Differences between skeletally immature and mature patients in recurrent patellar dislocation: a radiological study

To compare radiological characteristics between skeletally immature and mature patients with recurrent patellar dislocation (RPD).

A retrospective study was conducted involving 85 patients (106 knees) with RPD treated between January 2016 and September 2024. Patients were divided into skeletally immature and skeletally mature groups based on epiphysis closure. Patellar height was assessed using the Caton-Deschamps Index (CDI). Trochlear and patellar morphology were classified according to the Dejour and Wiberg classifications, respectively on computed tomography (CT). Additional CT measurements included tibial tubercle-trochlear groove (TT-TG) distance and patellar tilt angle (PTA). Lower-limb rotational alignment was evaluated in a subset of patients using tibial external rotation angle (TERA) and femoral anteversion angle (FAA) on full-length lower-limb CT.

The immature group comprised 24 patients (33 knees, mean age 13.5 ± 1.4 years), and the mature group 61 patients (73 knees, mean age 23.3 ± 6.0). Wiberg type III patellar dysplasia was significantly more prevalent in the mature group (71.2% vs.18.2%, P < 0.001). Type B trochlear dysplasia predominated in the immature group (51.5%), whereas type A was most common in the mature group (46.6%). Mean CDI was significantly higher in the immature group (1.5 ± 0.2 vs. 1.3 ± 0.2, P < 0.001), with patella alta being more frequent (84.8% vs. 60.3%, P = 0.012). PTA (31.3° vs. 27.1°, P = 0.043) and FAA (28.3 ± 9.8° vs. 21.1 ± 9.6°, P = 0.017) were significantly greater in the immature group.

In patients with RPD, patella alta is more severe and prevalent in skeletally immature individuals. Immature patients also exhibit greater patellar tilt and increased femoral anteversion but less severe patellar dysplasia compared with skeletally mature adults.

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