Prevalence and morphology of the vastus medialis oblique muscle in human cadavers.

ABSTRACT

BACKGROUND: The vastus medialis (VM) muscle has been described as being composed of two separate divisions the vastus medialis longus (VML) proximally and the vastus medialis oblique (VMO) distally. The VML is reported to directly contribute to knee extension, while the VMO provides medial stabilization of the patella during knee extension. Despite the prevalence of literature describing the morphology and function of the VMO as an individual muscle, very little literature exists which actually substantiates the existence of the VMO as a separate, distinct muscle from the VML. The purpose of this study was to examine a sufficiently large sample of human cadavers to quantify and substantiate the existence of the VMO as a separate, distinct muscle from the VML, and to establish a statistical parameter representative of a normal adult population. METHODS: Three hundred seventy-four adult human cadaver lower extremities were dissected, exposing the entire anterior thigh from the anterior superior iliac spine to the tibial tubercle. Examination of the cadavers included goniometric measurement of the fiber angles of the VML and VMO, determination of the existence and location of a fascial plane, and determination of the maximum VM fiber angle in all cadaver specimens. Descriptive statistics were performed on all fiber angle measurements and frequency of fascial plane presence. Analysis of variance was performed on the maximal VM fiber angle between muscles with and without a definitive fascial plane. Intrarater reliability tests were performed on all measures to ensure the reliability and increase the validity of all of the measurements taken. RESULTS: A statistical parameter for the appearance of VMO features as originally defined was set at 21.65% of the sample. No statistically significant differences existed in the maximal VM fiber angle between the groups demonstrating the presence or absence of a VM fascial plane. None of the cadavers possessed an aponeurotic sheet of epimysium anatomically separating the VMO from the VML. CONCLUSIONS: This study supports earlier research reporting a difference in fiber orientation between the proximal and distal VM fibers; however, contrary to statements in published literature, the VMO does not appear to be an anatomically separate structure from the VML inherent throughout the human population. The results of this study do not support the concept that the VMO and VML exist as anatomically separate structures in a sample of human cadavers.