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.

Purpose Achieving a balanced knee is accepted as an important goal in total knee arthroplasty; however, the deinition of ideal balance remains controversial. This study therefore endeavoured to determine: (1) whether medio-lateral gap balance in extension, midlexion, and lexion 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 lexion. Methods 135 patients were enrolled in a multicenter, multi-surgeon, prospective investigation using a robot-assisted surgical platform and posterior cruciate ligament sacriicing gap balancing technique. Joint gaps were measured under a controlled tension of 70-90 N from 10°-90° lexion. Linear correlations between joint gaps and one-year KOOS outcomes were investigated. KOOS Pain and Activities of Daily Living sub-scores were used to deine clinically relevant joint gap target thresholds in extension, midlexion, and lexion. Gap thresholds were then combined to investigate the synergistic efects of satisfying multiple targets. Results Signiicant linear correlations were found throughout extension, midlexion, and lexion. Joint gap thresholds of an equally balanced or tighter medial compartment in extension, medial laxity ± 1 mm compared to the inal insert thickness in midlexion, and a medio-lateral imbalance of less than 1.5 mm in lexion generated subgroups that reported signiicantly 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 satisied (median ∆ = 11.2, p = 0.002). Conclusion Gap thresholds identiied in this study provide clinically relevant and achievable targets for optimising soft tissue balance in posterior cruciate ligament sacriicing gap balancing total knee arthroplasty. When all three balance windows were achieved, clinically meaningful pain improvement was observed. Level of Evidence Level II.

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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.

Joint balance in total knee arthroplasty (TKA) has traditionally focused on achieving a tight symmetric extension gap and rectangular or trapezoidal gaps in flexion. This study sought to investigate the effect of femoral and tibial coronal rotation and femoral axial rotation on midflexion coronal joint balance and patient outcomes.A prospective multi-center study was performed with a mixture of tibia-first gap-balancing and femur-first approaches were performed using the Corin OMNIBotics robot-assisted TKA platform with APEX implant components. Coronal and axial femoral and tibial resections were recorded by the platform. Medial and lateral joint gaps were recorded while applying a computer-controlled load to the joint throughout flexion during trialing using the Corin BalanceBot device. In addition, 1-year Knee Injury and Osteoarthritis Outcome Score (KOOS) and PROMIS-10 global health scores were collected.231 surgeries were identified: 66.9±8.1 years, 31.4±4.8 kg/m2 and 57% female (121) with a mean pre-operative HKA angle of 4.5±5.2° varus. A significant correlation was found between the medio-lateral (ML) joint gap difference in midflexion and both extension and flexion joint line (p=0.003, r2=-0.20, p=0.001, r2=-0.22, respectively). A significant correlation was found between midflexion ML imbalance and KOOS stiffness questions at 3 M and 6 M post-op (r2=-0.15, p=0.036, r2=-0.18, p=0.013), in which a more balanced knee correlated with improved outcomes.Treating flexion and extension joint balance in isolation may not capture the effect on midflexion laxity. Component placement should take in to account the effect on joint gaps throughout flexion to target optimal joint balance.

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.

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 (p&lt;0.001) and higher UCLA activity scale scores at 3M and 6M (p&lt;0.013). Overall patient satisfaction in the predictive balance cohort was 91.2%, 92.4%, and 96.5% at 3M, 6M and 1YR, respectively. Average length of stay was 1.6 days (±0.8). Surgical complications in this cohort were typical of TKA.Limitations 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.