Forefoot inversion is an rare biomechanical problem due to the alignment of the structures in the pedal area. When the calcaneus is held vertical or in its neutral posture, the medial or inside of the pedal region is off the ground. To get the foot to the ground, the foot has to over-exert in the rearfoot to lower it. https://therunninginjury.com/forefoot-varus/37/