UlnarNerv

The ulnar nerve, or nervus ulnaris, is a peripheral nerve of the upper limb arising from the medial cord of the brachial plexus (ventral rami C8–T1). It runs medially along the arm, passing posterior to the medial epicondyle of the humerus, then enters the forearm by passing between the two heads of the flexor carpi ulnaris. It continues between the flexor carpi ulnaris and the flexor digitorum superficialis, giving motor branches to the flexor carpi ulnaris and the medial half of the flexor digitorum profundus.

In the wrist, the ulnar nerve travels through Guyon’s canal between the pisiform and the hook of the hamate, where it splits into a superficial sensory branch and a deep motor branch. The superficial branch provides sensation to the medial one and a half digits on both the palmar surface and the corresponding part of the dorsum. The deep motor branch innervates most intrinsic hand muscles, including the interossei, the medial two lumbricals, the hypothenar muscles (including abductor digiti minimi and flexor digiti minimi brevis), the adductor pollicis, and the deep head of the flexor pollicis brevis.

Functions of the ulnar nerve include motor control of many intrinsic hand muscles needed for finger abduction, adduction, and precision grip, as well as sensory perception over the medial hand. Clinically, the nerve is susceptible to entrapment at the elbow (cubital tunnel syndrome) and at the wrist (Guyon’s canal). Symptoms may include numbness in the little finger and ring finger, weakness of finger abduction/adduction, and, in advanced cases, a characteristic ulnar claw deformity. Diagnosis relies on clinical examination and electrodiagnostic testing.