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Objectives and questions: Hypermobile Ehlers-Danlos Syndrome (hEDS) is a connective tissue disorder characterized by joint hypermobility and ligamentous laxity, leading to a high prevalence of patellar instability. While anatomical risk factors for patellar dislocation have been extensively studied in the general population, their specific role in hEDS remains unclear. This study aimed to evaluate anatomical predictors of patellar dislocation in patients with hEDS by comparing individuals with and without this complication.

Material and methods: A retrospective analysis was conducted on 168 patients diagnosed with hEDS. Patients were screened to ensure they had MRI and X-ray imaging of the knee, identifying 17 patients (28 knees) with patellar dislocation (PD group) and 33 patients (38 knees) without dislocation (control group). Demographic data, imaging measurements, and patellar-specific parameters such as tibial tubercle lateralization, patellar height, axial alignment, trochlear morphology, and patellar shape were assessed. Statistical comparisons and regression analyses were performed to identify significant predictors.

Results: The PD group exhibited significantly smaller patellar width (p=0.03), higher Insall-Salvati ratios (p=0.04), and a greater prevalence of type C trochlear dysplasia (p=0.02) and type III patellar shape (p=0.02) compared to controls. Age was a significant predictor, with younger patients showing a higher likelihood of dislocation (p=0.004; OR= 0.076;95% CI, -0.128- -0.024). No significant differences were found in tibial tubercle lateralization or tibiofemoral rotation between groups. Correlation analysis revealed complex relationships among imaging parameters, highlighting the interplay of anatomical factors.

Discussion and conclusion: This study identified anatomical differences associated with patellar dislocation in hEDS, but none were pathological based on established norms. These findings highlight that a different manifestation and severity of the syndrome, along with its impact on connective tissue, may play a more significant role in patellar instability than isolated anatomical factors.