA (98.3%) (P=0.024). Conclusion: RA pedicle screw placement is an accurate and safe procedure in TLIF for lumbar degenerative disease.

Accuracy of Robot-Assisted Placement of Cervical Spine Screws: a Prospective Randomized Comparison to Conventional Fluoroscopy-Assisted Screw Implantation
PRESENTER: Mingxing Fan

ABSTRACT. Background Screw fixation plays an important role in cervical spinal surgery, however, cervical spinal surgery is difficult and dangerous, screw misplacement might lead not only decreased stability, but also neurological, vascular, and visceral injuries. Methods In this prospective randomized controlled study, we randomly assigned 135 patients who newly diagnosed with cervical spinal disease and required for screw fixation to undergo either robot-assisted cervical spinal surgery or conventional fluoroscopy-assisted cervical spinal surgery.The primary outcomes were Gertzbein and Robbins scale and the real discrepancies between the planned trajectories and actual screw position. Results 127 patients underwent the assigned intervention (61 robot-assisted and 66 conventional fluoroscopy-assisted). The baseline characteristics were similar in the two groups. A total number of 390 screws were planed and placed in the cervical vertebrae, 94.9% were acceptable. The Gertzbein and Robbins scales were better in robot-assisted group (p<0.001), and the robot-assisted group also have a better screw placement accuracy than the conventional fluoroscopy-assisted group with an associated p value smaller than 0.001 (0.99±0.76mm vs 2.15±1.18mm). These two groups did not differ significantly on the duration of operation (p=0.584) and length of stay after surgery (p=0.068). Furthermore, the robot-assisted group experienced a significantly lesser amount of blood loss during surgery than the conventional fluoroscopy-assisted group (259.02±328.68ml vs 476.90±483.72ml; p=0.005), and tends to have less economic stress (p=0.015). Neurological injury occurred in 1 case in the conventional fluoroscopy-assisted group. Conclusions The accuracy and clinical outcomes of cervical spinal surgery using robot-assisted technique tend to be superior to conventional fluoroscopy-assisted technique in this prospective, randomized, controlled trial.

16:10-17:00 Session 31: Special Session II: Providing Evidence for Clinical Adoption of CAOS Technologies

16:10 – 16:18     Alister HART, Professor, Royal National Orthopaedic Hospital and University College London, London, UK

Introduction: Overview of Computer Aided  Innovation in the UK Healthcare System”

16:18 – 16:26     Johann HENCKEL, MD, Royal National Orthopaedics Hospital, London, UK

“Measuring if it Works: Planned vs Achieved”

16:26 – 16:34     Peter WALKER, Professor, New York University, New York, USA

“Translation of Computer Aided TKR Designs”

16:34 – 16:42     Jim NEVELOS PhD, Stryker inc., USA

“MAKO Adoption: How Did Stryker Achieve This?”

16:42 – 16:50     Ferdinando RODRIGUEZ y BAENA, Professor, Imperial College, London, UK

Conclusion: Software Enabled surgery - From the Lab to the OR”

16:50 – 17:00     Roundtable Discussion

Location: Main Auditorium
17:00-18:00 Session 32: Guided Posters II
The Sensitivity of Balancing in Total Knee Surgery
PRESENTER: Gabriela Zapata

ABSTRACT. Background: Balancing is important to outcomes, but has been difficult to achieve due to the high sensitivity of the condylar forces to even small changes in ligament lengths. The first goal was to measure the effects of alignment and component placement errors on balancing. The second goal was to study equivalence between the collateral ligament forces, distraction forces, and condylar contact forces. Methods: The test rig flexed and extended synthetic knees, while condylar forces and ligament forces were measured. For ideal femoral component placement, the sagittal contours exactly matched anatomic. 2mm placement errors relative to anatomic were distal (too little distal femoral resection), proximal, anterior, and posterior. Condylar forces for anatomic placement were defined as reference, while forces for the different placement errors were measured relatively. Results: Condylar forces were significantly influenced by 2mm errors in femoral component placement. For distal placement error in combination with kinematic alignment, there were only small changes in the contact forces. Other placement errors produced large contact errors. For mechanical alignment medial forces were similar to kinematic, but lateral forces reduced to almost zero. The medial and lateral ligament and contact forces, distraction forces, and lift-off moments were highly correlated. Conclusions: The ideal situation was kinematic alignment, which could reproduce the condylar contact forces seen in intact anatomic knees. The least condylar force errors occurred when the femoral component was placed too distally, for the kinematic alignment bone cuts. Different balancing parameters can be used interchangeably.

