Subacromial Space in African Great Apes and Subacromial Impingement Syndrome in Humans

Abstract

The subacromial space is the anatomical region limited superiorly by the acromion and the coracoacromial ligament and inferiorly by the glenoid fossa and the humeral head. In humans, the main tissues that form it and that can be affected by subacromial impingement syndrome are the subacromial bursa and the supraspinatus tendon. The syndrome is the most common degenerative pathology affecting the human shoulder, and it is characterized by an uncertain etiopathogenesis. We compared different anatomical parameters of the scapula related to the subacromial impingement syndrome in humans, between modern humans and 2 species of African apes (Pan troglodytes and Gorilla gorilla). The 3 species we studied are orthograde primates and they present a similar structural pattern of the scapula and subacromial space, but anatomical differences exist owing to different types of locomotion used. The main differences indicate that African apes present a more curved and tilted acromion than humans, which does not, however, imply a difference in the relative size of the subacromial space among the 3 species studied. Humans also have a lower value of the relative size of the supraspinatus fossa than African great apes, and in human females have a relative lower value than males. We studied the anatomical structures of the shoulder in African apes that researchers have related to subacromial syndrome in humans to achieve a better understanding of the etiopathogenesis of the syndrome.