Anatomy of the ulnar nerve in the posterior compartment of the upper arm: Relationships with the triceps brachii muscle

Abstract

The aim of our descriptive anatomical study was to clarify the relationships between the ulnar nerve and the triceps brachii muscle in the posterior compartment of the upper arm. This study involved 30 fresh adult upper limbs. In all specimens, the ulnar nerve crossed from the anterior to posterior compartment in a space formed by the medial intermuscular septum and muscle fibers of the triceps' medial head. This transition zone was located an average of 126mm (115-135mm) proximal to the start of the ulnar groove. In the posterior compartment, the nerve descended vertically, and its anterior side was attached to the posterior side of the septum. Its posterior and lateral sides were covered by muscle fibers from the medial head. Its medial side was always free meaning that the nerve did not penetrate through the medial head. The other heads of the triceps muscle had no direct interactions with the ulnar nerve within this compartment. During its posterior course, the nerve was accompanied by the superior ulnar collateral artery. The ulnar nerve did not give off any branches in the upper arm.