Characterization of the tissue crossing the supratrochlear aperture of the humerus using histochemical techniques.

INTRODUCTION: The supratrochlear aperture (STA) is the opening observed in the septum that separates the olecranon from the coronoid fossae. Numerous studies have shown that there is considerable variation in the occurrence of this feature within and among populations. MATERIALS AND METHODS: Cadavers (n = 43) were assessed for the presence of the STA by means of X-ray. Ten samples of STA-bearing bones and an equal number of controls without STA were obtained from cadavers using a hole saw. These samples were decalcified, fixed in formalin and processed for histological assessment in differing (ascending) grades of alcohol before being embedded in paraffin wax. Sections (10 µm thick) were stained with haematoxylin and eosin (H&E) for general architecture as well as the rapid one-step Mallory-Heidenhain stain for bone and connective tissue. RESULTS: The STA samples exhibited an abundance of connective tissue arranged in regular bundles of fibers across the STA. In contrast, the controls showed only bone tissue in the septum. DISCUSSION AND CONCLUSION: The arrangement of connective tissue fibers organized in regular bundles is a characteristic of strength, which may indicate that the STA is under sustained stress or pressure from the olecranon and coronoid processes of the ulna. It remains debatable whether the STA should continue to be considered as a foramen in life as we demonstrate that it is obliterated by connective tissue. It contains no neurovascular structures, making it unlike other structures defined as foramina.

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.

Morphometric Characteristics of the Humerus and Ulna in Limbs Bearing the Supratrochlear Aperture (STA).

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.