Fact-sheet: Scapholunate ligament tear SLAC


Updated on 10/02/2020 at 3:52 PM

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Definition

Severe carpal sprains with permanent "static" instability are detected on frontal and lateral radiographs of the wrist. CT arthrography of the wrist is what allows ligamentous assessment. Scapholunate instability is the most common and the most severe, as it progresses to osteoarthritis (SLAC wrist: ScaphoLunate Advanced Collapse):
  • styloid-scaphoid osteoarthritis (SLAC 1),
  • then radioscaphoid (SLAC 2)
  • and finally lunocapitate (SLAC 3)

Clinical features

Post-traumatic wrist pain.

Radiography

Dynamic frontal views, in ulnar deviation and with clenched fist, allow detection of a non-permanent scapholunate diastasis indicating "dynamic" instability.

Scapholunate instability:

On the frontal radiograph, look for:

  • scapholunate diastasis > 3 mm
  • scapholunate dissociation with dorsal tilt of the lunate, which is in extension (wide, square anterior horn visible), contrasting with flexion of the scaphoid, which "lies down" (ring sign due to projection of its anterior tubercle).
On the lateral radiograph, look for: dorsal tilt of the lunate in DISI with a scapholunate angle > 60°, loss of radius–lunate–capitate–M3 alignment (increased radiolunate and lunocapitate angles > 30°). Scapholunate instability progresses to osteoarthritis:
  • styloid-scaphoid osteoarthritis (SLAC 1),
  • then radioscaphoid (SLAC 2)
  • and finally lunocapitate (SLAC 3)

Ultrasound

Limited value

Allows assessment of the integrity of the scapholunate ligament (dorsal bundle) and, if needed, detection of another lesion (ligamentous, osseous, or tendinous).

CT

CT arthrography after opacification of the midcarpal and radiocarpal joints:

Excellent sensitivity for cartilage assessment. Rupture of the scapholunate ligament (dorsal bundle in particular). Assessment for signs of static SL instability (same as radiography). Evaluate posterior subluxation of the scaphoid using the posterior radioscaphoid angle (N < 101°, on a sagittal slice)

MRI

Most commonly (90%), the ligament has a "V" shape, particularly in its central portion. The linear appearance is less common. It is a homogeneous structure with low signal intensity (or intermediate signal in one-third of cases).
• Partial tear: focal thinning or area of fluid-like high signal intensity within one or both segments of the SLL (often palmar, as it is weaker).
• Complete tear: discontinuity within all three segments of the SLL or non-visualization.
At an advanced stage, scapholunate diastasis or signs of stage IV chondropathy may be found. MR arthrography: Combines the advantages of CT arthrography and MRI, but with lower spatial resolution.

Management

Surgical treatment of scapholunate instability depends on the condition of the cartilage (CT arthrography): in acute sprain (less than 3 weeks old), the patient may benefit from reduction of the diastasis and ligamentoplasty; in a more chronic sprain with preserved cartilage, ligamentoplasty is discussed. At the osteoarthritis stage, ulnar styloid shortening, proximal row carpectomy, or arthrodesis are considered depending on the stage of osteoarthritis.