Scaphoid Fracture: Pathophysiology and Diagnosis

• The scaphoid bone, named for its boat-like shape (from the Greek "skaphos"), is the most frequently fractured carpal.
• Scaphoid fractures typically occur in men aged 20-30 due to high-impact injuries and roughly 10% involve another fracture.
• While scaphoid fracture diagnoses are uncertain, only ~10% of referred patients actually have one.

Pathophysiology

• The scaphoid is divided into the proximal pole, waist, and distal pole.
• The radial artery's branches supply blood, with the dorsal branch providing 80% and entering via the distal pole.
• Fractures can disrupt blood supply, leading to avascular necrosis (AVN) and wrist degeneration; proximal fractures pose a higher AVN risk.

Clinical Features

• Scaphoid fractures result from trauma, causing sudden wrist pain and potential bruising.
• Tenderness manifests in the anatomical snuffbox, scaphoid tubercle, and with thumb telescoping.

Anatomical Snuffbox

• The anatomical snuffbox is a triangular depression on the hand's dorsal side, at the carpal level.
• Laterally, it's defined by the abductor pollicis longus/extensor pollicis brevis tendons, and medially by the extensor pollicis longus tendon.
• The snuffbox contains the radial artery, superficial radial nerve, and cephalic vein.
• The floor includes the scaphoid, trapezium, and radial styloid; tenderness suggests a scaphoid fracture, but is not definitive.

Differential Diagnosis

• Alternative diagnoses for radial wrist pain after trauma include distal radial fracture, other carpal fractures, 1st metacarpal base fracture, ulnar collateral ligament injury, wrist sprain, or De Quervain's tenosynovitis.

Investigations

• Initial assessment involves plain radiographs, including anteroposterior, lateral, and oblique views of the scaphoid.
• Undisplaced fractures may not show on initial X-rays; if suspected, immobilize the wrist and repeat X-rays in 10-14 days.
• If repeat X-rays are negative but suspicion remains, an MRI is necessary for definitive diagnosis, with continued fracture management in the interim.

Managment

• Scaphoid fracture treatment depends on the fracture location and severity.
• Undisplaced fractures typically require immobilization with a thumb spica cast.
• Undisplaced proximal pole fractures have a high AVN risk, so surgery may be recommended, especially in the dominant hand of working-age individuals.
• Displaced fractures require surgical fixation, commonly with a percutaneous variable-pitched screw to compress the fracture.

Complications

• Avascular necrosis (AVN) occurs in ~30% of scaphoid fractures, more likely in proximal fractures.
• Non-union, or failure to heal, occurs in roughly 10% of cases, often from delayed diagnosis or improper management.
• Non-union is treated with internal fixation and bone grafts, but carries high morbidity even with surgery.

Key Points

• Scaphoid fractures are the most common carpal fracture, usually from falls on an outstretched hand.
• Diagnosis includes patient history, physical exam, and imaging.
• If initial X-rays are negative but clinical suspicion is high, treat conservatively and re-image in two weeks.
• Key complications include avascular necrosis and non-union.