Ulnar claw

An ulnar claw, also known as claw hand, or 'Spinster's Claw' is a deformity or an abnormal attitude of the hand that develops due to ulnar nerve damage causing paralysis of the lumbricals. A claw hand presents with a hyper-extension at the metacarpophalangeal joints and flexion at the proximal and distal interphalangeal joints of the 4th and 5th fingers. The patients with this condition can make a full fist but when they extend their fingers, the hand posture is referred to as claw hand. The ring- and little finger can usually not fully extend at the proximal interphalangeal joint (PIP). An ulnar claw, also known as claw hand, or 'Spinster's Claw' is a deformity or an abnormal attitude of the hand that develops due to ulnar nerve damage causing paralysis of the lumbricals. A claw hand presents with a hyper-extension at the metacarpophalangeal joints and flexion at the proximal and distal interphalangeal joints of the 4th and 5th fingers. The patients with this condition can make a full fist but when they extend their fingers, the hand posture is referred to as claw hand. The ring- and little finger can usually not fully extend at the proximal interphalangeal joint (PIP). This can be commonly confused with the 'Hand of benediction', which is caused by proximal (at elbow level) median nerve damage. Patients exhibiting an ulnar claw are also very frequently unable to spread (abduct) or pull together (adduct) the fingers against resistance. This occurs because the ulnar nerve also innervates the palmar and dorsal interossei of the hand. Patients with this deficit will become increasingly easy to identify over time as the paralysed first dorsal interosseous muscle atrophies, leaving a prominent hollowing between the thumb and forefinger. An ulnar claw may follow an ulnar nerve lesion which results in the partial or complete denervation of the ulnar (medial) two lumbricals of the hand. Since the ulnar nerve also innervates the 3rd and 4th lumbricals, which flex the MCP joints (aka the knuckles), their denervation causes these joints to become extended by the now unopposed action of the long finger extensors (namely the extensor digitorum and the extensor digiti minimi). The lumbricals and interossei also extend the IP (interphalangeal) joints of the fingers by insertion into the extensor hood; their paralysis results in weakened extension. The combination of hyperextension at the MCP and flexion at the IP joints gives the hand its claw like appearance. The ulnar nerve also innervates the ulnar (medial) half of the flexor digitorum profundus muscle (FDP). If the ulnar nerve lesion occurs more proximally (closer to the elbow), the flexor digitorum profundus muscle may also be denervated. As a result, flexion of the IP joints is weakened, which reduces the claw-like appearance of the hand. (Instead, the fourth and fifth fingers are simply paralyzed in their fully extended position.) This is called the 'ulnar paradox' because one would normally expect a more proximal and thus debilitating injury to result in a more deformed appearance.