Wrist instability and collapse - SNAC

Question 1

What is SNAC?

Answer 1

SNAC - Scaphoid nonunion advanced collapse - is a condition characterized by advanced collapse of the wrist and results from a chronic scaphoid nonunion.

Question 2

What is the pathoanatomy of SNAC?

Answer 2

The natural history of degenerative changes is that they first occur in the radioscaphoid area, followed by pancarpal/midcarpal arthritis

Question 3

What is the prognosis of SNAC?

Answer 3

• patients with scaphoid nonunions >5yrs duration or proximal pole AVN have less favourable 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 40-50%)

Question 4

What is the blood supply to the scaphoid?

Answer 4

• The major supply to the scaphoid:
  
  • dorsal carpal branch (branch of the radial artery)
  • enters the scaphoid in a non articular ridge along the dorsal surface and supplies 80% of the scaphoid via retrograde blood flow
• The minor supply to the scaphoid:
  
  • superficial palmar arch (branch of the volar radial artery)
  • enters the distal tubercle and supplies 20% of the scaphoid

Question 5

What is the motion of the scaphoid with movement of the wrist?

Answer 5

• both intrinsic and extrinsic ligaments attach and surround the scaphoid
• the scaphoid flexes with wrist flexion and radial deviation
• the scaphoid extends with wrist extension and ulnar deviation