Summary

This study analyzed the outcomes of skeletally immature and skeletally mature patients undergoing isolated medial patellofemoral ligament reconstruction for patellar instability. Results showed that skeletally immature patients experienced post-operative recurrent instability at a higher rate than skeletally mature patients.

Abstract

Introduction

Addressing patellofemoral instability in skeletally immature patients has historically posed challenges as it is essential to respect the growth plates. The purpose of this study was to compare post-operative outcomes between skeletally immature and skeletally mature patients who underwent isolated medial patellofemoral ligament reconstruction (MPFL-R).

Methods

Patients were enrolled from the prospectively collected multi-center Justifying Patellar Instability Treatment by Results (JUPITER) cohort study. Inclusion criteria were patients who underwent a primary, single-stage, isolated MPFL-R without concomitant boney procedure from January 2017-July 2022. Patients were excluded if there was no discrete treatment data, unknown skeletal maturity status, and no modification listed to address placement of the femoral tunnel in a skeletally immature patient. Age, sex, BMI, and Beighton score were collected. Radiographic parameters included Caton-Deschamps Index (CDI), tibial tubercle-trochlear groove distance (TT-TG), axial width of the patellar tendon beyond the lateral trochlear ridge (PT-LTR), and trochlear crossing sign. Surgical data included MPFL-R graft type and concomitant procedures. Patient reported outcome measures were collected at baseline, 1, 2, and 5 years. Paired and unpaired t-tests were used to assess the difference in means between the two groups, and Chi-square test of independence to examine the discrepancy in frequencies between the two groups.

Results

This study included 814 patients (16 ± 3.6 years old, 59.2% female) of which 319 (39%) were skeletally immature at the time of surgical intervention. Skeletally immature patients were younger (13.7 ± 1.9 vs. 17.5 ± 3.7 years, p < 0.0001), more often male (50.8% vs. 64.7%, p = 0.0002), and had a lower mean BMI (22.2 ± 5.4 vs. 25.5 ± 5.8, p < 0.0001) than skeletally mature patients. Skeletally immature patients were found to have increased incidence of patella alta (CDI > 1.2) (71% vs 67%, p < 0.0001) and a higher PT-LTR (9.9 ± 6.5, 7.9 ± 6.5, p = 0.0396). Skeletally immature patients had lower rates of chondroplasty (32.3% vs. 46.7%, p < 0.0001), higher rates of osteochondral fracture treatment (17.5% vs. 9.9%, p = 0.0018), and experienced significantly more post-operative recurrent instability (12.5% vs. 7.0%, p = 0.0126, at a mean time of 27.8 months). There was no significant difference in rates of return-to-sport between the groups (p = 0.2136). There were no significant differences in baseline PROMs. 1 year post-operatively, skeletally immature patients had higher KOOS Pain, KOOS Symptoms, KOOS ADL, KOOS JR, and Pedi-IKDC (p < 0.05), but this significance was not maintained at 5 years. The difference in Pedi-FABS between the two groups persisted through 5 years post-operatively.

Conclusion

Skeletally immature patients experienced post-operative recurrent instability at a higher rate than skeletally mature patients. Rates of recurrent instability are consistent with the current published literature; however, the rate of recurrent instability is lower than reported in previous literature, potentially representing an improvement in isolated MPFL-R techniques over time. The greater PROMs for skeletally immature patients at 1-year that becomes similar at 2 and 5 years may represent faster recovery in the immediate post-op period for the younger population, which balances out over time.