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

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 foun d 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 me tatarsal heads and heel during unpaced gait in orthopaedic footwear, using a bi-axial magneto-resistive shear transducer, Similar methodology was prev iously employed on a group of asymptomatic adults, thereby allowing compari sons to be made. Results. Overall the maximum shear stress for this patient group (73 kPa) w as 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, respectiv ely) and higher magnitudes under the first/second heads (73/64 vs. 35/31 kP a, respectively). indicating a medial shift. Step-to-step variability of ma ximum 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 i n the diabetic group.