Investigation of Radiological and Biomechanical Effect of Wedge-shaped Hindfoot Orthotic Insoles on Flexible Flatfeet

Research Type: Level 3 - Retrospective cohort study, Case-control study, Meta-analysis of Level 3 studies Introduction/Purpose: Wearing inverted orthotic insoles is a common clinical treatment for patient with flexible flatfeet, however, the mechanisms behind this was barely studied. Therefore, a study integrating computational modelling and clinical experiment was performed to investigate the radiological and biomechanical mechanisms of wedge-shaped hindfoot orthotic insoles (WHOI) for the correction of flatfeet. Methods: Weight-bearing X-ray were used to measure the talonavicular coverage angle (TNCA) and hindfoot valgus angle (HVA) before and after use of Orthotic insole. Muscle activities with barefoot and inverted insoles were measured with surface EMG (Noraxon EMG Ultium ESP，USA). The plantar pressure at standing condition was measured via an insole pressure measurement system (Novel Pedar System, Germany). Finite element (FE) model was developed in Abaqus/CAE 6.14 (Dassault, France), and FE analysis with and without Orthotic insole were studied. Results: The TNCA and HVA of participants with flexible flatfeet was corrected to normal range by wearing the orthotic insoles of 15° inverted angle (P < 0.001). The electromyography signal of gastrocnemius was increased by 89% and the pressure center of plantar was moved laterally with the application of the orthotic insoles. The FE results showed that the maximum stress on the talus-calcaneus contact surface was reduced by 39%, the talus-navicular reduced by 28%. The stress of medial ligaments and plantar fascia were reduced by 6% to 13% with inverted insoles compared to barefoot. Conclusion: It was concluded that the correction of flexible flatfeet by inverted insoles was mainly attributed to the active action of medical calf muscles, and is beneficial to ease the pain of ankle and reduce the risk of plantar fasciitis. Figure 1. The experimental processes. (A) X-ray on Saltzman view, (B) Orthotic insoles with different inversion angle, (C) Measurement of muscle activities by SEMG, (D) Collection of plantar pressure and partition. (E) Geometrical model, (F) FE model of barefoot, (G) FE model of foot with orthotic insole with a 15° inverted angle. (H,I) TNCA and HVA of barefoot and the 15° inverted insole. (J) Surface EMG of TA, PL, GM and SOL. (K) The plantar pressure distribution wearing insoles with different inversion angle measured by experiment. (L) Stress distribution predicted by FE analysis.