The TRIO orthotic is designed to resist excessive valgus rotation. It does this by inverting the calcaneus within the heel cup. In this way the mid tarsal joint integrity is maintained and damaging compensations are avoided. TRIO also supports the proximal medial arch of the foot providing navicular stability. It is essential to allow for the first MTP joint to extend during propulsion. TRIO is designed to facilitate this by means of a cushioned recess for the first ray.