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We simulated calipered kinematic alignment total knee arthroplasty (cKATKA) using alignment data and ligament tensions acquired during 607 consecutive robotic-assisted TKAs performed using a dynamic ligament tensor. The distal femur was resected parallel to the native joint line accounting for cartilage loss. The proximal tibial resection necessary to achieve extension gap balance was calculated for each knee. Similarly, symmetric posterior condylar resections prescribed by this method were simulated and the tibial resection needed to achieve a balanced flexion gap calculated. Finally, the resultant limb alignment and degree of joint balance in both flexion and extension of each knee were determined and categorized according to the preoperative knee alignment.Increasing preoperative varus deformity required a greater tibial varus cut to achieve a balanced extension gap (P.0001). There was no correlation between tibial varus angle and flexion gap balance (P.1). For mild varus deformities 81% and 95% of knees could be balanced and have an overall limb alignment within 3° and 5° from the mechanical axis respectively. For knees with moderate-severe varus, only 37% and 74% could be balanced within these alignment boundaries (P.01). Overall, 95% of these simulated knees could be balanced with an overall alignment within 0° ± 5°. However, 50% of the simulated TKAs had looser medial gaps in flexion compared to the lateral gap.Application of the cKATKA method can yield TKAs within 0° ± 5° of mechanical axis alignment by simply adjusting the proximal tibial resection without ligament releases. However, an undesirable flexion gap balance was predicted in nearly 50% of the TKAs.

The purpose of this study was to compare ligament balance and laxity profiles achieved throughout flexion in restricted kinematic alignment (rKA) and gap balancing (GB). rKA and GB both aim to improve soft tissue balance and reduce ligament releases in total knee arthroplasty (TKA).One surgeon performed 68 rKA, another performed 73 GB TKAs using the same CR implant and robotic system. rKA limited femoral valgus and tibial varus to 6°, with tibial recuts performed to achieve balance. GB limited tibial varus and femoral valgus to 2°, with femoral resections adjusted to achieve mediolateral balance throughout flexion using predictive-gap planning software. Final joint laxity was measured using a robotic ligament tensioner. Statistical analyses were performed to compare differences in mediolateral balance and joint laxity throughout flexion. Further analyses compared alignment, joint line elevation and orientation (JLO), and frequency of ligament releases and bone recuts.Both techniques reported greater lateral laxity throughout flexion, with GB reporting improved mediolateral balance from 10° to 45° flexion. GB resected 1.7 mm more distal femur (p ≤ 0.001) and had greater overall laxity than rKA throughout flexion (p ≤ 0.01). rKA increased JLO by 2.5° and 3° on the femur and tibia (p ≤ 0.001). Pre-operative and post-operative coronal alignment were similar across both techniques. rKA had a higher tibial recut rate: 26.5% vs 1.4%, p 0.001.rKA and GB both report lateral laxity but with different JLO and elevation. Use of a predictive-gap GB workflow resulted in greater mediolateral gap symmetry with fewer recuts.III, retrospective cohort study.

The optimal force applied during ligament balancing in total knee arthroplasty (TKA) is not well understood. We quantified the effect of increasing distraction force on medial and lateral gaps throughout the range of knee motion, both prior to and after femoral resections in tibial-first gap-balancing TKA. Twenty-five consecutive knees in 21 patients underwent robotic-assisted TKA. The posterior cruciate ligament was resected, and the tibia was cut neutral to the mechanical axis. A digital ligament tensioning tool recorded gaps and applied equal mediolateral loads of 70 N (baseline), 90 N, and 110 N from 90 degrees to full extension. A gap-balancing algorithm planned the femoral implant position to achieve a balanced knee throughout flexion. After femoral resections, gap measurements were repeated under the same conditions. Paired t-tests identified gap differences between load levels, medial/lateral compartments, and flexion angle. Gaps increased from 0 to 20 degrees in flexion, then remain consistent through 90 degrees of flexion. Baseline medial gap was significantly smaller than lateral gap throughout flexion (p

To describe the mediolateral (ML) gap balance in pre-resection arthritic knees undergoing robot-assisted (RA) total knee arthroplasty (TKA) within the nine phenotypes of the Coronal Plane Alignment of the Knee (CPAK) classification.A total of 1124 RA TKA cases were retrospectively reviewed. ML balance was calculated using a digital ligament tensioning device following tibial resection and prior to any femoral resection throughout flexion (10°, 40°, and 90°). Lateral distal femoral angle (LDFA) and medial proximal tibial angle (MPTA) were landmarked intra-operatively and adjusted for wear based on hip-knee-ankle angle (HKA). Knees were then subdivided into CPAK categories based on the arithmetic HKA (aHKA) and joint line obliquity (JLO). Differences in balance between CPAK phenotypes were compared.For aHKA, a greater medial gap was observed in varus compared to neutral or valgus knees at 10° (5.2 ± 3.0 mm vs 3.3 ± 3.2 mm vs - 0.4 ± 5.0 mm respectively; p 0.0001). A similar trend was observed for JLO in distal apex compared to neutral and proximal apex knees at 10° (3.4 ± 3.6 vs 1.1 ± 5.0 vs - 2.4 ± 6.3 respectively; p 0.0001). The greatest ML balance differences were found when combining JLO and aHKA at 10° (type I vs type VI: ∆6.6 mm; p 0.0001).There is a high degree of variability in arthritic ML balance within and between each CPAK phenotype. A single alignment philosophy based on bony landmarks alone may not be sufficient to balance all knees. Utilisation of robotics and digital ligament tensioning devices serves as important adjuncts to characterize the patient-specific soft tissue profile.

