A 24-year-old female cyclist falls on her outstretched left hand. Plain radiographs show a scaphoid waist fracture without obvious displacement. Clinical examination reveals tenderness in the anatomical snuffbox. The initial radiographs appear normal on standard views. Which investigation is most appropriate to confirm the diagnosis and assess for occult fracture?

Explanation

## Investigation of Choice for Occult Scaphoid Fracture ### Why MRI is Superior for Early Occult Scaphoid Fractures **Key Point:** MRI is the investigation of choice for detecting occult scaphoid fractures in the acute setting when clinical suspicion is high but plain radiographs are negative. **High-Yield:** MRI advantages in occult scaphoid fracture: - Detects fractures within 24–48 hours (before radiographic visibility) - Shows bone marrow edema at the fracture site - Assesses soft tissue injury (ligaments, cartilage) - Guides early immobilization and prevents complications - Sensitivity >95% for acute fractures ### Clinical Context: Why Early Detection Matters **Clinical Pearl:** Scaphoid fractures have high morbidity if missed: 1. **Nonunion risk** — up to 12% if untreated 2. **Avascular necrosis (AVN)** — proximal pole has tenuous blood supply 3. **Post-traumatic arthritis** — intra-articular fracture 4. **Carpal instability** — if associated ligament injury missed Early diagnosis via MRI allows timely immobilization and prevents these complications. ### Comparison of Investigations for Occult Scaphoid Fracture | Investigation | Sensitivity (Acute) | Timing | Cost | Clinical Use | |---|---|---|---|---| | **MRI** | >95% | 24–48 hrs | High | **Gold standard for occult fracture** | | **CT (thin-slice)** | 90–95% | 24–48 hrs | Moderate | Alternative if MRI unavailable | | **Repeat X-rays (10–14 days)** | 100% | 10–14 days | Low | Delayed diagnosis; allows bone resorption | | **Bone scintigraphy** | 95% | 72+ hrs | Moderate | Delayed; low specificity | **Mnemonic: MRI-FAST** — **M**agnetic **R**esonance **I**maging **F**inds **A**cute **S**caphoid **T**rauma ### Why MRI Over CT in This Case **Key Point:** Although CT with thin-slice protocol also has high sensitivity, MRI is preferred because: 1. It shows bone marrow edema (earliest sign of fracture) 2. It assesses associated soft tissue injury (scapholunate ligament) 3. No radiation exposure (important in young female) 4. Superior for detecting nondisplaced fractures **Warning:** Do NOT wait 10–14 days for repeat radiographs in a clinically suspicious case — this delays diagnosis and increases risk of complications.