Review Question - QID 213989

This patient has an isolated motor ulnar tunnel syndrome (UTS); thus, zone 2 is the affected zone.

Ulnar tunnel syndrome is a compressive neuropathy caused by direct compression within Guyon's canal. There are three zones of Guyon's canal: zone 1 which presents with mixed motor/sensory symptoms, zone 2 isolated motor symptoms, and zone 3 which presents with isolated sensory symptoms. A ganglion cyst is responsible in 80% of non-traumatic cases. Other common causes include repetitive trauma, ulnar artery thrombosis/aneurysm, and hook of the hamate fractures. Ganglion cysts and hook of hamate fractures are the most common causes for zone 1 and 2 UTS, while ulnar artery thrombosis/aneurysm is the most common cause for zone 3.

Bachoura et al. review ulnar tunnel syndrome. They describe the anatomy, causes, diagnostic tests, and treatment of ulnar tunnel syndrome. They conclude that UTS is less common than carpal tunnel or cubital tunnel syndrome, and that the cause is usually a compressive space-occupying lesion or repetitive trauma.

Subin et al. described a case of ulnar tunnel syndrome in which they utilized an MRI in order to diagnose a ganglion within Guyon's canal. Historically, the exact cause of ulnar nerve entrapment was determined during surgical exploration. They conclude that MRI can be a useful diagnostic method to determine the cause of compression in UTS.

Chen et al. review ulnar tunnel syndrome. They state that the condition is well-described but rare, and that paresthesias in the ulnar nerve distribution may be due to ulnar tunnel syndrome, cubital tunnel syndrome, or C8 radiculopathy. They conclude that in the case of anything other than mild disease, surgery is the mainstay of treatment.

Incorrect answers:
Answer 1: Zone 1 injury would present as mixed motor/sensory.
Answer 3: Zone 3 injury would present as isolated sensory.
Answer 4: Zone 4 does not exist. Guyon's canal has 3 zones.
Answer 5: There is adequate information in the question stem to determine that an isolated motor ulnar tunnel syndrome exists; thus. zone 2 is the affected zone.