Pelvic Tilt Cannot Be Accurately Predicted Using Anteroposterior Radiographs

ABSTRACT. ABSTRACT: INTRODUCTION: Pelvic positioning during total hip arthroplasty (THA) can affect the functional position of the acetabular component. A comprehensive understanding of pelvic orientation prior to THA is necessary to allow for proper cup positioning and mitigate the risks of complications associated with component malpositioning. Measurements using anteroposterior (AP) radiographs have been described as an effective means of accurately predicting pelvic orientation. The purpose of our study was to describe the accuracy of assessing pelvic tilt using AP radiographs. METHODS: An online survey was created and sent to a cohort of fellowship-trained adult reconstruction surgeons. The survey consisted of 65 standing AP pelvis radiographs. Participants were asked to score each radiograph as 1) anterior pelvic tilt > 10 degrees, 2) posterior pelvic tilt > 10 degrees, or 3) neutral. Responses were then compared to measurements of pelvic tilt made on lateral standing pelvic radiographs. Categorical and continuous variables were compared using chi-squared, unpaired, two-tailed student’s T tests, and ANOVA. RESULTS: 45 surgeons completed the survey. The average correct predictive value of pelvic tilt between all surgeons was 53.2%. 51.2% of responding surgeons performed greater than 100 cases per year. 50% of surgeons reported that they were “not so familiar” or “somewhat familiar” with the principles of spinopelvic mobility. 43.5% of surgeons reported that they did not routinely use spinopelvic mobility principles in THA planning. DISCUSSION AND CONCLUSIONS: The standing AP pelvis radiograph is poorly predictive of pelvic tilt. Pre-operative evaluation of spinopelvic parameters requires AP and lateral views for detailed assessment and accurate pre-operative planning.

Value of Robotics in Total Knee Arthroplasty - an Assessment of a Hospitals Experience in the Cms Bundled Payment for Care Improvement Model
PRESENTER: Dr. Jan Koenig

ABSTRACT. Introduction: Current CMS reimbursement policy for total joint replacement is aligned with more cost effective, higher quality care. Upon implementation of a standardized evidenced-based care pathway, we evaluated overall procedural costs and clinical outcomes over a 90 day episode of care period for patients undergoing total knee arthroplasty (TKA) with either conventional (Conv.) or robotic-assisted (RAS) instrumentation. Methods: In a retrospective review of the first seven consecutive quarters of BPCI participation beginning January 2014, we compared 90 day readmission rates, average Length of Stay (LOS), discharge disposition, gains per episode in relation to target prices and overall episode costs for surgeons who performed either RAS-TKA (3 surgeons, 147 patients) or Conv. TKA (3 surgeons, 85 patients) at a single institution. All Medicare patients from all surgeons performing more than two TKA’s within the study period were included. An evidence-based clinical care pathway was implemented prior to the start of the study that standardized anesthesia, pain management, blood management, and physical/occupational therapy throughout the LOS for all patients. Physician specific target prices were established from institutional historical CMS payment data over a prior three year period. Results: Patients undergoing RAS-TKA had a 6.2 % lower 90 day readmission rate (5.4% vs 11.7%), a 0.4 day shorter LOS (3.4 vs 3.8) and a 14% higher rate of discharge to home (62% vs 48%) versus Sub-acute Rehabilitation Facilities (SAR’s) as compared to the patients undergoing Conv-TKA. Conv-TKA and RAS-TKA procedures exhibited an average gain per episode of $5,579 and $7,600, respectively. The average total cost per episode was $4,041.73 lower across the patients receiving RAS-TKA compared to conventional instrumentation ($21,413.68 versus $25,455.40). Discussion and Conclusions: Implementation of a standardized care pathway across all service departments and physicians resulted in a reduction in overall episode of care costs, with further reductions in cost, 90 day readmission rates, and discharge to SARs observed with the use of RAS.

