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Scapholunate Dissociation
 Submitted by Jonathon Hill, MS IV

General Considerations

 

  • Loss of mechanical linkage between scaphoid and lunate
  • Usually relates to complete disruption of the scapholunate interosseous ligament (SLIL)
  • Rupture of SLIL most frequently results from fall onto an outstretched hand
  • Often associated with additional injuries
    • Displaced scaphoid fractures
    • Distal radial fractures
  • Scapholunate dissociation (SLD) represents first stage in spectrum of perilunate dislocations described by Mayfield et al
  • Rupture of the SLIL leads to varying degrees of
    • Volar flexion, ulnar deviation, and pronation of the scaphoid
    • Extension, supination, and radial deviation of the lunate and triquetrum
  • Dorsal intercalated segment instability (DISI) describes a dorsally extended position of lunate on lateral wrist radiographs, and is highly suggestive of SLIL injury 

 


Stability of the scapholunate joint is maintained primarily by the SLIL, in addition to many secondary stabilizers, including the volar carpal ligaments and the dorsal capsule.  Scapholunate dissociation is a spectrum of rotational abnormalities that is dependent on the severity of the injury and the resulting involvement of ligamentous abnormalities, and is one of the most common forms of carpal instability.  Carpal instability patterns may be classified as static or dynamic, based on the presence or absence of radiographically detectable abnormalities on routine studies.  Rupture of the SLIL alone typically results in dynamic scapholunate instability, requiring abnormal stress radiographs or motion studies to diagnose.  Rupture of at least one additional secondary stabilizer is necessary for static scapholunate diastasis to occur, evident on routine radiographic studies.
 

 

Clinical Findings

  • Complaints vary with severity of injury
  • Pain over the dorsoradial aspect of the wrist is common, often increased in dorsiflexion
  • Minimal or no edema
  • Grip strength weakness
  • Clicking or clunking of the wrist 

Imaging Findings

Frontal Conventional Radiographic Signs:

  • Terry Thomas Sign (AKA David Letterman sign)
    • Increased scapholunate joint space when compared to contralateral side
    • Any asymmetric gap measuring greater than 5 mm is diagnostic of SLD. 
  • Scaphoid Ring Sign
    • A radio-dense ring seen over the distal scaphoid representing rotary subluxation and foreshortening of the scaphoid
    • Only seen when ligaments attached to both ends of the scaphoid have failed, collapsing the scaphoid into flexion and pronation

Scaphoid Ring Sign (white arrow) (see text above)

Lateral Plain Film Signs

  • Increased Scapholunate Angle
    • Scapholunate angle-measured at an intersecting line between axis of lunate (which runs through the midpoints of the convex proximal and concave distal joint surfaces and can best be drawn by finding perpendicular to a line joining the distal palmar and dorsal borders of the bone) and axis of scaphoid (line through midpoints of its proximal and distal poles)
    • > 70 degrees suggestive of dorsal intercalated segment instability (DISI)
  • Palmar V sign
    • Seen when scaphoid is in abnormal flexion; normal “C”-shaped line formed by palmar margins of scaphoid and radius form an acute angle as palmar outline of scaphoid intersects outline of radial styloid, forming sharper “V”-shape

Differential Diagnosis

  • Kienböck disease
    • Condition of uncertain etiology that results in osteonecrosis of the carpal lunate
  • Preiser disease
    • Avascular necrosis of the scaphoid

 Treatment

  • Surgical repair of scapholunate interosseous ligament is usually required to prevent long-term complications
  • There are varying surgical approaches depending on the severity of the tear and involvement of secondary stabilizing ligaments

Complications

  • Complete SLIL rupture leads to significant changes in force transmission of the carpal bones and predisposes to degenerative changes of the carpus 
  • Cartilage degeneration
  • Loss of joint mobility
  • Scapholunate advanced collapse (SLAC)

 

Scapholunate Dissociation


Scapholunate Dissociation. There is increased distance of greater than 5 mm (black arrow) between the scaphoid (S) and the lunate (L) producing the so-called Terry Thomas or David Letterman sign.
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Lau, S., Swarna, S.S., Tamvakopoulos, G. (2009). Scapholunate dissociation: an overview of the clinical entity and current treatment options.  European Journal of Orthopaedic Surgery and Traumatology, 19, 377-385.

 

Manuel, J., Moran, S. (2007). The Diagnosis and Treatment of Scapholunate Instability. Orthopedic Clinics of North America, 38 (2), 226-277.

 

Pliefke, J., Stengel, D., Rademacher, G., Mutze, S., Ekkernkamp, A., Eisenschenk, A. (2008).  Diagnostic accuracy of plain radiographs and cineradiography in diagnosing traumatic scapholunate dissociation. The Journal of Skeletal Radiology, 37,139-145.

 

Resnick, D., & Kransdorf, M. (2004). Bone and Joint Imaging, 3rd edition. Elsevier/Saunders, (23), 1281-1288.

 

Taleisnik, J. (1988). Current Concepts Review: Carpal Instability. The Journal of Bone and Joint Surgery, 1262-1268.