title: Third head of the gastrocnemius: an MR imaging study based on 1,039 consecutive knee examinations.
abstract: OBJECTIVE
  The objectives of this study were to determine the frequency of a third head of the gastrocnemius and to describe the course, morphology, and insertion of the third head as seen on the basis of routine magnetic resonance (MR) imaging of the knee.
  
  
  METHODS
  This study was a prospective study of 1,039 consecutive knee MR examinations which were performed for symptoms of pain not associated with claudication. The examinations were performed between September 2004 and January 2005 and were evaluated for the presence of an anomalous third head of the gastrocnemius and to determine its origin and course. Examinations were performed on a variety of magnets ranging from 0.2 to 1.5 T.
  
  
  RESULTS
  Of the 1,039 knees, 20 (1.9%) demonstrated an anomalous third head of the gastrocnemius which was seen arising near the midline of the posterior distal femur, between the mid and medial aspect, and joining the medial aspect of the lateral head of the gastrocnemius. The size of the third head varied from a thin threadlike muscle to a rather bulky muscle. In all of these patients, the third head coursed lateral to the popliteal vessels, and none coursed between the vessels. One additional case of a third head of the gastrocnemius was seen which joined the medial head of the gastrocnemius.
  
  
  CONCLUSIONS
  A third head of the gastrocnemius joining the lateral head is not an uncommon variant, seen in 1.9% of knee MR examinations. Most are not associated with vascular symptoms.
authors.affiliation: Imaging Institute, Cleveland Clinic Foundation, Hb6, 9500 Euclid Ave, Cleveland, OH 44195, USA. koplasm@ccf.org
authors.forename: Monica C
authors.initials: MC
authors.lastname: Koplas
authors.forename: Paul
authors.initials: P
authors.lastname: Grooff
authors.forename: David
authors.initials: D
authors.lastname: Piraino
authors.forename: Michael
authors.initials: M
authors.lastname: Recht
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000033:anatomy & histology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000033:anatomy & histology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013710:Tendons / Q000033:anatomy & histology*; D055815:Young Adult