Claw Hand

Etiology

Anything that may lead to ulnar nerve palsy can cause claw hand. Ulnar nerve palsy can arise from a laceration anywhere along its course. Proximal injuries to the medial cord of the brachial plexus may also present with sensory loss distally. Ulnar nerve palsies can also be due to cubital tunnel syndrome and ulnar tunnel syndrome. These are compression neuropathies at the elbow and wrist. Another cause of ulnar nerve palsy may be a failure to splint the hand in an intrinsic-plus posture following a crush injury. There are a few systemic diseases that may also lead to ulnar nerve palsy. These include leprosy, syringomyelia, and Charcot-Marie-Tooth disease. However, these systemic diseases usually involve more than one nerve.[5][6]

When a claw hand results, it is usually due to paralysis of the lumbricals.

Epidemiology

Claw hand can be congenital or acquired. Men are more likely to acquire the condition than women, but the congenital form of claw hand is distributed evenly among both sexes. There are no racial or ethnic preferences for claw hand.

Pathophysiology

Pathoanatomic components relate to the imbalance between the extrinsic and intrinsic muscles. Weakened intrinsic muscles lead to a loss of MCP flexion and a loss of interphalangeal (IP) extension. Strong extrinsic muscles will lead to an unopposed extension of the MCP joints. The flexor digitorum profundus and flexor digitorum superficialis muscles not innervated by the ulnar nerve remain strong and lead to unopposed flexion of the PIP and DIP joints.

History and Physical

The initial presentation will include a decrease in normal hand function. 

The MCP joints will be hyperextended, and the IP joints flexed.

The second and third digits will not be as involved as the fourth and fifth digits with a true ulnar nerve palsy. This is because the median nerve innervates the lumbricals involving the second and third digits, and the ulnar nerve innervates the lumbricals involving the fourth and fifth digits.

The patient may also exhibit functional weakness while attempting a grasp, grip, or pinch.

A provocative test for claw hand is bringing the MCP joints into flexion. This will correct the DIP and PIP joint deformities.

Several other specific tests for ulnar nerve palsy include:

• Froment sign: Hyperflexion of the thumb IP joint while attempting to pinch. This indicates a substitution of flexor pollicis longus (innervated by median nerve) for adductor pollicis (innervated by ulnar nerve).
• Jeanne sign: Reciprocal hyperextension of the thumb MCP joint indicating substitution of flexor pollicis longus (FPL) for adductor pollicis.
• Wartenberg sign: Abduction of the small finger at MCP joint indicating deficient palmar intrinsic muscle (innervated by ulnar nerve) with abduction from extensor digiti minimi (innervated by the radial nerve).
• Duchenne sign: Clawing of the ring and small fingers, hyperextension of MCP joints, and flexion of PIP joints indicating deficient interosseous and lumbrical muscles of the ring and small fingers.

Evaluation

Electromyographic and nerve conduction velocity studies are used to evaluate the ulnar nerve pathology and to rule out other diagnoses.[7][8]

Treatment / Management

Nonoperative management is applied if a fixed flexion contracture of more than 45 degrees occurs at the PIP joint. A strenuous hand therapy program is utilized involving serial casting.[9][10]

Exercises that strengthen the interosseous muscles and lumbricals are recommended. The individual should be taught to exercise each finger and thumb in abduction and adduction motion while the hand is pronated. In addition, the MCP and ICP joints should be exercised, and over time the interosseous and lumbricals will gain strength.

The majority of cases will need operative management in the form of contracture release and passive tenodesis versus active tendon transfer. This treatment is reserved for those patients with a progressive deformity that is affecting their quality of life. The goal is to prevent lasting MCP joint hyperextension.

• Surgery is usually in the form of tendon transfers. This addresses issues including the lack of thumb adduction and lateral pinch, the claw deformity of the fingers that impairs object acquisition, and the loss of ring and small finger flexion. 
• The extensor carpi radialis brevis or the flexor digitorum superficialis is the most commonly used transfers to restore thumb adduction. The brachioradialis can be used if the extensor carpi radialis brevis is required for an intrinsic reconstruction of the fingers. 
• To correct the claw deformity of the fingers, include static procedures or dynamic transfers. A dynamic transfer uses the flexor digitorum superficialis, extensor carpi radialis longus, extensor carpi radialis brevis, or flexor carpi radialis as a donor muscle.
• To restore the ring and small finger extrinsic muscle function, a transfer of flexor digitorum profundus ring and small to flexor digitorum profundus middle is performed.

Differential Diagnosis

Differential diagnosis of a claw hand should include:

• Cervical radiculopathy
• Dupuytren contracture
• Klumpke paralysis
• Lower brachial plexopathy.

Prognosis

The prognosis depends on the type and extent of nerve injury. For mild nerve injury, recovery is possible, but if the nerve was transected, recovery is rare. Even those who recover may require prolonged hand rehabilitation and may never regain full strength of the hand muscles. Poor prognostic factors include:

• Advanced age
• Coexisting diabetes
• Absent sensory response
• Muscle atrophy

Some studies do not show much improvement even after transposition of the ulnar nerve.

Complications

• More complications occur after intrinsic tendon transfers than adductor-plasty because of the unique balance of the extensor hood mechanism.
• The transfer may not be suitable if the chosen muscle has insufficient strength or excursion. Elongation is also a problem with sewing the transfer into the lateral bands of the extensor hood.
• Tendon transfers that are not strong enough can be treated with a therapy program to strengthen the muscle but often require surgical revision.
• The transfer may also not be suitable if the chosen muscle has too much strength or too short of the excursion. When the transfer is sewn too tightly into the lateral band, it can produce a swan-neck deformity of the digit.
• Tendon transfers that are too tight or too strong can be treated with a passive range of motion therapy to allow stretching to occur.