Scapholunate Advanced Collapse (SLAC)

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.

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]

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.

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%) . 

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%.

A history of wrist injury, scaphoid fracture, carpal tunnel decompression, or carpal ganglion excision may be present. Many patients with scapholunate advanced collapse (SLAC) wrist have minimal symptoms and may present because of a secondary problem, such as carpal tunnel syndrome.

Patients may have a variable duration history of wrist pain during activity. They commonly relate their symptoms to increased activity and overuse. Postactivity pain may be present. Patients may have modified their activities, depending on the severity of symptoms. Many patients have used nonsteroidal anti-inflammatory drugs (NSAIDs) for pain relief.

Wrist edema may be present, and patients may have pain with motion, especially when loading the wrist in an extended position. Limited wrist range of motion (ROM) is typical, and an average wrist flexion-extension arc of 80-90° has been reported. Direct palpation of the scapholunate joint or radiocarpal joint generally elicits pain. Pain with resistance against active finger extension while the wrist is held in passive flexion is common.

A scaphoid shift test also elicits pain. To perform this maneuver, the examiner places the fingers of the same hand on the dorsum of the distal radius of the wrist being examined (ie, the left hand is used to examine left wrist). The examiner's thumb is placed volarly on the scaphoid tuberosity and pushed dorsally while the other hand passively deviates the patient's wrist radially and ulnarly. This stresses the periscaphoid ligaments and subluxes the scaphoid dorsally, thus eliciting pain if periscaphoid disease is present.

Plain wrist radiographs (posteroanterior [PA], lateral, and oblique) are usually sufficient to make the diagnosis of scapholunate advanced collapse (SLAC) and permit staging.[14] (See the images below.) They can reveal joint narrowing, sclerosis, osteophytes, cysts, scapholunate dislocation, and carpal collapse.

Early changes at the radioscaphoid articulation can appear as an elongated radial styloid process. The scaphoid may assume a vertical position with a cortical ring sign. In SLAC secondary to scapholunate dissociation, increased distance between the scaphoid and lunate, as well as lunate ulnar translocation, will be obvious. A lateral view can show an increase in the scapholunate angle with a dorsiflexion of the lunate (dorsal intercalated segment instability [DISI] deformity).

As the disease progresses, the whole radioscaphoid joint becomes narrowed. In subtle cases, PA and lateral wrist computed tomography (CT) can reveal these joint changes.

For imaging of the skeletal morphology or occult fracture, CT (particularly multidetector CT [MDCT]) is most useful.[14] CT arthrography can help identify ligament tears.

Magnetic resonance imaging (MRI) and MR arthrography provide excellent imaging of osseous and soft tissues.[14] If avascularity is a concern, then MRI is the best imaging modality.

Nagle recommended staging wrist arthroscopy for articular surface evaluation on the grounds that lunate fossa changes may be present in advanced cases of SLAC wrist but may not be appreciated on plain radiography.[15] Because scaphoid resection and ulnar column fusion are contraindicated in the presence of lunate fossa degenerative changes, accurate assessment of the radiolunate joint is critical for correct surgical planning. When necessary, staging arthroscopy is performed as part of the definitive procedure.

Asymptomatic scapholunate advanced collapse (SLAC) wrist generally does not warrant treatment, though some patients may require surgery for secondary problems (eg, carpal tunnel syndrome). Mild symptomatic SLAC also can often be managed nonoperatively.

For more symptomatic SLAC, operative intervention is warranted. Surgical planning is based on symptoms, physical findings, radiographic findings, and the surgeon's preference. Because more motion occurs at the radiocarpal joint than at the midcarpal joint and because the radiolunate joint is generally spared, a limited wrist fusion with scaphoid excision is an option, though a total wrist fusion is often more predictable in alleviating pain. In stage 1 SLAC with sparing of the capitolunate joint, a proximal-row carpectomy (PRC) may also be used to preserve partial wrist motion.

In a small study (13 wrists), Noback et al described good results with arthroscopic synovectomy, radial styloidectomy, and neurectomy for advanced (symptomatic stage 2 or 3) SLAC wrist.[16] Functional outcomes were good, and most patients experienced a reduction in pain with the ability to return to work.

It is not uncommon to encounter a patient with an asymptomatic SLAC wrist.[17] The patient should be informed of the problem but may not require any treatment. If symptoms are present, the patient should be informed of the various options for treatment.

