Medium term results of the cementless Oxford mobile bearing medial unicompartmental knee replacement.

BACKGROUND: Medial Unicompartmental Knee Replacement (UKR) has well-documented benefits over Total Knee Replacement in the treatment of anteromedial osteoarthritis of the knee. There has been an increasing move from cemented to cementless UKR over the last decade. This non-design centre study assesses the initial experience using the cementless Oxford medial partial knee replacement and provides medium term revision data, as well as Patient Reported Outcome Measures (PROMs). METHODS: A cohort of 200 consecutive patients undergoing medial UKR using the cementless Oxford were identified from our knee groups prospectively collected database. Cases were performed in a single centre under the care of one of four surgeons. All patients were beyond the 5-year minimum timepoint following UKR surgery in order to produce medium term results, at a mean of 7.9 years. Eligible patients completed a postal questionnaire to collect PROMs: Oxford Knee Score, WOMAC and modified American Knee Society Score questionnaires in January 2020 and had their clinical records reviewed. RESULTS: The survivorship in our cohort was 94.5% at a mean follow up of 7.9 years following surgery. There were 11 re-operations in total with a three percent risk of re-operation within the first 18 months following surgery. There was a sustained improvement in Oxford Knee Score with a near 20 points improvement on pre-operative scores. CONCLUSIONS: Our results provide further evidence that partial knee replacements using the cementless Oxford produce good clinical outcomes. Revision rates are similar to those published in the National Joint Registry. LEVEL OF EVIDENCE: III.

Virtual assessment of coronal balance prior to bone resection with the MAKO robotic-assisted system accurately predicts final balance in TKA.

Total knee arthroplasty (TKA) has traditionally relied on the surgeon's judgement and manual instruments to determine balance. The MAKO robotic system (Stryker Ltd, Kalamazoo, MI, USA) allows assessment of virtual compartmental gaps from CT-derived bone models intra-operatively as a predictor of soft tissue balance that will be achieved, prior to any bony resection. This study aims to assess the accuracy of this pre-resection balancing technique in determining the resultant final soft tissue balance of the TKA. A consecutive prospective cohort of 2027 Robotic-Assisted TKAs (RATKA) were performed between January'17 and March'22. Osteophytes were removed; initial virtual gaps on the virtual bone model were measured at 10° and 90° of flexion prior to bone resections. Optimization of the virtual component positions was then made and final pre-resection gaps were measured. The gaps were then re-assessed post-implantation and compared to the final pre-resection values. Virtual balancing in extension within 1 mm was achieved in 95% of cases. Of those, 98% maintained coronal balance within 1 mm after implantation, with 1.5% requiring a coronal plane soft tissue release. Inability to virtually balance a TKA within 2 mm prior to bone resection resulted in a soft tissue release in 44.4% of cases. The absolute values of the final gaps achieved were a mean of 1.3 mm greater than virtual gaps. The ability to balance a knee on the virtual bone model prior to bone resection, in conjunction with robotic-assisted execution of TKA, consistently achieves a balanced knee after component implantation.