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

Abstract

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. 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. 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. 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 III.