Correct Answer: A. A
The carpal bone most commonly fractured after a fall on an outstretched hand (FOOSH injury) is the scaphoid (navicular). This occurs in approximately 60–70% of all carpal bone fractures in the Indian population. The scaphoid's anatomical position at the radial wrist, combined with its role as the primary load-bearing bone during wrist extension and radial deviation, makes it vulnerable to direct compressive forces transmitted through the palm during FOOSH. The mechanism involves axial loading through the thumb and index finger, which concentrates force on the scaphoid's waist or proximal pole. Clinically, patients present with radial-sided wrist pain, swelling in the anatomical snuffbox, and loss of grip strength. The diagnosis is confirmed by X-ray (scaphoid views: PA, lateral, and 45° pronated oblique), though early fractures may be radiographically occult and require CT or MRI. The scaphoid's retrograde blood supply (entering distally) places proximal pole fractures at high risk for avascular necrosis (AVN) if untreated, making early recognition and immobilization critical in Indian orthopaedic practice.
Why the other options are wrong
B. D — Option D likely represents the lunate, which is the second most common carpal fracture but accounts for only 10–15% of cases. Lunate fractures typically occur with high-energy wrist dorsiflexion injuries or in association with perilunate dislocations, not isolated FOOSH. The lunate is more protected by surrounding carpal bones and is not the primary load-bearing bone in typical FOOSH mechanisms. C. B — Option B likely represents the triquetrum, which is fractured in only 5–10% of carpal injuries, usually from direct dorsal wrist trauma or ulnar-sided FOOSH. Triquetral fractures present with ulnar-sided pain and are far less common than scaphoid fractures. NBE may include this to test knowledge of carpal fracture distribution patterns. D. C — Option C likely represents the capitate or hamate, which are rarely fractured in isolation from FOOSH (< 5% incidence). These central carpal bones are protected by surrounding structures and typically fracture only with high-energy crush injuries or complex carpal dislocations, not simple FOOSH mechanisms.
High-Yield Facts
- Scaphoid fractures account for 60–70% of all carpal bone fractures and are the most common carpal injury after FOOSH.
- Anatomical snuffbox tenderness is the cardinal clinical sign of scaphoid fracture; pain on axial loading of the thumb is highly sensitive.
- Scaphoid blood supply is retrograde (distal to proximal), making proximal pole fractures prone to avascular necrosis if immobilization is delayed.
- Scaphoid fractures may be radiographically occult in the first 10–14 days; CT or MRI is indicated if clinical suspicion is high despite negative initial X-rays.
- Immobilization duration varies: non-displaced waist fractures require 8–12 weeks in a thumb spica cast; proximal pole fractures require 12–16 weeks or surgical fixation.
- Lunate is the second most common carpal fracture (10–15%), followed by triquetrum (5–10%); capitate and hamate fractures are rare in isolation.
Mnemonics
FOOSH → Scaphoid (Memory Hook) Fall On Outstretched Straight Hand → Scaphoid. The radial-sided load-bearing position of the scaphoid makes it the primary target in FOOSH injuries. Carpal Fracture Frequency (SALT) Scaphoid (60–70%), Avoid lunate (10–15%), Less triquetrum (5–10%), Tiny capitate/hamate (< 5%). Helps rank carpal fractures by incidence in Indian orthopaedic practice.
NBE Trap
NBE may pair scaphoid with "lunate" or "capitate" to test whether students confuse the most common carpal fracture with the most common carpal dislocation (lunate) or with central carpal bones. The trap is assuming all carpal injuries are equally distributed rather than recognizing scaphoid's anatomical vulnerability in FOOSH.
Clinical Pearl
In Indian emergency departments, any patient with radial wrist pain and snuffbox tenderness after FOOSH should be immobilized in a thumb spica cast immediately, even if X-rays are negative—delayed diagnosis of scaphoid fractures is a common cause of preventable avascular necrosis and chronic wrist disability in young working-age Indians.
_Reference: Bailey & Love Ch. 40 (Wrist & Hand Injuries); Rockwood & Green's Fractures in Adults, Ch. 8 (Carpal Fractures)_