Scapholunate Advanced Collapse (SLAC)

SLAC
Scapho-Lunate Advanced Collapse – SLAC Wrist

– primary injury is a disruption of the scapholunate ligament
– this results in rotary subluxation of the scaphoid – it flexes in a palmar direction
– when flexed palmarly, there is incongruous joint contact between the proximal scaphoid and distal radius, with significantly increased contact pressures.
– abnormal forces are transmitted from the scaphoid to distal radius, and from the capitate to lunate
– as the scaphoid shortens, the capitate experiences increased load and begins to fall into the gap between the scaphoid and lunate.

Stages

Stage I: radial styloid and distal-radial aspect of scaphoid degeneration

Stage IIA: entire radioscaphoid articulation involved
Stage IIB: radioscaphoid and STT joint arthritis

Stage III: radioscaphoid, scaphocapitate, and lunocapitate articulations involved

Surgical Treatment – SLAC Wrist

Stage I: radial styloid
– radial styloid excision to remove impingement on the radial side of the wrist – may be done alone or combined with distal scaphoid fusion: STT or scapho-capitate
– scaphoid-trapezium-trapezoid fusion (STT)
– scaphoid-capitate fusion

Stage II: radioscaphoid +/- scaphotrapezial/trapezoidal
– scaphoid excision plus limited intercarpal fusion (�four-corner� capitate-lunate-hamate-triquetrum fusion, or lunocapitate fusion)
– proximal row carpectomy – some evidence that PRC may preserve more motion than intercarpal fusion

Stage III: radioscaphoid, scaphocapitate, lunocapitate
– scaphoid excision and four-corner fusion
– scaphoid excision and lunocapitate fusion
– wrist arthrodesis

From a technical point of view, in all intercarpal fusions:
– thoroughly excise the cartilage and subchondral bone
– preserve carpal height
– bone graft generously
– correct capitate-lunate alignment; in particular, if a DISI pattern has developed, it is important to get the lunate out of its extended position to restore wrist extension and reduce radiocapitate impingement