A 68-year-old woman from Delhi falls on her outstretched hand while climbing stairs. She presents to the emergency department with severe pain and swelling over the dorsal aspect of the wrist. On examination, the wrist shows a characteristic 'dinner fork' deformity. X-ray confirms a fracture of the distal radius with dorsal angulation and dorsal displacement of the distal fragment. Which of the following best describes the mechanism of injury in this fracture?

Explanation

## Colles Fracture: Mechanism and Pathophysiology **Key Point:** Colles fracture is the most common fracture of the distal radius, accounting for approximately 90% of all distal radius fractures. It occurs when a person falls on an outstretched hand (FOOSH injury) with the wrist in dorsiflexion and supination. ### Mechanism of Injury **High-Yield:** The classic mechanism is: 1. Fall on outstretched hand (FOOSH) 2. Wrist in **dorsiflexion** (extended backward) 3. Forearm in **supination** (palm facing upward) 4. This position causes the distal radius to fracture with dorsal displacement and dorsal angulation ### Clinical Presentation | Feature | Colles Fracture | |---------|------------------| | **Deformity** | 'Dinner fork' (dorsal prominence) | | **Mechanism** | FOOSH with dorsiflexion + supination | | **Displacement** | Dorsal and radial | | **Angulation** | Dorsal angulation | | **Typical patient** | Elderly with osteoporosis; young patients with high-energy trauma | ### Anatomical Basis When the wrist is dorsiflexed and supinated during a fall: - The distal radius bears the brunt of the axial load - The dorsal cortex is compressed, leading to dorsal comminution - The distal fragment is displaced dorsally and radially - This creates the pathognomonic 'dinner fork' appearance on lateral X-ray **Clinical Pearl:** The 'dinner fork' deformity is visible both clinically (on examination) and radiographically (on lateral view). This is the hallmark sign that distinguishes Colles from other distal radius fractures. **Mnemonic:** **FOOSH-DS** = Fall On Outstretched Hand with Dorsiflexion and Supination → Colles fracture with Dorsal displacement and Dinner fork deformity. ### Contrast with Smith Fracture Smith fracture occurs with the opposite mechanism: - Fall on **palmar-flexed** wrist (flexed forward) - Forearm in **pronation** (palm facing downward) - Results in **volar (palmar) displacement** — 'reverse dinner fork' appearance [cite:Rockwood and Green's Fractures in Adults Ch 13]