A study of in-shoe plantar shear in normals

Objective. To quantify features of in-shoe plantar shear in asymptomatic adult gait. Design. In order to standardize footwear conditions and facilitate later comparison to patient groups, measurement is made in a group of adults walking freely in stock orthopaedic footwear. Background. Better data on plantar shear is required to complement well-documented pressure data for an overall picture of plantar stress. Methods. Measurements were made locally beneath the medial four metatarsal heads and heel using biaxial transducers mounted flush into an inlay. Pressure distribution was also measured. Results. The shear data revealed common features in the shear pattern occurring at defined phases of gait, with good inter-step reliability. For the five sites of interest, these values ranged from 24 kPa to 70.4 kPa, and 31 kPa to 86.5 kPa for individuals wearing nylon hose or hose-free respectively. Maximum shear occurred more laterally than maximum pressure. Conclusions. Features of plantar shear were not always as expected; for example the forward thrust at push-off was not reflected in the anteroposterior shear stress. Because of the inter-subject variability, study of a larger group is indicated. Relevance Mechanical stress at the plantar interface between foot and shoe is of particular clinical relevance to the formation and management of ulcers in diabetic neuropathy. It is also of relevance to shoe and orthotic design for various foot pathologies. This study provides reliable data on the shear component of plantar stress for which, unlike the well-documented pressure component, there is only sparse data so far available.