Coronal Alignment Changes in the Patellofemoral Joint Are Smaller Than Correction Angle and Have Little Impact on Clinical Scores and Cartilage Damage After Medial Open-Wedge High Tibial Osteotomy.

PURPOSE: To investigate the impact of the correction angle on changes in patellofemoral joint (PFJ) alignment in the coronal plane before and after medial open-wedge high tibial osteotomy and its effect on postoperative patient-reported outcome measures and PFJ cartilage damage. METHODS: Patients who underwent medial open-wedge high tibial osteotomy between 2019 and 2022 and had pre- and postoperative whole-leg computed tomography were included. Coronal PFJ alignment was investigated using angles of the patellar ridge, femoral trochlear groove, quadriceps femoris, and patellar tendon. All coronal angular measurements were formed along the x-axis. Knee Injury and Osteoarthritis Outcome Score obtained preoperatively and before implant removal and International Cartilage Repair Society grades of the PFJ based on primary and second-look arthroscopic findings were evaluated. The minimal clinically important difference was defined as half the standard deviation of the score changes. RESULTS: Forty-five knees of 39 patients were analyzed. Mean coronal correction angle on postoperative computed tomography was 9.3°. Changes in PFJ alignment indicators were significantly smaller than the correction angle, with the patellar ridge being less affected than the quadriceps femoris (3.0° vs 6.8°, P < .001). Only the Knee Injury and Osteoarthritis Outcome Score for activities of daily living decreased as the patellar tendon angle increased (r = -0.333). More than 70% of patients achieved an improvement greater than the minimal clinically important difference for the Knee Injury and Osteoarthritis Outcome Score subscales. The difference in the pre- and postoperative International Cartilage Repair Society grades of the patellar cartilage worsened slightly (P = .004). No significant correlations were found between changes in the International Cartilage Repair Society grade and any clinical scores before and after medial open-wedge high tibial osteotomy. CONCLUSIONS: Changes in PFJ alignment indicators were significantly smaller than those in the coronal correction angle, particularly for bony indicators. The correlations between clinical scores or PFJ cartilage damage and changes in PFJ alignment indicators were negligible in the coronal plane. LEVEL OF EVIDENCE: Level IV, retrospective case series.