## Most Common Site of Scaphoid Fracture **Key Point:** The waist (middle third) of the scaphoid is the most common site of fracture, accounting for approximately 60–70% of all scaphoid fractures. ### Anatomical Distribution | Site | Frequency | Clinical Significance | |------|-----------|----------------------| | **Waist (middle third)** | 60–70% | Most common; moderate blood supply; intermediate healing risk | | Proximal pole | 20–25% | Poorest blood supply; highest non-union rate (up to 50%) | | Distal pole | 10–15% | Best blood supply; lowest non-union rate; best prognosis | | Tubercle | <5% | Rare; usually avulsion injuries | ### Why the Waist is Most Common 1. **Biomechanics of FOOSH injury:** The force is transmitted through the radial wrist, and the waist bears the greatest shear stress during dorsiflexion and radial deviation. 2. **Anatomical vulnerability:** The waist is the narrowest part of the scaphoid, making it mechanically weaker. 3. **Blood supply gradient:** While the waist has moderate vascularity (retrograde flow from distal and proximal branches), it is a transition zone where healing is slower than the distal pole but faster than the proximal pole. **High-Yield:** Remember the **"60-20-10 rule"** for scaphoid fracture distribution: - 60% waist - 20% proximal pole - 10% distal pole - 10% other (tubercle, comminuted) **Clinical Pearl:** Proximal pole fractures have the worst prognosis due to retrograde blood supply; distal pole fractures have the best prognosis due to robust antegrade supply. Waist fractures occupy the middle ground and represent the majority of clinical cases. ### Healing and Non-union Risk Non-union rates correlate inversely with blood supply: - Proximal pole: 10–50% non-union - Waist: 5–12% non-union - Distal pole: <5% non-union [cite:Rockwood & Green's Fractures in Adults Ch 9]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.