The supratrochlear aperture (STA) is a perforation of the septum found between the olecranon and coronoid fossae of the humerus. Its prevalence is population specific and varies by sex. There is no consensus on the etiology of this feature despite decades of investigation. Two aspects of the mechanical theory, which states that the STA is formed when the ulnar olecranon and coronoid processes impinge upon the septum separating the olecranon and coronoid fossae, were investigated. First, osteometric measures of bone size were used to test the proposition that larger humeri are less prone to STA formation. We compared the dimensions of STA bearing humeri with those lacking STAs and investigated which skeletal features discriminate among South African populations. To specifically evaluate the mechanical theory that articulation with the olecranon and coronoid fossae may result in STA formation, dimensions of the olecranon and coronoid processes were compared. Our results verified that smaller individuals are prone to STA formation and that a significantly longer olecranon process is associated with the aperture. The olecranon process length and olecranon-coronoid distance were the main contributors to STA presence. Variables that contributed the most towards discrimination among the South African populations were the olecranon fossa depth and right humeral head circumference. An inverse relationship between the olecranon process length and olecranon fossa depth was also associated with presence of the STA.