title: Human evolution and tears of the rotator cuff.
abstract: OBJECTIVE
  Humans differ from other great ape species in their propensity to develop tears of the rotator cuff. The aim of this study was to compare the anatomical risk factors for subacromial impingement and rotator cuff tears amongst the great apes and to determine which features may be accentuated in humans and therefore play a more significant role in disease aetiology.
  
  
  METHODS
  Orthogonal digital photographs of 22 human, 17 gorilla, 13 chimpanzee and 12 orangutan dry bone scapula specimens oriented in the glenoid plane were taken. Anatomical measurements were preformed using a calibrated digital image technique and the results scaled according to scapula vertebral border length.
  
  
  RESULTS
  Of the ten anatomical features associated with subacromial impingement and rotator cuff tears in humans, none were shown to be accentuated and significantly different to the other species studied. However the human supraspinatus fossa was shown to be significantly smaller.
  
  
  CONCLUSIONS
  These results indicate that an alternative primary aetiological factor for rotator cuff tears must exist. A reduction in the size of the supraspinatus fossa in human scapulae suggests that structural insufficiency of the supraspinatus or a change in rotator cuff force vectors could play a role.
authors: Department of Orthopaedics, Epsom General Hospital, Dorking Road, Epsom, Surrey, KT18 7EG, UK, jcraik82@gmail.com.
authors: Johnathan D
authors: JD
authors: Craik
authors: Ravi
authors: R
authors: Mallina
authors: Vijayraj
authors: V
authors: Ramasamy
authors: Nick J
authors: NJ
authors: Little
mesh_terms: D000818:Animals; D005075:Biological Evolution; D006071:Gorilla gorilla; D006801:Humans; D007700:Kinetics; D018482:Muscle, Skeletal / Q000033:anatomy & histology; D015588:Observer Variation; D002679:Pan troglodytes; D057079:Pongo; D012307:Risk Factors; D017006:Rotator Cuff / Q000033:anatomy & histology*; D000070636:Rotator Cuff Injuries; D012540:Scapula / Q000033:anatomy & histology; D019534:Shoulder Impingement Syndrome / Q000453:epidemiology* / Q000209:etiology