Simultaneous measurement of plantar pressure and shear forces in diabetic individuals.

Plantar foot ulceration is a diabetic complication whose underlying causative factors are still not fully understood. The goal of the current work was to simultaneously record plantar pressure and shear and examine the interrelationship of these forces; specifically, if peak shear and pressure occurred at the same site/time and whether adjacent shear forces had a greater tendency to be directed towards or away from each other. A custom built 16 transducer array was used to record forefoot shear and pressure during gait initiation in a cohort of 12 neuropathic diabetic individuals. The individuals were barefoot and the transducers were covered with a 5 mm thick layer of Minorplast. The greatest pressure occurred in the medial metatarsal heads (189 kPa) and the greatest shear in the lateral metatarsal heads (33 kPa). The interaction of the shear forces revealed that the plantar tissue was stretched to a greater magnitude than it was bunched (24 kPa vs 12 kPa, averaged over all regions). Normal distributions were determined for stretching and bunching in both the medial-lateral and anterior-posterior directions. When shear and pressure were considered in combination, half of the neuropathic individuals had peak shear and pressure occurring at the same site. These peak stresses did not occur at the same time (average difference of 0.186 s). The results of this study help to further characterize tissue stresses experienced on the plantar surface of the foot during gait initiation in neuropathic diabetic individuals.