## Mechanism of Colles Fracture **Key Point:** Colles fracture is the most common distal radius fracture, characterized by dorsal angulation and dorsal displacement of the distal fragment. It occurs when the wrist is in **extension** at the moment of impact. ### Pathophysiology When a person falls on an outstretched hand (FOOSH injury) with the wrist in extension: 1. The dorsal cortex of the distal radius bears the brunt of the compressive force 2. The radius fractures and the distal fragment is driven dorsally and angulates dorsally 3. This creates the characteristic "dinner fork" deformity on lateral X-ray ### Clinical Features of Colles Fracture | Feature | Details | |---------|----------| | **Mechanism** | FOOSH with wrist in extension | | **Deformity** | Dorsal angulation (dinner fork sign) | | **Displacement** | Distal fragment displaced dorsally | | **Associated injury** | Ulnar styloid fracture (50–60%) | | **Age group** | Elderly with osteoporosis; young with high-energy trauma | **High-Yield:** The position of the wrist at the moment of impact determines the fracture pattern: - **Extension** → Colles (dorsal angulation) - **Flexion** → Smith (volar angulation) ### Contrast: Smith Fracture Smith fracture occurs with a fall on outstretched hand in **flexion**, resulting in volar (palmar) angulation and displacement—the reverse of Colles. It is less common than Colles but more common in younger patients. **Clinical Pearl:** Colles fracture is the most common distal radius fracture overall, accounting for ~90% of all distal radius fractures in the elderly population. The mechanism (FOOSH in extension) is the defining feature that distinguishes it from Smith fracture.
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