A 28-year-old male construction worker presents to the emergency department after a fall onto his outstretched left arm while climbing scaffolding. He reports severe pain in the proximal forearm and inability to pronate/supinate the forearm. On examination, there is swelling over the proximal third of the forearm with a palpable deformity. X-rays reveal a fracture of the proximal third of the ulna with anterior angulation and an associated anterior dislocation of the radial head. What is the most likely diagnosis?

Explanation

## Diagnosis: Monteggia Fracture-Dislocation **Key Point:** A Monteggia fracture-dislocation is defined as a fracture of the proximal or middle third of the ulna combined with an anterior dislocation of the radial head. [cite:Rockwood & Green's Fractures in Adults Ch 25] **High-Yield:** The classic triad of Monteggia injury: 1. Fracture of the proximal/middle third of ulna 2. Anterior dislocation of the radial head 3. Mechanism: fall on outstretched hand (FOOSH) with forced pronation **Clinical Pearl:** The radial head dislocation is often missed on initial radiographs if the clinician focuses only on the ulnar fracture. Always check the radiocapitellar line on all forearm X-rays — it should pass through the center of the capitellum on all views. **Mnemonic:** **MONU** = **M**onteggia = **O**lna fracture + **N**ew (anterior) dislocation of **U**lna's companion (radius) ### Classification (Bado) | Type | Ulnar Fracture | Radial Dislocation | Frequency | Prognosis | |------|---|---|---|---| | I | Proximal/middle third | Anterior | 60% | Good with proper reduction | | II | Proximal/middle third | Posterior | 15% | Poorer; often missed | | III | Metaphyseal (distal) | Anterior | 20% | Better; usually stable | | IV | Radius AND ulna | Anterior | 5% | Complex; requires surgery | ### Management 1. **Closed reduction** of ulnar fracture first (restores length) 2. Radial head usually reduces spontaneously with ulnar reduction 3. If radial head remains dislocated → open reduction required 4. Immobilization: long-arm cast in supination (Type I) or pronation (Type II) for 8–12 weeks 5. Early mobilization after union to prevent stiffness **Warning:** Posterior dislocation (Type II) is frequently missed because the radial head may appear only slightly displaced on AP views. Always obtain lateral radiographs and maintain high clinical suspicion.