The impact of fulfillment of patient expectations throughout recovery on satisfaction in total knee arthroplasty (TKA) is not well understood. Utilizing a standardized TKA method with a robotically assisted (RA) platform, we investigated the impact of expectation fulfillment at 3-month (M) and 6-M on 1-year (Y) and 2-Y satisfaction. We hypothesize that early fulfillment of patient expectations is associated with improved midterm patient satisfaction. We also compare improvements in outcomes with RA-TKA to those of a recent large national TKA cohort study to determine whether RA-TKA meets or exceeds the current standard of care. One hundred six patients were prospectively enrolled and underwent robotic-assisted TKA by a single surgeon using the OMNIBotics system. Patients completed KOOS and New Knee Society Score (KSS) preoperatively and at 3M, 6M, 1Y, and 2Y postoperatively. Expectation fulfillment was subdivided into patients who were below or above the average expectation score pre-operatively, or fulfillment of expectation score at 3M and 6M post TKA. The satisfaction of each group was then compared at 1Y and 2Y post TKA. Study cohort outcomes were compared to contemporary literature from the Function and Outcomes Research for Comparative Effectiveness in Total Joint Replacement (FORCE–TJR) database. Patients with greater than average KSS expectation fulfillment at 3M reported significantly higher KSS satisfaction scores at 1Y (34.9 ± 5.3 vs 30.6 ± 6.7, p = 0.0012), and patients with greater than average 6M expectation fulfillment reported improved satisfaction at 1Y (33.9 ± 5.9 vs 31.1 ± 6.7, p = 0.0330) and 2Y (35.2 ± 4.8 vs 32.4 ± 6.8, p = 0.0323). When compared to the FORCE-TJR database, no significant differences in post-operative KOOS outcomes were observed except for Sports and Recreation, for which the RAS group demonstrated higher scores (65.5 ± 30.0 vs 53.0 ± 27.1 p

New technologies exist which may assist surgeons to better predict final intra-operative joint balance. Our objectives were to compare the impact of (1) a predictive digital joint tensioning tool on intra-operative joint balance; and (2) joint balance and flexion joint laxity on patient-reported outcomes. Two-hundred Eighty patients received posterior cruciate ligament sacrificing TKA with ultra-congruent tibial inserts using a robotic-assisted navigation platform. Patients were divided into those in which a Predictive Plan with a digital joint-tensioning device was used (PP) and those in which it was not (NPP), in all cases final post-operative joint gaps were collected immediately before final implantation. Demographics and KOOS were collected pre-operatively. KOOS, complications and satisfaction were collected at 3, 6 and 12 months post-operatively. Optimal balance difference between PP and NPP was defined and compared using area-under-the-curve analysis (AUC). Outcomes were then compared according to the results from the AUC. AUC analysis yielded a balance threshold of 1.5 mm, in which the PP group achieved a higher rate of balance throughout flexion compared to the NPP group: extension: 83 vs 52%; Midflexion: 82 vs 55%; Flexion 89 vs 68%; Flexion to Extension 80 vs 49%; p ≤ 0.003. Higher KOOS scores were observed in knees balanced within 1.5 mm across all sub-scores at various time points, however, differences did not exceed the minimum clinically important difference (MCID). Patients with > 1.5 mm flexion laxity medially or laterally had an increased likelihood of 2.2 (1.1–4.4) and 2.5 (1.3–4.8), respectively, for failing to achieve the Patient Acceptable Symptom State for KOOS Pain at 12 months. Patient satisfaction was high in both the PP and NPP groups (97.4 and 94.7%, respectively). Use of a predictive joint tensioning tool improved the final balance in TKA. Improved outcomes were found in balanced knees; however, this improvement did not achieve the MCID, suggesting further studies may be required to define optimal balance targets. Limiting medial and lateral flexion laxity resulted in an increased likelihood of achieving the Patient Acceptable Symptom State for KOOS Pain.

Achieving a balanced knee is accepted as an important goal in total knee arthroplasty; however, the definition of ideal balance remains controversial. This study therefore endeavoured to determine: (1) whether medio-lateral gap balance in extension, midflexion, and flexion are associated with improved outcome scores at one-year post-operatively and (2) whether these relationships can be used to identify windows of optimal gap balance throughout flexion. 135 patients were enrolled in a multicenter, multi-surgeon, prospective investigation using a robot-assisted surgical platform and posterior cruciate ligament sacrificing gap balancing technique. Joint gaps were measured under a controlled tension of 70–90 N from 10°–90° flexion. Linear correlations between joint gaps and one-year KOOS outcomes were investigated. KOOS Pain and Activities of Daily Living sub-scores were used to define clinically relevant joint gap target thresholds in extension, midflexion, and flexion. Gap thresholds were then combined to investigate the synergistic effects of satisfying multiple targets. Significant linear correlations were found throughout extension, midflexion, and flexion. Joint gap thresholds of an equally balanced or tighter medial compartment in extension, medial laxity ± 1 mm compared to the final insert thickness in midflexion, and a medio-lateral imbalance of less than 1.5 mm in flexion generated subgroups that reported significantly improved KOOS pain scores at one year (median ∆ = 8.3, 5.6 and 2.8 points, respectively). Combining any two targets resulted in further improved outcomes, with the greatest improvement observed when all three targets were satisfied (median ∆ = 11.2, p = 0.002). Gap thresholds identified in this study provide clinically relevant and achievable targets for optimising soft tissue balance in posterior cruciate ligament sacrificing gap balancing total knee arthroplasty. When all three balance windows were achieved, clinically meaningful pain improvement was observed. Level II.

