Ulnar tunnel syndrome

Ulnar tunnel syndrome, also known as Guyon's canal syndrome or Handlebar palsy, is ulnar neuropathy at the wrist where it passes through the ulnar tunnel (Guyon's canal). The most common presentation is a palsy of the deep motor branch of the ulnar nerve causing weakness of the interosseous muscles. Ulnar tunnel syndrome is usually caused by a ganglion cyst pressing on the ulnar nerve, other causes include traumas to the wrist and repetitive movements, but often the cause is unknown (idiopathic). Long distance bicycle rides are associated with transient alterations in ulnar nerve function. Sensory loss in the ring and small fingers is usually due to ulnar nerve entrapment at the cubital tunnel near the elbow, which is known as cubital tunnel syndrome, although it can uncommonly be due to compression at the wrist.

Causes
Ulnar neuropathy at the wrist is often associated with a mass such as a ganglion cyst or thrombosis or an aneurysm of the ulnar artery. The role of activities and exposure is less certain.

Classification


Ulnar tunnel syndrome may be characterized by the location or zone within the Guyon's canal at which the ulnar nerve is compressed. The nerve divides into a superficial sensory branch and a deeper motor branch in this area. Thus, Guyon's canal can be separated into three zones based on which portion of the ulnar nerve are involved. The resulting syndrome results in either muscle weakness or impaired sensation in the ulnar distribution. Zone 2 type syndromes are most common, while Zone 3 are least common.

Treatment
The role of gloves which help protect the ulnar nerve from compression is unclear. Palsy of the ulnar motor nerve isolated to the wrist is treated with operative decompression, often with concomitant ganglion excision. The surgery is to divide the volar carpal ligament which forms the roof of Guyon's canal, thereby reducing compression on the ulnar nerve.