Unrestricted kinematic alignment total knee arthroplasty provides favourable five‐year outcomes regardless of varus severity in Japanese patients

Abstract Purpose To evaluate 5‐year patient‐reported outcomes and radiographic alignment in Japanese patients undergoing unrestricted kinematic alignment total knee arthroplasty (urKA‐TKA), and to assess whether pre‐operative coronal alignment severity influences mid‐term outcomes. Methods This retrospective cohort study included 184 consecutive knees treated with urKA‐TKA using a medial pivot implant (GMK Sphere) between June 2019 and November 2020. Five‐year patient‐reported outcome measures included the Forgotten Joint Score (FJS) and the 2011 Knee Society Score (KSS). Radiographic parameters, including the hip–knee–ankle angle (HKA), mechanical lateral distal femoral angle and medial proximal tibial angle, were assessed pre‐operatively and at final follow‐up. Knees were stratified into four groups based on pre‐operative HKA (0°–5°, 5°–10°, 10°–15° and ≥15°), and outcomes were compared among groups. Results Of the 184 knees included, 100 completed 5‐year follow‐up, with complete KSS data available for 90 knees and FJS data for 79 knees. The mean age at surgery was 76 ± 8 years. Mean HKA changed from 11 ± 5° pre‐operatively to 3° ± 4° post‐operatively. At 5 years, the mean FJS was 64 ± 25 and the mean total KSS was 127 ± 29. No significant differences were observed among the four alignment groups in total KSS, KSS satisfaction or functional activity scores. FJS values tended to be higher in knees with severe pre‐operative varus (HKA ≥ 15°); however, this difference did not reach statistical significance across the four groups. Conclusions UrKA‐TKA provided excellent 5‐year outcomes, with no revisions observed during the 5‐year follow‐up in Japanese patients with varus osteoarthritis. Pre‐operative coronal alignment severity, including severe varus deformity, did not adversely affect mid‐term clinical outcomes, supporting the safe application of urKA across a wide spectrum of varus alignment. Level of Evidence Level III.