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OBJECTIVE -The purpose of this study was to determine whether custom insoles tailored to contours of the barefoot pressure distribution and shape of a patient's foot can reduce plantar pressures in the metatarsal head (MTH) region to a greater extent than conventional custom insoles.RESEARCH DESIGN AND METHODS -Seventy regions of elevated barefoot pressures (mean peak 834 kPa under MTHs) were identified in 20 subjects with diabetes. Foam box impressions of their feet were sent to three different orthotic supply companies for fabrication of custom insoles. One company was also given plantar pressure data, which were incorporated into the insole design. Measurements of in-shoe plantar pressures were recorded during gait for the three custom insoles in a flexible and a rocker-bottom shoe. Peak pressure and force-time integral were extracted for analysis.RESULTS -In 64 of 70 regions, the shape-plus-pressure-based insole in the flexible shoe achieved superior unloading compared with the two shape-based insoles. On average, peak pressure was reduced by 32 and 21% (both P Յ 0.0001) and force-time integral by 40 and 34% (both P Ͻ 0.0001) compared with the shape-based insoles. At the midfoot, force-time integral was increased by 51 and 33% (both P Ͻ 0.01). Similar trends were found using the rockerbottom shoe.CONCLUSIONS -Compared with insoles based only on shape, the use of foot shape with barefoot plantar pressure measurements in designing custom insoles results in enhanced offloading of high-pressure areas under the forefoot. This offloading was achieved by a greater transfer of load to the midfoot without additional loading of other forefoot structures.

Diabetic foot ulcers are known to have a biomechanical etiology. Among the mechanical factors that cause foot lesions, shear stresses have been either neglected or underestimated. The purpose of this study was to determine various plantar pressure and shear variables in the diabetic and control groups and compare them. Fifteen diabetic patients with neuropathy and 20 non-diabetic subjects without foot symptoms were recruited. Subjects walked on a custom-built platform capable of measuring local normal and tangential forces simultaneously. Pressure-time integral quantities were increased by 54% (p=0.013) in the diabetic group. Peak AP and resultant shear magnitudes were found to be about 32% larger (p<0.05), even though diabetic subjects walked at a slower velocity. Lower AP and ML stress range (peak-to-peak) values were observed in the control subjects (p<0.05). Shear-time integral values were increased in the diabetic group by 61% and 132% for AP and resultant shear cases, respectively (p<0.05). Plantar shear is known to be a factor in callus formation and has previously been associated with higher ulcer incidence. During gait, shear stresses are induced with twice the frequency of pressure characteristically. Therefore, plantar shear should be investigated further from a broader perspective including the temporal specifications and fatigue failure characteristics of the affected plantar tissue.

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Plantar shear stresses are believed to play a major role in diabetic ulceration. Due to the lack of commercial devices that can measure plantar shear distribution, a number of mathematical models have been developed to predict plantar frictional forces. This study assessed the accuracy of these models using a custom built platform capable of measuring plantar stresses simultaneously. A total of 48 (38 healthy and 10 diabetic) human subjects (75 ± 20kg, 41 ± 20 yrs, 32 male, 16 female) were recruited in the study. Plantar force data were collected for 2 seconds at 50Hz. Two models (M1 and M2) reported in the literature by different groups were used to predict local shear stresses. Root mean squared errors (RMSE) were calculated to compare model data with the actual data, focusing on three parameters: location, magnitude and timing of peak shear components. RMSE values of estimated peak AP and ML shear locations were 3.1 cm and 2.2 cm for M1 and 3.1 cm and 2.1 cm for M2, respectively. Magnitude RMS error values for M1 were found to be 86.6 kPa in AP shear and 38.5 kPa in ML shear, whereas these values were determined to be 97.8 kPa and 63.5 kPa respectively by M2. Time to peak shear RMSE values averaged 17.2% in terms of the gait duration. In conclusion, shear models that were evaluated in this study performed variously depending on the shear parameter.