title: Vastus medialis: anatomical and functional considerations and implications based upon human and cadaveric studies.
abstract: OBJECTIVE
  To provide an electrophysiological and functional description of the vastus medialis (VM) and contrast it to an anatomical description.
  
  
  METHODS
  Motor points of all superficial portions of the quadriceps were identified on the dominant side of 8 human subjects and electrically stimulated to achieve a light contraction to trace and measure the orientation of the fibers. Electromyography of the VM was then recorded over 2 motor points during isometric and isokinetic maximum knee extensions. An independent laboratory dissected 39 cadaveric specimens focusing on fiber orientations and distal insertions of the VM.
  
  
  RESULTS
  Results revealed 5 motor points for the quadriceps: 1 point for the vastus lateralis, 1 point for the rectus femoris (RF), and 3 points for the VM. The 3 VM motor points suggest 3 separate groups of fibers: proximal (pf), median (mf), distal (df). Fiber orientations ranged from 45 degrees for VMpfs to 55 degrees for VMdfs. Motor point stimulation and anatomical dissection clearly showed that the VMpfs and VMmfs were inserted on a tendon common to the RF, whereas VMdfs were attached directly to the medial aspect of the patella. Furthermore, the VMpfs were more active (P < .05) than VMdfs during maximum knee extensions.
  
  
  CONCLUSIONS
  The anatomy, motor points, and electromyography clearly support an important distinction between the VMpfs and VMdfs. The role of the VMpfs would be one of assisting the RF in knee extension, whereas the VMdfs would track the patella medially without participating in knee extension. Because of these anatomical and functional differences, the VMpfs and VMdfs should be addressed very differently during quadriceps rehabilitation in patellofemoral dysfunctions.
authors.affiliation: Département de Kinanthropologie, Université du Québec à Montréal, Montreal, Quebec, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Lefebvre
authors.forename: Alain
authors.initials: A
authors.lastname: Leroux
authors.forename: Georges
authors.initials: G
authors.lastname: Poumarat
authors.forename: Bruno
authors.initials: B
authors.lastname: Galtier
authors.forename: Michel
authors.initials: M
authors.lastname: Guillot
authors.forename: Guy
authors.initials: G
authors.lastname: Vanneuville
authors.forename: Jean P
authors.initials: JP
authors.lastname: Boucher
mesh_terms: D000328:Adult; D002102:Cadaver; D004558:Electric Stimulation; D004576:Electromyography; D004594:Electrophysiology; D006801:Humans; D007537:Isometric Contraction; D009119:Muscle Contraction; D018485:Muscle Fibers, Skeletal / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D010329:Patella / Q000033:anatomy & histology; D013710:Tendons / Q000033:anatomy & histology; D013848:Thigh