Ulnar tunnel syndrome (Guyon canal)
This is the triangular canal at the base of the ulnar side of the palm. It is bordered laterally by the hook of the hamate and the transverse carpal ligament. The medial wall is formed by the pisiform and the attachments of the pisohamate ligament. Both the ulnar nerve and artery traverse the canal to enter the hand. The dorsal cutaneous branch of the ulnar nerve branches before the nerve enters the Guyon canal.
Causative factors include repeated blunt trauma from power tools and gripping or hammering with the palm of the hand. Fractures of the hook of the hamate can impinge on the nerve. Other etiologies include tumors such as ganglia or lipomas, anomalous muscle bellies, or hypertrophy of the palmaris brevis. Thrombosis or aneurysm of the artery may compress the nerve.
These may include numbness and tingling, paresthesias and pain in an ulnar distribution of the palm and the 1.5 digits of the ulnar aspect, cold intolerance in the ring and small fingers, normal sensation in the dorsal sensory cutaneous branch of the ulnar nerve, and a positive Tinel or Phalen sign.