Cross Comparison Shopping Guide to Robot-Assisted Surgical Systems
PRESENTER: Nicholas Parody

ABSTRACT. Robot-assisted surgical systems in hip/knee arthroplasty (TKA/THA) procedures have made strides to improve pre-, intra-, and postoperative surgical performance. Four systems are primarily used today, with each having unique characteristics that must be considered. These systems include a semi-active robot, a handheld burring system, tension adjusted cutting blocks, and an open-active platform. A comparison was conducted by evaluating each system from the relative perspectives of the patient, surgeon, and hospital. This included: initial/ancillary costs, the number of procedures each system can perform, image-based reliance, learning curves to achieve consistent end-results, and potential risks to the patient. Initial cost values range [$0-$1 million, average $337,500] while ancillary costs range [$350-$1500]. The semi-active robot is FDA approved for THAs, TKAs, and UKAs. The handheld system performs TKAs and UKAs. The cutting blocks are only designed for TKAs. The open-active platform is currently only FDA approved for THAs in the US. The semi-active and open-active platforms rely on preoperative image-based information, while the other two do not. Each system has its own learning curve, with a range [8-35 cases]. The field of robot-assisted surgical systems is growing at a rapid pace to match the expected increase in hip and knee procedures. This anticipated surge brings an expectation for these systems to become more commonplace. The four current systems are still expanding their application use, while new platforms are also being developed. To handle this advancing technology, a comprehensive guide is necessary to keep all parties informed.

Spine Surface Segmentation from Ultrasound Using Multi-Feature Guided CNN
PRESENTER: Ahmed Alsinan

ABSTRACT. Accurate, robust, and real-time segmentation of bone surfaces is an essential objective for ultrasound (US) guided computer assisted orthopedic surgery (CAOS) procedures. In this work, we present a convolutional neural network (CNN)-based technique for segmenting spine surfaces from in vivo US scans. Proposed design utilizes fusion of feature maps extracted from multimodal images to abate sensitivity to variations caused by imaging artifacts and low intensity bone boundaries. In particular, our multimodal inputs consist of B-mode US images and their corresponding local phase filtered counterparts. Validation studies performed on 261 in vivo US scans obtained from 10 subjects achieved a mean localization accuracy of 0.1 mm with an F-score of 97%. Comparison against state-of-the-art CNN networks show an improvement of 89% in bone surface localization accuracy.

Less Iatrogenic Soft Tissue Damage Utilizing Robotic Assisted Total Knee Arthroplasty When Compared with a Manual Approach: a Blinded Assessment
PRESENTER: Emily Hampp

ABSTRACT. Background: Haptically-bounded sawblade in robotic assisted total knee arthroplasty (TKA) can potentially help limit surrounding soft tissue injuries. However, there is limited data characterizing these injuries, for cruciate retaining (CR) TKA. Therefore, this study compared the extent of soft tissue damage sustained during TKA through a robotic assisted (RATKA) haptically-guided versus a conventional, manual TKA approach.

Methods: Four surgeons each prepared 3 RATKA and 3 MTKA specimens for cruciate-retaining TKAs. RATKA was performed on one knee, with MTKA on the other. Postoperatively, 2 additional blinded surgeons, assessed and graded damage to 14 key anatomic structures. A Kruskal-Wallis hypothesis test was performed in order to assess for statistical differences soft tissue damages between RATKA and MTKA cases. A p-value <0.05 was used as the threshold for statistical significance, and p-values were adjusted for equivalent evaluations.

Results: Significantly less damage occurred to the PCL in the RATKA than the MTKA specimens (p<0.0001). RATKA specimens also had less damage to the dMCL (p=0.149), ITB (p=0.580), popliteus (p=0.248), and patellar ligament (p=0.317). The sMCL, posterior oblique ligament, semimembranosus muscle tendon, gastrocnemius muscle medial head, gastrocnemius muscle lateral head, lateral retinaculum, LCL, quadriceps tendon, and extensor mechanism had minimal soft tissue damage in all MTKA and RATKA specimens.

Conclusion: The results of this study indicate that less soft tissue damage can occur utilizing RATKA when compared to MTKA. The findings are likely due to the enhanced preoperative planning with the robotic software, real-time intraoperative feedback, and the haptically-bound sawblade, all of which can help protect the surrounding soft tissue and ligaments.

The Interleaved Partial Active Shape Model (IPASM) Search Algorithm – Towards 3D Ultrasound-Based Bone Surface Reconstruction

ABSTRACT. Several orthopedic applications require a three-dimensional model of the bone. Ultrasound is a radiation-free and cheap alternative to the state-of-the-art imaging modalities if its limitations in terms of image quality and viewing range can be overcome. This work presents in-vitro as well as in-vivo experiments evaluating the IPASM search, a method for combined segmentation, registration as well as extrapolation. The algorithm is capable to reconstruct the distal surface of a phantom femur with an average surface distance error of roughly 1mm in case of in-vitro as well as below 2mm for in-vivo records, even if the shape varies strongly from the initial model.