Mild symptomatic SLAC can often be managed nonoperatively with periodic steroid injections, splinting, and NSAIDs. If the grip strength of the SLAC wrist is greater than 80% of that of the uninvolved wrist and the condition is not giving rise to significant impairment, then living with SLAC is a valid option.[18]

SLAC reconstruction (limited wrist fusion)

A SLAC reconstruction involves excision of the scaphoid and arthrodesis of the capitate, lunate, hamate, and triquetrum.[19]

Two parallel dorsal transverse incisions, a lazy S incision, or a central longitudinal incision over the distal radiocarpal joint and styloid process is made. The extensor retinaculum is incised through the third dorsal compartment. The terminal branch of the posterior interosseous nerve in the floor of the fourth extensor compartment can be sacrificed as an adjunctive pain relief measure. The wrist capsule is opened over the capitolunate joint.

The scaphoid is resected in piecemeal fashion. Articular cartilage and subchondral bone are removed from the capitate, lunate, hamate, and triquetrum. Care should be taken to maintain the anatomic relations of the intercarpal intervals. Cancellous bone is harvested from the distal radius, the proximal ulna, or the iliac crest.

Lunate dorsal intercalated segment instability (DISI) should be corrected, and five percutaneous Kirschner wires (K-wires) are used. Two wires are placed through the capitate into the lunate, one each through the hamate and through the triquetrum into the lunate, and a fifth through the triquetrum into the capitate. Cancellous bone graft is packed between the interstices of the four bones.

A long arm splint is placed after the procedure. After a week, the splint is replaced with a long arm cast, which is maintained for 3 weeks. A short arm cast is then placed and maintained for an additional 2-4 weeks. The cast and wires are removed when fusion is evident on radiographs. (See the images below.)

Some fixation methods in this four-quadrant fusion include the use of intercalary screws and a dorsal carpal plate marketed especially for this fusion. The relevant question is whether the increased cost of such devices results in improved outcomes. More solid fixation does allow the use of a short arm cast and earlier initiation of wrist range-of-motion (ROM) therapy.[20]  In a study by Tielemans et al, a four-corner fusion that used a locking plate without a bone graft yielded results equal to those reported with grafting.[21]

Arthroscopic assistance may be considered.[22]  Arthroscopic four-corner arthrodesis is technically demanding and has a steep learning curve.[23]

Patients with radiolunate changes are not candidates for SLAC reconstruction. A wrist arthrodesis should be performed instead.

Proximal-row carpectomy

PRC requires resection of the proximal row of wrist bones to allow articulation of the capitate within the lunate fossa.[24, 25, 26]

For a successful procedure, both the proximal capitate articular surface and the lunate fossa should ideally be free of pathology. The procedure is usually effective only when the disease is restricted to the radioscaphoid joint. PRC yields the best ROM (average arc, 71°) but may be associated with painful narrowing of the radiocapitate joint. It is not indicated for stage 2 SLAC wrist. It may serve as a salvage procedure for stages 1A and 1B when limited wrist fusion is not indicated. If PRC fails, conversion to wrist arthrodesis is necessary.

A dorsal longitudinal or transverse incision is made. The extensor tendons are retracted. A longitudinal capsulotomy is extended radially and ulnarly. The capitate is identified, and its articular surface is inspected. In the presence of capitate degenerative changes, the procedure should not be performed.

If both the proximal capitate articular surface and the lunate fossa are free of pathology, the scaphoid, lunate, and triquetrum are excised. Both the radioscaphocapitate ligament and the long radiolunate ligament are preserved. Wrist collapse follows, with placement of the capitate head in the lunate fossa along with radial deviation of the wrist. If impingement between the radial styloid and the trapezium is present, a limited radial styloidectomy is performed. The capsulotomy incision is closed snugly.

After the procedure, the wrist is splinted for 4 weeks. Early active digital flexion and extension are recommended. ROM exercises start 4 weeks after the procedure. Strengthening exercises and heavy lifting may begin 3 months after the procedure.

