New Insights Into the Anconeus Epitrochlearis Muscle and Its Relationship to the Ulnar Nerve: Anatomical Study

Ulnar neuropathy due to compression at the cubital tunnel is common. However, our understanding of the relationships between this type of nerve compression and the variant anconeus epitrochlearis muscle (AEM) is poorly understood. Therefore, the present anatomical study was performed to better elucidate these relationships. In 162 adult cadavers (324 sides), the roof of the cubital tunnel was dissected. The prevalence and gross anatomy of the AEM were documented. Histological and microCT analyses were performed on selected specimens to evaluate the microanatomy and radiological findings in relation to the underlying nerve, soft tissues, and bone. Additionally, with the range of motion of the elbow and artificial contraction of the AEM, the effects of the AEM on the ulnar nerve were observed. AEMs were identified on 32 (10%) of the sides. Histologically, a connective tissue connection between the AEM and ulnar nerve was found in all specimens, and a direct connection between the AEM and the underlying joint capsule was found in most specimens. No grossly visible compression of the ulnar nerve by the overlying AEM was observed with flexion or extension of the elbow. With artificial contraction of the AEM, the ulnar nerve was found to move out of the depths of the ulnar groove in roughly half of the sides. Previously unreported relationships between Osborne's ligament, 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. During surgery in this area, care should be taken to avoid injuring the ulnar nerve when applying traction to the AEM.