title: MRI of the distal biceps femoris muscle: normal anatomy, variants, and association with common peroneal entrapment neuropathy.
abstract: OBJECTIVE
  The objectives of our study were to describe the previously unreported normal MR anatomy of the distal biceps femoris muscle and its relationship with the common peroneal nerve and to present a case in which previously unreported MR evidence of an anatomic variation in the distal biceps femoris muscle was associated with common peroneal entrapment neuropathy.
  
  
  METHODS
  One hundred consecutive 1.5-T knee MR studies of 97 asymptomatic patients were retrospectively reviewed by two observers in consensus for, first, normal anatomy of the distal biceps femoris muscle; second, anatomic variations of the muscle; and, third, the relationship of the muscle to the common peroneal nerve. Measurements of the distal and posterior extents of the short and long heads of the biceps femoris were performed. An MR study of a symptomatic patient with clinical evidence of common peroneal neuropathy associated with a surgically proven anatomic variation of the distal biceps femoris was reviewed.
  
  
  RESULTS
  Two MR anatomic patterns were seen in the asymptomatic patient group: First, in 77 knees (77%), the common peroneal nerve was located within abundant fat posterolateral to the biceps femoris; and, second, in 23 cases (23%), the common peroneal nerve traversed within a narrow fatty tunnel between the biceps femoris and lateral head of the gastrocnemius muscles. There was a positive correlation between the distal and posterior extents of the short head of the biceps femoris muscle and the presence of the tunnel.
  
  
  CONCLUSIONS
  Variations in the posterior and distal extents of the biceps femoris muscle can produce a tunnel in which the common peroneal nerve travels. We also described a case of common peroneal neuropathy secondary to tunnel formation.
authors: Department of Radiology, New York University School of Medicine and NYU Hospital for Joint Diseases, 301 E 17th St., New York, NY 10003, USA.
authors: Renata La Rocca
authors: RL
authors: Vieira
authors: Zehava Sadka
authors: ZS
authors: Rosenberg
authors: Kiril
authors: K
authors: Kiprovski
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001132:Arm / Q000294:innervation / Q000473:pathology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000002:abnormalities* / Q000473:pathology*; D009408:Nerve Compression Syndromes / Q000209:etiology* / Q000473:pathology*; D010543:Peroneal Nerve / Q000473:pathology; D020427:Peroneal Neuropathies / Q000209:etiology* / Q000473:pathology*