Practice Essentials
Scapholunate advanced collapse (SLAC) of the wrist is the most common pattern of degenerative arthritis in the wrist. The hallmark of SLAC is scaphoid or scapholunate ligament injury with collapse on the radial side of the wrist. [1]
Watson and Ballet coined the term SLAC wrist in 1984. [2] Findings of bilateral SLAC wrist on a prehistoric skeleton from the Hassi-el-Abiod site in Malian Sahara provide paleopathologic evidence of the existence of this disease 7000 years ago.
Many patients with SLAC wrist have minimal symptoms and may present because of a secondary problem, such as carpal tunnel syndrome. Wrist edema may be present, and patients may have pain with motion, especially when loading the wrist in an extended position.
Plain wrist radiographs (posteroanterior [PA], lateral, and oblique) are usually sufficient to make the diagnosis of SLAC and permit staging. For imaging of the skeletal morphology or occult fracture, computed tomography (CT) is most useful. If avascularity is a concern, then magnetic resonance imaging (MRI) is the best imaging modality. When necessary, staging arthroscopy is performed as part of the definitive procedure.
Asymptomatic SLAC wrist generally does not warrant treatment, though some patients may require surgery for secondary problems. Mild symptomatic SLAC also can often be managed nonoperatively. For more symptomatic SLAC, operative intervention is warranted (see Treatment).
For patient education resources, see the Arthritis Center, as well as Carpal Tunnel Syndrome.
Pathophysiology
The distal radius has two articular fossae for the scaphoid and the lunate. The scaphoid fossa is elliptical or ovoid and narrows toward the radial styloid in a dorsal-volar plane. Thus, the scaphoid proximal articular surface is shaped like a spoon. The lunate fossa is spherical. Injury to the scaphoid or its supportive ligaments can cause radial-side collapse with flexion of the scaphoid, thereby resulting in incongruence of the radioscaphoid joint.
Narrowing of the radioscaphoid joint begins at the radial styloid aspect (stage 1A). Radiographic changes appear as a sharp elongation on the radial styloid. As the disease progresses, the rest of the radioscaphoid joint is destroyed (stage 1B). In stage 1B, the entire scaphoid fossa is involved. Complete collapse of the radioscaphoid joint alters the normal load-bearing ability of the capitolunate joint. This results in a radial or dorsal radial position of the capitate.
Shear stress destroys cartilage in the capitolunate joint, leading to the most advanced stage, midcarpal SLAC (stage 2). In stage 2, the capitolunate joint is additionally narrowed and sclerotic. As the arthritic pattern progresses, it shifts from the scaphoid fossa of the radius to the midcarpal capitate articulation.
At all stages of SLAC wrist, the radiolunate joint is not involved, because of its spherical shape. The lunate is congruently loaded in every position and thus is highly resistant to degenerative changes. This sparing of the lunate fossa provides a basis for some of the motion-preserving procedures to treat SLAC wrist. SLAC wrist that is longstanding and goes untreated can lead to wrist pain at rest and during use, deterioration of range of motion (ROM), and decreased grip strength. The radiographic appearance of SLAC wrist does not always correlate with the symptoms.
Etiology
A SLAC wrist pattern is the result of many radial-side wrist pathologies (see the images below). Most common is scapholunate dissociation with rotatory subluxation of the scaphoid. Scaphoid nonunion advanced collapse (SNAC) is another very common cause. [3]
Scapholunate advanced collapse (SLAC) wrist from nonunion of the scaphoid. The patient underwent 4-bone fusion.
Scapholunate advanced collapse (SLAC) wrist from nonunion of the scaphoid. The patient underwent 4-bone fusion.
Other etiologies include Preiser disease (avascular necrosis [AVN] of the scaphoid), [4] midcarpal instability, intra-articular fractures involving the radioscaphoid or capitolunate joints, Kienböck disease (see the image below), [5] primary degenerative arthritis with attenuation of the scapholunate ligament and scapholunate dissociation, [6, 7] capitolunate degeneration, and inflammatory arthritis, as is seen in the crystalline deposition disorders of gout and calcium pyrophosphate dihydrate deposition disease (CPPD). [8, 9]
Initial treatment of the cause of the SLAC wrist (eg, scaphoid nonunion, scapholunate dissociation) may prevent subsequent degeneration.
Epidemiology
SLAC has been reported to be more common in men than in women and more common in persons who perform manual labor than in other individuals. It is most common in the dominant wrist. SLAC has been reported in people aged 19-82 years. The peak decade for corrective SLAC surgery is the fourth decade of life. The periscaphoid area is the site of 95% of all degenerative diseases of the wrist. The SLAC pattern is seen in 57% of patients with periscaphoid arthritis.
Murphy et al, in a study of the epidemiology of SLAC in 61 patients, found that in comparison with a control group of 61 patients with first CMC osteoarthritis, those with SLAC wrist were more likely to be male (80.3% vs 31.1%, to have a history of a traumatic injury (69.5% vs 25.9%), to have a longer duration of symptoms (10.3 ± 13.3 vs 3.5 ± 2.5 years), to have a job involving manual labor (49.0% vs 20.0%), and to be younger (53.1 ± 10.4 vs 58.3 ± 9.8 years). [10] Dominant hand involvement did not differ significantly between the two groups (49.2% vs 53.3%) .
Prognosis
Traverso et al reported the results of four-corner fusion for SLAC wrist at a minimum of 10 years' follow-up (average, 18 years; range, 11-27 years). [11] Among the 12 patients (15 wrists) available for follow-up, the average extension-flexion arc was 68.6°, the average radial-ulnar deviation arc was 32.9°, and the average QuickDASH score was 7.8. Although 73% of the patients had radiographic changes in the radiolunate joint, functional outcome was good, patient satisfaction high, and functional impairment low.
Rimokh et al assessed clinical and radiologic outcomes of scaphoid excision and four-corner arthrodesis with locking plate for treating SLAC and scaphoid nonunion advanced collapse (SNAC) wrist (mean follow-up, 5 years). [12] Mean flexion was 46% and mean extension 46% as compared with the contralateral side. An 18% gain was observed in grip strength. Mean postoperative QuickDASH score was 30. Patient satisfaction was 70%. Complete joint-space fusion was achieved in 55% of patients. Only one patient (2.5%) had no joint fusion. The joint between the lunate and the capitate was fused in 38 patients (95%). Nine patients suffered complications; eight of them required surgical revision (20%).
In a systematic review of 11 studies (436 wrists), Andronic et al assessed the long-term outcomes of four-corner fusion of the wrist (mean follow-up, 11 ± 4 years; range, 6-18). [13] At the final follow-up, the average cumulative rate of conversion to total wrist fusion was 6%, and the rate of conversion to total wrist arthroplasty was 0%.
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Stage 2 scapholunate advanced collapse (SLAC) wrist.
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Scapholunate advanced collapse (SLAC) wrist from Kienböck disease.
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Scapholunate advanced collapse (SLAC) wrist from nonunion of the scaphoid. The patient underwent 4-bone fusion.
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Scapholunate advanced collapse (SLAC) wrist from nonunion of the scaphoid. The patient underwent 4-bone fusion.
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Scapholunate advanced collapse (SLAC) wrist treated with total wrist fusion.
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Scapholunate advanced collapse (SLAC) wrist treated with total wrist fusion.
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Stage 2 scapholunate advanced collapse (SLAC) wrist treated with 4-bone fusion.
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Stage 2 scapholunate advanced collapse (SLAC) wrist treated with 4-bone fusion.
