The ulnar nerve can suffer injury anywhere between its proximal origin of the brachial plexus all the way to its distal branches in the hand. It is the most commonly injured nerve around the elbow. Although it can be damaged under various circumstances, it is commonly injured by local trauma or
physical impingement ("pinched nerve"). Injury of the ulnar nerve at different levels causes specific motor and sensory deficits.
At the elbow •
Common mechanisms of injury:
Cubital tunnel syndrome, fracture of the medial epicondyle of the humerus (causing direct ulnar nerve injury), fracture of the lateral epicondyle of the humerus (causing
cubitus valgus with tardy ulnar nerve palsy), Driver's Elbow •
Motor deficit: • Weakness in flexion of the hand at the wrist, loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand. (Note: Motor deficit is absent or very minor in
cubital tunnel syndrome as the ulnar nerve is
compressed in the cubital tunnel, rather than transected.) • Presence of a
claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the
metacarpophalangeal joints, and flexion at the
interphalangeal joints. • Weakness of adduction of the thumb, which may be assessed by the presence of
Froment's sign. •
Sensory deficit: Loss of sensation or
paresthesiae in ulnar half of the palm and dorsum of hand, and the medial 1½ digits on both palmar and dorsal aspects of the hand
At the wrist •
Common mechanism: penetrating wounds, Guyon canal cyst (and other lesions) •
Motor deficit: • Loss of flexion of ulnar half of digits, or the 4th and 5th digits, loss of ability to cross the digits of the hand. • Presence of a
claw hand deformity when the hand is at rest, due to hyperextension of the 4th and 5th digits at the
metacarpophalangeal joints, and flexion at the
interphalangeal joints. • The
claw hand deformity is more prominent with injury at the wrist as opposed to a lesion higher up in the arm, for instance, at the elbow, as the ulnar half of the
flexor digitorum profundus is not affected. This pulls the distal interphalangeal joints of the 4th and 5th digit into a more flexed position, producing a more deformed 'claw'. This is known as the
ulnar paradox. • Weakness of adduction of the thumb, which may be assessed by the presence of
Froment's sign. •
Sensory deficit: Loss of sensation or
paresthesiae in ulnar half of the palm, and the medial 1½ digits on the palmar aspect of the hand, with dorsal sparing. The dorsal aspect of the hand is unaffected as the posterior cutaneous branch of the ulnar nerve is given off higher up in the forearm and does not reach the wrist. In severe cases, surgery may be performed to relocate or "release" the nerve to prevent further injury. ==Additional images==