Pedobarographic Method to Evaluate the Stance-phase Deformability of the Shod Foot with Foot Orthosis

Introduction: Excessive foot motion during the stance phase of gait is the result of foot hyper-deformability, which is often treated with a foot orthosis. The effectiveness of a foot orthosis in reducing excessive foot motion by reducing the deformability of the foot during the stance phase of gait can be influenced by footwear. A foot orthosis designed to reduce excessive foot motion may not effectively reduce the stance-phase deformability of the shod foot. It is thus important to assess the influence of different footwear on the effectiveness of a foot orthosis in reducing excessive foot motion. A method to assess the effectiveness of a foot orthosis in reducing the stance-phase deformability of the shod foot has not been reported in the literature. Materials and Methods: This technical note addresses a novel procedure using digital platform-based pedobarography for evaluating the stance-phase deformability of the shod foot to assess foot orthotic effectiveness. The method involves first standardizing the acquisition of the plantar pressure profile of the shod foot by attaching a smooth and homogeneous removable outsole to the shoe, and then analyzing the deformation of the plantar pressure profile by fitting an ellipse to the profile and measuring the change in the ellipticity (axial ratio) of the best-fit ellipse. Because the ellipticity of the plantar pressure profile changes during the stance phase of gait, the true (logarithmic) strain in the axial ratio of the best-fit ellipse represents the correct relative measure of deformation of the profile. The stance-phase deformability of the shod foot is quantified as the total deformation of the plantar pressure profile throughout the stance phase of gait. An example of the method is provided with a single-subject assessment of foot orthotic effectiveness that has useful applications in clinical biomechanics. Results: The same foot orthosis designed to reduce excessive foot motion for a single subject was inserted into two different shoes: a dress shoe and an athletic shoe. Whereas the foot orthosis in the athletic shoe effectively reduced the stance-phase deformability of the shod foot, the foot orthosis in the dress shoe did not reduce excessive foot motion. Conclusions: Evaluating the stance-phase deformability of the shod foot is important for assessing the effectiveness of foot orthoses in reducing excessive foot motion in different footwear. The method is easy to implement in a clinical setting, and may promote successful clinical outcomes when dispensing foot orthoses to treat excessive foot motion. Clinical Relevance: This technical note describes a clinically accessible approach to evaluate the stance-phase deformability of the shod foot for assessing the effectiveness of foot orthoses in reducing the deformability of the hyper-deformable foot. The method has clinical implications for potentially improving functional outcomes in the orthotic treatment of foot pathomechanical disorders.