Variations in anatomy of the ulnar nerve at the cubital tunnel: Pitfalls in the diagnosis of ulnar neuropathy at the elbow

Abstract

Two processes account for most instances of ulnar neuropathy at the elbow: compression in the retroepicondylar groove, and compression by the humeroulnar aponeurotic arcade joining the two heads of the flexor carpi ulnaris. While conventional electrodiagnostic criteria may localize an ulnar neuropathy to the elbow, separating retroepicondylar compression from humeroulnar arcade compression is more difficult. In 130 cadaver elbows, we examined the relationships between the medial epicondyle, flexor carpi ulnaris, and ulnar nerve. The humeroulnar arcade lay from 3 to 20 mm distal to the medial epicondyle, the intramuscular course of the nerve through the flexor carpi ulnaris ranged from 18 to 70 mm, and the nerve exited the flexor carpi ulnaris 28 to 69 mm distal to the medial epicondyle. In 6 specimens, dense fibrous bands bridged directly between the medial epicondyle and the olecranon proximal to the cubital tunnel proper; accessory epitrochleoanconeus muscles were present in 14 specimens: both may cause ulnar neuropathy at the elbow. Anatomical variations may contribute to the difficulty in separating causes of ulnar neuropathy at the elbow.

Short Segment Conduction Study and Localization Features in Ulnar Neuropathy at the Elbow: A Retrospective Study of 57 Patients

“…On the other hand, according to Posner, there are five potential compression regions with the addition of the arcade of Struthers to the abovementioned regions (26). RTC is the region between the medial epicondyle and olecranon, HUA is approximately 3-25 mm distal to the medial epicondyle, and MIS starts from approximately 2 cm proximal to the medial epicondyle and extends on the upper arm (15,18,26). The arcade of Struthers is a fibrous structure located 6-10 cm proximal to the medial epicondyle, and its existence was revealed in 70% of people (27).…”

“…The entrapments in the immediate proximity of the medial epicondyle were evaluated as RTC, and the ones ≥2 cm proximal were evaluated as the medial intermuscular septum (MIS) entrapment (15).…”

“…In the results based on latency and amplitude changes, the classification of entrapments was performed as HUA when abnormal conduction was in the 1 st and 2 nd segments, as RTC when it was in the 3 rd segment, and as MIS when it was in the 4 th and 5 th segments (14,15).…”

Separate muscle bundles of the flexor digitorum superficialis overlying the ulnar nerve

“…Ulnar nerve compression occurs commonly in the cubital tunnel, but also (although rarely) in the region of the upper forearm below the cubital tunnel [9]. The structures thought to be responsible for ulnar nerve compression below the cubital tunnel are the muscular fascia under the FCU [20] and the intermuscular aponeurosis (IMA) between the FCU and the FDS [2,5]. The muscle bundles of the FDS attached to the IMA between the FCU and the FDS reportedly create a muscle tunnel over the ulnar nerve [13].…”

“…The deep border of the lowest bundle was composed of the tendinous fibres in 22% and was closely contiguous with the ulnar nerve. It has been proposed that the IMA between the FDS and FCU could cause persistent symptoms following surgical release in cubital tunnel syndrome, and be the site of ulnar neuropathy at the elbow [2,5,10].…”