The effect of a midfoot cut in the outer sole of a shoe on intrinsic foot kinematics during walking

Modifications in shoe outer soles are frequently made with the intention of altering biomechanics of the foot inside the shoe. These modifications are however, generally based upon intuition with little or no scientific data for support. The purpose of this study was to quantify changes in intrinsic foot segmental kinematics between walking in a neutral shoe and a shoe modified with a clear cut forming a break underneath the midfoot, approximating the Lisfrancs joint. Five healthy male subjects participated in the study. Intracortical pins were inserted under sterile conditions and local anaesthetic in nine different bones of the foot and shank. The subjects performed 10 walking trials in both a neutral, standard, flatsoled, flexible walking shoe and in the same shoe with an approximately 1 cm deep cut aligned with the subjects’ Lisfrancs joint. Material tests showed that the cut reduced midfoot shoe bending stiffness by 23% to 38% and torsional stiffness by 23% to 28%. A helical axis approach was applied for calculating the 3D rotations about relevant joints. Kinematic trajectories in the sagittal, frontal, and transverse planes were normalised to the stance phase for seven selected joints to compare rotation patterns when wearing the two shoe conditions. Although one out of 21 ranges of motion (ROM) showed a significant difference, there is strong reason to regard this as the result of a type 1 error. Apart from this no differences in ROM occurred between the shoe conditions. The low subject number reduced the statistical power of the results. However, the study indicated that outer sole modifications that may be assumed to have clear effects upon foot kinematics, do not necessarily do so.