Which of the following is the primary mechanism of injury in a Smith fracture?

Explanation

## Smith Fracture: Mechanism of Injury **Key Point:** Smith fracture (reverse Colles) is a transverse fracture of the distal radius with **volar (palmar) displacement** of the distal fragment. The mechanism is fundamentally different from Colles fracture. ### Mechanism of Injury **High-Yield:** Smith fractures result from: 1. **Fall on outstretched hand (FOOSH) with the wrist in FLEXION** — the most common mechanism 2. **Direct volar blow** to the forearm or wrist 3. **Reverse FOOSH** — landing on the back of the hand with the wrist already flexed Both mechanisms drive the distal fragment volarly (palmward), opposite to Colles. ### Distinguishing Features from Colles | Aspect | Colles | Smith | |--------|--------|-------| | **Mechanism** | FOOSH + wrist dorsiflexion | FOOSH + wrist flexion OR direct volar blow | | **Distal fragment** | Dorsal + radial | Volar + ulnar | | **Deformity** | Dinner fork (dorsal bump) | Reverse dinner fork (volar bump) | | **Frequency** | 90% of distal radius fractures | 10% of distal radius fractures | | **Age group** | Elderly (osteoporosis) | Younger adults, higher energy trauma | ### Clinical Pearl **Clinical Pearl:** Smith fractures are sometimes called "reverse Colles" because the deformity is the opposite. They are less common than Colles but often result from higher-energy mechanisms or direct trauma. In younger patients with Smith fracture, always consider high-energy injury or direct assault. ### Radiographic Appearance On lateral radiograph, the distal fragment shows: - **Volar (palmar) angulation** — the distal fragment is flexed palmward - **Loss of dorsal cortex alignment** — the dorsal cortex is disrupted - **Volar prominence** — the distal fragment creates a "reverse dinner fork" silhouette [cite:Rockwood & Green's Fractures in Adults Ch 18]