Pattern of abnormal tangential forces in the diabetic neuropathic foot
Introduction
Abnormal plantar pressures are considered to play a major role in the pathogenesis of neuropathic ulcers in the diabetic foot [1], [2], [3], [4], [5].
Stokes [1] noticed that ulcers develop in the sites of the highest load, such as the plantar surfaces of the metatarsal heads and toes. Since then, many other authors have described “high plantar pressures” in the diabetic neuropathic foot and their relationship with ulcer development [2], [3], [4], [5].
However, several authors have also formulated the hypothesis that the increased plantar pressure alone, and thus the increased vertical stress, is not the only determinant of tissue breakdown, and that tangential stress should also be considered. The hypothesis was mainly based on the following grounds:
- 1.
the ulcer risk threshold, in terms of plantar pressure peaks, has not yet been clearly established (there is a wide overlap between normal plantar pressure peaks distribution and pressure peaks distribution recorded in neuropathic patients with ulcers) [6], [26];
- 2.
although callus formation appears to have a mechanical etiology, not all areas of high plantar pressures develop callus (the exact mechanical stimulus for callus formation is still unclear) [7];
- 3.
not all ulcers develop at highest-pressure sites [8].
Conversely, the dynamometric platforms measure all three GRF components. The main drawback is that they only record the resultant of GRF measured under the whole foot during a walking cycle; this means that these devices do not extrapolate forces acting on specific foot subareas. Moreover, they do not show the foot position on the platform, which prevents the identification of the above subareas and the computation of their contribution to total GRF [9], [10].
The recent implementation of a piezo-dynamometric integrated platform, obtained by superimposing a pressure platform over a force platform [11], has allowed us to compute the three components of GRF expressed by specific selected foot subareas.
The aim of the present study was therefore to describe the tangential and vertical forces for total foot and selected subareas of interest in diabetic patients, with or without neuropathy or previous ulceration, and to compare them with those recorded for control subjects.
Section snippets
Population
Sixty-one subjects from an outpatient clinic were recruited for the study: 27 diabetics without neuropathy (D) and 34 diabetics with neuropathy, 19 of whom without previous ulceration (DN) and 15 with previous ulceration (DPU). 21 age-matched healthy volunteers were recruited to serve as control group; the anamnesis and an objective clinical examination excluded neuro-musculo-skeletal pathologies in all the volunteers that may influence their gait.
The study was approved by the local ethics
Results
Demographic data are provided in Table 1. There were no significant differences between groups for age, BMI, metabolic control or diabetes duration. VPT and NDS were significantly increased in DN with respect to D and C; in DPU they were significantly increased also with respect to DN.
Discussion
The study of the three GRF components for total foot and for the three major subareas of interest allowed us to describe in detail the foot loading during the different time points of the stance phase of the gait cycle.
As reported in Section 1, the relationships used to estimate the tangential forces acting on foot subareas have been analytically deduced under simplified hypotheses. Neverthless the following observation supports the validity of the estimation procedure.
Fig. 5 reports the time
Conclusions
The availability of an innovative instrumentation, that measures the three GRF components under well-defined subareas of the foot, namely the heel, metatarsals, and hallux, has made it possible to describe some of the changes that these components show in patients with peripheral neuropathy. The main conclusions from the above discussed data can be summarized as follows:
- •
the evaluation of the three GRF components for the whole foot and for selected subareas provides substantial evidence of
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