A 28-year-old construction worker sustains a wrist injury from a fall at height. Clinical examination reveals tenderness in the anatomical snuffbox, positive scaphoid compression test, and pain on radial deviation. Imaging is being planned. What is the most common mechanism of injury in scaphoid fractures?

## Most Common Mechanism of Scaphoid Fracture **Key Point:** Fall on outstretched hand (FOOSH) with wrist dorsiflexion and radial deviation is the most common mechanism of scaphoid fracture, accounting for >90% of cases. ### Mechanism of Injury Analysis | Mechanism | Frequency | Pathophysiology | |-----------|-----------|------------------| | **FOOSH (dorsiflexion + radial deviation)** | >90% | Load transmitted through radial-sided wrist; compressive and shear forces at scaphoid waist | | Direct dorsal blow | <5% | Rare; usually causes other carpal injuries | | Crush injury | <3% | Uncommon; more likely to cause multiple carpal fractures | | Hyperextension alone | <2% | Insufficient force; radial deviation component is critical | ### Biomechanics of FOOSH Injury **High-Yield:** The classic FOOSH mechanism involves three simultaneous components: 1. **Wrist dorsiflexion** — extends the wrist backward 2. **Radial deviation** — deviates the wrist toward the thumb side 3. **Axial load** — compressive force through the forearm This combination creates maximum compressive and shear stress at the scaphoid waist, the narrowest part of the bone. ### Why Radial Deviation Is Critical **Clinical Pearl:** The radial deviation component is essential. Dorsiflexion alone (without radial deviation) rarely causes scaphoid fracture. The combination of dorsiflexion + radial deviation aligns the scaphoid perpendicular to the direction of force, maximizing stress concentration. ### Common Clinical Scenarios - **Sports injuries:** Fall during volleyball, basketball, skiing, or gymnastics - **Occupational injuries:** Fall from height in construction workers - **Motor vehicle accidents:** Bracing against dashboard or steering wheel - **Pedestrian injuries:** Fall onto outstretched arm **Mnemonic:** **FOOSH = Fall On OutStretched Hand** — the classic mechanism in >90% of scaphoid fractures. Remember: **Dorsiflexion + Radial Deviation = Scaphoid stress.**