Ulnar Claw Hand (Main en Griffe)

Definition

Ulnar claw hand is a deformity characterized by hyperextension at the metacarpophalangeal (MCP) joints and flexion at the proximal and distal interphalangeal (PIP and DIP) joints of the ring and little fingers (4th and 5th digits), resulting from ulnar nerve paralysis.

Dorsal, palmar, and lateral views of ulnar claw hand showing MCP hyperextension, IP flexion, hypothenar wasting, and interosseous hollowing

Anatomy and Pathophysiology

The deformity arises due to loss of intrinsic muscle function supplied by the ulnar nerve:

Muscle	Action Lost
Interossei (dorsal & palmar)	MCP flexion + IP extension
3rd and 4th lumbricals	MCP flexion + IP extension of ring & little fingers
Hypothenar muscles	Abduction/opposition of little finger
Adductor pollicis	Adduction of thumb

Mechanism:

Normally, the lumbricals and interossei flex the MCP joints and extend the IP joints
When the ulnar nerve is injured, these intrinsic muscles are paralyzed
Unopposed action of extensor digitorum communis (radial nerve) causes MCP hyperextension
Unopposed action of flexor digitorum superficialis and profundus (median/ulnar nerve) causes IP flexion
Result: the classic "claw" posture in the ring and little fingers

The Ulnar Paradox

More proximal ulnar nerve injuries produce LESS clawing

Level of Injury	Clawing
Wrist (distal)	Severe clawing of ring & little fingers
Elbow (proximal)	Milder clawing

Reason: In high (elbow-level) lesions, the flexor digitorum profundus (FDP) to ring and little fingers is also paralyzed. Without FDP, there is no force to maintain IP flexion, so the claw is less pronounced.

Causes

A. Traumatic

Fracture of medial epicondyle
Elbow dislocation
Fractures of the hamate/wrist

B. Compressive (Entrapment)

Cubital tunnel syndrome (elbow) — most common
Guyon's canal compression (wrist)

C. Infective

Leprosy — most common cause worldwide (bilateral claw hand due to ulnar + median nerve involvement) (Bailey & Love, p. 100)
Tuberculosis (cold abscess)

D. Vascular

Volkmann's ischemic contracture (associated)

E. Other

Cervical rib (thoracic outlet syndrome)
Cubitus valgus deformity (tardy ulnar nerve palsy) — late complication of malunited lateral condyle fractures (Bailey & Love, p. 505)

Clinical Features

Posture:

Clawing of ring and little fingers (hyperextended MCPs, flexed IPs)
Index and middle fingers relatively spared (supplied by median nerve lumbricals)

Wasting:

Hypothenar eminence wasting
Hollowing of interosseous spaces (dorsal guttering)
Flattening of the medial palm

Sensory Loss:

Little finger and medial half of ring finger (palmar and dorsal)
Medial aspect of palm (Guyon's canal lesion spares dorsum)

Motor Loss / Special Tests:

Froment's sign — patient grips paper between thumb and index; uses FPL (flexor pollicis longus) instead of adductor pollicis → thumb IP joint flexes
Wartenberg's sign — little finger abducted at rest (unopposed abductor digiti minimi)
Card test / Egawa's test — inability to abduct/adduct fingers

Differences: High vs. Low Ulnar Nerve Lesion

Feature	High (Elbow)	Low (Wrist)
FDP to ring & little finger	Paralyzed	Intact
Clawing severity	Less (ulnar paradox)	More severe
Sensory loss	Ring, little, medial forearm	Ring, little finger only
Hypothenar wasting	Yes	Yes
Flexor carpi ulnaris	Paralyzed	Intact

Management

Conservative

Splinting: Knuckle-bender splint — maintains MCP flexion to restore intrinsic-plus position
Physiotherapy and occupational therapy
Treat underlying cause (e.g., dapsone + MDT for leprosy)

Surgical

A. For the nerve:

Decompression (cubital tunnel release, Guyon's canal release)
Ulnar nerve transposition (anterior transposition at elbow)
Nerve repair/grafting for transection injuries

B. For the deformity (static correction):

Fowler's procedure — release of extensor mechanism at MCP level
Zancolli lasso procedure — FDS tendon looped through A1 pulley to flex MCP joint
Tendon transfers — e.g., FDS to lateral bands (Brand's procedure) to restore intrinsic function
Capsulodesis of MCP joints

Summary

Ulnar claw hand results from ulnar nerve palsy causing loss of intrinsic muscles (interossei + medial two lumbricals), leading to unopposed extrinsic flexion and extension producing clawing of the ring and little fingers. The ulnar paradox dictates that distal lesions cause more clawing than proximal ones. Management depends on the level and cause of the lesion, ranging from splinting and nerve decompression to tendon transfer procedures.

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