Scaphoid nonunion advanced collapse (SNAC) is a complication that can occur with scaphoid fractures, specifically non-union of scaphoid fractures. It is essentially the same sequela of wrist injury causing scapholunate dissociation as seen in scapholunate advanced collapse (SLAC).
In a SNAC wrist, the proximal scaphoid fragment usually remains attached to the lunate (which rotate together during extension), while the distal scaphoid fragment rotates into flexion. This results in abnormal contact in the radioscaphoid compartment, characterised by early styloid osteoarthritis between the distal scaphoid fragment and the radial styloid process.
Radiographic signs will depend on the stages of osteoarthritis in a SNAC wrist 4:
- osteoarthritis between the distal scaphoid fragment and the radial scaphoid fossa
- same as stage 1 with the addition of osteoarthritis between the scaphoid and the capitate
- osteoarthritis affecting the radial styloid, proximal scaphoid, and scaphocapitate with progression to the lunocapitate
- there is lateral proximal radial migration of the capitate dorsal to the lunate, which is a DISI configuration
- this is followed by non-articulation between the capitate and radius
Treatment and prognosis
Patients with advanced degenerative changes may undergo a four-corner fusion for pain relief and some improvement in functionality.
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