SLAC wrist or Scapholunate advanced collapsed wrist is the final stage of scapholunate instability spectrum, where there is a specific pattern of osteoarthritis and subluxation which results from untreated chronic scapholunate dissociation.
The condition however can also occur in cases of from chronic scaphoid nonunion and degenerative changes abnormal loading.
Scapholunate dissociation is said to occur when a complete tear of the scapholunate ligament and one or more secondary ligaments allows the scaphoid to rotate into flexion with increase in the scapholunate interval. The rotation of the lunate becomes independent of the scaphoid.
This leads to static deformity which can be visualized on static xrays.
With further passage of time, a dorsal intercalated segment deformity develops which is characterized by
- Flexion of the scaphoid
- Extension of the lunate and triquetrum
- Dorsal and proximal translation of the capitate and distal carpal row
The postural changes become irreversible with time and the changed kinematics [the way forces would be handled] lead to abnormal articular loading and progressive degenerative changes known as Scapholunate advanced collapse (SLAC).
Types of SLAC Wrist
Depending on the extent of arthritis, the SLAC wrist can be divided into
SLAC wrist I – Arthritis along the scaphoid facet of the distal radius. It is the first stage
SLAC wrist II – In addition to above, the arthritis develops along the proximal radioscaphoid joint.It is second stage.
SLAC wrist III – The arthritis also develops in radial midcarpal joint. This is third stage.
SLAC wrist IV – The arthritis involves radiolunate joint and entire carpus. This is final stage and occurs after many years of initial injury.
The xrays would reveal the deformities and arthritis depending on the stage of SLAC.
These patients usually require surgical treatment.
Surgical options for SLAC wrist vary according to the joints that are involved.
It means removal of radial styloid. It is a good option for patient with stage I SLAC wrist. It will change the progression of the degenerative process, but is at most short- to midterm treatment to avoid intercarpal arthrodesis.
It can be considerd in patients with SLAC II disease with preservation of the midcarpal joint. The procedure is typically combined with distal scaphoid excision.
This option can be exercised in patients with a relatively well-preserved midcarpal joint. This is a motion sparing surgery.
This is done in patients with extensive degenerative changes at the midcarpal joint, with preservation of the radiolunate joint.
The four corner arthrodesis involves arthrodesis of capitate–lunate–hamate–triquetral arthrodesis.
Four-corner arthrodesis can be performed for SLAC I, II, and III disease as well.
Advantage of wrist arthroplasty is that it preserves motion and should be done in patients with low demands.
Should be done in patients with high demands.
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