A 35-year-old man presents to the emergency department after a fall on an outstretched hand while playing cricket. Radiographs reveal a fracture of the proximal third of the radius with an anterior dislocation of the radial head. What is the most common mechanism of injury in Monteggia fractures?

## Monteggia Fracture: Mechanism of Injury **Key Point:** Monteggia fractures consist of a fracture of the proximal or middle third of the ulna combined with an anterior dislocation of the radial head. The mechanism is critical to understanding the injury pattern. ### Most Common Mechanism The most common mechanism of Monteggia fracture is a **fall on an outstretched hand (FOOSH) with the forearm in pronation**. This mechanism accounts for the majority of cases in both children and adults. **Why pronation matters:** - When the forearm is pronated and a fall occurs, the radial head is forced anteriorly - The pronator teres and other pronator muscles pull the radius forward - Simultaneously, the ulna fractures from the impact - This creates the classic anterior radial head dislocation pattern ### Mechanism-Injury Correlation | Mechanism | Radial Head Dislocation | Ulnar Fracture Site | Frequency | | --- | --- | --- | --- | | FOOSH + pronation | Anterior | Proximal/middle third | Most common | | Direct blow to posterior forearm | Posterior | Middle/distal third | Rare | | Hypersupination | Anterior | Variable | Uncommon | | Forced supination | Posterior | Distal third | Rare | **High-Yield:** The pronated position of the forearm at the time of injury is the key distinguishing factor that predisposes to anterior radial head dislocation in Monteggia fractures. **Clinical Pearl:** In children, Monteggia fractures often occur from falling on an outstretched pronated hand, whereas in adults, direct blows or motor vehicle accidents are also common mechanisms. ### Bado Classification Context - **Type I (60%):** Anterior radial head dislocation + proximal/middle ulnar fracture — from pronation injury - **Type II (15%):** Posterior radial head dislocation + ulnar fracture — from direct posterior blow - **Type III (20%):** Anterior radial head dislocation + metaphyseal ulnar fracture — usually in children - **Type IV:** Fracture of both radius and ulna with radial head dislocation — rare **Mnemonic:** **PROM** = **PR**onation → **O**steochondral **M**onteggia (anterior dislocation) [cite:Rockwood & Green's Fractures in Adults Ch 24]