Plantar pressures are elevated in the neuroischemic and the neuropathic diabetic foot

Clinical observation has noted that diabetic neuropathic ulcers occur frequently on the plantar surface, whereas neuroischemic ulcers seem to occur often on the foot margins. The reason for this difference in the site of ulceration is unknown, but it may be related to differences in pressure loading. The aim of the study was to compare vertical in-shoe foot pressures measured during walking (using the F-SCAN system) in four groups of patients whose degree of neuropathy was measured by vibration perception threshold (VPT).

Subjects included 14 neuroischemic diabetic patients (VPT 29.3 +/- 13.5 V) with history of ulceration on the margins of the foot, 18 patients with neuropathy alone (VPT 38.7 +/- 12.7 V) and previous history of ulceration on the plantar surface, 10 diabetic control patients (VPT 9.9 +/- 2.7 V), and 15 nondiabetic control subjects (VPT 7.0 +/- 0.5 V).

When compared with the other three groups, neuroischemic patients had higher foot pressures when measured as mean peak pressures and highest peak pressures under four areas of the foot: medial and lateral forefoot, hallux, and heel. Furthermore, when measuring the maximum pressures developed at any point under the plantar surface, the neuroischemic patients also had the most elevated pressures (757.6 +/- 135.9 kPa), significantly higher than those found in the neuropathic group (482.8 +/- 68.6 kPa, P = 0.04) and in both diabetic control patients (310.2 +/- 34.7 kPa, P = 0.008) and nondiabetic controls subjects (365.1 +/- 49.8 kPa, P = 0.007).

Despite having increased plantar pressures and a comparable degree of neuropatny, the neuroischemic patients did not have a history of ulceration on the plantar surface. These observations may have relevance to different mechanisms of ulcer formation in the neuroischemic and neuropathic foot.