To understand the extent and frequency of soft-tissue adjustment required to achieve mediolateral (ML) balance in measured resection (MR) vs gap-balancing (GB) total knee arthroplasty, this study compared ML balance and joint laxity throughout flexion between the 2 techniques. The precision of predictive GB in achieving ML balance and laxity was also assessed.Two surgeons performed 95 robot-assisted GB total knee arthroplasties with predictive balancing, limiting tibial varus to 3° and adjusting femoral positioning to optimize balance. A robotic ligament tensioner measured joint laxity. Planned MR (pMR) was simulated by applying neutral tibial and femoral coronal resections and 3° of external femoral rotation. ML balance, laxity, component alignment, and resection depths were compared between planned GB (pGB) and pMR. ML balance and laxity were compared between pGB and final GB (fGB).The proportion of knees with2 mm of ML imbalance in flexion or extension ranged from 3% to 18% for pGB vs 50% to 53% for pMR (MR led to tighter joints than GB, with ML gap imbalances3 mm in 30% of knees. GB planning improved ML balance throughout flexion but increased femoral posterior rotation variability and bone resection compared to MR. fGB laxity was likely not clinically significantly different than pGB.

The objective of this study was to investigate the impact of alignment and soft tissue release on patient outcomes following total knee arthroplasty (TKA).In a multicenter study, soft tissue releases during TKA were prospectively documented in 330 robotic-assisted TKAs. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were captured postoperatively. Delphi analysis was used to determine inlier and outlier component alignment boundaries: Tibia Coronal (TC): ±3°, Femur Coronal (FC): ±3°, Femoral Axial (FA): 3°Int-6°Ext, Hip-Knee-Ankle (HKA): 3°Val-4°Var, and Tibiofemoral Axial (TFA): 3°Int-6°Ext. Kruskal-Wallis analysis of variance tests were used to compare groups.No significant differences were found between any individual or grouped inlier and outlier alignment criterion and KOOS at any timepoint. Outlier alignment frequencies were: TC: 0%, FC: 12%, FA: 8%, HKA: 9%, TFA: 8%, and Any: 23%. Soft tissue releases were performed in 18% of cases. Knees with soft tissue releases reported significantly worse KOOS scores at: 6M: Symptoms (80.0 versus 75.3, P = .03), activities of daily living (ADL) (86.2 versus 80.8, P = .030), quality of life (70.1 versus 60.9, P = .008), 12M ADL (90.0 versus 85.1, P = .023), and 24M ADL (91.9 versus 87.2, P = .016). A higher proportion of patients achieved Minimal Clinically Important Difference for pain at 6 months for those having no releases versus released (92.3% versus 81.0%, P = .021). No significant associations were found between preoperative deformity and preoperative or postoperative KOOS.The addition of soft tissue releases after bony cuts is associated with worse KOOS scores out to 2 years and was more prevalent in knees with worse deformity, while no such association was found for alignment.

Background: Achieving balanced gaps is a key surgical goal in total knee arthroplasty, yet most methods rely on subjective surgeon feel and experience to assess and achieve knee balance intraoperatively. Our objective was to evaluate the ability to quantitatively plan and achieve a balanced knee throughout the range of motion using robotic-assisted instrumentation in a tibia-first, gap-balancing technique. Methods: A robotic-assisted, gap-balancing technique was used in 121 consecutive knees. After resection of the proximal tibia, a computer-controlled tensioning device was inserted into the knee joint and the pre-femoral-resection knee gaps were acquired dynamically throughout flexion under controlled load. Predicted gap profiles were used to plan the femoral implant by adjusting the implant alignment and position within certain boundaries to achieve a balanced knee throughout the range of flexion. Femoral cuts were then made according to this plan using a miniature robotic-assisted cutting guide. The tensioning device used to measure the pre-femoral-resection gaps was then reinserted into the joint to quantify the final gap balance under known tension. The final gap profiles were then compared with the predictive gap plans. Results: The overall root mean square error between the predicted and achieved gaps was 1.3 mm and 1.5 mm for the medial and lateral sides, respectively. Use of robotic assistance resulted in over 90% of knees having mediolateral balance within 2 mm across the flexion range. Gaps at 0° flexion were 2 mm smaller than the gaps at 90°. This difference decreased to less than 1 mm when comparing the tibiofemoral gaps at 10°, 45°, and 90°. Conclusions: Imageless, robotic-assisted total knee arthroplasty accurately predicts postoperative gaps before femoral resections. This allows surgeons to virtually plan femoral implant alignment and optimize gap balance throughout the range of motion. The accurate prediction of gaps throughout the arc of motion combined with precise, robotically assisted femoral resection produces accurate postoperative ligament balance consistently. Keywords: Soft-tissue balance, Total knee arthroplasty, Robotic-assisted, Prediction, Kinematics, Gaps

