Important variations in the position of the ulnar nerve

The knowledge of the topographical relationship of some body structures was one of our aims in the study of the position and topography of the ulnar nerve in the lower third of the upper arm and the elbow region. The elbow region, because of its close relation to the ulnar nerve, especially the relation to the medial epicondyle of the humerus and the nerve, may explain some injuries of the nerve trunk. In this region the anterior dislocation of the ulnar nerve may occur, as well. We studied 60 specimens of the foetuses, newborn infants and adult persons of both sexes, by using macro and micro dissection. Almost in all cases (96.7%) the ulnar nerve passed from the upper arm to the forearm through the bony-fibrous opening ("the elbow tunnel") on the posterior side of the elbow. The anterior wall of the tunnel was sulcus n. ulnaris, while its posterior-medial wall was a strong, fibrous arch-shaped band that connected olecranon and the tip of the medial epicondyle. In the majority of cases (75%) this fibrous arc was thick and strong, high, and did not reach the top of the medial epicondyle. Thus it prevented the anterior dislocation of the ulnar nerve in the elbow flexion. Rarely (21.7%) this fibrous are was situated lower, even 15 mm below the medial epicondyle top. This disposition could favour the anterior dislocation of the ulnar nerve. Only rarely (3.3%) the ulnar nerve passed in front of the medial epicondyle.