Topographic relationship between the medial intermuscular septum and the ulnar nerve in the upper arm: Laboratory investigation

Object. The authors have observed that the ulnar nerve (UN) passes through the medial intermuscular septum (MIMS) into the posterior compartment of the upper arm in more complicated patterns than those described in anatomy textbooks. Given that these unreported patterns might be related to the idiopathic UN entrapment at the midarm, this study focused on the relationship between the MIMS and the UN. Methods. One hundred upper arms were dissected. The site at which the UN pierced the MIMS was analyzed and measured from the medial epicondyle. Results. The relationship between the MIMS and the UN could be classified into 3 types according to whether the nerve pierced the MIMS and whether it ran through a fibrous tunnel within the septum. The UN pierced the MIMS in the middle third of the upper arm. Conclusions. The results of this study are expected to further understanding of the relationship between the MIMS and the UN. They could also be helpful for surgeons aiming to relieve UN entrapment at the midarm, especially in nerve lesions of idiopathic origin.