Evaluating tibial rotation in recurrent patellar dislocation with four-dimensional computed tomography.

Objective: This study is to investigate the three-dimensional (3D) kinematic changes in the knee joint in patients with recurrent patellar dislocation using four-dimensional computed tomography (4DCT) imaging and the 3D-3D surface registration technique.

Materials and methods: Ten knees from nine patients with recurrent patellar dislocation and seven knees from seven controls (unaffected side of patients with unilateral anterior cruciate ligament injury) were analyzed using 4DCT. The patients were asked to extend their knees from 60° of flexion to full extension for 10 s in the CT gantry. We used the 3D-3D registration technique, and the 3D angles of the patella and tibia relative to the femur were evaluated.

Results: In the dislocation group, the patellar lateral tilt increased as the knee extended. Significant differences were found between the two groups at 0°-20° of knee flexion. The tibia rotated externally as the knee extended in the dislocation group. Significant differences between the two groups were found at 0°-10° of knee flexion.

Conclusion: This study demonstrated significant differences in the timing and magnitude of tibial external rotation between patients with recurrent patellar dislocation and controls. Specifically, the tibia began to externally rotate during the early phase of knee extension in the dislocation group. These findings provide new insights into knee kinematics that may inform future treatment strategies for patellar dislocation.