Isolated Medial Patellofemoral Ligament Reconstruction Reduces Patellar Height and Is Associated With Quadriceps Dysfunction

PURPOSE: To assess whether isolated double-limbed medial patellofemoral ligament reconstruction (MPFLR) affects patellar height, measured via the Caton-Deschamps Index (CDI), and determine association with preoperative patella alta and postoperative quadriceps dysfunction. METHODS: A retrospective review was performed on subjects that underwent isolated MPFLR from 2016 to 2022. INCLUSION CRITERIA: age 13 to 62 years, patellofemoral instability, no prior ipsilateral surgery, and no bony procedures. CDI was measured on standardized perfect lateral radiographs. The first available preoperative perfect lateral radiograph and the first available postoperative perfect lateral radiograph closest to the date of surgery were used for analysis. Patella alta was defined as CDI > 1.2. Quadriceps function was assessed by straight leg raise postoperatively at the same time of the first postoperative perfect lateral radiograph. Statistical tests included Wilcoxon signed-rank, Mann-Whitney U, and linear regression. RESULTS: Eighty-one knees were included (mean age 21.0 ± 8.7 years, 62% female). Postoperative radiographs were obtained a mean of 38.78 ± 58.18 (1-351) days after surgery. Mean CDI decreased significantly following MPFLR. Patients with preoperative patella alta showed greater reduction in CDI compared with those without patella alta, and increasing preoperative CDI was weakly but significantly associated with greater CDI change. CDI reduction varied by postoperative quadriceps function, with progressively larger decreases observed in patients with extensor lag or inability to perform straight leg raise. Among patients with extensor lag, those with higher preoperative CDI experienced significantly greater CDI reduction. CONCLUSIONS: Isolated double-limbed MPFLR significantly reduces patellar height, with a CDI reduction of about 0.05 even with good quadriceps function. However, larger early postoperative decreases in CDI are likely artificial, reflecting transient quadriceps inhibition rather than true distalization of the patella. LEVEL OF EVIDENCE: Level IV, retrospective case series.