1Institute of Evolutionary Medicine, University of Zuerich, 2Anthropological Institute and Museum, University of Zuerich, Switzerland
March 26, 2015 2:30, Grand Ballroom C
The morphology of the shoulder girdle not only plays an important role in the discussion of the locomotor behaviour of early hominins, but it may also be an aetiological factor in degenerative shoulder disorders including rotator cuff disease or shoulder impingement syndrome. Lesions of the rotator cuff (supraspinatus, infraspinatus, subscapularis and teres minor) are common in modern humans, but virtually absent in great apes even at an advanced age. Humans are reported to have relatively smaller supraspinatus muscle. It has therefore been theorized that shoulder impingement results from overload of the supraspinatus tendon due to dysbalance and weakness of the rotator cuff muscles.
Here, we perform a landmark-based three-dimensional analysis of the scapular morphology in extant great apes (71 Hylobates lar; 20 Pongo sp.; 39 Gorilla gorilla; 44 Pan troglodytes), MH2 (Australopithecus sediba), a cast of KNM-WT 15000 (Homo erectus), and a sample of 89 modern human scapulae. In contrast to previous studies that were based on linear measurements and indices, we find that the supraspinous fossa and by inference the supraspinatus muscle have the same relative size in all examined species. Also the subacromial space is virtually identical in great apes and humans relative to body size. This challenges common theories about the aetiology of shoulder impingement syndrome. Moreover, our study demonstrates that linear measurements do not acknowledge the complex 3D anatomy of the shoulder girdle.
Funding: A.H. Schultz Stiftung, Mäxi Stiftung