If the talar head 'fully unwinds' (during the 1st trimester of the developing embryo), there is no foot lesion.  When the foot is placed in its anatomical neutral position, the big toe rests on the ground.

If the talar head does not 'fully unwind', there is a foot lesion (e.g., Primus Metatarsus Supinatus).  When the foot is placed in its anatomical neutral position, the big toe does not rest on the ground.

In the Primus Metatarsus Supinatus foot, during mid-stance, as the body’s weight is transferred anteriorly towards the forefoot, the hallux (big toe) does not touch the ground.  This occurs because the first metatarsal is elevated and inverted.  In order for the hallux (big toe) to become weight bearing, the foot must abnormally pronate (e.g., roll inward and downward).  This motion places the hallux on the ground and allows it to load (accept weight) during toe-off.






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