A 65-year-old postmenopausal woman falls on her outstretched hand while walking. X-ray shows a distal radius fracture with dorsal displacement and dorsal angulation of the distal fragment. What is the most common mechanism of injury in this type of fracture?

## Colles Fracture: Mechanism of Injury **Key Point:** Colles fracture is the most common distal radius fracture, accounting for approximately 90% of all distal radius fractures in elderly patients. The classic mechanism is a fall on an outstretched hand (FOOSH) with the wrist in dorsiflexion and the forearm pronated. ### Mechanism Breakdown The typical scenario involves: - **Wrist position:** Dorsiflexed (extended) - **Forearm position:** Pronated - **Force direction:** Axial loading through the extended wrist - **Result:** Dorsal displacement and dorsal angulation of the distal fragment **High-Yield:** The pronated forearm position is crucial — it prevents the forearm from rotating to absorb the impact, concentrating force on the distal radius. This is why Colles fractures are so common in elderly patients who fall forward onto outstretched hands. ### Clinical Pearl The classic "dinner fork deformity" seen on lateral X-ray is pathognomonic for Colles fracture and results from the dorsal displacement and angulation caused by the FOOSH mechanism with dorsiflexion and pronation. ### Contrast with Smith Fracture Smith fracture (reverse Colles) occurs with a fall on a palmar-flexed wrist or direct blow to the dorsal forearm, resulting in volar (palmar) displacement — the opposite mechanism and appearance.