Ulnar nerve and ulnar artery
Mnemonic
“Ulnar nerve and ulnar artery”, and nothing else.
Boundaries: the pisiform medially, the hook of hamate laterally, the flexor retinaculum as the floor and the volar carpal ligament as the roof.
“Guyon’s canal is superficial to the flexor retinaculum; the carpal tunnel is deep to it.” That single relation explains why carpal tunnel syndrome spares the ulnar nerve, and why the two syndromes are distinct.
Ulnar tunnel syndrome causes clawing of the ring and little fingers with sensory loss on the ulnar side of the palm, but spares the dorsum of the hand, because the dorsal cutaneous branch arises proximal to the wrist. That sparing distinguishes a canal lesion from a lesion at the elbow.
Causes include a ganglion, hook of hamate fracture, ulnar artery thrombosis and prolonged pressure, classically handlebar palsy in cyclists.
Expansion
Guyon’s canal (the ulnar canal) transmits:
- Ulnar nerve
- Ulnar artery
It lies superficial to the flexor retinaculum, between the pisiform and the hook of hamate, separate from the carpal tunnel.