A study of in-shoe plantar shear in patients with diabetic neuropathy

Abstract

Objective. To quantify in-shoe plantar shear in diabetic neuropathic feet. Design. Plantar shear stresses are measured in a group of six patients with a history of diabetic neuropathic ulceration. Background. Although elevated pressure between foot and shoe frequently found in diabetic neuropathic patients has been linked to a raised incidence of plantar ulceration, the shear component of stress at this interface is as yet unquantified. It is suggested that its effects may be equally damaging. Methods. Measurements of shear were made locally beneath the medial four metatarsal heads and heel during unpaced gait in orthopaedic footwear, using a bi-axial magneto-resistive shear transducer. Similar methodology was previously employed on a group of asymptomatic adults, thereby allowing comparisons to be made. Results. Overall the maximum shear stress for this patient group (73 kPa) was not significantly different to that in the asymptomatic group (87 kPa). However the patient group exhibited lower magnitudes of shear stress under the third/fourth metatarsal heads (average 51/39 vs. 86.5/71 kPa, respectively) and higher magnitudes under the first/second heads (73/64 vs. 35/31 kPa, respectively), indicating a medial shift. Step-to-step variability of maximum shear measured under the third metatarsal head showed an increase in the transverse component (coefficient of reliability 67% vs. 98%). Conclusions. Although the overall patterns of shear are broadly similar to the asymptomatic group, these pilot trials indicate a medial shift in shear loading under the forefoot coupled to increased step-to-step variability in the diabetic group. 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. Whereas the pressure component of stress is widely studied, the shear component is poorly described although it may be of equal importance.