Courtesy: Prof Nabil Ebraheim, University of Toledo, Ohio, USA

Ulnar Claw Hand

Definition

Ulnar claw hand is an abnormal hand posture caused by injury to the ulnar nerve, most commonly from a distal (low) ulnar nerve lesion.

It is characterized by clawing of the:

• Ring finger (4th digit)
• Little finger (5th digit)

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Clinical Features

The deformity becomes most obvious when the patient attempts finger extension.

Typical posture includes:

• Hyperextension at the MCP joints
• Flexion at the PIP and DIP joints

The deformity predominantly affects:

• Ring finger
• Little finger

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Pathophysiology

The deformity results from paralysis of:

• Interossei muscles
• Ulnar two lumbricals (4th and 5th digits)

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Normal Function of These Muscles

The intrinsic muscles normally:

• Flex the MCP joints
• Extend the IP joints

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Mechanism of Clawing

Loss of intrinsic muscle function produces imbalance between intrinsic and extrinsic muscles.

This results in:

• Unopposed Extensor Digitorum Communis (EDC)
  • Causes MCP hyperextension
• Unopposed Flexor Digitorum Profundus (FDP)
  • Causes flexion at PIP and DIP joints

The final posture is the classic claw deformity.

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Low vs High Ulnar Nerve Lesion

Low Ulnar Nerve Lesion

Location

• Wrist-level lesion

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Findings

The FDP to the ring and little fingers remains intact.

Features include:

• More prominent clawing
• Preserved sensation over dorsum of hand

This occurs because the dorsal cutaneous branch is spared.

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Clinical Memory Aid

“Low lesion = more clawing”

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High Ulnar Nerve Lesion

Location

• Above elbow

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Findings

The FDP to the ring and little fingers is also paralyzed.

Features include:

• Less clawing deformity
• Loss of sensation over dorsum of hand

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Ulnar Paradox

Despite being a more severe lesion, the clawing appears less obvious because the FDP is weak.

This is called the:

• Ulnar paradox

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Clinical Memory Aid

“High lesion = less clawing”

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Why the Index and Middle Fingers are Spared

The lumbricals to the:

• Index finger
• Middle finger

are supplied by the median nerve.

These lumbricals maintain:

• MCP flexion
• IP extension

Therefore, clawing is prevented in these digits.

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Comparison with Intrinsic Minus Hand

Ulnar Claw Hand

Features

• Only ring and little fingers affected
• Due to ulnar nerve injury

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Intrinsic Minus Hand (True Claw Hand)

Features

• All fingers affected
• Represents generalized intrinsic muscle loss

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Causes

Common causes include:

• Volkmann ischemic contracture
• Compartment syndrome
• Charcot-Marie-Tooth disease
• Leprosy
• Improper splinting after trauma

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Key Biomechanical Concept

The claw deformity occurs because of:

• Weak intrinsic muscles
• Strong extrinsic muscles

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Muscle Imbalance

Extensor Digitorum Communis (EDC)

• Produces MCP hyperextension

FDP and FDS

• Produce flexion of PIP and DIP joints

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Final Hand Posture

The characteristic deformity consists of:

• MCP hyperextension
• PIP and DIP flexion

primarily involving the ring and little fingers.