Medial Patellofemoral Ligament Repair for Recurrent Patellar Instability: Successful Outcomes Among Patients With Low Coronal Malalignment and Normal Patellar Height.

Medial patellofemoral ligament (MPFL) repair is discouraged for the treatment of chronic, recurrent patellar instability (RPI) because of high reported failure rates. However, the senior author uses MPFL repair for chronic RPI in the setting of low tibial tubercle-trochlear groove (TT-TG) distance. In this retrospective case series, we report results and evaluate outcome predictors. We used billing records to identify all patients, 14 years or older, who underwent isolated repair for chronic RPI performed by a single surgeon between September 2010 and February 2019. The TT-TG distance, patellar height (Caton-Deschamps Index [CDI]), and trochlear depth were measured on preoperative magnetic resonance imaging; postoperative reports were reviewed; and post hoc Kuala scores were obtained to extend outcome length. Patellar dislocation or revision surgery was considered a failure. Nonfailures were categorized as excellent or fair, based on the most recent report. Univariable generalized estimating equation models were used to evaluate associations of predictors (radiographic parameters, age, ligamentous laxity, primary presenting complaint) with failure and/or success. A total of 93 isolated MPFL repairs were performed. After exclusions were made for workers' compensation insurance (n=4), substance abuse (n=3), major secondary trauma less than 3 months postoperatively (n=3), and follow-up of less than 12 months (n=42), 41 knees (38 patients) had median follow-up of 32 months (interquartile range, 19-48 months). All repairs were patellar sided. Outcomes for 4 knees were considered failures, 23 were excellent, and 14 were fair. Only increased CDI was associated with increased risk of failure (odds ratio, 1.70; 95% CI, 0.98-2.92; P=.06). Mean CDI was 1.23 mm (SD, 0.13 mm) for failures vs 1.08 mm (SD, 0.16 mm) for nonfailures. Failure rate was less than 10% following patellar-sided MPFL repair for treatment of chronic RPI among patients with low TT-TG distance. Increased patellar height was associated with higher risk of failure. [Orthopedics. 2022;45(1):e23-e29.].