A Deeper Understanding of the Anconeus Epitrochlearis, Osborne’s Ligament, and the Ulnar Nerve: Application to Decompression of the Cubital Tunnel

Tulane University School of Medicine

INTRODUCTION: Ulnar neuropathy due to compression at the cubital tunnel is common. However, our understanding of the relationships between this type of nerve compression and Osborne’s ligament (OL) and the variant anconeus epitrochlearis muscle (AEM) is poorly understood. Therefore, the present anatomical study was performed to elucidate these relationships better.

METHODS: In 120 adult cadavers (240 sides), the roof of the cubital tunnel was dissected. When present, the relationship between OL and the AEM to the ulnar nerve was observed. The prevalence of the AEM was documented. Histological and microCT analyses were performed on selected specimens to evaluate the microanatomy between the underlying nerve, soft tissues, and bone. Additionally, with range of motion of the elbow, videography was performed to capture the effect of the AEM on the ulnar nerve.

RESULTS: Multiple variations of the AEM and OL were identified. In many specimens, OL coexisted with the AEM. Although similar, the OL and AEM seemed to have distinct morphologies. Histologically, the OL often contains skeletal muscle fibers. Other previously unreported findings include a connective tissue connection between the AEM and ulnar nerve and a direct connection between the AEM and underlying joint capsule in some specimens. With range of motion of the elbow and artificial contraction of the AEM, the ulnar nerve was found to move out of the depths of the ulnar groove.

CONCLUSIONS: Previously unreported relationships between OL, the AEM, and the underlying ulnar nerve were found. These findings will improve our understanding of the relationship between these structures and the ulnar nerve at the elbow.