Abstract There remains controversy over whether the vastus medialis (VM) is a single anatomical structure or whether it is composed of two separate portions, the vastus medialis longus (VML) proximally and the vastus medialis obliquus (VMO) distally. The objective of this study was to assess the evidence base of investigations into muscle fiber orientation, presence of a fibrofascial plane, and the innervation of the VM in human cadaver specimens and subjects. In addition to a hand search of specialist journals, an electronic search of AMED, British Nursing Index, CINAHL, the Cochrane database, EMBASE, ovid Medline, Pubmed, and Zetoc were performed from their inception to September 2008. All human subject papers assessing VM fiber orientation, presence of a fibrofascial plane, and the innervation of the VM where reviewed. Twenty‐six papers, assessing 699 healthy knees, and 591 specimens with patellofemoral dysfunction were reviewed. The majority of nonpathological and pathological cases presented with a substantial alteration in fiber alignment seen between proximal and distal muscle portions of VM. Both cohorts presented with either one or two nerve branches to the VM. A fibrofascial plane dividing these two muscles was seen in a small proportion of both pathological and nonpathological knees. There was, however, insufficient good quality evidence to state whether the VM is composed of two separate components, the proximal VML and the distal VMO. Further study is recommended to evaluate the pathophysiological implications of such findings and to assess whether these correlate to functional electromyographic findings between the VML and VMO muscles. Clin. Anat. 22:183–199, 2009. © 2008 Wiley‐Liss, Inc.