Aims Neither a surgeon’s intraoperative impression nor the parameters of computer navigation have been shown to be predictive of the outcomes following total knee arthroplasty (TKA). The aim of this study was to determine whether a surgeon, with robotic assistance, can predict the outcome as assessed using the Knee Injury and Osteoarthritis Outcome Score (KOOS) for pain (KPS), one year postoperatively, and establish what factors correlate with poor KOOS scores in a well-aligned and balanced TKA. Methods A total of 134 consecutive patients who underwent TKA using a dynamic ligament tensioning robotic system with a tibia first resection technique and a cruciate sacrificing ultracongruent TKA system were enrolled into a prospective study. Each TKA was graded based on the final mediolateral ligament balance at 10° and 90° of flexion: 1) < 1 mm difference in the thickness of the tibial insert and that which was planned (n = 75); 2) < 1 mm difference (n = 26); 3) between 1 mm to 2 mm difference (n = 26); and 4) > 2 mm difference (n = 7). The mean one-year KPS score for each grade of TKA was compared and the likelihood of achieving an KPS score of > 90 was calculated. Finally, the factors associated with lower KPS despite achieving a high-grade TKA (grade A and B) were analyzed. Results Patients with a grade of A or B TKA had significantly higher mean one-year KPS scores compared with those with C or D grades (p = 0.031). There was no difference in KPS scores in grade A or B TKAs, but 33% of these patients did not have a KPS score of > 90. While there was no correlation with age, sex, preoperative deformity, and preoperative KOOS and Patient-Reported Outcomes Measurement Information System (PROMIS) physical scores, patients with a KPS score of < 90, despite a grade A or B TKA, had lower PROMIS mental health scores compared with those with KPS scores of > 90 (54.1 vs 50.8; p = 0.043). Patients with grade A and B TKAs with KPS > 90 were significantly more likely to respond with “my expectations were too low”, and with “the knee is performing better than expected” compared with patients with these grades of TKA who had a KPS score of < 90 (40% vs 22%; p = 0.004). Conclusion A TKA balanced with robotic assistance to within 1 mm of difference between the medial and lateral sides in both flexion and extension had a higher KPS score one year postoperatively. Despite accurate ligament balance information, a robotic system could not guarantee excellent pain relief. Patient expectations and mental status also significantly affected the perceived success of TKA. Cite this article: Bone Joint J 2021;103-B(6 Supple A):67–73.

The impact of fulfillment of patient expectations throughout recovery on satisfaction in total knee arthroplasty (TKA) is not well understood. Utilizing a standardized TKA method with a robotically assisted (RA) platform, we investigated the impact of expectation fulfillment at 3-month (M) and 6-M on 1-year (Y) and 2-Y satisfaction. We hypothesize that early fulfillment of patient expectations is associated with improved midterm patient satisfaction. We also compare improvements in outcomes with RA-TKA to those of a recent large national TKA cohort study to determine whether RA-TKA meets or exceeds the current standard of care.One hundred six patients were prospectively enrolled and underwent robotic-assisted TKA by a single surgeon using the OMNIBotics system. Patients completed KOOS and New Knee Society Score (KSS) preoperatively and at 3M, 6M, 1Y, and 2Y postoperatively. Expectation fulfillment was subdivided into patients who were below or above the average expectation score pre-operatively, or fulfillment of expectation score at 3M and 6M post TKA. The satisfaction of each group was then compared at 1Y and 2Y post TKA. Study cohort outcomes were compared to contemporary literature from the Function and Outcomes Research for Comparative Effectiveness in Total Joint Replacement (FORCE-TJR) database.Patients with greater than average KSS expectation fulfillment at 3M reported significantly higher KSS satisfaction scores at 1Y (34.9 ± 5.3 vs 30.6 ± 6.7, p = 0.0012), and patients with greater than average 6M expectation fulfillment reported improved satisfaction at 1Y (33.9 ± 5.9 vs 31.1 ± 6.7, p = 0.0330) and 2Y (35.2 ± 4.8 vs 32.4 ± 6.8, p = 0.0323). When compared to the FORCE-TJR database, no significant differences in post-operative KOOS outcomes were observed except for Sports and Recreation, for which the RAS group demonstrated higher scores (65.5 ± 30.0 vs 53.0 ± 27.1 p 0.0001); however, the study cohort reported significantly greater improvements in KOOS Pain, Symptoms, Sports and Recreation, and Quality of Life at multiple time points up to 2 years post TKA.High early-expectation fulfillment was associated with improved satisfaction at 1Y and 2Y, indicating the importance of managing patient-specific post-operative care to ensure patients reach their pre-operative goals. Greater improvements in all KOOS sub-scores and in absolute Sports and Recreation at 1Y and 2Y were observed in this robotic-assisted cohort compared to a large contemporary database, indicating that RAS meets or exceeds current standard of care benchmarks for patient-reported outcomes.

New technologies exist which may assist surgeons to better predict final intra-operative joint balance. Our objectives were to compare the impact of (1) a predictive digital joint tensioning tool on intra-operative joint balance; and (2) joint balance and flexion joint laxity on patient-reported outcomes.Two-hundred Eighty patients received posterior cruciate ligament sacrificing TKA with ultra-congruent tibial inserts using a robotic-assisted navigation platform. Patients were divided into those in which a Predictive Plan with a digital joint-tensioning device was used (PP) and those in which it was not (NPP), in all cases final post-operative joint gaps were collected immediately before final implantation. Demographics and KOOS were collected pre-operatively. KOOS, complications and satisfaction were collected at 3, 6 and 12 months post-operatively. Optimal balance difference between PP and NPP was defined and compared using area-under-the-curve analysis (AUC). Outcomes were then compared according to the results from the AUC.AUC analysis yielded a balance threshold of 1.5 mm, in which the PP group achieved a higher rate of balance throughout flexion compared to the NPP group: extension: 83 vs 52%; Midflexion: 82 vs 55%; Flexion 89 vs 68%; Flexion to Extension 80 vs 49%; p ≤ 0.003. Higher KOOS scores were observed in knees balanced within 1.5 mm across all sub-scores at various time points, however, differences did not exceed the minimum clinically important difference (MCID). Patients with 1.5 mm flexion laxity medially or laterally had an increased likelihood of 2.2 (1.1-4.4) and 2.5 (1.3-4.8), respectively, for failing to achieve the Patient Acceptable Symptom State for KOOS Pain at 12 months. Patient satisfaction was high in both the PP and NPP groups (97.4 and 94.7%, respectively).Use of a predictive joint tensioning tool improved the final balance in TKA. Improved outcomes were found in balanced knees; however, this improvement did not achieve the MCID, suggesting further studies may be required to define optimal balance targets. Limiting medial and lateral flexion laxity resulted in an increased likelihood of achieving the Patient Acceptable Symptom State for KOOS Pain.

