Preoperative Medial Proximal Tibial Angle of Less Than 84° Does Not Compromise Two-Year Clinical Outcomes After Unrestricted Kinematic Alignment Total Knee Arthroplasty: A Propensity Score-Matched Study.

Abstract

Unrestricted kinematic alignment (KA) total knee arthroplasty (TKA) may accept tibial component varus beyond conventional thresholds, yet outcomes in marked proximal tibial varus remain understudied in Southeast Asian populations. Our study evaluated two-year outcomes after unrestricted KA-TKA in patients who had severe proximal tibial varus, using mechanically aligned TKA (MA-TKA) as control. This retrospective, propensity score-matched cohort study included 238 unrestricted KA-TKAs and 476 MA-TKAs with minimum two-year follow-up. The KA cohort was stratified by preoperative medial proximal tibial angle (MPTA): ≥ 84° (Group 1, n = 156, mean MPTA 86.6°) versus less than 84° (Group 2, n = 82, mean MPTA 81.6°). The following variables were compared: (1) demographic data, (2) patient-reported outcome measures (PROMs) including Short-Form 36 (SF-36) domains, Oxford Knee Score (OKS), Knee Society Function and Knee Score (KSFS and KSKS), patient satisfaction and expectations, and (3) radiological parameters including MPTA, lateral distal femoral angle, arithmetic hip-knee-ankle angle, and joint line obliquity. Kaplan-Meier analysis assessed revision-free survival. At six months, Group 1 demonstrated significantly better KSKS than Group 2 and MA-TKA (P = 0.033 and P < 0.001, respectively). This persisted for two years, with Group 1 achieving significantly better KSKS (P = 0.032) than MA-TKA, but not against Group 2 (P = 0.555). There were no between-group differences detected for other PROMs, but significantly more patients were satisfied in Groups 1 and 2 compared with MA-TKA at six months and two-year follow-up (P = 0.015 and P = 0.017, respectively). Kaplan-Meier curves showed excellent two-year revision-free survival with two surgical revisions and four knee manipulations. At two-year follow-up, in patients who have severe proximal tibial varus (mean MPTA 81.6°), unrestricted KA-TKA achieved comparable PROMs, excellent patient satisfaction, and survivorship relative to patients who had less severe deformity and the MA-TKA cohort.