Standing foot pressure image analysis for variations in foot sole soft tissue properties and levels of diabetic neuropathy

This paper presents the results of the study undertaken on diabetic neuropathic subjects to find the relationship between the standing foot pressure parameter, power ratio (PR, ratio of high frequency power to the total power in the power spectrum of standing foot pressure image distribution obtained by optical pedobarograph), the foot sole hardness, and foot sole thicknesses at different levels of sensation loss. Spatial frequency distributions in the standing foot pressure images are analyzed to calculate the PR in each foot sole area for different levels of foot sole sensation loss and mechanical properties of foot sole hardness and thicknesses. The results show that the increase in PR in the upper foot sole hardness or Shore levels (30-40) is 1.4-3.7 times the corresponding increase in lower Shore levels (20-30), implying a higher possibility of development of plantar ulcers when the plantar surface becomes hard, combined with increase in sensation loss. It is observed that plantar ulcers are found to develop (i) for foot sole hardness or Shore values of 30 at sensation level of 4.5 gm and (ii) for Shore values of 40 and above at sensation levels of 10 and >10 gm, PR being high (29, 48 and 58, respectively) and the foot sole thicknesses are also greater than the corresponding normal values. Thus, different degrees of increase of all the three factors, namely, hardness, thickness and foot pressure distribution parameters in different levels of loss of foot sole sensation (or degrees of neuropathy) contribute to formation of foot sole ulcers in diabetic subjects. ? 2003 Elsevier SAS. All rights reserved.