Anatomical Basis of Claw Hand

Biomechanics and Pathophysiology

Claw hand is a deformity resulting from nerve damage affecting the intrinsic muscles of the hand. It primarily stems from ulnar nerve palsy, leading to hyperextension of the metacarpophalangeal (MCP) joints and flexion of the interphalangeal (IP) joints.

Anatomy Involved

Ulnar Nerve Function

The ulnar nerve supplies the majority of the intrinsic hand muscles, including the lumbricals (medial two), interossei, hypothenar muscles, and the adductor pollicis. Damage to this nerve results in impaired fine motor control and the characteristic claw-like appearance.

Muscle Contributions

• Lumbricals: Normally flex the MCP joints and extend the IP joints.
• Interossei: Assist lumbricals in fine motor movements.
• Extrinsic Flexors and Extensors: Overcompensate for intrinsic muscle loss, exacerbating the clawing.

Pathophysiology

Ulnar nerve injury disrupts the balance between extrinsic and intrinsic muscle forces, causing MCP hyperextension and IP joint flexion.

Clinical Presentation

• Permanent claw-like deformity of the medial two digits.
• Weakness in grip strength.
• Loss of fine motor skills.
• Atrophy of the hypothenar eminence.

Treatment and Management

Non-Surgical Approaches

• Physical therapy to strengthen remaining muscles.
• Splinting to maintain joint positioning.
• Nerve stimulation techniques.

Surgical Intervention

In severe cases, tendon transfers or nerve repair may be necessary to restore function.