Frame 1 - foot supinatus at approximately week 8 post-ovulation.  The entire plantar surface of the foot is in supinatus relative to the posterior compartment of the leg.  This is a structural relationship, not a positional change.

Frame 2 – skeletal supinatus at approximately week 8 post-ovulation (same picture as Frame 1 but with the skin removed).  If the foot stops unwinding at this point, the entire foot remains in supinatus. Podiatrists have identified this foot type as a combination rearfoot/forefoot varum.  Rothbart refers to this foot structure as the preclinical clubfoot deformity (both the calcaneus and talus remain in supinatus).

Frame 3 – early in the 8th week post ovulation, the calcaneus (and with it, the metatarsals 2-5, adjoining phalanges, middle/lateral cuneiforms and cuboid) torsionally unwind from a supinatus into a plantargrade position.  At this point only the medial column of the foot remains in supinatus (e.g., talar supinatus).  If the foot stops its torsional development at this point, it is clinically termed Primus Metatarsus Supinatus.  Prior to 2002, this foot structure was not recognized.

Frame 4 – later in the 8th week post ovulation, the talus (and with it, the navicular, medial cuneiform, first metatarsal and adjoining phalanges) torsionally unwinds from a supinatus into its adult position.  The entire plantar surface of the foot is now plantargrade (perpendicular to the leg).

Foot Embryogenesis


The animated model above demonstrates the structural unwinding of the foot during the first 8 weeks of development (Fetal Development):


  • At Stage 16 (approximately 42 days post-ovulation), the limb buds emerge with the plantar surfaces of the feet and posterior compartments of the legs facing caudadly (upwards).
  • At Stage 21 (approximately 52 days post-ovulation), the legs begin to structurally unwind.
  • At Stage 23 (approximately 63 days post-ovulation), the legs have unwound.  The entire plantar surface of the foot is in supinatus relative to the posterior compartment of the leg.

Fetal Ontogenetic Development of the Foot