Effects of extrinsic foot musculature on hindfoot kinematics during stance phase: Implications for flatfoot pathology

Background Flatfoot deformity is a common condition, characterized by a collapse of the medial foot arch. Specific muscle dysfunctions relate to kinematic changes of the hind foot (plantarflexion, abduction and valgus) inducing the onset of flatfoot deformity. However, to determine a causal relation between individual muscle action, foot bone motion and flatfoot, in vitro experiments are needed. Our hypothesis states that inducing altered muscle forces in cadaveric feet causes alterations in kinematics, representative for flatfoot deformity [1,2]. Materials and methods A gait simulator was used to test seven cadaveric feet. Pneumatic actuators applied forces to the foot tendons, simulating flatfoot related pathologies: contracture of M. Triceps Surae (C-TS) and Mm.Peronei (C-PE); weakness of M.Tibialis Posterior (W-TP) and the pretibial muscles (W-PT); combined contracture of TS and PE (P1) and combined TS contracture with TP weakness (P2). Trajectories of bone-embedded LED clusters were measured during a one second roll-off and resulting ankle, subtalar and talonavicular joint motion was calculated.