Extreme trochlear morphology in pediatric patients with fixed lateral patellar dislocation: a radiographic study

Fixed lateral patellar dislocations (FLPD) are a rare subtype of chronic patellofemoral instability (PFI) where the patella remains dislocated in flexion and extension. The aim of this study was to describe radiographic morphological features in pediatric patients with FLPD and determine how they differ from those with acute patellar dislocation (APD) and unaffected controls.

Pediatric patients who underwent medial patellofemoral ligament reconstruction for FLPD or APD were identified and age- and sex-matched to controls without PFI. On axial magnetic resonance imaging, bony sulcus angle (BSA), cartilaginous sulcus angle (CSA), patellar tilt, trochlear depth, patellar lateralization, and tibial tubercle-trochlear groove (TT-TG) distance for all patients were recorded.

Fifteen FLPD extremities, 30 APD extremities, and 30 control extremities were included. Ten FLPD patients had associated syndromic or congenital conditions. In the FLPD cohort, MPFL reconstructions were concomitantly performed with lateral release (15 extremities), quad-tendon lengthening (10 extremities), and tibial tubercle osteotomy (10 extremities). FLPD group had greater BSA, CSA, lateral patellar inclination angle, patellar lateralization, and TT-TG compared to both control and APD groups (p < 0.001 for all measurements). The FLPD group had 2.76 mm less trochlear depth compared to the control group (p < 0.001).

This study represents one of the largest FLPD cohorts, demonstrating markedly greater patellofemoral abnormalities than controls and APD patients, including a flatter trochlea, greater patellar lateralization/inclination, and increased TT-TG. These findings support a role for absent patellar contact in progressive trochlear flattening and support surgical intervention to improve function and quality of life.