A 32-year-old construction worker sustained a FOOSH injury 3 weeks ago. He was initially treated conservatively for suspected scaphoid fracture. Now he presents with persistent wrist pain, weakness of grip, and imaging shows a scaphoid fracture with delayed union. Which clinical feature best distinguishes scaphoid fracture from a fracture of the distal radius in terms of healing complications and long-term morbidity?

Explanation

## Healing Complications: Scaphoid vs. Distal Radius Fracture ### Avascular Necrosis—The Unique Threat to Scaphoid **Key Point:** Avascular necrosis (AVN) of the proximal pole is the most characteristic and discriminating complication of scaphoid fracture. This occurs in 5–12% of scaphoid fractures and is virtually pathognomonic to scaphoid injury among carpal bones, making it the best distinguishing feature. **High-Yield:** The scaphoid has a retrograde blood supply that enters through a single nutrient artery in the distal pole. Fractures of the proximal pole or waist interrupt this blood supply, leaving the proximal fragment avascular. This is why scaphoid fractures carry a much higher risk of AVN than distal radius fractures. ### Anatomical Basis ```mermaid flowchart TD A[Scaphoid Fracture]:::outcome --> B{Fracture Location}:::decision B -->|Proximal pole or waist| C[Blood supply disrupted]:::action B -->|Distal pole| D[Retrograde supply preserved]:::action C --> E[Proximal fragment becomes avascular]:::urgent E --> F[Avascular Necrosis develops]:::urgent D --> G[Healing proceeds normally]:::action ``` **Mnemonic:** **SCAPHOID AVN** = **S**ingle nutrient artery, **C**arpal bone, **A**vascular **P**roximal pole, **H**igh risk, **O**ccurs in 5–12%, **I**nterrupted blood flow, **D**istal pole spared ### Comparison Table: Scaphoid vs. Distal Radius Fracture Complications | Complication | Scaphoid Fracture | Distal Radius Fracture | |--------------|-------------------|------------------------| | **Avascular necrosis** | **5–12% (proximal pole)** | **Rare; distal radius is well-vascularized** | | Malunion | Possible but less common | Common (radial angulation, radial shortening) | | Post-traumatic OA | Occurs (late, secondary to AVN/malunion) | Common (intra-articular fractures) | | CRPS | Possible | Possible (similar incidence) | | Nonunion | 5–10% | Rare (good blood supply) | **Clinical Pearl:** AVN of the scaphoid proximal pole is often asymptomatic initially but leads to progressive collapse, scaphoid nonunion advanced collapse (SNAC) wrist, and severe osteoarthritis. This is why early diagnosis and immobilization are critical in scaphoid fractures. ### Why Scaphoid is Unique The scaphoid is the only carpal bone with a retrograde (distal-to-proximal) blood supply. Fractures that disrupt this single nutrient artery leave the proximal fragment without collateral circulation, making AVN a signature complication. Distal radius fractures, by contrast, have robust periosteal and intraosseous blood supply from multiple sources and rarely develop AVN. **Tip:** When a scaphoid fracture patient presents with persistent pain beyond 12 weeks, think AVN of the proximal pole and order advanced imaging (CT or MRI) to assess for early signs of collapse.