## Most Common Mechanism of Supracondylar Fracture **Key Point:** Fall on outstretched hand (FOOSH) with the elbow in extension accounts for approximately 90–95% of supracondylar fractures of the humerus. ### Mechanism of Injury When a child falls forward and instinctively extends the arm to break the fall, the force is transmitted along the long axis of the humerus. The supracondylar region, being the narrowest and weakest part of the distal humerus, fractures under this longitudinal compressive and hyperextension stress. ### Why This Mechanism Predominates 1. **Natural reflex:** Children instinctively extend their arms to cushion a fall 2. **Biomechanics:** The supracondylar region is a stress-riser zone—narrower than the condyles above and the shaft below 3. **Age factor:** Peak incidence is 5–8 years, when children are active and have incomplete skeletal maturity ### Associated Complications | Complication | Frequency | Clinical Significance | |---|---|---| | Anterior displacement | >95% | Stretches brachial artery | | Brachial artery injury | 10–20% | Pulseless hand, compartment syndrome risk | | Median nerve injury | 10–15% | Loss of pronation, thumb flexion | | Radial nerve injury | 2–5% | Wrist drop | | Compartment syndrome | 5–10% | Orthopedic emergency | **High-Yield:** The supracondylar region is vulnerable because it is the narrowest part of the distal humerus, making it a natural weak point under longitudinal stress. **Clinical Pearl:** Always assess for a pulseless hand and median nerve function (anterior interosseous nerve — thumb IP flexion) before and after reduction, as these are the most common neurovascular injuries in supracondylar fractures. [cite:Rockwood & Green's Fractures in Adults 9e Ch 27]
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