## Investigation of Choice for Monteggia Fracture **Key Point:** Plain radiographs (AP, lateral, and oblique views) of the forearm are the gold standard for diagnosing Monteggia fractures and detecting the associated radial head dislocation. ### Why Plain Radiographs? **High-Yield:** A Monteggia fracture is defined as a fracture of the proximal or middle third of the ulna combined with an anterior dislocation of the radial head. This injury pattern is best visualized on standard orthogonal radiographs. 1. **Visualization of both components:** - Ulnar fracture (usually proximal or middle third) - Radial head dislocation (typically anterior) 2. **Multiple views optimize detection:** - **AP view:** Shows the radial head position relative to the capitellum - **Lateral view:** Demonstrates anterior radial head dislocation and ulnar fracture angulation - **Oblique views:** Clarify fracture lines and subtle dislocations **Clinical Pearl:** The radial head dislocation is sometimes missed on initial radiographs if only AP and lateral views are obtained. Oblique views increase sensitivity for detecting the dislocation. ### Monteggia Fracture Classification (Bado) | Type | Ulnar Fracture | Radial Head Dislocation | Frequency | |------|---|---|---| | Type I | Proximal/middle third | Anterior | 60% | | Type II | Proximal/middle third | Posterior | 15% | | Type III | Metaphyseal (distal ulna) | Anterior | 20% | | Type IV | Proximal radius + ulna | Anterior | 5% | **Mnemonic:** **MAPO** — **M**onteggia = **A**nterior (most common) radial head dislocation with **P**roximal/middle ulnar fracture **O**n plain radiographs. ### Why Other Investigations Are Not First-Line While CT or MRI may be used for surgical planning in complex cases or to assess soft tissue injury, they are not required for initial diagnosis. Plain radiographs are rapid, cost-effective, and diagnostic in the vast majority of cases. 
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