Achieving a balanced knee is accepted as an important goal in total knee arthroplasty; however, the definition of ideal balance remains controversial. This study therefore endeavoured to determine: (1) whether medio-lateral gap balance in extension, midflexion, and flexion are associated with improved outcome scores at one-year post-operatively and (2) whether these relationships can be used to identify windows of optimal gap balance throughout flexion.135 patients were enrolled in a multicenter, multi-surgeon, prospective investigation using a robot-assisted surgical platform and posterior cruciate ligament sacrificing gap balancing technique. Joint gaps were measured under a controlled tension of 70-90 N from 10°-90° flexion. Linear correlations between joint gaps and one-year KOOS outcomes were investigated. KOOS Pain and Activities of Daily Living sub-scores were used to define clinically relevant joint gap target thresholds in extension, midflexion, and flexion. Gap thresholds were then combined to investigate the synergistic effects of satisfying multiple targets.Significant linear correlations were found throughout extension, midflexion, and flexion. Joint gap thresholds of an equally balanced or tighter medial compartment in extension, medial laxity ± 1 mm compared to the final insert thickness in midflexion, and a medio-lateral imbalance of less than 1.5 mm in flexion generated subgroups that reported significantly improved KOOS pain scores at one year (median ∆ = 8.3, 5.6 and 2.8 points, respectively). Combining any two targets resulted in further improved outcomes, with the greatest improvement observed when all three targets were satisfied (median ∆ = 11.2, p = 0.002).Gap thresholds identified in this study provide clinically relevant and achievable targets for optimising soft tissue balance in posterior cruciate ligament sacrificing gap balancing total knee arthroplasty. When all three balance windows were achieved, clinically meaningful pain improvement was observed.Level II.

A well-balanced knee is a critical goal for total knee arthroplasty (TKA) across all surgical technique. Some controversy exists however about the method in which various techniques achieve soft tissue balance. Technology for balancing gaps in the tibia first approach has progressed from manual tensioners and laminar spreaders to digital tensioning tools integrated with robot-assisted navigation platforms, however there has been no comparison between femur first measured resection and tibia first techniques with this new technology. Our objective was to prospectively investigate joint balance accuracy and precision between a femur first measured resection and tibia first gap balancing technique utilizing a digital gap balancing tool.A consecutive series cohort undergoing TKA were investigated. The cohort was divided in to 4 groups: 1) Femur First Blinded to gap data, 2) Femur First Non-Blinded to gap data, 3) Tibia first Blinded to gap data, 4) Tibia first Non-Blinded to gap data. Implanted medio-lateral (ML) gap difference was used to calculate joint balance.94 patients were enrolled. No significant difference was found between the average ML gaps, however, the frequency of outlier balance throughout flexion, was significantly reduced in Group 4. Significant differences in the variance of the post-operative gap balance were also found, in which Group 4, reported reduced variance compared to group 3 and 2 throughout flexion and compared to group 1 at 90°.Ideal joint balance may remain a controversial topic, nonetheless a tibia first approach with digital balancing allows surgeons to accurately achieve a desired joint balance target.

This study reports on the one-year clinical results and patient reported outcomes (PROMs) associated with a new ‘predictive balance’ tibia-cut first total knee arthroplasty (TKA) technique that uses a robotic ligament tensioner. PROMs are compared to registry data and historical results in the literature.Five hundred and thirty-three patients were prospectively enrolled and underwent robotic TKA (mean age: 67.7±8.4; females: 320; BMI: 31.2±4.9). Pre-op, three, six and 12-month WOMAC, UCLA activity scale, and HSS-Patient satisfaction assessments were completed by 533, 352, 314, and 256 patients, respectively, and compared to WOMAC registry data from the Shared Ortech Aggregated Repository (SOAR) and to historical satisfaction reports in the literature.Despite having equivalent baseline PROM scores, predictive balance patients had significantly higher WOMAC scores at all post-operative timepoints (pLimitations to this study include the lack of a closely matched control group. Nonetheless, first year results are promising with improved objective measures compared to large registry databases and recently reported patient satisfaction measures.

Achieving a balanced knee is a critical aspect of Total Knee Arthroplasty (TKA). Coronal and axial boundaries for femoral component placement to achieve balance however, are not well defined. Our aim is to investigate the effect of femoral component and long leg coronal and axial alignment on patient outcomes when using a tibia-first gap balancing technique.All surgeries were performed using the OMNIBotics robot-assisted TKA platform and BalanceBot device. A total of 197 patients were prospectively enrolled into this study and received TKA surgery using the OMNIBotics platform and completed 1-year KOOS outcome scores. Femoral component and tibiofemoral alignment were categorized as inliers or outliers in the coronal and axial planes. Knee Injury and Osteoarthritis Outcome Score (KOOS), and University of California at Los Angeles Activity Scale (UCLA) was collected at 1-year post-op.No significant differences were found between the KOOS subscores or UCLA outcome and femoral coronal or tibiofemoral coronal and axial alignment. Significant differences were found between the KOOS pain and sports sub-scores and femoral axial alignment (∆ = 5.4, p = 0.007, ∆ = 8.3, p = 0.03 respectively), in which outlier femoral rotation reported higher scores.Component alignment limits for improved survival and patient outcomes are a source of ongoing debate. The data presented here indicates that when utilizing a tibia-first gap balancing technique, small deviations outside of traditional ±3°alignment boundaries did not negatively affect KOOS or UCLA outcomes, indicating balance may have a stronger link to patient outcome than alignment.

