Ulnar nerve lesions
The ulnar nerve arises from the brachial plexus and supplies most of the intrinsic muscles of the hand.
Most injuries occur at the elbow, although open wounds can arise anywhere. The ulnar nerve passes down the anterior medial aspect of the upper arm and wraps posteriorly round the medial epicondyle of the humerus where it is vulnerable to fracture of the elbow or chronic pressure. It enters the hand on the ulnar side, and can be damaged by pressure or lacerations at the wrist.
Low lesions (at wrist): There is wasting of all the small muscles of the hand except the thenar eminence and there is a clawing of the ring and little fingers. Sensation is lost over the ulnar one and a half fingers.
High lesions (at elbow): The claw deformity is less due to paralysis of the ulnar side of flexor digitorum profundus.
If the ulnar nerve is severed, repair is may be attempted, stretching can be avoided by transposing the nerve to the front of the elbow. Failure of recovery can be overcome by tendon transfer. Nerve entrapment is treated with decompression and transposition of the nerve.