Which nerve is compressed in Guyon's canal?

• A. Ulnar nerve
• B. Median nerve
• C. Radial nerve
• D. Axillary nerve

Answer: (A)

The nerve compressed in Guyon's canal is the ulnar nerve. Guyon's canal is a narrow passage at the wrist formed by the pisiform and hook of the hamate, through which the ulnar nerve (and the ulnar artery) travels. When this nerve is compressed there, the motor fibers to most intrinsic hand muscles (via the deep branch) and the sensory fibers to the ulnar side of the hand can be affected, leading to numbness in the little finger and half of the ring finger and weakness of finger abduction/adduction due to interossei weakness and impaired intrinsic hand function. Causes include repetitive trauma or a nearby ganglion cyst. The other nerves listed don’t pass through Guyon’s canal (median nerve is through the carpal tunnel, radial and axillary nerves traverse different regions), so they aren’t the ones compressed there.