A 72-year-old man with a history of osteoporosis presents with right hip pain after a mechanical fall. Plain radiographs of the pelvis show no obvious fracture line, but there is subtle loss of the normal trabecular pattern in the femoral neck. The patient is unable to bear weight and has severe pain on internal rotation. What is the most appropriate next investigation to confirm the diagnosis?

Explanation

## Diagnosis of Occult Femoral Neck Fracture ### Clinical Scenario Analysis This patient presents with classic features of a femoral neck fracture: - High-risk demographics (elderly, osteoporotic) - Mechanism of injury (mechanical fall) - Clinical signs (inability to bear weight, severe pain on internal rotation) - Radiographic suspicion (loss of trabecular pattern) However, plain radiographs are inconclusive—a common presentation in non-displaced or stress fractures. ### Why MRI is Superior **Key Point:** MRI is the gold standard for detecting occult femoral neck fractures when plain radiographs are negative or inconclusive. It can detect fractures within 24 hours of injury with near-perfect sensitivity. **High-Yield:** In elderly patients with high clinical suspicion and inconclusive plain X-rays, MRI should be obtained urgently. Delaying diagnosis increases the risk of: - Displacement of non-displaced fractures - Avascular necrosis (AVN) due to disruption of blood supply - Prolonged immobility and associated complications (DVT, pneumonia) **Mnemonic: FRACTURE DETECTION PRIORITY — MRI First** - **M**RI: Most sensitive (>95%), detects early - **R**epeat X-rays: Delayed (2 weeks), not recommended - **I**maging: CT useful for surgical planning, not diagnosis - **C**linical: High suspicion warrants advanced imaging immediately ### Timeline of Radiographic Changes ```mermaid flowchart TD A[Femoral neck fracture occurs]:::outcome --> B[Day 0-2: Plain X-ray may be negative]:::action B --> C{High clinical suspicion?}:::decision C -->|Yes| D[MRI immediately]:::action C -->|No| E[Conservative follow-up]:::action D --> F[Fracture confirmed]:::outcome E --> G[Repeat X-ray in 2 weeks]:::action G --> H[Fracture line visible]:::outcome ``` **Clinical Pearl:** Waiting 2 weeks for repeat radiographs in a patient with high clinical suspicion is inappropriate and dangerous. By then, a non-displaced fracture may have displaced, complicating treatment and worsening prognosis. ### Why Other Options Are Suboptimal | Investigation | Why Not Ideal | |---|---| | Repeat plain X-rays in 2 weeks | Delays diagnosis; fracture may displace in interim; increases AVN risk | | DEXA scan | Assesses bone density, not acute fracture diagnosis; not indicated for acute trauma | | CT with 3D reconstruction | Useful for surgical planning in confirmed fractures; less sensitive than MRI for non-displaced fractures | **Tip:** In the exam, any question about occult or non-displaced femoral neck fracture with inconclusive plain films → answer MRI. This is high-yield for NEET PG. [cite:Campbell's Operative Orthopaedics 13e Ch 56; Harrison 21e Ch 333]