Comparisons between PRC and other techniques were published by Vanhove et al[27] and Dacho et al.[28] Van Riet and Bain presented findings using memory staples in the three-corner wrist fusion technique.[29]  A systematic review and meta-analysis of 15 studies by Ahmadi et al recommended PRC over four-corner arthrodesis as the preferred procedure, though the quality of the evidence was not high.[30]

Total wrist arthrodesis

Total wrist fusion (see the images below) diminishes pain, but wrist function is sacrificed. Patients may have functional limitations that interfere with their lifestyles, and total fusion does not always result in complete pain relief.

A central dorsal longitudinal incision is made, and the extensor retinaculum is incised. The incision is carried down to bone surface from the middle-finger metacarpal to the distal radius, raising capsular and periosteal flaps.

Articular cartilage and subchondral bone are resected from the radioscaphoid, radiolunate, lunocapitate, scaphocapitate, and middle-finger carpometacarpal (CMC) joints. The radioulnar joint should not be entered. The index-finger CMC joint may also be opened for fusion. The radial metaphysis is generally used for the necessary cancellous bone graft, and more distal harvest is not required.

Bone grafts are placed in the radiocarpal, midcarpal, and CMC fusion sites, and a wrist fusion plate is applied.[31] The fusion plate is secured with screws at the middle-finger metacarpal, the capitate, and the radius. The periosteal and capsular flaps are reapproximated. A short arm splint is applied until fusion can be seen on radiographs. Fusion is usually evident in 6-8 weeks.[32, 33]

Total wrist arthroplasty

Total wrist arthroplasty is an alternative for diffuse arthrosis of the wrist, especially in rheumatoid arthritis and in the presence of bilateral disease.[34] With bilateral disease, a combination of a total wrist arthroplasty and a contralateral total wrist fusion is an option. Numerous implants have been used; however, major complications (eg, implant loosening and wear of the components) are common.

Mosillo et al performed a systematic review of seven studies involving the adaptive proximal scaphoid implant (APSI), a device made from pyrocarbon that is used to replace the proximal part of the scaphoid.[35] In all of the studies, grip strength and the flexion extension arch were improved in comparison with preoperative values; 17.3% of patients reported progression of osteoarthritis with the APSI, and the implant mobilization rate was 5.1%.

SLAC reconstruction

In a series of 250 procedures, Watson and Weinzweig reported nonunion in 1%, wound infection in 1%, reflex sympathetic dystrophy in 1.5%, and capitate-radial impingement necessitating revision arthroplasty in 13%.[36]  The high incidence of dorsal impingement was the result of noncorrection of the lunate DISI deformity. A flexion/extension arc of 60-65° can be expected with a four-bone fusion. Brown and Erdmann presented complications after 50 consecutive limited wrist fusions.[37]

Proximal-row carpectomy

Krakauer et al compared SLAC reconstruction with PRC and found that patients with PRC had 71° of motion, whereas patients with SLAC reconstruction had 54° of motion.[38] They recommended PRC for patients without lunate pathology and SLAC reconstruction for patients with capitolunate arthritis.

Wyrick et al presented similar results and recommendations.[39]  In the PRC group, total wrist motion was 85° and grip strength 94%; in the SLAC reconstruction group, total wrist motion was 67° and grip strength 74%.

Imbriglia et al presented the results of long-term follow-up after PRC.[40]  Four years after the procedure, 26 of 27 patients had pain relief, ROM did not deteriorate, and 80% of patients improved their grip strength.

PRC appears to offers better ROM and almost normal grip strength. In some patients, conversion to wrist arthrodesis may be required because of the persistence of severe pain.[41, 42, 43, 44]

Kiefhaber et al reported a higher number of complications in the four-corner fusion group, including nonunion and hardware-related problems.[45] The failure rate and the need to convert to a fusion were greater in patients who have a PRC and are younger than 35 years. The authors preferred a four-corner fusion for patients younger than 35 years and for middle-aged patients with high demand, while favoring a PRC for all others.

Total wrist arthrodesis

Hastings et al reported a 2% nonunion rate with total wrist fusion.[46]  The most common nonunion site was the middle-finger CMC joint. To prevent this complication, complete decortication of the dorsal 80% of the CMC joint is recommended. Other complications were tendon adhesions (in 3.5% of patients), carpal tunnel syndrome, and iliac crest harvest site problems (in 1.7% of patients).

Weiss et al discussed upper-extremity function after arthrodesis.[47]  Dacho et al described long-term results.[48]

Total wrist arthroplasty

Major complications, including implant loosening and wear of the components, are common.