Which of the following is the most common associated injury in a Colles fracture?

Explanation

## Associated Injuries in Colles Fracture **Key Point:** Ulnar styloid fracture is the most common associated injury in Colles fractures, occurring in 50–60% of cases. It results from the same high-energy mechanism and avulsion by the triangular fibrocartilage complex (TFCC). ### Frequency of Associated Injuries | Associated Injury | Frequency | Mechanism | | --- | --- | --- | | **Ulnar styloid fracture** | 50–60% | TFCC avulsion, same mechanism | | **Scaphoid fracture** | 5–10% | Compression during FOOSH | | **Anterior interosseous nerve (AIN) injury** | 1–2% | Rare; usually from fragment displacement or swelling | | **Posterior interosseous nerve (PIN) injury** | <1% | Very rare; dorsal swelling or fragment | | **Median nerve compression** | 5–10% | Acute swelling or displacement | **High-Yield:** The mnemonic "**CUPS**" for Colles fracture associations: **C**omminution, **U**lnar styloid fracture, **P**ain (severe), **S**welling (dorsal). ### Why Ulnar Styloid Fracture is Most Common 1. **Direct mechanism:** The FOOSH injury with supination causes the ulnar styloid to be avulsed by the TFCC attachment. 2. **Anatomical vulnerability:** The ulnar styloid is a thin, prominent bony projection with strong ligamentous attachments. 3. **Clinical significance:** Ulnar styloid fractures may lead to TFCC injury and chronic ulnar-sided wrist pain if not recognized. **Clinical Pearl:** Always assess for ulnar-sided wrist tenderness and perform the ulnar fovea sign (tenderness in the fovea between flexor carpi ulnaris and ulnar artery) to detect associated TFCC injury. ### Nerve Injuries in Colles Fracture - **AIN injury** (option 2) is rare (<2%) and usually occurs with severely displaced fragments or during reduction. - **PIN injury** (option 4) is extremely rare (<1%) and typically associated with dorsal swelling or posterior displacement. - Both are much less common than ulnar styloid fracture.