Fact-sheet: SNAC wrist - scaphoid non union advanced collapse
Updated on 04/19/2018 at 7:00 PM
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Definition
SNAC = Scaphoid Non-union Advanced Collapse.
Complication of scaphoid fractures, especially in cases of non union: during wrist flexion the proximal fragment remains attached to the lunate while the distal fragment undergoes rotation --> abnormal contact within the radioscaphoid joint, characterized by early osteoarthritis between the distal scaphoid fragment and the radial styloid process.
Clinical features
Osteoarthritic pain.
Wrist deformity depending on the fracture pattern.
Radiography
stage 1: radial styloid-scaphoid osteoarthritis.
stage 2: same as 1 + scaphocapitate osteoarthritis
stage 3: lunocapitate osteoarthritis.
Assessment for signs of lunate instability (= DISI: dorsal intercalated segment instability).
Ultrasound
Scaphoid fracture:
- cortical disruption of the scaphoid +/- hematoma.
- often non union
CT
Similar to radiographs
CT arthrography is useful for cartilage and ligament assessment.
MRI
Absence of enhancement of the proximal scaphoid fragment = necrosis.
Scaphoid non union: T2 hyperintensity due to edematous changes.
MR arthrography for ligament and cartilage assessment.
Management
Four-corner fusion in advanced stages to relieve pain and slightly improve function.
Classification
See radiographs.
Differential diagnosis
Post-traumatic osteoarthritis of the wrist: SLAC (scapho-lunate advanced collapse), radial articular fractures, neglected necrosis of the lunate or scaphoid, Madelung-type wrist deformity.
Non-traumatic osteoarthritis:
- Primary osteoarthritis
- Microcrystalline: SCAC (Scapho-Chondrocalcinosis Advanced Collapse).