Structural and functional aspects of the diabetic foot

INTRODUCTION:: It has been well documented that, on average, patients with diabetes mellitus (DM) have higher plantar pressures than persons without DM, and there are several hypotheses why this may be -- many focused on the role of peripheral neuropathy. The purposes of this study were: (A) To identify and quantify structural differences between age-matched diabetic and non diabetic subjects, and (B) to develop predictive equations for peak pressure in these same patients. METHODS:: Standardized lateral and dorsi-plantar weight bearing plain radiographs of the right foot and ankle of 50 symptom free (NDM), 32 diabetic with no signs of neuropathy (NNP), and 73 diabetic neuropathic (NP) subjects were taken by a single radiographer. Twenty six angular and linear measurements were then made from the films. Plantar pressure distribution from three first step walking trials were collected and peak pressures at 10 discrete sites were determined for each step, and averaged. A one-way ANOVA with Tukey post hoc tests was conducted to test for differences between the means of each of the 26 radiographic measurements at the 0.01 significant level. Regression analysis was also used to predict the ln(pressure) under the heel, midfoot, mth1, mth2, and mth5 regions from the radiographic measurements, range of motion at the talocrural and first metatarsophalangeal joints and weight, for each of the 3 groups independently. RESULTS:: Significant differences were found among the three groups in 5 of the 26 radiographic measurements (Table 1). These included the thickness of the first, second and third metatarsals from the AP view (MT1, MT2 and MT3 -- generally > in NP), and the sesamoid height (NP > others) and fifth metatarsal head height (NDM < others). In addition, non significant trends were found in 4 other radiographic measurements. Regression analysis identified groups of up to five[Table: see text] predictors which accounted for between 27% and 62% of the variance in peak plantar pressure in different subject groups and foot regions. DISCUSSION AND CONCLUSIONS:: We conclude that objective differences in foot structure are present in diabetic neuropathic subjects, and that DM per se is apparently not a factor in these differences. We also concluded that static foot structure accounts for anywhere between approximately 30% to 60% of the variance in regional peak pressure, depending on the region investigated. In most cases predictions were higher in the midfoot and forefoot.