In spite of its importance for movements of the upper limbs, the clavicle is an infrequently studied shoulder bone. The present study compares clavicular morphology among different extant primates. Methods have included the assessment of clavicular curvatures projected on two perpendicular planes that can be assessed overall as cranial and dorsal primary curvatures. Results showed that in cranial view, three morphologies can be defined. One group exhibited an external curvature considerably more pronounced than the internal one (Gorilla, Papio); a second group was characterized by an internal curvature much more pronounced than the external one (Hylobates, Ateles); and a third group contained those with the two curvatures equally pronounced (Pan, Homo, Pongo, Procolobus, Colobus). Clavicle curvatures projected on the dorsal plane could be placed into four groups. The first group is characterized by two curvatures, an inferior and a superior (Apes, Spider monkeys). The second included monkeys, whose clavicles have an inferior curvature much more pronounced than the superior one. The third group includes only Hylobates, whose clavicles possess only the superior curvature. The last group includes only modern humans, whose clavicles show only the inferior curvature, which is less pronounced than that which exists in monkeys. Curvatures in cranial view relate information regarding the parameters of arm elevation while those in dorsal view offer insights into the position of the scapula related to the thorax. The use of clavicular curvature analysis offers a new dimension in assessment of the functional morphology of the clavicle and its relationship to the shoulder complex. Anat Rec Part A, 288A: 944-953, 2006. 2006

The high prevalence of rotator cuff tendinopathy in modern humans may be partly related to the shape acquired by the scapula as species changed throughout evolution. Here, we compared the anatomic features of the scapula across members of the Hominoid group. The results support the hypothesis that the scapula of Homo sapiens sapiens exhibits distinctive anatomic characteristics compared to that of other Hominoids. We studied 89 scapulae from five species. For each scapula, we measured eight parameters and determined six index. We then compared the results across species. We identified two distinctive characteristics of the lateral aspect of the human scapula, namely, a lateral orientation of the glenoid cavity and a narrow coraco-acromial arch. Similar to the gorilla acromion, the human one is steeply sloped and, above all, larger and squarer than the acromion of other Hominoids. These features may explain, in part at least, the pathogenesis of rotator cuff tendinopathy in modern man.