Changes in Femoral Posterior Condylar Offset, Tibial Posterior Slope Angle, and Joint Line Height after Cruciate-Retaining Total Knee Arthroplasty

PURPOSE: Changes in the femoral posterior condylar offset (PCO), tibial posterior slope angle (PSA), and joint line height (JLH) after cruciate-retaining total knee arthroplasty (CR-TKA) were evaluated to determine their influence on the flexion angle. MATERIALS AND METHODS: A total of 125 CR-TKAs performed on 110 patients were retrospectively reviewed. Pre- and postoperative PCO, PSA, and JLH were compared using correlation analysis. Independent factors affecting the postoperative flexion angle of the knee were analyzed. RESULTS: The PCO was 28.2±2.0 mm (range, 24.5 to 33.1 mm) preoperatively and 26.7±1.8 mm (range, 22.2 to 31.2 mm) postoperatively (r=0.807, p<0.001). The PSA was 10.4°±4.9° (range, 1.6° to 21.2°) preoperatively and decreased to 4.9°±2.0° (2.2° to 10.7°) postoperatively (r=–0.023, p=0.800). The JLH was 16.2±3.0 mm (range, 10.2 to 27.5 mm) preoperatively and 16.1±2.6 mm (range, 11.1 to 24.8 mm) postoperatively (r=0.505, p<0.001). None of the independent factors affected the flexion angle (p>0.291). CONCLUSIONS: Although the PCO and JLH did not change significantly after CR-TKA, the PSA decreased by 5.5° with a small range of variation. Restoration of the PCO and JLH could promote optimization of knee flexion in spite of the decreased PSA after CR-TKA.