Dependence of Knee Range of Motion on the Alignment of Femoral and Tibial Components after Medial Unicompartmental Knee Arthroplasty

This study evaluated the relationship between postoperative knee flexion angles and the position of femoral and tibial components in unicompartmental knee arthroplasty (UKA). Eighteen patients (a total of 22 knees: three men, four knees; 15 females, 18 knees) who underwent navigation-assisted UKA were included. Pre- and postoperative computed tomography images were applied on 3D software, which were matched and used to calculate the position of femoral and tibial components. Correspondingly, we investigated the relationship between the knee range of motion (ROM) at 1-year postoperative follow-up and the position of femoral and tibial components. At 1-year post-UKA, the knee flexion angle was associated with the posterior flexion angle of tibial components. This particular angle was significantly greater in the group with equal or greater postoperative knee ROM compared to preoperative ROM (5.2 ± 2.1°) than in the group with less postoperative knee ROM compared to preoperative ROM (2.6 ± 1.6°, p < 0.01). There was no significant difference between both groups in the femoral component position, preoperative posterior slope of the medial tibial plateau, change in the pre- to postoperative posterior tibial slope, and postoperative knee society score. The posterior flexion angle of the tibial component affected the improvement/deterioration of the postsurgery knee flexion angle in navigation-assisted UKA. For improved outcomes after UKA using navigation systems, surgeons should aim to achieve a 5° to 8° posterior flexion angle of the tibial component.