Carpal instability

Luno-triquetral Dissociation

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Definition

Lunotriquetral dissociation refers to instability between the lunate and triquetrum, often due to ligamentous injury, resulting in altered wrist mechanics and pain.

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Epidemiology

• Less common than scapholunate dissociation.

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Anatomy

• Lunotriquetral Ligament:
  • Composed of dorsal, volar, and a weak interosseous part.
  • volar LT ligament thickest and strongest portion. Mcq ❓️
• Supporting Structures:
  • Dorsal Radiocarpal Ligament.
  • Long and Short Volar Radiolunate Ligaments.

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Etiology

1. Traumatic:
   • Axial loading with wrist extension and abduction.
2. Positive Ulnar Variance: Mcq ❓️
   • Can cause attritional lunotriquetral ligament injury.

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Pathophysiology

• Lunate: Flexes → Volar Intercalated Segment Instability (VISI).
• Triquetrum: Extends.
• Note: VISI may occur in uninjured wrists with ligamentous laxity, whereas DISI is always pathological.

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Clinical Presentation

• Symptoms:
  • Similar to scapholunate dissociation but localized to the dorsal and ulnar aspects of the wrist.
  • Pain aggravated by loading, extension, and ulnar deviation.
• Examination Findings:
  • Positive Lunotriquetral Shuck Test (Reagan test).
  • Positive Shear Test.
  • Variable Lunotriquetral Compression Test results.

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Imaging

X-rays:

• Similar to scapholunate imaging but with specific findings:
  • May appear normal in early stages.
  • Break in Gilula’s Arcs.
  • Scapholunate angle <30° (Normal: 30–60°).
  • Capitolunate angle may be abnormal.
  • Lunotriquetral overlap or triquetral proximal translation.
  • Positive ulnar variance may be evident.

CT and MRI:

• Useful for assessing ligament injuries and associated abnormalities.

Arthrography:

• May show abnormal dye flow between radiocarpal and midcarpal spaces.

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Differential Diagnosis

• Similar to scapholunate dissociation:
  • TFCC injuries.
  • Ulnar impaction syndrome.
  • Kienböck’s disease.

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Management

Acute Injury (<6 weeks)

1. Closed Reduction + Pinning.
2. Immobilization in a cast for 6 weeks.

Chronic Injury (>6 weeks)

1. Open Surgical Repair:
   • Lunotriquetral ligament reconstruction.
   • Capsulodesis or tenodesis techniques.
2. Salvage Procedures:
   • Partial wrist fusion (e.g., lunotriquetral fusion).
   • Total wrist fusion for severe instability or advanced degenerative changes.

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