In-Shoe Foot Pressure Measurements in Diabetic ... - Diabetes Care

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igh foot pressures are common in diabetic neuropathic patients and are caused by small muscle atrophy, clawing of the toes, and prominence of the metatarsal heads (1,2). Recent studies have shown that high foot pressures are risk factors for foot ulceration and may be helpful in identifying at-risk patients (3). Optical pedobarography, which can only measure foot pressures MARC R. SARNOW, DPM BARRY I. ROSENBLUM, DPM without shoes, has been used in most of ARISTIDIS VEVES, MD JAMES S. CHRZAN, DPM JOHN M. GIURINI, DPM GEOFFREY M. HABERSHAW, DPM these studies, and therefore, little is known about the effect of shoes in reducing and/or redistributing these high foot OBJECTIVE — To measure in-shoe foot pressures in diabetic patients and healthy pressures (4). The recent development of small, subjects and compare them with the foot pressures when they walked without their thin sensors has allowed the reliable meashoes. surement of in-shoe foot pressures (5,6). RESEARCH DESIGN A N D M E T H O D S — Forty-four diabetic patients at Because diabetic patients wear shoes for risk of foot ulceration and 65 healthy subjects were matched for age, sex, race, and most of the day, in-shoe foot pressure weight. Neuropathy was evaluated clinically, and the F-Scan program was used to measurements may be more important in measure the foot pressures. Foot pressures were measured with the sensors placed in predicting foot ulceration than are bare the shoes (S measurements), between the foot and the sock with shoes (H measure- foot measurements. The same technique may also play a pivotal role in the design ments) or with their socks alone (B measurements). of proper footwear that will be able to reRESULTS— In the control group, significant differences were found between S duce high foot pressures and prevent foot (4.77 ± 1.87kg/cm2)andHmeasurements(5.12 ± 1.87kg/cm 2 ,P 5 was considered abnormal. The vibration perception threshold (VPT) was measured at the great toe on the dominant side of each patient using a Biothesiometer (Bio-Medical, Newbury, Ohio). The age-related upper normal limits were derived from previously published data (6). The cutaneous pressure perception threshold (CPPT) was examined by using the Semmes-Weinstein monofilaments (Gillis W. Long, Hansens Disease Center, Carville, LA). The CPPT was considered abnormal in patients who were unable to perceive mononlament grade 5.07 or more (7). Peripheral neuropathy was diagnosed when at least two of the previous four tests (NSS, NDS, VPT, and CPPT) were abnormal. Peripheral vascular disease was assessed according to the presence or absence of foot pulses and/or a history of claudication. The F-Scan program (Tek-Scan, Boston, MA) was used to measure foot pressures. The principles of this technique have been described elsewhere (10). The F-Scan uses an insole consisting of 960 sensor units or elements. This results in a spatial resolution of 5 mm2 representing the size of the individual ele-

1994

ment. In short, our study used a fourelement square equivalent to 10 mm'. The sensor is 0.018 cm thick and can be adjusted to accommodate any shoe size. It can then be inserted in the shoe or taped under the foot of the subject. When the subject is walking, vertical forces are measured by each 5 mm2 element. The sensor is calibrated using a single-limb support model. Subjects' body weights are entered into the computer, which sets the value according to the force generated in single-limb support. Once calibrated, the various testing parameters are performed without any other need for recalibration. The sum of the elemental forces generated are stored in the computer. Using this raw data, the computer generates a force-time curve. The peak of these curves is then analyzed relative to body weight to estimate the accuracy of the calibration, boot pressures in each subject were evaluated under three conditions. First, the sensors were placed in the shoes to measure the pressure between socks and shoe insoles (S measurements). The sensors were then taped to the bare foot, the subjects wore their shoes and socks, and the pressure between the hosiery and the foot was measured (H measurements). Finally, the subjects removed their shoes, and the pressure was measured while the subjects were walking in their socks alone (B measurements). The total force under each foot and the highest pressure under the heel, the forefoot, and/or any other area under the foot were measured for three consecutive footsteps for each condition, and their mean was entered for statistical analysis.

Statistical analysis The Minitab statistical package (State College, PA) for personal computers was used for the statistical analysis. The Mann-Whitney U test was used for comparisons between the different groups, Wilcoxon's rank-sum test for the comparison of the same variable in the same group under different conditions, and the Spearman correlation coefiicient r for the

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In-shoe foot pressure measurements

Table 2—Results offoot pressure and total force measurements

Pressures

Diabetic group

Control group

S max H max B max S heel Hhcel B heel S forefoot H forefoot B forefoot S force H force B force

5.28 ± 2.22 5.27 ± 2.39 8.77 ± 4.68 3.56 ± 1.41 3.48 ± 1.41 6.46 ± 4.24 5.09 ± 2.19 5.10±2.42 8.17 ± 3.98 99 ± 22 100 ± 24 96 ± 23

4.77 5.12 7.23 3.31 3.58 5.08 4.68 4.96 6.86 96 97 96

P

± 1.87 ± 1.87 ± 2.95 ± 1.19 ± 1.11 ± 2.06 ± 1.92 ± 1.92 ± 2.80 ± 22 ± 22 ±22

NS NS