The ulnar nerve is a peripheral nerve which originates at the brachial plexus from the medial cord of nerve roots C8 and T1. This nerve is the largest unprotected nerve of the human body, thus making it prone to injury.
The ulnar nerve runs along the medial aspect of the arm passing posteriorly to the medial epicondyle of the humerus, and entering the forearm deep to the aponeurosis of the flexor carpi ulnaris muscle, supplying this muscle as well as the medial half of the flexor digitorum profundus. It continues its descent running alongside the ulnar artery, than enters the hand passing under the Hook of Hamate, within the tunnel of Guyon.
A lesion to this nerve describes any pathological process capable of negatively affecting the nerve’s function.
Most of the intrinsic hand muscles are innervated by the ulnar nerve.
There are numerous causes and entrapment sites, which can affect the ulnar nerve.
- Klumpke paralysis
- Cubital tunnel syndrome
- Impact to the ulnar nerve at the medial epicondyle
- Excessive valgus stress at the elbow (throwing athletes)
- Compression by flexor carpi ulnaris
- Bony spurs at the olecranon and medial epicondyle
- Carpal bone dislocation
- Colles fracture
A common presentation for a patient suffering with a lesion to the ulnar nerve is weakness of the muscles supplied by that nerve. As the condition progresses, these muscles (refer to the â€œdefinitionâ€ section of this condition) may start to atrophy. The patient may also report altered sensations in the portion of the hand supplied by the ulnar nerve. Ulnar â€œclawâ€ hand may be appreciated.
The examination should involve sensory testing of the hand, observing the hand and forearm for any asymmetry, active muscle testing, percussion of the Tunnel of Guyon and flexor carpi radialis muscles, thorough case history taking to discriminate between the possible causes described above.