Impact of Insall-Salvati index on clinical outcomes after medial patellofemoral ligament reconstruction in children: a retrospective single-center study

Background Patella alta is a recognized risk factor for patellar instability, yet its influence on outcomes after medial patellofemoral ligament (MPFL) reconstruction in pediatric patients remains poorly defined. This study evaluated the association between preoperative patellar height, measured by the Insall-Salvati index (ISI), and clinical outcomes following MPFL reconstruction in children with recurrent patellar instability, with the Caton-Deschamps index (CDI) assessed as a comparator measure of patellar height. Methods This retrospective single-center study included pediatric patients (<18 years) who underwent MPFL reconstruction for recurrent lateral patellar dislocation between January 2022 and April 2025, with a median follow-up of 29.9 months (range 9–51 months). Patients were stratified into a patella alta group (ISI > 1.2) and a normal patellar height group (ISI ≤ 1.2). The primary outcome was the Kujala score at final follow-up. Secondary outcomes included the Lysholm score, redislocation and subluxation rates, and ISI change. Correlations between preoperative ISI and functional outcomes were analyzed, and multivariable regression models were used to determine whether preoperative ISI was independently associated with outcomes after adjustment for potential confounders. Results Of 103 patients, 49 (47.6%) were classified as patella alta. Both groups demonstrated significant postoperative ISI reductions, with a greater decrease observed in the patella alta group. At final follow-up, the patella alta group had significantly lower Kujala and Lysholm scores, and higher rates of redislocation, subluxation, and overall poor outcomes compared with the normal group. Preoperative ISI correlated negatively with the final Kujala score ( ρ = −0.457, P < 0.001), whereas the Caton-Deschamps index (CDI) showed no significant correlation. After multivariable adjustment, each 0.1-unit increase in preoperative ISI remained associated with a poor outcome (adjusted odds ratio 1.36, P = 0.040) and with a lower final Kujala score ( P < 0.001). Postoperative ISI normalization, achieved in 24 of 49 patients (49.0%) in the patella alta group, was not associated with improved clinical outcomes. Conclusion Preoperative patella alta, as defined by an elevated ISI, was associated with inferior functional and stability outcomes after MPFL reconstruction in children. In this cohort, the ISI was more strongly associated with clinical outcomes than the CDI, and this association persisted after multivariable adjustment; however, given the retrospective observational design, these findings should be regarded as hypothesis-generating and warrant confirmation in larger prospective studies. These findings suggest that preoperative ISI assessment may be valuable for risk stratification and patient counseling when planning isolated MPFL reconstruction in children.