A rare cause of ulnar nerve entrapment at the elbow area illustrated by six cases: The anconeus epitrochlearis muscle

Ulnar nerve entrapment is the second most common compressive neuropathy after carpal tunnel syndrome. The accessory anconeus epitrochlearis muscle – present in 4% to 34% of the general population – is a known, but rare cause of ulnar nerve entrapment at the elbow. The aim of this article was to expand our knowledge about this condition based on six cases that we encountered at our hospital between 2011 and 2015. Every patient had a typical clinical presentation: hypoesthesia or sensory deficit in the fourth and fifth fingers; potential intrinsics atrophy of the fourth intermetacarpal space; loss of strength and difficulty with fifth finger abduction. Although it can be useful to have the patient undergo ultrasonography or MRI to aid in the diagnosis, only electromyography (EMG) was performed in our patients. EMG revealed clear compression in the ulnar groove, with conduction block and a large drop in nerve conduction velocity. Treatment typically consists of conservative treatment first (splint, analgesics). Surgical treatment should be considered when conservative treatment has failed or the patient presents severe neurological deficits. In all of our patients, the ulnar nerve was surgically released but not transposed. Five of the six patients had completely recovered after 0.5 to 4 years follow-up. Ulnar nerve entrapment at the elbow by the anconeus epitrochlearis muscle is not common, but it must not be ignored. Only ultrasonography, MRI or, preferably, surgical exploration can establish the diagnosis. EMG findings such as reduced motor nerve conduction velocity in a short segment of the ulnar nerve provides evidence of anconeus epitrochlearis-induced neuropathy.