SLAC Wrist

1. SLAC Wrist Sepein Chiang, D.O. Garden City Hospital

2. Introduction • Originally recognized in 1981 • Most common pattern of degenerative disease • Accounts for 60% of peri-scaphoid arthritis • Caused by any injury to the scaphoid or its support mechanism • Causes, pathomechanics, classification and treatment

3. Causes • Rotary subluxation of the scaphoid • Scaphoid nonunion • Preiser’s disease • Kienböck’s disease • Midcarpal instability • Intraarticular fxs involving the radioscaphoid or capitolunate joints

4. Rotary Subluxation of the Scaphoid • Scapholunate articulation is disrupted and the wrist develops a pattern of instability with loading • When the ligamentous support is disrupted, diastasis develops between the scaphoid and lunate (Terry Thomas sign)

5. Rotary Subluxation of the Scaphoid • Proximal pole of the scaphoid rotates dorsally • Distal pole displaces volarly • Increased scapholunate angle on a lateral radiograph • Abnormal motion leads to abnormal stresses at the radioscaphoid joint

6. RSS Pathomechanics • Distal radius has 2 articular fossae • Scaphoid: elliptical • Lunate: spherical

7. RSS Pathomechanics • High stress loading at the edges of the radius and proximal pole of the scaphoid • Increased load at the capitolunate joint • Capitate is driven off the radial edge of the lunate

8. RSS Pathomechanics • Hamate also migrates proximally • Destruction of the lunate-hamate joint • Radiolunate joint is spared due to the spherical shape of the joint • Impingement of the trapezium and trapezoid on the neck of the scaphoid dorsally

9. Classification: Stage IA • Degenerative changes at the radial styloid

10. Classification: Stage IB • Involvement of the remainder of the radioscaphoid joint

11. Classification: Stage II • Destruction of the capitolunate joint

12. Scaphoid Nonunion • Second most common cause • Resembles scapholunate dissociation • Can lead to rotary subluxation of the distal fragment

13. Kienböck’s Disease • Collapse of the lunate permits proximal migration of the capitate • Increased stress at the radial wrist • Scaphoid and lunate dissociates • Scaphoid driven into rotary subluxation

14. Midcarpal Instability • Stability of the midcarpal joint is dependent on the periscaphoid ligaments • Disruption allows the distal carpal row to collapse on the proximal row

15. Treatment • Key to reconstruction of the SLAC wrist lies in the lunate • Radiolunate joint is highly resistant to degeneration due to the spherical shape • Radiolunate joint is preserved in all stages, even with DISI or VISI patterns

16. SLAC Wrist Reconstruction • Excision of the scaphoid • Four corner arthrodesis • Arthrodesis of the capitate, lunate, hamate and triquetrum • Pts with lunate or radiolunate pathology in addition to SLAC wrist are NOT candidates • Salvage procedures: proximal row carpectomy or wrist arthrodesis

17. SLAC Wrist Reconstruction • Load is transferred thru the single fused unit and subsequently thru the radiolunate joint • Bring the capitate ulnarly to center it on the lunate

18. SLAC Wrist Reconstruction • Most important step is avoidance of the common tendency for DISI deformity • Capitate must be volarly displaced on the lunate to prevent fusion on the dorsum of the lunate in a DISI position

19. SLAC Wrist Reconstruction • Avoid silicone implants for replacement of the scaphoid • Silicone particulate synovitis • Average ROM is 60% of normal • Average grip strength is 80% of normal • Long term f/u shows no secondary degenerative change at the radiolunate joint or adjacent joints

20. Complications • 1% nonunion • Inadequate immobilization • Inadequate preparation of the bones to fused • 1.5% RSD • Inadequate reduction of the DISI deformity leads to dorsal impingement of the capitate and radius