Does a clear X-ray (XR) and computed tomography (CT) scan rule out an occult fracture in a patient with persistent pain in the anatomic snuff box following a fall onto an outstretched hand (FOOSH) injury?

Management of Persistent Anatomic Snuff Box Pain After Normal XR and CT

Despite negative X-ray and CT findings, an occult fracture cannot be ruled out in a patient with persistent anatomic snuff box pain following a FOOSH injury, and MRI without contrast is recommended as the next imaging study to definitively exclude an occult scaphoid fracture. 1, 2

Why Further Imaging is Necessary

• Negative radiographs may miss 20-30% of scaphoid fractures, even with dedicated scaphoid views 2
• CT has excellent visualization of cortical and trabecular bone detail (94.4% sensitivity, 100% specificity) but may still miss certain occult fractures 2
• Persistent anatomic snuff box tenderness is highly sensitive for scaphoid fracture, warranting further investigation despite negative initial imaging 3

Recommended Diagnostic Algorithm

1. Initial assessment: Persistent anatomic snuff box tenderness following FOOSH injury with negative X-ray and CT suggests possible occult fracture

2. Next imaging study: MRI without contrast

   • Highest sensitivity for detecting occult fractures (19-37% in patients with normal initial X-rays) 2
   • Can detect bone marrow edema and subtle fracture lines not visible on X-ray or CT 1
   • More sensitive for bone bruises and soft-tissue injuries than CT 1

3. Alternative if MRI unavailable/contraindicated: Bone scan

   • High sensitivity but lower specificity than MRI or CT 1, 2
   • Can reliably exclude occult scaphoid fracture 1
   • Typically positive 1-2 weeks after injury 1

Management While Awaiting Further Imaging

• Immobilize with a short arm-thumb spica cast or splint until definitive diagnosis is established 2
• Early MRI is more cost-effective than prolonged immobilization and serial radiographs for suspected occult fractures 2

Important Clinical Considerations

• The scaphoid is particularly vulnerable to avascular necrosis due to its tenuous blood supply, making early diagnosis crucial
• Missed scaphoid fractures can lead to significant morbidity including nonunion, malunion, and post-traumatic arthritis
• CT may be preferable for specific circumstances like suspected hook of hamate fractures, but MRI has superior overall sensitivity for occult wrist fractures 1

Pitfalls to Avoid

• Relying solely on initial radiographs and CT when clinical suspicion remains high
• Failing to obtain dedicated scaphoid views on initial X-rays (carpal tunnel or semipronated oblique projection) 2
• Delaying appropriate immobilization while awaiting definitive diagnosis
• Using ultrasound as primary diagnostic tool (low sensitivity 47%, specificity 61%) 2

By following this evidence-based approach, you can minimize the risk of missing an occult fracture and optimize patient outcomes in terms of morbidity, mortality, and quality of life.