Predictors of post‐operative decline in knee flexion after cruciate‐retaining total knee arthroplasty

This study aimed to identify risk factors associated with deterioration in knee flexion range of motion (ROM) following cruciate-retaining total knee arthroplasty (CR-TKA). A total of 129 consecutive patients who underwent CR-TKA and completed a 2-year follow-up were included. A decrease of ≥9° in flexion ROM was considered clinically significant. Patients were classified into two groups based on the change in flexion ROM at 2 years post-operatively: Group D (≥9° decrease; n = 44) and Group C (<9° decrease; n = 85). Demographic data were compared using Student's t test or Fisher's exact test. Logistic regression analysis was performed to identify factors associated with ROM deterioration. Receiver operating characteristic (ROC) curve analysis was conducted to determine cut-off values for the identified factors. Demographic characteristics were comparable between the two groups. Preoperative flexion ROM was significantly higher in Group D than in Group C (128.6 ± 9.5° vs. 115.5 ± 12.3°, p < 0.001). Logistic regression analysis revealed that greater preoperative flexion ROM (odds ratio [OR], 1.18; 95% confidence interval [CI], 1.10-1.27; p < 0.001), a larger distal medial femoral resection (DMFR) (OR, 1.98; 95% CI, 1.14-3.43; p = 0.015) and lower anterior-posterior translation at 30° of flexion 1 year post-operatively (1y30AP) (OR, 0.73; 95% CI, 0.57-0.93; p = 0.012) were independently associated with a ≥9° reduction in flexion ROM. ROC analysis identified cut-off values of >130.0° for preoperative flexion ROM (AUC: 0.80, 95% CI: 0.72-0.88), >7.5 mm for DMFR (AUC: 0.60, 95% CI: 0.50-0.71) and <5.1 mm for 1y30AP (AUC: 0.62, 95% CI: 0.51-0.72). Preoperative flexion ROM, DMFR and 1y30AP were associated with worse flexion ROM at 2 years following CR-TKA. Level III, retrospective comparative study.