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

OBJECTIVE: 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). RESEARCH DESIGN AND METHODS: 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). RESULTS: 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). CONCLUSIONS: 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.

The effect of regular callus removal on foot pressures.

The optimum frequency of callus removal is unknown. This study shows that in-shoe dynamic plantar pressure measurement can quantify the effect of callus removal in relation with the frequency of podiatric treatment in diabetic ulcer patients. Three groups of diabetic neuropathic patients were studied. Group 0 consisted of six patients who presented for the first time ever for callus removal and who did not have a history of ulceration. The other two groups had a history of ulceration and required regular podiatry treatment: every 6-8 weeks for 10 patients in group A, and every 3-4 weeks for eight patients in group B. Peak plantar pressures were measured using the F-SCAN system, before and after removal of callus, which was weighed to further quantify the effect of podiatry. When callus was removed, peak pressures fell by 32.1 +/- 8.4% (p = .014) in group 0, by 30.9 +/- 4.5% (p < .005) in group A, and by 24.8 +/- 4.0% (p = .005) in group B. The mean weight of callus removed was not significantly different in the three groups. This suggests that the weight of callus is unlikely to be a reliable guide to assess the time intervals between podiatry appointments. However, the measurement of plantar pressures using a dynamic in-shoe plantar pressure device has proven to be a functional, objective, and quantifiable indicator in the assessment of podiatric treatment.

NO-dependent smooth muscle vasodilatation is reduced in NIDDM patients with peripheral sensory neuropathy.

In order to determine the involvement of denervation in endothelium-independent, nitric oxide (NO)-dependent smooth muscle vasodilation, we have measured vascular endothelial and smooth muscle function in three groups of age- and sex-matched patients: 8 patients with non-insulin-dependent (Type 2) diabetes mellitus (NIDDM) with neuropathy; 7 NIDDM patients without neuropathy; and 10 non-diabetic control subjects. Laser Doppler probes were used to measure blood flow in the dorsum of the left foot. Vascular endothelial response was assessed by measuring vasodilatory responses to iontophoretic application of acetylcholine to the dorsum of the foot. Vascular smooth muscle activity was assessed by the response to iontophoresis of sodium nitroprusside (SNP)-a NO donor and direct vasodilator. The vasodilator response to acetylcholine, expressed as the ratio of peak to basal blood flow, was significantly reduced in both diabetic groups when compared to non-diabetic controls (geometric mean x/divided by anti-logged SD 9.81 x/divided by 1.65 versus patients with neuropathy 3.50 x/divided by 2.03, p < 0.005 and diabetic non-neuropathic subjects 3.49 x/divided by 1.67, p < 0.005). The difference between the two groups of diabetic patients was not significant. In contrast, the vasodilatation to nitroprusside was significantly reduced only in the diabetic neuropathic patients, significantly lower than in either the non-neuropathic diabetic controls or the non-diabetic controls (2.1 x/divided by 2.0 versus 6.42 x/divided by 1.56 and 7.02 x/divided by 2.05, p < 0.005). This indicates that neuropathy is important in abnormalities of endothelium-independent vasodilatation.

Time-dependent behaviour of a force-sensitive resistor plantar pressure measurement insole.

Thin pressure-measuring insoles have enabled new clinical studies of in-shoe distribution of plantar pressure. One of these new devices, based on force-sensitive resistor (FSR) technology, exhibits time-varying behaviour due to the mechanical properties of the sensor materials. This has been variously attributed to initial bedding in, wear or time-dependency behaviour. Cyclic and sustained loading were used in laboratory conditions to investigate this phenomenon. The results show that the sensitivity of the sensor varies rapidly over the first minute of loading. There is also a slower long-term effect which reduces over time. From this information, procedures for optimal calibration and use are suggested.

The value of the Neurometer in assessing diabetic neuropathy by measurement of the current perception threshold.

The Neurometer is a relatively new device for assessing neuropathy by measuring current perception threshold (CPT). The study aim was to assess the ability of the Neurometer to distinguish between different types of nerve fibre damage by using different frequencies (2000 Hz, 250 Hz, and 5 Hz) of electric stimulus (high frequencies for large fibres and low frequencies for small fibres) and comparing the results with standard sensory tests of vibration perception threshold (VPT) and thermal perception threshold (TPT). CPT was determined on index finger and great toe of 51 patients with diabetic neuropathy and 28 non-diabetic control subjects, age and sex matched. CPT in neuropathic patients could be distinguished from controls at all three frequencies in both feet and hands (p < 0.05). The best correlation was found between CPT at 2000 Hz and VPT (r = 0.48, p < 0.001) in the feet suggesting a degree of neuroselectivity. Internal correlations between CPT at the three frequencies showed the weakest correlation between CPT at 2000 Hz and 5 Hz (r = 0.27, p < 0.005), suggesting also that possibly different types of fibres were examined. CPT reproducibility was better in control (CV = 6.4-27.7%), than in neuropathic subjects (CV = 28.4-52.3%), although the coefficient of variation was comparable to that of standard tests of sensory function, VPT and TPT. The Neurometer is a simple instrument to use in clinical practice. It has a degree of neuroselectivity but like all subjective sensory tests has a large variability.

Abnormal digital pressure measurements in diabetic neuropathic foot ulceration.

The diabetic neuropathic ulcer is typically slow to heal and recurrent. Macrovascular insufficiency is usually excluded as foot pulses are present and ankle:brachial pressure ratios are not decreased. These assessments cannot however exclude more distal vascular disease. Digital pressure measurements enable a reliable assessment of the distal peripheral vascular status to be made. The aim of this study was therefore to use toe pressures to assess the contribution of distal ischaemia in the pathogenesis of the neuropathic ulcer. Sixteen diabetic patients with recurrent neuropathic foot ulceration had their toe pressures compared to 10 neuropathic patients without a history of foot ulceration, 10 diabetic control subjects, and 11 normal subjects. Four non-diabetic patients with neuropathy and foot ulceration were also assessed. All subjects had ankle:brachial pressure indices > or = 1. Toe pressure was assessed using laser Doppler flowmetry to record the return of skin blood flow. The toe:brachial pressure index (TBI) was then calculated. The diabetic patients with a history of recurrent neuropathic ulceration, had the lowest mean TBI, 0.63 +/- 0.14 (SD), compared to the non-ulcerated diabetic neuropathy patients, the diabetic control subjects, and the normal subjects. 0.84 +/- 0.11, 0.82 +/- 0.1, and 0.81 +/- 0.07, p < 0.01, respectively. Three of the four non-diabetic patients with neuropathic foot ulceration also had an abnormally low TBI. Reduced toe pressure measurements are thus found to be associated with neuropathic foot ulceration. The contribution of distal ischaemia in the pathogenesis of the diabetic neuropathic foot ulcer needs to be evaluated.