Monday, July 4, 2011

Traumatic AVN of Scaphoid

PA radiograph of the wrist with scaphoid deviation shows a fracture of the waist of the scaphoid bone (arrow) with loss of trabecular pattern in the distal fragment.

T1 weighted images of the same patient 3 months after trauma showing hypointensity in the distal fractured fragment consistent with avascular necrosis.

Scaphoid fractures are the most common carpal fractures, resulting from a fall on an outstretched hand. 70 % of these occur at the waist, 20 % at the proximal pole, and 10 % at the distal pole. Blood supply for the proximal pole enters at the waist. If this blood supply is interrupted due to fracture, the proximal pole is at risk for avascular necrosis unlike out case where the distal fragment is involved. Special scaphoid views with the hand in ulnar deviation may be needed to detect these fractures.

Avascular necrosis
  • More common in scaphoid because of peculiar blood supply
  • Up to 30% of scaphoid fractures may display increased density of the proximal pole
  • Often reversible
  • May be due to relative ischemia of proximal pole
  • Occurs in 15-30% of scaphoid fractures
  • Almost always involves proximal pole
  • The more proximal is the fracture line, the risks of avascular necrosis increase
  • The radiographic hallmarks of AVN are collapse and fragmentation
  • MRI may be more sensitive to AVN than conventional radiographs but is not 100% sensitive.

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