Scaphoid Nonunion Advance Collapse (SNAC)

SNAC
Scaphoid Nonunion Advanced Collapse – SNAC Wrist

– similar in is natural history to SLAC wrist, with comparable stages of joint degeneration
– can occur after malunion or after established nonunion
– it is felt that degenerative arthritis is almost inevitable after a scaphoid nonunion
– the fact that this joint degeneration can occur even after healing of the scaphoid fracture emphasizes the precise role that the scaphoid plays in normal wrist kinematics.
– if the scaphoid shape or volume is altered (by malunion, or by nonunion and subsequent bony resorption), the process of degeneration can be initiated.
– ligamentous injury can also occur with scaphoid fracture and contribute to the pathogenesis of degenerative change
– with an unstable scaphoid fracture, the distal segment flexes, the proximal fragment extends under the influence of the lunate (if the scapholunate ligament is still intact). Joint congruity between the distal radius and scaphoid and between the scaphoid and capitate is decreased.

Stages

Stage I: Arthritis localized to the distal scaphoid and radial styloid

Stage II: Radioscaphoid plus scaphocapitate arthritis, but preservation of the lunocapitate joint

Stage III: Periscaphoid arthritis involving radiostyloid, distal scaphoid, scaphocapitate, and
lunocapitate joints.
Surgical Treatment – SNAC Wrist

Stage I: radial styloid
– radial styloid excision plus bone graft of scaphoid nonunion

Stage II: radioscaphoid, scaphocapitate
– proximal scaphoid fused to capitate and lunate with excision of distal scaphoid (Viegas)
– scaphoid excision, four-corner fusion

Stage III: radioscaphoid, scaphocapitate, lunocapitate
– scaphoid excision, four corner fusion
– wrist arthrodesis

In the end, comparison of results for motion, strength, and functional use does not demonstrate vast differences between any of the procedures. In general, proximal row carpectomy provides more motion, a little less strength, and progression of arthritis in some cases. Midcarpal fusion with scaphoid excision provides fair-good motion and strength equal to coemplete fusion, but with some risk of arthritis progression. Total wrist arthrodesis provides good strength, but leaves no motion