Factors Affecting Successful Restricted Kinematic Alignment With Robotic Assisted Total Knee Arthroplasty in Patients With Severe Varus Preoperative Alignment

Abstract

Background: Total knee arthroplasty (TKA) remains challenging in severe varus knees. We evaluated the impact of hip-knee-ankle varus deformity and osteophyte size on achieving restricted kinematic alignment (rKA) in robotic-arm-assisted TKA. Methods: This retrospective study included 244 knees (194 patients) that underwent robotic-arm-assisted TKA for varus primary knee osteoarthritis at an academic institution. Intraoperative hip-knee-ankle angle (HKA) and soft tissue balance were monitored to assess the success of rKA with osteophyte resection alone. For those that failed, medial collateral ligament needle pie-crusting was performed. Results: Mean age was 65.3 years (range, 48-83). Mean preoperative HKA was 11.9° varus (range, 1.0°-32.0°), and HKA after osteophyte resection was 5.1° varus (range, 0°-19.0°). Mean HKA correction was 6.8° (range, 0°-18.0°). rKA was achieved in 36.9% at a boundary of ≤3° varus and up to 72.1% at ≤6° varus. Preoperative varus HKA was lower in successful cases across all target alignments (P < .05). Medial tibial osteophyte size was 6.1% ± 2.9% and was smaller in all groups that achieved rKA (P < .05). Both were positively correlated with degree of deformity correction, r = 0.718 (P < .01) and r = 0.281 (P < .01), respectively. Conclusions: This study highlighted the importance of varus deformity and medial tibial osteophytes when adopting rKA. They were associated with increased failure to achieve rKA. rKA was reliably achieved in minimal varus deformities (HKA ≤ 5°), we recommend an expanded protocol of HKA ≤ 6° varus for mild deformities (HKA 6°-10°), and consider medial soft tissue release for moderate (HKA 11°-15°) and severe deformities (HKA ≥ 16°).