What is a scapholunate injury?

Scapholunate Injury: Diagnosis and Management

A scapholunate injury is a tear or disruption of the scapholunate ligament complex that connects the scaphoid and lunate carpal bones in the wrist, representing the most common form of carpal instability. 1, 2

Anatomy and Pathophysiology

• The scapholunate ligament complex consists of dorsal, volar, and proximal components, with the dorsal portion being the most critical for stability of the scapholunate articulation 3, 4
• Injuries typically result from a fall on an outstretched hand, causing disruption of the ligament and potentially leading to carpal instability 5
• When left untreated, scapholunate injuries can progress to scapholunate advanced collapse (SLAC), a degenerative wrist condition 6, 2

Diagnostic Evaluation

Imaging Studies

• Initial evaluation should include conventional radiographs with careful positioning to assess for carpal malalignment 1, 3
• Key radiographic findings include:
  • Scapholunate diastasis >4 mm (widening between scaphoid and lunate)
  • Dorsal intercalated segmental instability (DISI) with dorsal tilt of the lunate >10° 1
• Advanced imaging options include:
  • CT arthrography: Highest sensitivity (nearly 100%), specificity, and accuracy for detecting scapholunate ligament tears 1, 3
  • MRI: Commonly used with sensitivities of 65-89% for scapholunate ligament tears, with 3T MRI providing better results 1, 3
  • MR arthrography: More accurate than non-contrast MRI for determining which specific segments of the ligament are torn 7
  • Ultrasound: High-frequency ultrasound with dynamic "clenched fist" maneuvers can detect tears of the dorsal band with sensitivity of 46-100% and specificity of 92-100% 1, 8, 3

Imaging Considerations

• CT arthrography and MR arthrography have similar accuracy for scapholunate ligament lesions 7
• CT arthrography may be more sensitive for tears of the biomechanically important dorsal ligament fibers compared to conventional MRI 7
• MRI and MR arthrography are more sensitive for diagnosis of extra-articular findings (like ganglion cysts and tendon disorders) that can cause radial-sided pain 7
• Ultrasound offers the advantage of real-time dynamic assessment but is highly operator-dependent 8

Classification and Staging

• Scapholunate injuries can be classified as:
  • Acute: Less than 6 weeks since injury, with potential for ligament healing 6
  • Chronic: More than 6 weeks since injury, when ligament healing is no longer possible 6
• Further classification includes:
  • Dynamic instability: Abnormal motion between scaphoid and lunate during stress but normal alignment at rest 2
  • Static instability: Persistent abnormal alignment visible on static radiographs 2
  • Reducible vs. non-reducible: Determines treatment options based on whether normal alignment can be restored 5

Treatment Approaches

• Treatment selection depends on the chronicity of the injury, degree of instability, and presence of arthritic changes 2
• For acute injuries, direct repair of the torn ligament is preferred, which can be performed through open or arthroscopic techniques 4, 9
• For chronic injuries with reducible instability, ligament reconstruction or tenodesis techniques may be used 6
• Arthroscopic techniques offer advantages of less soft tissue damage, preservation of blood supply, and potentially faster rehabilitation 5, 4

Common Pitfalls and Considerations

• Scapholunate injuries may be missed on initial presentation, leading to chronic instability and eventual degenerative changes 2
• Isolated scaphoid fractures can occasionally be associated with scapholunate ligament tears, requiring careful assessment 9
• The dorsal portion of the scapholunate ligament is the most critical for stability, and its repair or reconstruction should be prioritized 5, 4
• Dynamic imaging techniques (such as clenched fist views or stress maneuvers) may be necessary to detect subtle instability patterns 8, 3

Prognosis

• Early diagnosis and appropriate treatment of scapholunate injuries can prevent progression to degenerative arthritis 2
• Without treatment, scapholunate instability can lead to scapholunate advanced collapse (SLAC) wrist, a predictable pattern of degenerative arthritis 5, 2
• Outcomes are generally better with early intervention before the development of static instability or arthritic changes 9