A poorly balanced, unstable or stiff joint is a leading cause of dissatisfaction and revision after surgery. The quantitative definition of a well-balanced joint, however, remains a source of controversy. This study investigates joint gaps measured by a digitally-controlled ligament tensioning device throughout flexion and its effect on post- operative outcome.Surgeries were performed using the OMNIBotics robot-assisted TKA platform and BalanceBot device. Joint gaps were recorded by the BalanceBot throughout flexion during trialing. Knee Injury and Osteoarthritis Outcome Score (KOOS) was collected at 1-year post-op. Correlations between joint gaps and KOOS outcome were investigated.Knees that reported: a medial gap ≤ lateral gap in extension (p = 0.007, median ∆ = 8.3); an average joint gap of between 1 mm tighter and 1 mm looser than the final insert thickness in midflexion (p = 0.006, median ∆ = 5.5); and an imbalance of less than 1.5 mm in flexion (p = 0.012, median ∆ = 2.8) reported significantly improved pain scores. Patients which satisfied both extension and flexion criteria, or midflexion and flexion criteria reported improved outcomes compared to those which satisfied only one or neither criterion (p = 0.0002, median ∆ = 9.7, p = 0.0019, median ∆ = 8.4 respectively).KOOS Pain scores correlated with joint gap measurements across all flexion angles investigated. Combining joint gap windows, subgroups of patients were found that reported a change in the median KOOS Pain outcome beyond the minimally clinically important difference.

The goal of total knee arthroplasty (TKA) is to position the prosthesis with a bal- anced soft tissue envelope throughout the flexion cycle. Determining a desirable amount of ligament tension is crucial as instability is a leading cause for revision surgery. This is challenging due to the subject specific, and non-linear, nature of ligament mechanical properties. This study aims to characterize ligament stiffness profiles intraoperatively and identify the stiffness transition point (STP) using a ligament balancing robot. The study will also identify how the surgeon selected joint force relates to the stiffness transition point.45 patients were reviewed. After the proximal tibial resection, intraoperative assessment of the medial and lateral ligaments was performed via a load cycle ramped up from 50N to 120N, then down from 120N to 50N. This was performed at extension (10◦) and in flexion (90◦). Force and displacement data were processed to determine the stiffness profiles for the medial and lateral soft tissue envelope. A bilinear fit model was used to determine the slopes and STP.The average STP was between 83N and 90N, varying widely with standard deviations approaching 14N. The median joint tension selected by the surgeon was 80N. On average the selected joint force was 3N to 8.9N below the STP.The medial compartment behaved similarly in extension and flexion. The lateral com- partment had higher stiffness in extension than in flexion. Across all loading conditions, the down-cycle data was more consistent than the up-cycle data.The STP is a proposed target for ligament tension as this theoretically avoids the high stiffness regime. The results show the joint tension selected by the surgeons, based on their experience and intraoperative feel, is similar to the STP. Due to the high patient variability observed in the STP, using a patient specific method to determine the joint tension is recommended. Future work will investigate how joint tension relative to the STP affects patient outcomes. This will provide insight into optimizing joint tension during TKA.

Soft tissue releases are often required to correct deformity and achieve balance in total knee arthroplasty (TKA). However, releasing soft tissues can be subjective, highly variable and is perceived as an ‘art’ in TKA. The objective of this study was to compare the rate of soft tissue release required to achieve a balanced knee in tibial-first gap- balancing versus conventional, measured resection TKA, and its effect on outcomes.Soft tissue releases were documented and reviewed in 1256 robotic-assisted gap- balancing and 85 robotic-assisted measured-resection TKAs. Knees were stratified by coronal deformity (varus: >2° varus; valgus: >2° valgus). Rates of releases were compared between the two groups and literature. A subset of these patients were also enrolled in a prospective study. KOOS outcomes were captured pre-operatively and at 6M post TKA.The frequency of soft tissue release was significantly lower in the robotic gap- balancing group, with 21% of knees requiring release versus 40% (p=0.001) in the robotic measured resection group and 67% (pRobotic assisted TKA with predictive gap balancing was found to reduce the number of releases across all coronal angles compared to conventional instruments. Furthermore, performing a soft tissue release rather than bone resection to achieve balance, correlated with worse outcomes. Further research is required to understand when imbalance should be corrected with bone resection adjustment versus soft tissue release.

