Medial patellofemoral ligament (MPFL) reconstruction improves radiographic measures of patella alta in children

Background: Patellofemoral instability has previously been associated with patella alta. The purpose of this study was to evaluate adolescents undergoing MPFL reconstruction for standardized indices of patellar height on pre- and post-operative radiographs to determine if these radiographic parameters change after MPFL reconstruction.

Methods: Twenty-seven children (mean age 14.9years old) who underwent MPFL reconstruction without a distal realignment procedure were evaluated pre- and post-operatively for Insall-Salvati Ratio, Modified Insall-Salvati Ratio, and Caton-Deschamps Index by three blinded raters. Intrarater reliability and interrater reliability were calculated for each index, and means of each were compared pre- and post-operatively to determine if MPFL reconstruction was associated with improved patellar height.

Results: All three indices of patellar height indicated that there was patella alta present in this cohort preoperatively. Furthermore, all three measures were significantly improved postoperatively (paired t-tests, P<0.001 for all) to within normal childhood ranges. Interrater reliability was excellent for both the Insall-Salvati Ratio (ICC=0.89) and Caton-Deschamps Index (ICC=0.78), and adequate for the Modified Insall-Salvati Ratio (ICC=0.57); intrarater reliability was excellent for all three (ICCs: 0.91, 0.82, 0.80 respectively).

Conclusions: MPFL reconstruction in children using hamstring autograft was associated with consistently improved patellar height indices to within normal childhood ranges. This associated improvement of patellar height as measured on a lateral radiograph may subsequently improve patellofemoral mechanics by drawing the patella deeper and more medially into the trochlear groove.

Level of evidence: Level 4.