Postoperative Medial Tilting of the Joint Line and Preoperative Kinematics Influence Postoperative Medial Pivot Pattern Reproduction in Total Knee Arthroplasty

BACKGROUND: Reproducing the medial pivot pattern after total knee arthroplasty (TKA) is known to improve patient satisfaction. However, the factors affecting the postoperative medial pivot pattern in TKA are controversial. The purpose of this study was to examine the factors affecting the postoperative medial pivot pattern in posterior-stabilized TKA. METHODS: This study involved 30 cases with knee osteoarthritis who underwent primary posterior-stabilized TKA. The preoperative and postoperative kinematics were measured using a computed tomography–free navigation system, and the patients were divided into the following 2 groups: the medial pivot pattern (MP) group and non–medial pivot pattern (non-MP) group. In addition, we measured each of the following angles on X-ray films (preoperative and postoperative femorotibial angle, hip-knee-ankle angle, mechanical lateral distal femoral angle, medial proximal tibial angle). We examine the factors affecting the postoperative medial pivot pattern. RESULTS: There were 14 cases in the MP group and 16 cases in the non-MP group at the preoperative knee kinematic assessment and 17 cases in the MP group and 13 cases in the non-MP group at the postoperative knee kinematic assessment. The preoperative kinematic pattern was conserved after the surgery at a rate of 76.7%. The postoperative MP-group showed a significantly smaller preoperative femorotibial angle and hip-knee-ankle and a significantly smaller postoperative mechanical lateral distal femoral angle and medial proximal tibial angle in comparison to the postoperative non-MP group. CONCLUSIONS: Preoperative kinematics and postoperative mechanical lateral distal femoral angle and medial proximal tibial angle may be important factors that affect the postoperative medial pivot pattern.