What is Scapholunate Advanced Collapse (SLAC wrist), how is it staged, and what imaging and treatment options are recommended for a patient with chronic dorsal wrist pain, clicking, reduced grip strength, and limited motion after a prior wrist sprain?

Scapholunate Advanced Collapse (SLAC) Wrist

Definition and Pathophysiology

SLAC wrist is the most common pattern of degenerative arthritis in the wrist, resulting from progressive carpal instability following scapholunate ligament injury or scaphoid nonunion. 1, 2, 3

• The condition develops when the scapholunate ligament is disrupted (traumatically or atraumatically), causing the lunate to assume an abnormal extended posture since it is no longer restrained by the distal scaphoid. 3
• This creates a dorsal intercalated segment instability (DISI) deformity with abnormal joint kinematics that progressively damages the radiocarpal and midcarpal articulations. 3
• Atraumatic causes include calcium pyrophosphate deposition disease, rheumatoid arthritis, neuropathic diseases, and β2-microglobulin-associated amyloid deposition. 3

Staging System

SLAC wrist progresses through three distinct radiographic stages that directly determine surgical management:

• Stage I: Degenerative arthritis isolated to the radioscaphoid joint. 1
• Stage II: Arthritis extends to involve the radioscaphoid and scaphocapitate joints. 1
• Stage III: Arthritis involves the radioscaphoid, scaphocapitate, and capitolunate joints (pancarpal arthritis). 1

Diagnostic Imaging Algorithm

Initial Evaluation

Obtain three-view wrist radiographs (posteroanterior, lateral, and 45-degree semipronated oblique) as the mandatory first imaging study. 4, 5

• Radiographs identify positive ulnar variance, carpal collapse patterns, scapholunate interval widening, and the stage of degenerative changes. 4, 6
• Look specifically for scapholunate diastasis (>3mm gap), DISI deformity (lunate extension), and progressive arthritis patterns. 3

Advanced Imaging for Ligamentous Assessment

When radiographs show early or equivocal findings, CT arthrography is the preferred next study, achieving nearly 100% sensitivity and specificity for scapholunate ligament tears. 4, 7

• CT arthrography demonstrates 80-100% accuracy for intrinsic ligament tears and 94-100% accuracy for articular cartilage abnormalities. 4
• CT arthrography is particularly superior for detecting tears of the biomechanically critical dorsal segment of the scapholunate ligament compared to 1.5T MRI. 4
• An interdisciplinary consensus of hand surgeons and radiologists specifically endorses CT arthrography for clinically suspected scapholunate instability and cartilage defects. 4

MR arthrography serves as an alternative with 63-100% sensitivity for ligament tears and provides critical information about which specific ligament segments remain repairable. 4, 7

• Direct MR arthrography with radiocarpal injection has higher sensitivity than non-contrast MRI for both complete and incomplete scapholunate ligament tears. 4, 5
• Wrist traction during MR arthrography improves detection of cartilage, TFCC, and intrinsic ligament injuries. 4

Non-contrast 3.0T MRI is appropriate when soft tissue pathology (ganglion cysts, tendon disorders) is the primary consideration or when arthrography is contraindicated. 4, 6

• Standard MRI has only 70-87% sensitivity for scapholunate tears at 3.0T, making it less reliable than arthrographic techniques for definitive ligament assessment. 4, 7

Treatment Algorithm Based on Stage

Stage I and II SLAC (Without Capitolunate Arthritis)

Proximal row carpectomy (PRC) is the preferred motion-preserving procedure for Stage I-II disease, avoiding the technical demands, prolonged immobilization, and nonunion risk of arthrodesis. 1, 2

• PRC provides satisfactory pain relief, functional performance, and preserves 6.2 degrees more flexion/extension range of motion compared to four-corner arthrodesis. 1, 2
• Grip strength is 1.52% higher and pain scores are 0.3 points lower with PRC versus four-corner fusion, though these differences are small. 2
• PRC requires the capitolunate joint to be intact and free of arthritis for optimal outcomes. 1

Arthroscopic resection arthroplasty represents an emerging alternative for early-stage SLAC with excellent 5-year outcomes. 8

• Arthroscopic treatment reduces pain from 7/10 preoperatively to 0.18/10 postoperatively, with DASH scores improving from 48 to 3. 8
• Total arc of motion increases from 114 degrees to 126.5 degrees, and grip strength improves from 41 kg to 49 kg. 8
• Patient satisfaction averages 4.8 out of 5 at final follow-up. 8

Stage III SLAC (With Capitolunate Arthritis)

Four-corner arthrodesis with scaphoid excision is recommended for Stage III disease because PRC provides unsatisfactory pain relief when capitolunate arthritis is present. 1

• Four-corner fusion addresses the pancarpal arthritis pattern by eliminating the arthritic capitolunate joint while preserving radiocarpal motion. 1, 3
• This procedure requires lengthy postoperative immobilization (typically 8-12 weeks) and carries nonunion risk. 1
• Despite slightly reduced range of motion compared to PRC, four-corner fusion provides equivalent pain relief and functional outcomes in Stage III disease. 2, 3

Postoperative Protocol

Immobilize the wrist in neutral position with forearm in neutral rotation for 4 weeks minimum following any surgical reconstruction. 7

• Begin gentle active wrist motion only after completing the 4-week immobilization period, as premature mobilization leads to repair failure and persistent instability. 6, 7
• Introduce strengthening exercises between weeks 8-12. 6, 7
• Return to heavy tasks and sports requires a minimum of 3 months from surgery. 6, 7
• Obtain radiographs at 3 weeks postoperatively and at immobilization cessation to confirm healing and assess carpal alignment. 7

Critical Pitfalls to Avoid

Do not perform PRC in patients with radiographic evidence of capitolunate arthritis (Stage III), as this leads to symptomatic radiocarpal arthritis requiring conversion to total wrist arthrodesis. 1

Do not rely on standard non-contrast MRI alone for surgical planning, as it has only moderate sensitivity (65-89%) for scapholunate tears and may miss the full extent of injury. 4, 7

Ensure adequate immobilization duration, as premature mobilization is a predictor of poor outcomes with ongoing pain and functional limitation. 6, 7

Incomplete correction of lunate extension during four-corner fusion results in diminished wrist extension compared to PRC. 1