U01.11.006 Distortions of the hand

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Learning Objectives

  • Explain the biomechanical basis of “Clawing” versus “Benediction.”
  • Contrast the clinical presentations of proximal and distal nerve lesions.
  • Identify the characteristic atrophy associated with median and ulnar nerve damage.

1. The Mechanics of the Hand Distortions

A normal hand at rest maintains a balance between the extrinsic flexors/extensors and the lumbricals.

  • The Lumbrical Rule: These muscles normally flex the MCP and extend the PIP/DIP.
  • Clawing: When the lumbricals are paralyzed (distal lesion), the extrinsic extensors pull the MCP into extension, while the extrinsic flexors pull the PIP/DIP into flexion.
  • The Ulnar Paradox: In proximal lesions, the clawing is less pronounced because the extrinsic flexors (Flexor Digitorum Profundus) are also paralyzed, meaning the fingers can’t flex as tightly.

2. Ulnar and Median Nerve Lesion Summary

Clinical Sign Context Nerve Location Presentation
Ulnar Claw At Rest / Extending Distal Ulnar Hyperextension of MCP; flexion of 4th/5th digits.
Median Claw At Rest / Extending Distal Median Hyperextension of MCP; flexion of 2nd/3rd digits.
Hand of Benediction Making a Fist Proximal Median Inability to flex 2nd/3rd digits.
Trouble making a fist Making a Fist Proximal Ulnar Inability to flex the 4th/5th digits.

3. Muscular Atrophy

Long-term nerve compression or injury leads to visible wasting of the hand’s fleshy mounds.

  • Median Nerve: Causes atrophy of the thenar eminence (base of the thumb).
  • Ulnar Nerve: Causes atrophy of the hypothenar eminence (base of the pinky) and the interosseous spaces.

Clinical Notes & Corrections:

  • The “When” Matters: To differentiate these on the exam, always ask: Is the patient extending their fingers or making a fist?
  • Ape Hand: Note that a proximal median nerve injury will result in both “Ape Hand” (at rest) and “Hand of Benediction” (on fist-making).

Activity: Hand Distortion Challenge

Memory Hooks:

Distal = Claw: If the injury is Distant, you Display the claw.

Proximal = Power: If the injury is Proximal, you lose Power to make a fist.

Ulnar Paradox: The closer the lesion is to the hand, the worse it looks.

Activity