U01.11.005 Wrist region

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Learning Objectives

  • Memorize the eight carpal bones and their anatomical arrangement.
  • Explain the clinical risks of Scaphoid fractures, specifically avascular necrosis.
  • Identify the complications associated with Lunate dislocation and Hamate fractures.
  • Understand the boundaries and contents of the Carpal Tunnel and Guyon Canal.

1. Carpal Bone Anatomy

The wrist consists of eight bones arranged in two rows (proximal and distal).

  • Proximal Row (Lateral to Medial): Scaphoid, Lunate, Triquetrum, Pisiform.
  • Distal Row (Medial to Lateral): Hamate, Capitate, Trapezoid, Trapezium.
  • Anatomic Snuff Box: The Scaphoid is palpable here. Tenderness in this area after a fall is highly suggestive of a fracture.

 

2. Clinical Correlates: Fractures & Dislocations

Bone Involved Mechanism / Injury Clinical Complication
Scaphoid Fall on outstretched hand (FOOSH). Avascular necrosis and nonunion due to retrograde blood supply from the radial artery.
Lunate Traumatic dislocation. Acute Carpal Tunnel Syndrome via median nerve impingement.
Hamate Fracture of the hook of the hamate. Guyon Canal Syndrome (ulnar nerve compression).

3. The Carpal Tunnel vs. Guyon Canal

These two fibro-osseous tunnels house critical nerves and vessels passing into the hand.

  • Carpal Tunnel: Contains the Median Nerve and 9 tendons (FDS, FDP, and FPL).
    • Boundaries: Carpal bones (floor) and Flexor Retinaculum (roof).
  • Guyon Canal (Ulnar Canal): Contains the Ulnar Nerve and Ulnar Artery.
    • Location: Between the hook of the hamate and the pisiform.

Clinical Notes & Corrections:

  • Occult Fractures: A scaphoid fracture may not appear on an initial X-ray. If clinical suspicion is high (snuff box tenderness), the wrist should be splinted and re-imaged in 7–10 days.
  • Radial Artery: The blood supply to the scaphoid enters at the distal pole. This is why a fracture at the waist or proximal pole is so dangerous for the blood supply.

Activity: Wrist Anatomy Challenge

Memory Hooks:

Mnemonic: So Long To Pinky, Here Comes The Thumb.

TrapeziUM: Is by the ThUMB.

TrapezoID: Is Inside (medial to trapezium).

Activity: