The development of a kinematic model to quantify in-shoe foot motion

Methods and material Twenty-four participants (mean age 21.8 yrs ± 3.5 yrs, height 1.75 m ± 0.09 m and body mass 71.0 kg ± 10.6 kg) were recruited. A marker set consisting of 20 x 10 mm markers was developed to track in-shoe joint kinematics [1]. Reliability and accuracy estimates of calibration marker placement on the shoe were determined. To track inshoe foot motion, 12 mm diameter holes were punched in the shoe upper, with 25 mm marker wands mounted on the skin through the shoe (Figure 1). The marker set defined a four-segment kinematic model of the foot and ankle (shank, hindfoot, midfoot-forefoot complex and hallux). To define model parameters and moments of inertia, a CT scan was taken of 12 participant’s feet. The reconstruction of 3-D bone geometries from two-dimensional grey scale images (DICOM format) was conducted in Simpleware software. Shoe-mounted marker offsets and moments of inertia were inputted to Visual3D. The kinematics of the shoe were described before and after modification to quantify post-modification shoe integrity. The model was deemed sensitive if it detected changes in joint kinematics between conditions that were both statistically significant and greater than the calculated Standard Error of Measurement (SEM) [2].