The traditional goal of the gap-balancing method in total knee arthroplasty is to create equal and symmetric knee laxity throughout the arc of flexion. The purpose of this study was to (1) quantify the laxity in the native and the replaced knee throughout the range of flexion in gap-balancing total knee arthroplasty (TKA) and (2) quantify the precision in achieving a targeted gap profile throughout flexion using a robotic-assisted technique with active ligament tensioning.Robotic-assisted, gap-balancing TKA was performed in 14 cadaver specimens. The proximal tibia was resected, and the native tibiofemoral gaps were measured using a robotic tensioner that dynamically tensioned the soft-tissue envelope throughout the arc of flexion. The femoral implant was then aligned to balance the gaps at 0° and 90° of flexion. The postoperative gaps were then measured during final trialing with the robotic tensioner and compared with the planned gaps.The native gaps increased by 3.4 ± 1.7 mm medially and 3.7 ± 2.1 mm laterally from full extension to 20° of flexion (P.001) and then remained consistent through the remaining arc of flexion. Gap balancing after TKA produced equal gaps at 0° and 90° of flexion, but the gap laxity in midflexion was 2-4 mm greater than at 0° and 90° (P.001). The root mean square error between the planned gaps and actual measured postoperative gaps was 1.6 mm medially and 1.7 mm laterally throughout the range of motion.Aiming for equal gaps at 0° and 90° of flexion produced equal gaps in extension and flexion with larger gaps in midflexion. Consistent soft-tissue balance to a planned gap profile could be achieved by using controlled ligament tensioning in robotic-assisted TKA.

Total knee arthroplasty is an ideal surgical application for robotic assistance because accurate soft-tissue balance and implant positioning are critical for achieving superior clinical outcomes. OMNI has developed and commercialized the world’s first robotic-assisted system that integrates robotic ligament tensioning with bone resection planning to predict and achieve a well-balanced and well-aligned knee replacement. A novel robotic ligament tensioning tool, called the BalanceBot, is inserted into the knee to quantify the soft-tissue envelope throughout the range of knee motion. Predictive Balancing then allows the surgeon to predict postoperative ligament balance based on a virtual 3D implant plan before making bone cuts. The bone anatomy is reconstructed intraoperatively based on image-free 3D BoneMorphing technology, which eliminates the need for preoperative 3D imaging modalities and their associated cost, time, and radiation exposure burdens. A miniature semiactive bone-mounted robotic cutting guide called the OMNIBot is used to guide the resections according to the surgeon’s plan. The BalanceBot is then used to assess the final soft-tissue tension and balance achieved, closing the loop on the surgeon’s plan and minimizing the amount of ligament releases required to achieve a balanced knee. In this chapter we describe the evolution of the development of the system, with a specific focus on the initial development, validation, and clinical application of the BalanceBot. Early clinical results demonstrate a high level of patient satisfaction and warrant further clinical use and studies to evaluate the impact on longer term patient outcomes.

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 final intra-operative coronal balance throughout the knee range of motion in navigated robotic-assisted TKA when performed with quantifiable feedback from a robotic ligament tensioning tool versus with standard trials and navigation measurements alone.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: a non-sensor-assisted group (n=25) and a subsequent sensor-assisted group (n=27). Once bony cuts and soft tissue balancing was performed in the non-sensor cohort, the final tibiofemoral gaps were measured throughout the knee range of motion 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 data 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 ± 0.7 mm with maximum difference of 7.8 mm for the non-sensor cohort. The sensor cohort had an average mediolateral difference of 1.5 ± 0.6 mm and a maximum difference of 3.8 mm. The difference between the two groups was statistically significant from 60 to 90 degrees of flexion. 38-41% of knees were balanced to within 1 mm mediolaterally in the non-sensor group compared to 48-70% for the sensor group when measured at various flexion angles. 65-76% of knees were balanced to within 2 mm for the non-sensor group compared to 78-86% for the sensor-assisted group. The number of knees requiring subsequent soft tissue releases was similar in each group. 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.

Total knee arthroplasty is a successful procedure. However, there is still area for improvement as up to 15-20% of patients remain unsatisfied. Robotic-assisted surgery (RAS) may improve patient outcomes by providing a reproducible way of obtaining neutral mechanical alignment of the limb, which has been shown to reduce early revisions and correlate with patient reported outcomes after surgery.We prospectively enrolled 106 patients undergoing robotic-assisted TKA by a single surgeon performing a measured-resection femur-first technique using the OMNIBotic system. Patients completed a KOOS and New Knee Society Score (KSS) pre-operatively and at 3, 6, 12, and 24 months (M) postoperatively. Changes in the five KOOS sub-scales were compared to available literature data from the FORCE – TJR cohort, as well as to individual studies reporting on conventional and computer-assisted TKA.When compared to FORCE-TJR 6-month (M) and 2-year (Y) data, the RAS cohort had significantly higher improvements at 6M for pain (40.5 vs. 31.1, pDespite having poorer joint function and higher pain pre-operatively, robotic-assisted TKA patients achieved excellent self-reported outcomes, with significantly higher levels of improvement through two years post-surgery when compared with large national cohort studies. Further controlled clinical studies are warranted to determine if these results translate to other groups of surgeons, centers and patients.

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 reportedRecipients 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.

To gain widespread acceptance, robotic-assisted surgery must add value to total joint arthroplasty by demonstrating improved outcomes and reduced overall costs associated with the episode of care. We review the surgical technique as well as clinical and economic results associated with the introduction of a commercially available robotic-assisted total knee arthroplasty system (OMNIBotics®) in both an academic teaching and a community hospital setting. Clinical results demonstrate highly accurate and reproducible component placement and overall leg alignment, high patient satisfaction and knee functional outcomes as measured by the new Knee Society and KOOS scores, as well as a shortened length of stay and reduced 90-day readmission rates and overall episode of care costs when compared with manual intramedullary-based instrumentation.

