## Investigation of Choice for Occult Neck of Femur Fracture ### Clinical Context When plain radiographs are inconclusive or negative in a patient with clinical signs and symptoms highly suggestive of neck of femur fracture, **MRI is the gold standard** for detecting occult fractures. ### Why MRI? **Key Point:** MRI has 100% sensitivity for detecting femoral neck fractures, even when plain radiographs are negative. It is superior for detecting non-displaced and stress fractures. **High-Yield:** MRI can detect fractures within 24–48 hours of injury, whereas plain radiographs may take 10–14 days to show callus formation in some cases. This makes MRI the fastest confirmatory test when clinical suspicion is high. ### Comparison of Imaging Modalities | Investigation | Sensitivity for Occult Fracture | Cost | Availability | Time to Diagnosis | |---|---|---|---|---| | Plain radiographs | 60–90% (misses non-displaced) | Low | Immediate | Variable (10–14 days for callus) | | CT scan | 95–98% | Moderate | Good | Minutes to hours | | MRI | 100% | High | Limited | 24–48 hours | | Bone scan | 85–90% | Moderate | Limited | 3–5 days | | Ultrasound | 70–80% | Low | Operator-dependent | Minutes | ### Clinical Pearl In elderly patients with high clinical suspicion (pain, inability to bear weight, external rotation deformity) and negative plain radiographs, **MRI should be obtained within 48 hours** to confirm diagnosis and guide early surgical intervention, which reduces complications (avascular necrosis, non-union) and improves outcomes. ### Mechanism of Detection MRI detects bone marrow edema (T2 hyperintensity) at the fracture site before callus formation occurs on plain radiographs, making it ideal for early diagnosis of occult fractures. 
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