Geometric morphometrics: does the appearance of the septal aperture depend on the shape of ulnar processes?

Many theories have been suggested to explain the etiology of septal apertures (SA) of the humerus. The influence of genes, the size of ulnar processes, joint laxity, and bone robusticity, have been discussed; however, the problem has not yet been solved. The main aim of this study was to examine the influence of ulnar and humeri shape on septal aperture formation, using geometric morphometric analyses. Skeletal material from an early-mediaeval cemetery located in Western Poland was used. The material comprised two groups: (1) ulnae and humeri with septal apertures, (2) ulnae and humeri without septal apertures. From a CT image, three-dimensional reconstructions were obtained for all bones. Then, 25 landmarks were distributed on each proximal end of the ulnae and 30 landmarks on the distal ends of the humeri. Shape differences between ulnae in joints with and without SA were significant for the left and right sides of the body. The shapes of the left and right distal ends of humeri with SA differed significantly from those without SA. Similar results were obtained for the right side of the body. Ulnae from joints with SA were characterized by a more pronounced olecranon process, a smaller articulated coronoid process and a more tightly curved trochlear notch than ulnae from joints without SA. Humeri with SA included wider and deeper olecranon fossae and smaller and less curved articular surfaces. These results partly coincide with the results of other research indicating the influence of olecranon processes on lamina perforation.