Introduction. Soft-tissue balancing methods in TKA have evolved from surgeon feel to digital load-sensing tools. Such techniques allow surgeons to assess the soft-tissue envelope after bone cuts, however, these approaches are ‘after-the-fact’ and require soft-tissue release or bony re-cuts to achieve final balance. Recently, a robotic ligament tensioning device has been deployed which characterizes the soft tissue envelope through a continuous range-of-motion after just the initial tibial cut, allowing for virtual femoral resection planning to achieve a targeted gap profile throughout the range of flexion (figure-1). This study reports the first early clinical results and patient reported outcomes (PROMs) associated with this new technique and compares the outcomes with registry data. Methods. Since November 2017, 314 patients were prospectively enrolled and underwent robotic-assisted TKA using this surgical technique (mean age: 66.2 ±8.1; females: 173; BMI: 31.4±5.3). KOOS/WOMAC, UCLA, and HSS-Patient Satisfaction scores were collected pre- and post-operatively. Three, six, and twelve-month assessments were completed by 202, 141, and 63 patients, respectively, and compared to registry data from the Shared Ortech Aggregated Repository (SOAR). SOAR is a TJA PROM repository run by Ortech, an independent clinical data collection entity, and it includes data from thousands of TKAs from a diverse cross-section of participating hospitals, teaching institutions and clinics across the United States and Canada who collect outcomes data. PROMs were compared using a two-tailed t-test for non-equal variance. Results. When comparing the baseline PROM scores, robotic patients had equivalent womac knee stiffness (p=0.58) and UCLA activity scale (p=0.38) scores but slightly higher womac knee pain (p=0.002) and functional scores (p=0.014, figure-2). 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 six-month scores in the robotic group for all categories (p<0.001). Overall patient satisfaction in the RB cohort was 90.3%, 95.0% and 91.8% at 3M, 6M and 1Y, respectively (figure-3). Average length of hospital stay was 1.6 days (±0.8). Surgical complications in this cohort included one infection four months post-op, 6 post-operative knee manipulations, one pulmonary embolism and one wound dehiscence from a fall. Discussion. We postulated that the ability to use gap data prospectively under known loading conditions throughout the knee range-of-motion would allow femoral cut planning that resulted in optimum balance with fewer releases and better long-term results. While the study group patients had slightly higher baseline knee pain and function than registry patients and showed similar net improvements at the three-month mark, study patients showed significantly better improvements in all areas between three months and six months compared to registry data. WOMAC stiffness and UCLA activity scores were equal between the two groups at baseline and significantly improved at three months and six months. Better ligament balance may have significantly contributed to these gains and to the high rates of satisfaction reported in the study patients compared to the historical literature. Limitations to this study include the small number of patients and the lack of a closely matched control group. For any figures or tables, please contact authors directly

INTRODUCTION. Clinical trials have generally failed to demonstrate superior clinical effectiveness of minimally invasive surgical approaches for total knee arthroplasty (TKA). The hypothesis of the current study was that avoiding incision of the quadriceps tendon would result in a significantly faster recovery of ambulatory function after total knee arthroplasty, compared to a technique that incised the quadriceps tendon. METHODOLOGY. The MIKRO (Minimally Invasive Knee Replacement Outcomes) Study is a prospective, level 1 RCT that enrolled 128 patients with knee osteoarthritis who had failed non-operative treatment, and had decided to proceed with TKA. After skin incision, 64 patients each were randomized to either a subvastus (SV) or medial parapatellar arthrotomy (MPPA) approach. All surgeries were done with the same TKA implant, with anesthesia, post-operative analgesia, and physical therapy standardized for both groups. A Patient Diary methodology was used as the primary outcome measure for ambulatory function. During the first 8 weeks after TKA, a research assistant blinded to treatment assignment telephoned each patient and completed study forms that documented indoor and outdoor walking relative to use of ambulatory devices, as well as Knee Society Score (KSS) and the UCLA activity scale. The UCLA score and change in KSS from baseline at 4- and 12-week follow-up were used to begin the validation process for an Ambulatory Function Score (AFS) derived from diary indoor and outdoor scores. RESULTS. There was a trend for the SV group to report more independent ambulation than the MPPA group at week 1 after surgery, as indicated by self-reported AFS (p < .052). Both treatment groups demonstrated significant week to week AFS gains through 5 weeks, after which weekly changes were minimal. As expected, outdoor AFSs were initially slower to improve than indoor AFSs, but by 6 weeks the initial 20-pt difference was less than 10-pts. AFS scores were significantly correlated with UCLA scores across all 8 weeks. Knee Society Scores (KSS) at baseline were rarely correlated with AFS scores across the 8 weeks. However, 1-month and 3-month KSS scores were significantly correlated with AFS scores at p < .05 beginning with weeks 2 or 3 and through week 8. CONCLUSION. Avoiding incision of the quadriceps tendon during primary TKA resulted in a short-lived trend of quicker improvement in the AFS score in the SV TKA group versus the MPPA group. However, there appeared to be a similar rate of subsequent AFS improvement across the subsequent 8 weeks between the two groups. Preliminary results suggest a pattern of results – general improvement across 5–6 weeks that was maintained through the 8 weeks of evaluation, and significant correlations with UCLA and KSS scores after 2–3 weeks – that are consistent with the notion that the AFS is sensitive to change, and is variable depending on context (indoor vs. outdoor ambulation). Although related to UCLA and KSS scores, observed correlation magnitudes were not so high as to suggest that UCLA or KSS scores might be reasonable proxies for AFS