What is the assessment and treatment approach for suspected ligamentous damage to the thumb from a laceration?

Assessment of Ligamentous Damage to Thumb from Laceration

Begin with plain radiographs (2-3 views including oblique) to exclude fracture or avulsion fragments, followed by direct physical examination of ligament stability—if the laceration allows direct visualization of the ligament, this provides definitive diagnosis; otherwise, stress testing should be performed looking for lack of a definite endpoint rather than comparing to the contralateral side. 1, 2

Initial Imaging Assessment

• Obtain radiographs first to detect fracture fragments or bony avulsions that may accompany ligamentous injuries 1
• Most thumb fractures are visible on 2-view radiographic examination, though adding an oblique projection increases diagnostic yield 1
• Large fracture fragments may require open reduction and internal fixation, making their detection critical 1
• Radiographs detect osseous avulsions at ligament insertion sites, which change surgical management 1

Physical Examination for Ligament Integrity

The key clinical finding for complete ligament rupture is the absence of a definite endpoint on stress examination, not comparison to the opposite thumb 2

• In 34% of normal individuals, there is ≥10° difference between right and left thumbs in extension, and 22% show ≥10° difference in flexion 2
• Comparison with the uninjured contralateral thumb is unreliable in many individuals due to normal asymmetry 2
• Test in both extension and 30° of flexion to assess different portions of the collateral ligament complex 2

Direct Visualization Through Laceration

• If the laceration provides direct access to the ligament, direct visualization is the most definitive assessment method 3, 4
• Look for complete disruption, partial tears, or avulsion from insertion sites 3
• Assess for Stener lesion configuration (retracted ligament with interposed adductor aponeurosis) if examining the ulnar collateral ligament 1

Advanced Imaging When Diagnosis Remains Unclear

MRI Without Contrast

MRI is the gold standard for soft tissue assessment when physical examination is equivocal or the wound does not permit adequate visualization 1

• MRI demonstrates 100% sensitivity and specificity for thumb ulnar collateral ligament tears 1
• Sensitivity of 100% and specificity of 94% for detecting displaced ulnar collateral ligament tears (Stener lesions) 1
• MRI is ideal for surgical planning as it shows the level of ligament retraction, quality of the ligament stump, and associated injuries 1
• Can identify Stener lesions where the adductor aponeurosis becomes interposed between the ruptured ligament and its insertion site 1

Ultrasound

• US can identify Stener lesions by showing absence of the ulnar collateral ligament and presence of a hypoechoic mass proximal to the metacarpal tubercle 1
• Dynamic examination demonstrates the relationship of the aponeurosis to the retracted ligament stump 1
• Operator-dependent and requires experienced technician 1

Critical Management Considerations

• Severe collateral ligament disruption causing joint instability requires surgical treatment 5
• Untreated complete ligament tears can result in chronic instability, contractures, or joint laxity 1
• Type C injuries (joint instability from severe collateral ligament disruption) require surgical intervention rather than conservative management 5

Common Pitfall

Do not rely on side-to-side comparison for stress testing, as normal anatomic variation makes this unreliable—instead, assess for presence or absence of a firm endpoint 2