Review Question - QID 211820

Osteoarthritis resulting from scapholunate advanced collapse (SLAC) progresses in stages originally described by Watson: (1) radial styloid and scaphoid, (2) entire radioscaphoid, (3) capitolunate. A fourth stage involving the radiolunate articulation has since been described by other authors, although its association in SLAC wrist remains controversial.

SLAC is a condition of progressive instability resulting from injury to the scapholunate (SL) ligament. Standard wrist PA radiographs reveal SL diastasis greater than 3mm while lateral radiographs reveal a dorsal intercalated segmental instability (DISI) deformity and subluxation of the capitate dorsally. Resultant scaphoid flexion and lunate extension create abnormal force distribution among the midcarpal and radiocarpal joints. This causes arthritis that advances in a predictable pattern. Surgical treatments include 4-corner fusion, capitolunate fusion, complete wrist fusion, proximal row carpectomy (PRC), radial styloidectomy, and wrist denervation.

Watson et al. reviewed 210 wrist x-rays to establish the pattern of sequential changes in degenerative arthritis of the SLAC wrist in their 1984 landmark paper. Arthritis between the scaphoid, lunate and radius was most common (57%); second occurred between the scaphoid, trapezium, and trapezoid (27%); and a combination of these two patterns occurred in 15%. They noted sparing of the lunate-radius articulation. They concluded degenerative arthritis progresses in a predictable pattern beginning at the radioscaphoid articulation and advancing to the capitolunate articulation.

Dr. Strauch reviewed SLAC and scaphoid nonunion advanced collapse (SNAC) patterns of wrist arthritis and treatment options. Surgical options include 4-corner fusion, capitolunate fusion, complete wrist fusion, proximal row carpectomy (PRC), radial styloidectomy, and wrist denervation. Four-corner arthrodesis is the classic surgical treatment using either k-wire or circular plate fixation. Alternatively, PRC has shown excellent results with the advantages of earlier motion, no need for fusion, and no hardware.

Trehan et al. reviewed nomenclature and differential diagnosis for SLAC. The authors note pseudogout also affects the wrist in four progressive stages, termed scaphoid chondrocalcinosis advanced collapse (SCAC), with the final stage consisting of pancarpal arthritis involving the radiolunate articulation. The authors conclude clinicians should consider infection, idiopathic osteonecrosis (Kienböck’s disease, Preiser’s disease), crystalline arthropathy, inflammatory arthritis, scaphotrapezium-trapezoidal (STT) arthritis, and scaphoid nonunion as possible etiologies of wrist pain upon patient presentation.

Figure A demonstrates widening of the scapholunate interval and the cortical ring sign caused by scaphoid flexion consistent with SL ligament disruption. Figure B demonstrates a DISI deformity and increased scapholunate angle.

Illustration A measures the scapholunate angle at approximately eighty-seven degrees, normal SL values range from 30 to 60 degrees. Illustration B demonstrates Watson stage I SLAC. Illustration C demonstrates Watson stage II. Illustration D demonstrates Watson stage III.

Incorrect Answers
Answer 1: Osteoarthritis affecting the radiolunate articulation has been described as the fourth stage of SLAC, although pancarpal arthritis should alert the clinician to a different etiology of wrist arthritis
Answer 3: Involvement of the radial styloid and scaphoid articulation is the first stage of SLAC
Answer 4: Progression to the entire radioscaphoid articulation is the second stage of SLAC
Answer 5: The lunotriquetral articulation is spared in SLAC