Scaphoid Lunate Advanced Collapse (SLAC) - Hand

Summary
- Scaphoid Lunate Advanced Collapse (SLAC) describes the specific pattern of degenerative arthritis seen in chronic dissociation between the scaphoid and lunate.
- Diagnosis is made clinically with progressive wrist pain and wrist instability with radiographs showing advanced arthritis of the radiocarpal and midcarpal joints (radiolunate joint spared).
- Treatment involves observation, NSAIDs and splinting in early stages of disease. A variety of operative procedures may be indicated depending on severity of disease and patient's symptoms.

Etiology
- Pathoanatomy
  - chronic SL ligament injury creates a DISI deformity
    
    scaphoid is flexed and lunate is extended as scapholunate ligament no longer restrains this articulation
    
    scapholunate angle > 70 degrees
    
    lunate extended > 10 degrees past neutral
  - resultant scaphoid flexion and lunate extension creates
    
    abnormal distribution of forces across midcarpal and radiocarpal joints
    
    malalignment of concentric joint surfaces
  - initially affects the radioscaphoid joint and progresses to capitolunate joint
    
    notably the radiolunate joint is spared

Classification

Watson classification

describes predictable progression of degenerative changes from the radial styloid to the entire scaphoid facet and finally to the unstable capitolunate joint, as the capitate subluxates dorsally on the lunate

key finding is that the radiolunate joint is spared, unlike other forms of wrist arthritis, since there remains a concentric articulation between the lunate and the spheroid lunate fossa of the distal radius

Watson Classification
Stage I	Arthritis between scaphoid and radial styloid
Stage II	Arthritis between scaphoid and entire scaphoid facet of the radius
Stage III	Arthritis between capitate and lunate
note: radiolunate joint spared

While original Watson classification describes preservation of radiolunate joint in all stages of SLAC wrist, subsequent description by other surgeons of "stage IV" pancarpal arthritis observed in rare cases where radiolunate joint is affected
- validity of "stage IV" changes in SLAC wrist remains controversial and presence pancarpal arthritis should alert the clinician of a different etiology of wrist arthritis

Presentation
- Symptoms
  - difficulty bearing weight across wrist
  - patients localize pain in region of scapholunate interval
  - progressive weakness of affected hand
  - wrist stiffness
- Physical exam
  - tenderness directly over scapholunate ligament dorsally
  - decreased wrist ROM
  - weakness of grip strength
  - Watson scaphoid shift test
    
    patients may have positive Watson scaphoid shift test early in the process,
    
    will not be positive in more advanced cases as arthritic changes stabilize the scaphoid
    
    technique
    
    with firm pressure over the palmar tuberosity of the scaphoid, wrist is moved from ulnar to radial deviation
    
    positive test seen in patients with scapholunate ligament injury or patients with ligamentous laxity, where the scaphoid is no longer constrained proximally and subluxates out of the scaphoid fossa resulting in pain
    
    when pressure removed from the scaphoid, the scaphoid relocates back into the scaphoid fossa, and typical snapping or clicking occurs
    
    must compare to contralateral side

Imaging
- Radiographs
  - obtain standard PA and lateral radiographs
    
    PA radiograph will reveal greater than 3mm diastasis between the scaphoid and lunate
    
    Stage I SLAC wrist
    
    PA radiograph shows radial styloid beaking, sclerosis and joint space narrowing between scaphoid and radial styloid
    
    Stage II SLAC wrist
    
    PA radiograph shows sclerosis and joint space narrowing between scaphoid and the entire scaphoid fossa of distal radius
    
    Stage III SLAC wrist
    
    PA radiograph shows sclerosis and joint space narrowing between the lunate and capitate, and the capitate will eventually migrate proximally into the space created by the scapholunate dissociation
    
    lateral radiograph
    
    will reveal DISI deformity and subluxation of capitate dorsally onto lunate
  - stress radiographs unnecessary
- MRI
  - unnecessary for staging, but will show
    
    thinning of articular surfaces of the proximal scaphoid
    
    scaphoid facet of distal radius and capitatolunate joint with synovitis in radiocarpal and midcarpal joints

Differential
- SNAC wrist

Treatment
- Nonoperative
  - NSAIDs, wrist splinting, and possible corticosteroid injections
    
    indications
    
    mild disease
- Operative
  - radial styloidectomy and scaphoid stabilization
    
    indications
    
    Stage I
    
    technique
    
    prevents impingement between proximal scaphoid and radial styloid
    
    may be performed open or arthroscopically via 1,2 portal for instrumentation
  - PIN and AIN denervation
    
    indications
    
    Stage I
    
    technique
    
    since posterior and anterior interosseous nerve only provide proprioception and sensation to wrist capsule at their most distal branches, they can be safely dennervated to provide pain relief
    
    can be used in combination with below procedures for Stage II or III
  - proximal row carpectomy
    
    indications
    
    Stage II
    
    contraindicated if there is an incompetent radioscaphocapitate ligament
    
    contraindicated with caputolunate arthritis (Stage III) because capitate articulates with lunate fossa of the distal radius
    
    technique
    
    excising entire proximal row of carpal bones (scaphoid, lunate and triquetrum) while preserving radioscaphocapitate ligament (to prevent ulnar subluxation after proximal row carpectomy)
    
    outcomes
    
    provides relative preservation of strength and motion
  - scaphoid excision and four corner fusion
    
    indications
    
    Stage II or III
    
    technique
    
    also provides relative preservation of strength and motion
    
    wrist motion occurs through the preserved articulation between lunate and distal radius (lunate fossa)
    
    outcomes
    
    similar long term clinical results between scaphoid excision/ four corner fusion and proximal row carpectomy
  - wrist fusion
    
    indications
    
    Stage III
    
    any form of pancarpal arthritis
    
    outcomes
    
    wrist fusion gives best pain relief and good grip strength at the cost of wrist motion