Clinical outcomes after medial patellofemoral ligament reconstruction: an analysis of changes in the patellofemoral joint alignment

Purpose Medial patellofemoral ligament (MPFL) reconstruction using the hamstring tendon is widely performed to treat recurrent patellar dislocation. MPFL reconstruction includes a post-operative process of necrosis and reperfusion of the hamstring tendon graft. We hypothesise that the patella gradually shifts laterally because of this process, ultimately affecting the patellofemoral joint alignment. This study aimed to analyse the chronological changes in the patellofemoral joint alignment and the outcomes of MPFL reconstruction. Methods In this retrospective case-series study, the Knee Society, Lysholm, and Kujala scores were evaluated in 24 consecutive patients (27 knees). To evaluate patellar tracking defects, radiographic indices including the tilting angle, the lateral shift ratio, and the congruence angle were measured before, immediately after, and three, 12, and 36 months after MPFL reconstruction. Results Post-operative Kujala, Knee Society, and Lysholm scores for the study population significantly improved relative to the pre-operative scores. The tilting and congruence angles at three months after the operation significantly increased relative to those recorded immediately after the operation. The tilting and congruence angles were not significantly different at three, 12, and 36 months after the operation. Conclusions The post-operative outcomes of MPFL reconstruction for recurrent patellar dislocation were favourable. Insufficient union between the bone tunnel and tendon graft, along with an elongation of the necrotic tendon graft, may change the alignment of the patellofemoral joint within three months after the operation. Therefore, we believe it is necessary to refrain from knee rotation that places lateral stress on the patella until three months after the operation.