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Blood supply of the Wrist and Scaphoid

  • Certain intraosseous vascularity configurations are associated with higher AVN rates secondary to trauma
  • Bones which rely on a single vessel or group of vessels entering on one surface
    • Femoral Head
    • Scaphoid
    • 8% of Lunates
  • Extraosseous pattern doesn't seem to relate to AVN, intraosseous pattern more important

 

  • Extraosseous
    • Carpus Supply
    • 6 transverse arches
    • Radial artery & Ulna artery make up longitudinal medial & lateral borders of these arches
    • Palmar arches (except deep palmar arch) are in volar capsule
  • 6 Transverse Arches
      • Dorsal Intercarpal
      • Palmar Intercarpal
      • Dorsal & Palmar Radiocarpal
        • Occurs in 3/4
          Supplies distal Radius & Lunate & Triquetrum
          &Triquetrum
      • Dorsal Basal Metacarpal
        • Only present 1/3
      • Deep Palmar
        • Always present
        • Usually complete
        • Continuation of the radial artery (dives between two heads of 1st dorsal interosseous then between the oblique & transverse heads of adductor pollicis) anastomosing with deep branch of ulnar artery
        • Lies deep to flexor tendons 1cm proximal to superficial arch
    • 3 Dominant Arches
      • Dorsal Intercarpal
        • Consistent
        • Largest
      • Palmar Radiocarpal
      • Deep Palmar
  • Superficial Palmar Arch
    • Direct continuation of ulnar artery
    • Lies just under palmar aponeurosis
    • Complete in 1/3
    • Hockey-stick in 2/3
  • Scaphoid, Pisiform & Trapezium have direct branches off the Radial & Ulnar arteries
  • A rich anastomotic network near the surface entry of the nutrient vessel supplies each carpal bone

Intraosseous Vascularity

  • 3 Groups of bones
    • Group 1
      • Only vessels entering one surface or large areas of bone dependent on single vessel
        • Scaphoid
        • Capitate
        • 8% Lunates
    • Group 2
      • Two or more sites of vessels entry
      • Lack significant anastomosis
        • Hamate
        • Trapezoid
    • Group 3
      • Numerous anastomoses
      • Rich internal network
        • Trapezium
        • 92% Lunates
        • Triquetrum
        • Pisiform

Blood supply of the Scaphoid

  • Scaphoid fractures only account for 2% of all fractures but is Second only to femoral head for post-traumatic AVN
  • Major supply from radial artery
    • Collateral supply from anterior interosseous a. (predominantly dorsal)
    • All vessels enter via nonarticular surface in areas of ligamentous attachment
    • Two major vessels
      • Dorsal scaphoid br
      • Volar scaphoid br
  • Dorsal branch
    • Arises from radial artery
    • Consistent major anastomoses with dorsal br of anterior interosseous a
    • Enters scaphoid at distal half through the waist along the dorsal ridge (lies obliquely between the articular surfaces of radius, trapezium, trapezoid)
    • Supplies 70-80% of scaphoid
  • Volar branch
    • Arises directly from radial a (75%) or superficial palmar br of radial a (25%)
    • May gain anastomosis from volar br of anterior interosseous a
    • Enters scaphoid at distal half
    • Supplies 20-30% of scaphoid
  • Internal vascularity
    • No anastomosis between dorsal and volar branches
    • Proximal 70-80% is supplied by dorsal vessels
    • Distal 20-30% is supplied by volar scaphoid br
  • Vascularity of the proximal pole of scaphoid is least traumatized by a volar approach

Blood Supply of the Lunate

  • 4 patterns of vascularity (Gelberman dye studies)
    • X
    • Y
    • I
    • Incomplete Palmar
  • Proximal subchondral region worst supplied
    • Y = 60% (50% inverted) }
    • I = 30% } Group 3 supply
    • X = 10% }
    • Incomplete palmar = 8% - Group 1 supply
  • Hence 8% with a single palmar supply are at risk of AVN after a severe hyperextension injury
  • Other 92% need multiple microtraumatic events to produce AVN ± Long radius