The prevalence and combined prevalences of anatomic factors associated with recurrent patellar dislocation: a magnetic resonance imaging study.

Background: Anatomic factors, including patella alta, increased tibial tubercle-trochlear groove (TT-TG) distance, rotational deformities, and trochlear dysplasia, are associated with dislocation of the patella. Identifying the presence of these anatomic factors both in isolation and in combination may influence treatment in patients with patellar dislocation.

Purpose: The aim of this study was to compare the prevalence and combined prevalences of these anatomic factors using magnetic resonance imaging in a group of patients with and without histories of recurrent dislocation of the patella.

Study Design: Case-control study; Level of evidence, 3.

Methods: The prevalence and combined prevalences of patella alta, increased TT-TG distance, rotational deformity, and trochlear dysplasia on magnetic resonance imaging were reported and compared in 60 patients (60 knees) with and 120 patients (120 knees) without histories of recurrent patellar dislocation.

Results: Patients with recurrent patellar dislocation possessed higher rates of patella alta (60.0% vs. 20.8%), increased TT-TG distance (42.0% vs. 3.2%), rotational deformity (26.7% vs. 2.5%), and trochlear dysplasia (68.3% vs. 5.8%) compared with patients without histories of patellar dislocation. Multiple anatomic factors were identified in 58.3% of patients (35/60) with recurrent dislocation compared with only 1.7% of controls (2/120).

Conclusion: Recurrent patellar dislocation is associated with an increased prevalence of patella alta, increased TT-TG distance, rotational deformity, and trochlear dysplasia compared with patients with no histories of patellar dislocation. Multiple anatomic factors were identified in the majority of patients with recurrent dislocation. Further research may identify which factors play a greater role in patellar stability and may allow physicians to predict which first-time dislocation patients are more likely to sustain recurrence.