Incidence of the coracoclavicular joint in South African populations.

The presence of a diarthrotic coracoclavicular joint, as represented by an articular facet on the conoid tubercle of the clavicle and the superior surface of the coracoid process of the scapula, was investigated. The sample consisted of 60 white and 180 black South African (60 Sotho, 60 Xhosa and 60 Zulu) skeletons. Each group consisted of 30 male and 30 female skeletons. The presence of the articular facet was recorded as either bilateral, unilateral left or unilateral right. The effect of clavicular length, scapular size and first rib angle on the presence of the coracoclavicular joint was also investigated. The presence of the articular facet was noted in 23 (9.6%) of the 240 individuals studied. Of these 23 individuals, 6 (26.1%) were white and 17 (73.9%) were black. Males (56.5%) presented a higher incidence of this anomaly than females (43.5%). The articular facet occurred bilaterally in 47.9% (11/23), unilaterally on the left in 30.4% (7/23) and unilaterally on the right in 21.7% (5/23). Sexual, racial and tribal differences were not statistically significant. Individuals possessing the joint showed statistically significantly (P < 0.01) larger scapulae (increased border lengths and superior angles), longer clavicles and longer first ribs. No statistically significant differences in the first rib angles were observed between individuals who possessed the joint and those who did not, thus implying similar thoracic inlet size. It is proposed that the aforementioned morphometry of the scapulae, clavicles and first ribs may restrict associated movements of the scapulae, resulting in the development of the coracoclavicular joint.