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Updated: May 21 2023

Scaphoid Nonunion Advanced Collapse (SNAC)

  • Summary
    • Scaphoid Nonunion Advanced Collapse (SNAC) describes the specific pattern of progressive arthritis of the wrist that results from a chronic scaphoid nonunion.
    • Diagnosis is made clinically with progressive wrist pain and wrist instability with radiographs showing scaphoid fracture nonunion with advanced arthritis of the radioscaphoid joint.
    • Treatment involves observation in early stages of disease. A variety of operative procedures may be indicated depending on severity of disease and patient's symptoms.
  • Etiology
    • Pathophysiology
      • pathoanatomy
        • natural history of degenerative changes first occurs at the radioscaphoid area followed by pancarpal / midcarpal arthritis
  • Anatomy
    • Scaphoid anatomy
      • blood supply
        • major blood supply is dorsal carpal branch (branch of the radial artery)
          • enters scaphoid in a nonarticular ridge on the dorsal surface and supplies proximal 80% of scaphoid via retrograde blood flow
        • minor blood supply from superficial palmar arch (branch of volar radial artery)
          • enters distal tubercle and supplies distal 20% of scaphoid
      • motion
        • both intrinsic and extrinsic ligaments attach and surround the scaphoid
        • the scaphoid flexes with wrist flexion and radial deviation and it extends during wrist extension and ulnar deviation (same as proximal row)
      • also see Wrist Ligaments and Biomechanics for more detail
  • Classification
      • Radiographic Classification
      • Stage I
      • Arthrosis localized to the radial side of the scaphoid and radial styloid
      • Stage II
      • Scaphocapitate arthrosis in addition to Stage 1
      • Stage III
      • Periscaphoid arthrosis (proximal lunate and capitate may be maintained)
  • Presentation
    • Symptoms
      • weakness
        • reduced grip and pinch strength
      • stiffness
        • stiffness with extension and radial deviation
    • Physical exam
      • palpation
        • localized tenderness of the radioscaphoid articulation
      • motion
        • decreased wrist motion on extension and radial deviation
  • Imaging
    • Radiographs
      • recommended view
        • ap and lateral of wrist
      • findings
        • see radiographic classification above
  • Differential
    • SLAC wrist 
    • Scaphoid fracture nonunion 
  • Treatment
    • Nonoperative
      • observation alone
        • indications
          • medically frail and low functioning patients only
    • Operative
      • radial styloidectomy plus scapholunate reduction and stabilization
        • indications
          • stage I
      • distal pole excision
        • indications
      • proximal row carpectomy
        • indications
          • stage II and III
        • outcomes
          • disadvantages
            • reduction of wrist motion and grip strength
            • procedure should be avoided if there are capitate head degenerative changes
      • four-corner fusion or capitolunate arthrodesis
        • indications
          • stage II and III
        • outcomes
          • retains 60% of wrist motion and 80% of grip strength
      • wrist arthrodesis
        • indications
          • stage II and III
  • Prognosis
    • Patients with scaphoid nonunions of > 5 years duration or proximal pole necrosis have less favorable outcomes
    • Punctate bleeding of bone during surgery is a good prognostic indicator of union
      • 92% union with obvious bleeding, 71% with questionable bleeding, 0% with no bleeding
      • results show decreased rate of arthritis (down to 40-50%)
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