Scapholunate dissociation

Background

• Caused by rupture of scapholunate ligament
  • Most commonly injured ligament of the wrist
• Injury most commonly occurs from FOOSH

Clinical Features

• Pain/swelling on radial side of wrist
• "Clicking" sensation with wrist movement

Diagnosis

Black arrow: Scapholunate joint space widening; White arrow: Cortical ring sign

Dorsal intercalated segment instability

Imaging

• A grip compression view or wrist in ulnar deviation may be necessary in addition to PA/lateral views
• Any of the following signs may be seen:
  • Widening of the scapholunate joint space >3mm
    • Know as Terry-Thomas sign (or David Letterman sign)
  • Rotary subluxation of the scaphoid
    • Lateral view: Scapholunate angle >60 degrees
    • PA view: Cortical ring sign (circular cortex of the bone is more prominent)
  • Dorsal intercalated segment instability
    • Dorsal angulation of lunate relative to radius resulting in capitolunate angle > 20°
    • Seen as loss of the normal collinear arrangement of the capitate, lunate, and radius

Differential Diagnosis

Carpal Dislocations

• Lunotriquetral ligament instability
• Scapholunate dissociation
• Perilunate and lunate dislocations

Carpal fractures

AP view

• Scaphoid fracture
• Lunate fracture
• Triquetrum fracture
• Pisiform fracture
• Trapezium fracture
• Trapezoid fracture
• Capitate fracture
• Hamate fracture

Treatment

• Radial gutter splint or forearm volar splint
• Ortho referral

Disposition

• Generally outpatient followup