The varus/valgus angle of the femoral component relative to the tibial component can lead to a deviation of the bearing position in mobile bearing unicompartmental knee arthroplasty which can increase the risk of bearing dislocation

Purpose: This study aimedto evaluate the relationship between the bearing position and relative angle of the femoral and tibial components using postoperative radiological measurements. Methods : This study included 120 patients who underwent MB-UKA at our hospital between January and August 2023. Standard anteroposterior-view radiographs were obtained postoperatively using C-arm fluoroscopy. We developed a 3D-2D image matching method to measure the femoral component varus/valgus angle and internal/external rotation (IR/ER) relative to the tibial component. The bearing position parameters were measured. Patients were divided into varus/valgus groups and IR/ER groups according to the femoral component varus/valgus angle and IR/ER angle. The bearing position parameters of each group were compared separately. Results: There were 57 patients in the varus group, 63 in the valgus group, 59 in the IR group, and 61 in the ER group. The W-BED (the distance between the bearing lateral edge and the lateral wall) was significantly lower in varus group than in the valgus group (1.9 (0 to 6.4) vs 2.8 (0.3 to 7.7) mm; P <0.001). No differences were observed in any bearing position parameters. The varus/valgus angle of the femoral component showed a significant negative correlation with the W-BED. The IR/ER angle of the femoral component showed no significant correlation with any of the positional parameters. Conclusion: The varus/valgus angle of the femoral component relative to the tibial component can lead to a deviation of the bearing position. The IR/ER of the femoral component had no effect on the final bearing position.