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.