Evaluating the Association Between Vastus Medialis Oblique Characteristics and Patellar Instability: A Comprehensive Case-Control Study

Background: The contribution of vastus medialis oblique muscle (VMO) weakness or dysfunction to patellofemoral pain syndrome is well recognized, yet its role in lateral patellar instability and recurrent patellar dislocations remains unclear. This study investigates the association between VMO characteristics and patellar instability. Hypothesis: Altered VMO structure, characterized by differences in muscle elevation and cross-sectional area (CSA), is associated with patellar instability. Study Design: A case-control study. Level of Evidence: Level 3. Methods: The study included 204 participants, matched on a 1:1 ratio by age and sex, from a local hospital registry from 2005 to 2020. VMO measurements were taken via magnetic resonance imaging, and included muscle elevation, CSA, fiber angulation, and CSA-to-thigh circumference ratio. Univariate analysis, and multivariable regression model with adjustment for potential confounders were constructed. In addition, a secondary analysis was performed to evaluate the variations in VMO characteristics and mass across primary and recurrent patellar instability groups. Results: Patients with patellar instability demonstrated significant differences in VMO characteristics compared with controls, including increased muscle elevation (13 mm vs 5.9 mm; P < 0.01), increased muscle fiber angulation (42.5° vs 35.3°; P < 0.01), reduced CSA (716 mm 2 vs 902 mm 2 ; P < 0.01), and a lower CSA-to-thigh circumference ratio (0.05 vs 0.07; P < 0.01). These findings remained significant in the multivariable adjusted model. Moreover, the secondary analysis revealed that both primary and recurrent instability patients had similar VMO characteristics alterations compared with controls, with slightly more pronounced reductions in VMO CSA in those sustaining recurrent instability episodes. Conclusion: This study confirms a statistically significant association between altered VMO characteristics and patellar instability, emphasizing the importance of considering VMO characteristics in the evaluation and management of patients with patellar instability.