Which of the following is the most common mechanism of injury for a Smith fracture of the distal radius?

Explanation

## Smith Fracture: Mechanism of Injury **Key Point:** Smith fracture results from a fall on an outstretched hand with the wrist in **flexion**, not extension. This is the inverse mechanism of Colles fracture. ### Mechanism Details **High-Yield:** The mechanism is crucial for distinguishing Smith from Colles: - **Smith:** FOOSH with **wrist flexion** → volar angulation - **Colles:** FOOSH with **wrist extension** → dorsal angulation ### Why Flexion Causes Volar Displacement When the wrist is flexed during impact: 1. The force is transmitted through the flexed wrist 2. The distal fragment is driven **volarly** (anteriorly) 3. The distal fragment also shifts **ulnarly** 4. Results in "reverse dinner fork" deformity ### Clinical Scenarios - **Elderly patient:** Falls forward onto a flexed wrist (common in osteoporotic bone) - **Younger patients:** High-energy trauma with wrist in flexion - **Occupational:** Falls while trying to catch oneself with flexed wrist ### Comparison Table | Aspect | Smith | Colles | |--------|-------|--------| | **Mechanism** | FOOSH + flexion | FOOSH + extension | | **Distal fragment direction** | Volar + Ulnar | Dorsal + Radial | | **Deformity** | Reverse dinner fork | Dinner fork | | **Common age** | Elderly (osteoporosis) | Middle-aged to elderly | | **Associated injuries** | Anterior soft tissue damage | Posterior soft tissue damage | **Mnemonic:** **SMITH = Flexion** (remember: "Smile" = flexion of lips; Smith = flexion of wrist). **COLLES = Extension** (remember: "Colles" sounds like "calls" — reach out with extended arm).