There are five sites of potential ulnar nerve entrapment around the elbow: arcade of Struthers, medial intermuscular septum, medial epicondyle, cubital tunnel, and deep flexor pronator aponeurosis.
The ulnar nerve emerges from the medial intermuscular septum, under the arcade of Struthers, and lies on the medial head of the triceps. At the level of the elbow, the ulnar nerve continues distally toward the posterior aspect of the condylar groove, passing between the medial epicondyle and olecranon to enter the cubital tunnel. The roof is formed by the arcuate (Osborne’s) ligament. This ligament blends distally with the antebrachial fascia superficial to the aponeurosis and connects the ulnar and humeral heads of the FCU. The ligament of Struthers is a fibrous band extending from the supracondylar process of the humerus to the medial epicondyle which can cause compression of the median nerve.
Elhassan et al discuss the pathogenesis, evaluation, and treatment of entrapment neuropathy of the ulnar nerve.
Illustration A shows the various site of compression at the elbow. Illustration V shows a submuscular ulnar nerve transposition performed Dr. Susan E. Mackinnon
Elhassan B, Steinmann SP: Entrapment neuropathy of the ulnar nerve. J Am Acad Orthop Surg 2007;15:672-681.
PMID:17989418 (Link to Abstract)
Bainbridge C: Cubital tunnel syndrome, in Berger RA, Weiss APC (eds): Hand Surgery. Philadelphia, PA, Lippincott Williams & Wilkins, 2004, pp 887-896.