Preaxial and postaxial borders describe where the flexor and extensor compartments of the limb meet during fetal limb bud development. These borders are also conveniently marked out by veins.
Preaxial (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: preaxial polydactyly involves first digit of the hand (radial side) or first digit of the foot (big toe)
Postaxial (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: postaxial polydactyly refers to an additional digit on the ulnar side of the hand, or lateral to the 5th toe