How to immobilize a suspected scaphoid fracture with normal X-ray and unavailable MRI?

Immobilization of Suspected Scaphoid Fracture with Normal X-ray

For a 15-year-old boy with suspected scaphoid fracture after a FOOSH injury with tenderness in the anatomical snuffbox and normal X-rays, immobilization should be done with a short arm thumb spica cast until definitive diagnosis can be established, ideally with MRI.

Clinical Assessment and Diagnosis

The clinical presentation strongly suggests a scaphoid fracture:

• Fall on outstretched hand (FOOSH) mechanism
• Tenderness in the anatomical snuffbox
• Pain on active range of motion
• Normal initial X-rays

This presentation represents a classic "clinical scaphoid fracture" scenario, where radiographs are negative but clinical suspicion remains high. The scaphoid is the most common carpal bone fracture, representing 70% of carpal bone fractures 1.

Immediate Management Algorithm

1. Initial Immobilization: Apply a short arm thumb spica cast that immobilizes the wrist and the first metacarpophalangeal joint while leaving the interphalangeal joint free

2. Advanced Imaging: Arrange for MRI as soon as possible

   • MRI is superior to bone scan, CT, or ultrasound for both ruling in and ruling out scaphoid fractures in patients with normal initial X-rays 1
   • If MRI is unavailable in the short term, maintain immobilization until follow-up

3. Follow-up: Schedule follow-up within 7-10 days if MRI cannot be obtained immediately

Evidence-Based Rationale

The ACR Appropriateness Criteria strongly supports MRI as the preferred next study for suspected occult fractures when initial radiographs are negative 2. MRI without IV contrast can detect fractures of the carpal bones with high sensitivity and can lead to changes in diagnosis in 55% of patients and changes in management in 66% of patients 2.

While the traditional approach has been to immobilize and repeat radiographs in 10-14 days, this results in unnecessary immobilization for many patients 3. However, given that MRI is unavailable in this case, proper immobilization is essential to prevent displacement of a potential fracture.

Immobilization Technique Details

• Type of Cast: Short arm thumb spica cast
• Position: Wrist in slight extension (10-20 degrees)
• Coverage: From below the elbow to the interphalangeal joint of the thumb, including the first metacarpal
• Thumb Position: Slight abduction and opposition
• Duration: Until definitive diagnosis (ideally with MRI) or for 10-14 days if advanced imaging remains unavailable

Common Pitfalls to Avoid

1. Inadequate immobilization: Failure to include the thumb in the cast may allow movement at the scaphoid, risking displacement of an occult fracture

2. Over-reliance on negative X-rays: Plain radiographs are insufficient to rule out scaphoid fractures in patients with suggestive mechanism and radial-sided tenderness 1

3. Delayed diagnosis: Prolonged immobilization without definitive diagnosis can lead to unnecessary disability and loss of productivity 3

4. Missing alternative diagnoses: MRI and CT have the added benefit of identifying alternative causes of post-traumatic wrist pain 1

The absence of snuffbox tenderness has a negative likelihood ratio of 0.15, making it useful to rule out scaphoid fracture, but its presence (as in this case) is not specific enough to confirm the diagnosis without further imaging 1.

For this adolescent patient with a suspected scaphoid fracture, proper immobilization with a thumb spica cast is crucial until definitive diagnosis can be established with MRI to prevent potential complications like nonunion or avascular necrosis.