When is it appropriate to x-ray the thumb?

When to X-ray the Thumb

X-ray the thumb immediately when there is focal tenderness over bony structures (metacarpal or phalanx), visible deformity, significant mechanism of injury, or clinical suspicion of fracture or dislocation following trauma. 1

Initial Clinical Assessment

When evaluating acute thumb trauma, obtain x-rays if any of the following are present:

• Focal bony tenderness over the metacarpal, proximal phalanx, or distal phalanx 1
• Visible deformity or gross malalignment 1
• Significant mechanism of injury (motor vehicle accident, crush injury, high-force trauma) 1
• Joint instability on examination, particularly at the metacarpophalangeal (MCP) joint suggesting ligamentous injury with possible avulsion fracture 2
• Penetrating injury to the thumb 1
• Unreliable examination due to altered mental status, intoxication, or inability to cooperate 1

Standard Radiographic Protocol

When x-rays are indicated, obtain a minimum 3-view examination including:

• Posteroanterior (PA) view 3
• True lateral view 3
• Oblique view (externally rotated) 3

A true anteroposterior view of the thumb is essential—lack of this view is the most frequent reason for missed thumb fractures (71% of diagnostic errors). 4 Some centers include a PA view of the entire hand, while others focus on the injured digit alone. 3

Common Pitfalls to Avoid

• Never accept only 2 views—this is inadequate for detecting thumb fractures 3
• Never accept poor quality radiographs—superimposition or improper positioning leads to missed or misdiagnosed fractures 4
• Do not rely solely on radiographs for ulnar collateral ligament (UCL) injuries—MRI has 100% sensitivity and 94-100% specificity for detecting Stener lesions and complete UCL tears 1

When Initial X-rays Are Normal But Clinical Suspicion Remains High

If radiographs are negative but you strongly suspect a fracture based on:

• Persistent focal tenderness over the thumb metacarpal or phalanx
• Mechanism consistent with fracture
• Inability to bear load through the thumb

Consider MRI without IV contrast rather than immobilizing and repeating x-rays in 10-14 days. 3 This approach prevents unnecessary immobilization of the 76% of patients who don't have fractures. 5

Special Considerations for Ligamentous Injuries

For suspected UCL or radial collateral ligament (RCL) injuries:

• Obtain stress radiographs if >30° angulation or ≥3mm palmar subluxation is suspected 2
• MRI is ideal for evaluating complete ligament tears, Stener lesions, and surgical planning 1
• Ultrasound can identify Stener lesions by showing absence of the UCL and presence of a hypoechoic mass proximal to the metacarpal tubercle 1

Avulsion fractures with >2mm diastasis or >30-45° fragment rotation on conventional x-ray warrant surgical consultation. 2

Advanced Imaging Indications

CT is rarely indicated for acute thumb metacarpal or phalangeal fractures 3, but may be useful for:

• Complex intra-articular fractures requiring surgical planning 6
• Evaluation when MRI is contraindicated

MRI without IV contrast is the preferred advanced imaging when:

• Initial x-rays are negative but clinical suspicion remains high 3
• Tendon injury assessment is needed 1
• Ligamentous injury requires characterization for surgical planning 1