Effect of foot orthoses on 3-dimensional kinematics of flatfoot: A cadaveric study

Objective: To test in cadaveric feet the hypothesis that prefabricated foot orthoses will improve arch alignment in flatfoot deformity. Design: Experimental, paired comparisons. Setting: Biomechanics laboratory. Cadavers: Nine cadaveric lower-extremity specimens with no abnormalities. Interventions: To evaluate the performance of 2 orthoses specimens were tested in 4 combinations: intact, flatfoot, flat-foot with shoe and orthosis 1, and flatfoot with shoe and orthosis 2. To simulate the midstance phase of gait, loads were applied to 5 tendons and an axial load equivalent to two thirds of the standing load was applied to the foot's plantar surface. Main Outcome Measures: Arch height and tarsal bone positions before and after a flatfoot deformity created by ligament sectioning; tarsal bone positions determined with a magnetic tracking system. Results: After ligament sectioning, the average decrease in arch height with a shoe applied was 4.6±1.6mm (8%); with orthosis 1, mean arch height increased 0.7±0.6mm (P=.008); with orthosis 2, it increased 0.3±0.5mm (P=.05). With both orthoses, arch height after sectioning was significantly less than that of the normal arch. Compared with the flatfoot condition, metatarsal-talar alignment improved in plantar flexion and inversion with both orthoses but did not approximate normal with either orthosis. Calcaneal-tibial position did not improve with either orthosis and was markedly different from that in the intact foot with either orthosis. No difference was found between the 2 orthoses except for metatarsal-talar motion in external rotation (P=.014) and eversion (P=.026). Conclusions: Arch alignment improved significantly but to a limited degree (<2%) in cadaveric feet with the use of orthoses. Hindfoot valgus malalignment did not consistently improve by the use of shoe inserts.