Relevanz des Musculus vastus medialis obliquus als Prädispositionsfaktor für die Entstehung der akuten und chronischen Patellaluxation

Abstract

Lateral patellar instability is a common clinical picture in trauma surgery and orthopaedics. Stability of the patellofemoral joint is maintained by a complex interplay of active, passive and static stabilizers represented by muscles, ligaments and joint geometry. To choose the most appropriate treatment it’s important to understand the relevant contributions of the different patellar-stabilizing mechanism in the context of the individual patient’s anatomy. This study investigates the morphology of the vastus medialis obliquus (VMO) muscle in the anatomical setting of an unstable patella. Magnetic resonance imaging was used to measure the VMO cross-sectional area, muscle-fiber angulation, and the craniocaudal extent of the muscle in relation to the patella. Eighty-two consecutive subjects were prospectively enrolled in this study. The groups were composed of thirty patients with an acute primary patellar dislocation, thirty patients with recurrent patellar dislocation, and twenty-two controls. Groups were adjusted according to sex, age, body mass index, and physical activity (BAECKE-Score). No significant difference was found with respect to all measured VMO parameters between primary dislocation, recurrent dislocation, and control subjects. In comparison to the control group, primary and recurrent dislocators showed the typical anatomical risk profile of lateral patellar instability with a dysplastic trochlear groove, patella alta, and increased TT-TG distance. This finding indicates that a normal constituted VMO is not able to prevent lateral patellar dislocations in patients with the typical anatomical risk profile. The main results obtained from this investigation indicate that in the clinical setting of lateral patellar dislocations, the VMO muscle plays only a subordinate role in the complex interplay between the different stabilizers of the patellofemoral joint.