A 65-year-old woman falls on her outstretched hand with the wrist in dorsiflexion. X-ray shows a fracture of the distal radius with dorsal displacement of the distal fragment and dorsal angulation. Which single radiographic feature best distinguishes this injury from a Smith fracture?

## Distinguishing Colles from Smith Fracture ### Key Radiographic Features **Key Point:** The direction of angulation and displacement of the distal radial fragment is the PRIMARY discriminator between Colles and Smith fractures. | Feature | Colles Fracture | Smith Fracture | |---------|-----------------|----------------| | **Mechanism** | Fall on dorsiflexed wrist | Fall on flexed wrist (reverse Colles) | | **Distal fragment angulation** | Dorsal angulation ("dinner fork" deformity) | Volar (palmar) angulation | | **Distal fragment displacement** | Dorsal displacement | Volar displacement | | **Direction of deformity** | Dorsal (backward) | Volar (forward) | | **Ulnar styloid involvement** | Common (50–60%) | Less common | | **Age group** | Elderly (osteoporotic bone) | Younger patients, high-energy trauma | ### Clinical Pearl **High-Yield:** The **dorsal angulation and dorsal displacement** seen on lateral X-ray is pathognomonic for Colles fracture. This creates the classic "dinner fork" deformity when viewed from the side. In contrast, Smith fracture shows **volar angulation** — the opposite direction. ### Mnemonic **DORSAL = Colles** (Dorsal displacement = Colles) **VOLAR = Smith** (Volar displacement = Smith) ### Why This Matters Both fractures involve the distal radius, both may involve the ulnar styloid, and both may be comminuted. However, the **direction of the distal fragment** (dorsal vs. volar) is the single most reliable radiographic discriminator and determines the mechanism of injury and reduction technique. [cite:Rockwood & Green's Fractures in Adults Ch 11]