Ulnar Nerve Entrapment
What is it: The ulnar nerve travels along the ulnar side of the hand and thru Guyon's canal, which is just ulnar to the more commonly known carpal tunnel. It also runs through the hook of the hamate.
How does it present: Compression of the ulnar nerve can occur at Guyon's canal with activities that provide pressure or repetitive trauma to this area, such as cycling and operating a jack hammer. Compression of the nerve can also occur with fractures of the hook of the hamate. These fractures may occur with the above conditions, but will more commonly occur with a force that hits that portion of the hand, such as a when a hockey player checks someone with their stick in their hand, a golfer hits an immovable force such as the ground instead of hitting the golf ball, or a baseball player hits a ball with the bat. In these cases, the patient may present with ulnar sided hand pain and numbness or paresthesias into the fifth finger and ulnar side of the fourth finger. In the case of acute trauma, there may also be mild swelling or bruising present.
Common exam findings: In the case of entrapment at Guyon's canal, a Tinel's Test at Guyon's canal may reproduce symptoms of paresthesias to the fourth and fifth digits. In the case of fractures of the hook of the hamate, the patient may have swelling and tenderness over the site of the hook of the hamate, and palpation of this region may increase paresthesias as well. In addition to testing for the sensory component, the ulnar nerve innervates the intrinsic muscles of the hand, which can be tested by having the patient cross their index and middle fingers.
Tests and treatment: Compression of the ulnar nerve at Guyon's canal can be made clinically. An EMG may be considered in difficult cases, but may not always be reliable. In appropriate cases, x-rays of the wrist can be done to evaluate for fractures of the hook of the hamate. A carpal tunnel view or ulnar oblique view of the wrist is necessary to visualize fractures of the hook of the hamate. Hook of the hamate fractures may need to be treated operatively to remove the compressing fragment and should be considered for referral to orthopedics. Compression of the nerve at Guyon's canal may be treated by avoiding the aggravating activity and splinting. In resistant cases, referral to orthopedics for consideration of surgical decompression can be made.