A Modular Software System for Three Patterns of Acetabular Deficiency Analysis

ABSTRACT. In order to help orthopedists, evaluate the morphological characteristics of the acetabulum of patients with osteoarthritis, a 3-dimensional (3D) acetabular morphologic parameters measurements software dedicated to the hip was developed. The system includes three modules: 1) Identify the anterior pelvic plane (APP) of the pelvis model; 2) Identify the circular rim of the acetabular wall; 3) Automatically and interactively measure the 3D morphological parameters of the dysplastic acetabulum. The automatic parameter measurement function of this software could fast and accurately measure the 3D morphological parameters of the dysplastic acetabulum. These automatically measured parameters were close to those measured manually with error generally less than 2mm. This software was used to measure acetabular morphological parameters in 61 patients. Two types of dysplastic acetabula were identified by the thickness of the medial wall on the lower margin of the acetabulum Tb: type I was a thin acetabulum (35 cases, Tb≤10.0 mm) and type II was a thick acetabulum (26 cases, Tb >10.0 mm). the result of the acetabular morphological characteristic analysis, it can be found that the thickness of the medial wall is an important morphological characteristic for the THA preoperative surgical planning, and the thickened medial wall could be a misleading factor for the suboptimal placement of the cup.

3D Extended Field-of-View of the Knee Joint Bones Using Ultrasound: Application in Orthopaedics

ABSTRACT. Patient Specific Instruments (PSIs) have been introduced into the surgical workflow as a modern way to assist the surgeon in performing femur and tibia resection in Total Knee Arthroplasty (TKA). These PSIs are based on an accurate reconstruction of the surface of the knee’s bones. In this work, we propose two 3D-3D image-based registration methods to reconstruct an extended field-of-view of the knee joint using only a motorized ultrasound transducer. Those methods are: (1) a dense voxel-based registration method, which needs to preprocess the ultrasound images and form an ultrasound volume. Then, computing the Mutual Information (MI) for each relative displacement to align every pair of volumes, (2) a sparse point-based registration method, which takes into account the point set located on the surface of the bone in ultrasound images. This method detects bony features using ORB detector and matches the corresponding points to find the best transformation using Coherent Point Drift (CPD). The preliminary qualitative results performed in vitro show that starting from a set of consecutive ultrasound volumes, an extended field-of-view can be reconstructed using only ultrasound images without any trackers. Results of the voxel-based approach show that MI is more robust against noise comparing to other similarity metrics. On the other hand, results of point-based approach show that is much faster in computation with a low false-positive rate compared to other feature-detectors like SIFT and SURF. Furthermore, experiments show that CPD is less affected by noisy data compared to the classical ICP, which is promising to continue evaluating our work in vivo.

Navigation Improves the Ten to Fifteen-Year Survival Rate After Mobile Bearing Total Knee Arthroplasty. a French Multicentric Nationwide Study
PRESENTER: Jean-Yves Jenny

ABSTRACT. 1 Introduction The primary hypothesis of this study was that the use of navigation assistance during implantation will improve the 10-year survival rate in comparison to conventionally implanted mobile bearing TKAs.

2 Material and methods All patients operated on between 2001 and 2004 in all participating centers for implantation of a mobile bearing TKA (whatever design used) were eligible for this study. All patients were contacted after the 10-year follow-up for repeat clinical and radiological examination (KSS, Oxford knee questionnaire and knee plain X-rays). Survival curve was plotted according to the actuarial technique, using the occurrence of TKA revision for mechanical reason as end-point. The influence of the implantation technique was assessed with a logrank test at a 0.05 level of significance.

3 Results 1,604 TKAs were implanted during the study time-frame. 289 patients deceased before the 10 year follow up (18%). Final follow-up was obtained for 926 cases (58%). 26 prosthetic revisions were performed for mechanical reasons during the follow-up time (2%). No component was considered loose at the final radiographic evaluation. No polyethylene wear was detected at the final radiographic evaluation. Considering mechanical revision only, the 10-year survival rate of conventional TKAs was 98.6% vs 98.7% for navigated TKAs (NS). However, the 13-year survival rate were 95.2% and 98.3% respectively (p<0.05).

4 Discussion A more consistent anatomical reconstruction and ligamentous balance of the knee should lead to more consistent survival of the TKA.

18:00-22:00 CAOS 2019 Gala Event

Harvard Club of New York City
35 W 44th St, 
New York, NY 10036

  1. 18:30 Cocktails and Appetizers 
  2. 19:30 Reception Dinner and Awards