Pre-axial and post-axial borders

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Pre-axial and post-axial borders describe where the flexor and extensor compartments of the limb meet during foetal limb bud development. These borders are also conveniently marked out by veins.

Pre-axial (cranial) border

  • demarcates portion of the limb bud that lies cranial to the axis of the limb e.g radial aspect of upper limb and tibial aspect of lower limb
  • marked out by the cephalic vein in the upper limb, and the great saphenous vein in the lower limb
  • clinical relevance: pre-axial polydactyly involves first digit of the hand (radial side) or first digit of the foot (big toe)

Post-axial (caudal) border

  • demarcates portion of the limb bud that lies caudal to the axis of the limb e.g. ulnar aspect of upper limb and fibular aspect of lower limb
  • marked out by the basilic vein in the upper limb, and the small saphenous vein in the lower limb
  • clinical relevance: post-axial polydactyly refers to an additional digit on the ulnar side of the hand, or lateral to the 5th toe