The aim of this study was to quantify the effects of distal femoral cut height on maximal knee extension and coronal plane knee laxity.Seven fresh-frozen cadaver legs from hip-to-toe underwent a posterior stabilized TKA using a measured resection technique with a computer navigation system equipped with a robotic cutting guide. After the initial femoral resections were performed, the posterior joint capsule was sutured until a 10° flexion contracture was obtained with the trial components in place. Two distal femoral recuts of +2mm each were then subsequently made and the trials were reinserted. The navigation system was used to measure the maximum extension angle achieved and overall coronal plane laxity [in degrees] at maximum extension, 30°, 60° and 90° of flexion, when applying a standardized varus/valgus load of 9.8 [Nm] across the knee.For a 10 degree flexion contracture, performing the first distal recut of +2mm increased overall coronal plane laxity by approximately 4.0° at 30° of flexion (p=0.002) and 1.9° at 60° of flexion (p=0.126). Performing the second +2mm recut of the distal femur increased mid-flexion laxity by 6.4° (p0.0001) at 30° and 4.0° at 60° of flexion (p=0.01), compared to the 9 mm baseline resection (control). Maximum knee extension increased from 10° of flexion to 6.4° (± 2.5° SD, p0.005) and to 1.4° (± 1.8° SD, p0.001) of flexion with each 2mm recut of the distal femur.Recutting the distal femur not only increases the maximum knee extension achieved but also increases coronal plane laxity in midflexion.

article i nfo Introduction: The quantitative effects of medial bone loss of the knee on both leg alignment and coronal plane stability are poorly understood. Materials and methods: Utilizing computer navigation, 5 mm bone defects of the medial distal femur (MDF), medial posterior femoral condyle (MPF), and medial tibial plateau (MT) were simulated in 10 cadaveric limbs, and alignment of the knee at various degrees of flexion were analyzed when applying standardized varus and valgus loads. Results: The 5 mm MPF defect significantly increased varus laxity at 90° of flexion by 3.3°±1.2° (p=0.019), a 5 mm MDF defect resulted in a 2.2°±1.7° (p=0.037) and a 2.1°±1.3° (p=0.023) increase in laxity at 0° and 30° of flexion, respectively, and a 5 mm MT defect increased varus laxity at all flexion angles by 4.0° to 7.0°, but was only statistically significant at 30° (p=0.026). Discussion: This study confirms and quantifies the theories of flexion and extension gap balancing, and pseu- dolaxity of the medial collateral ligament in the varus knee, the results of which can be used in preoperative planning and intraoperative decision making for both total knee and unicondylar arthroplasty.

To quantify the average deviation in tibial mechanical axis registration when registering the ankle centre using (a) the extreme medial and lateral points and (b) the most distal points, of the respective malleoli, and to identify whether body mass index (BMI) had any significant effect on mechanical axis registration error.The preoperative standing hip-knee-ankle radiographs of 40 patients who underwent navigated TKR at our institution were reviewed. The divergence from the anatomic ankle centre in degrees and millimetres was compared when using the Extremes Midpoint and the Distal Midpoint techniques.No significant divergence was measured with either the Extremes Midpoint (0.2° lateral, SD = 0.5°; 1.1 mm lateral, SD = 2.6 mm) or the Distal Midpoint (0.2° lateral, SD = 0.6°; 1.7 mm lateral, SD = 2.3 mm) techniques. BMI had no significant effect on these differences.Both the Extremes Midpoint and the Distal Midpoint techniques offer accurate registration of the ankle centre. BMI does not seem to affect the registration of the ankle centre with either technique. The findings of this study will help knee surgeons when choosing an ankle registration technique. These results may also lead to more accurate knee replacement navigation systems.

The accuracy and efficiency of automated cutting guides in CAS systems have not been previously compared with conventional CAS techniques. Therefore, it is not yet clear if these more advanced technologies are warranted. We hypothesized that a novel automated cutting guide with CAS for total knee arthroplasty would be more efficient and more accurate than conventional navigation with sequential cutting blocks. Twelve cadaver legs were used in total. Each leg was randomly assigned to either an automated guide positioning or a conventional freehand computer-navigated guide positioning. The guide positions postosseous fixation and the final bone-cut surfaces were digitized and compared to the targeted cutting planes. The final location of the impacted trial implant was also digitized and compared to the planned implant location. The time for each step and the total time taken to prepare the femur were measured for both groups. The mean femoral preparation time was shorter with the automated cutting guide than the conventional method (5.5 min versus 13.8 min, p0.001). The average deviation in the final bone resections from the planned resections was significantly lower for the automated cutting guide in the frontal/rotational plane (0.55° versus 1.1°), sagittal plane (0.75° versus 2.0°), and cut height direction (0.56 mm versus 1.6 mm). Therefore, based on these results, we concluded that automated cutting-guide positioning resulted in more efficient and more accurate femoral cuts in comparison to the conventional navigation method in a cadaveric model.

Computer-navigation in total knee arthroplasty has been reported to increase accuracy but also procedure duration. We compared surgical time and precision using a novel adjustable cutting block vs freehand navigation with conventional blocks on 12 bilateral cadaver tibiae. The mean time required was significantly less to position the adjustable block than the conventional block (2 minutes 10 seconds vs 6 minutes 35 seconds, P = .006). Guide positioning precision (standard deviation) for the adjustable block vs conventional block was as follows: varus/valgus, 0.24 degrees vs 1.16 degrees (P = .015); posterior slope, 0.35 degrees vs 0.74 degrees (P = .13); and cut height, 0.37 vs 1.41 mm (P = .010). There were no significant differences in the final bone cut accuracy between the 2 groups. The use of adjustable cutting blocks simplifies navigated procedures and may reduce the time required to perform a navigated total knee arthroplasty.