A radiographic investigation of the relationships between humeral cortical bone thickness, medullary canal width and the supratrochlear aperture (STA).

The supratrochlear aperture (STA) is a perforation of the septum between the olecranon and coronoid fossae of the humerus. Bones with STA are prone to supracondylar fractures and are thought to have narrower medullary canals. Our aim was to explore the relationship of the STA with medullary canal width and humeral size. The study employed a case-control research design with approximately equal numbers of individuals with and without STA from South African Whites, Blacks, and the Mixed ethnic group. Radiographs were taken anteroposteriorly using a Lodox Statscan and Image J software was used to acquire measurements from the radiographs. In the proximal diaphysis, the mean medullary canal width was significantly smaller for STA humeri (13.59 vs. 14.72 mm). The same was true for the midshaft (10.21 vs. 10.84 mm) and the distal portion (10.05 vs. 10.63 mm). While STA humeri appeared to have narrower medullary canal dimensions, this was not the case after standardizing for bone size. The smaller medullary canal width reported in the literature for STA-bearing humeri is, therefore, due to bone size differences and not STA presence. This is supported by the strong positive correlation between bone size and medullary canal width irrespective of STA status. Thus, the medullary canal width increases with bone size independent of STA status. We, therefore, propose that bone size, and not STA presence, is the major factor to consider when choosing rods for intramedullary fixation.