U01.11.021 Wrist and hand injuries

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Learning Objectives

  • Identify the anatomical boundaries and clinical causes of Guyon Canal Syndrome.
  • Explain the sensory and motor deficits in Carpal Tunnel Syndrome, specifically why thenar sensation is spared.
  • Correlate systemic conditions (e.g., pregnancy, hypothyroidism) with the development of median nerve entrapment.
  • Recognize the mechanism and presentation of a Boxer’s Fracture.

1. Guyon Canal Syndrome (Ulnar Nerve)

Also known as ulnar tunnel syndrome, this involves compression of the ulnar nerve as it passes between the pisiform and the hook of the hamate.

  • Classic Cause: Cyclists due to prolonged pressure on the handlebars (“Handlebar palsy”).
  • Traumatic Cause: Fracture of the hook of the hamate (e.g., from a golf club or baseball bat impact).
  • Presentation: Numbness/tingling in the ulnar 1.5 fingers and weakness of intrinsic hand muscles.

2. Carpal Tunnel Syndrome (Median Nerve)

This is the most common entrapment neuropathy, occurring when the median nerve is compressed beneath the flexor retinaculum (transverse carpal ligament).

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  • Clinical Signs:
    • Tinel Sign: Percussion of the wrist reproduces symptoms.
    • Phalen Maneuver: Flexing wrists to 90° for 60 seconds reproduces symptoms.
  • The “Sensation Paradox”: While the thenar eminence may atrophy (ape hand), sensation over the thenar eminence is spared because the palmar cutaneous branch of the median nerve passes superficial to the carpal tunnel.
  • Associated Conditions: Pregnancy (edema), Rheumatoid Arthritis, Hypothyroidism, Diabetes, and Dialysis-related amyloidosis (\beta_2 -microglobulin).

3. Metacarpal Neck Fracture (Boxer’s Fracture)

A fracture usually involves the neck of the 5th metacarpal, though the 4th can also be involved.

  • Mechanism: Direct trauma to a closed fist (e.g., punching a wall or a person).
  • Presentation: Loss of the 5th knuckle prominence, swelling, and reduced grip strength.

Clinical Notes & Step 1 Pearls:

  • Lunate Dislocation: Acute carpal tunnel syndrome can be caused by anterior dislocation of the lunate bone.
  • Amyloidosis: In patients on long-term hemodialysis, the buildup of \beta_2 -microglobulin often deposits in the carpal tunnel.
  • Hamate Hook: If a patient presents with ulnar nerve deficits after a fall or sports injury, always look for a fracture of the hook of the hamate on imaging.

Activity: Hand Injury Differential

Quick Mnemonics:

Carpal Tunnel: Tinel = Tapping; Phalen = Praying (inverted).

Guyon: Guyon = Going on a bike.

Boxer: 5th metacarpal (the pinky side takes the hit).

Activity: