Equivalent Functional Outcomes in Cruciate-Retaining and Posterior-Stabilized Total Knee Arthroplasty for Knee Osteoarthritis with Severe Fixed Flexion Deformity: A Propensity Matched-Pair Analysis.

Abstract

Cruciate-retaining (CR) total knee arthroplasty (TKA) is generally avoided in knees with severe fixed flexion deformity (FFD). The need for additional distal femoral resection, posterior soft-tissue releases, and gap balancing typically favors posterior-stabilized (PS) implants. This study compared CR- and PS-TKA in severe FFD by evaluating clinical and patient-reported outcomes at two years: (1) range of motion (ROM), (2) Knee Society Score (KSS), (3) Oxford Knee Score (OKS), (4) Short-form 36 (SF-36) Physical (PCS) and (5) Mental (MCS) Component Scores. Patients who had severe preoperative FFD ≥ 15˚ from our institution's TKA registry were propensity-matched according to age, sex, body mass index, and preoperative scores. A total of 294 knees (147 CR-TKAs and 147 PS-TKAs) were matched and analyzed. Patients were evaluated preoperatively, at six months, and at two years. Postoperative manipulation under anesthesia (MUA) was recorded. Both groups achieved significant correction of FFD at two years (CR-TKA: 20.8˚ [95% confidence interval (CI), 19.7 to 21.9] to 4.0° [95% CI, 3.1 to 4.9]; PS-TKA: 19.9˚ [95% CI, 19.0 to 20.8] to 3.8° [95% CI, 3.0 to 4.6]; both P < 0.001) with no intergroup differences (P = 0.534). All patient-reported outcomes improved significantly from baseline (P < 0.001) and were comparable between groups. The PS-TKA achieved greater knee flexion and overall ROM (both P < 0.001), but demonstrated more antero-posterior laxity ≥ five mm (P < 0.05). Stair-climbing functions and MUA rates were comparable (P > 0.05). The CR-TKA achieved outcomes comparable to PS-TKA in knees with severe FFD, with deformity correction maintained at two years. Although PS-TKA provided greater knee ROM, CR-TKA demonstrated lower antero-posterior laxity. These differences did not compromise functional outcomes. Both CR-TKA and PS-TKA remain viable options for patients who have severe FFD when careful intraoperative balancing is attained.