Forefoot orientation predicts amplitude and duration of pronation
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Prior research has shown that an individual with a large forefoot varus is five times as likely to have a total hip replacement. However the biomechanical mechanism underlying these injuries remains poorly understood. It is proposed that this may be because of two factors. First, the traditional clinical measure of rearfoot and forefoot structure has poor reliability and questionable validity. Second, few studies include forefoot kinematics when investigating the relationship between foot structure and injury. We conducted two studies to investigate the validity of a new clinical measure of foot orientation. The purposes of both studies (walking and running) were twofold: 1) To determine if a new non-weight bearing clinical measure of forefoot and rearfoot orientation is a valid predictor of measures of forefoot and rearfoot orientation at forefoot and rearfoot contact respectively, during gait; and 2) to determine the differences in duration and amplitude of pronation between two groups divided on degree of varus foot orientation. Methods: All fourteen subjects had a forefoot varus greater than or equal to 15° using a new clinical orientation measure. For the new measure, clinical forefoot and rearfoot orientations were obtained from digital photographs. Using a 3D motion capture system forefoot and rearfoot orientations at ground contact were captured while walking at three speeds and running at three speeds. Duration of pronation was defined as the percent of stance between contact and re-supination. Results: The new clinical measure of forefoot orientation predicted the forefoot orientation at ground contact but the clinical rearfoot orientation did not. The group of individuals with a large forefoot varus orientation at forefoot contact had greater amplitude and duration of forefoot pronation during walking and greater amplitude of forefoot and rearfoot pronation during running. Rearfoot orientation, measured clinically and at ground contact did not predict any of the stance variables. Conclusions: These studies suggest that a new clinical measure of forefoot structure using an extrinsic reference frame can predict foot behavior during gait and that forefoot structure may significantly contribute to musculoskeletal injuries associated with foot structure.
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