The plantar lateral heel area of the positive cast is “flattened” to create a valgus wedge effect within the heel cup. This causes the center of the force that the orthosis is applying to the heel to shift laterally, increases pronatory torque, and acts to limit inversion or encourage eversion of the rearfoot on the orthosis. This modification is useful when treating pathologies caused by excessive supination such as lateral ankle instability, pes cavus and medial knee osteoarthritis.