Diabetic feet at risk of plantar ulcers: a new method of analysis of walking foot pressure images with changes in foot sole properties

This paper presents the results of the research study undertaken on diabetic neuropathic subjects to find the relationship between the walking foot pressures parameter power ratio, PR (the ratio of high frequency power to the total power in the power spectrum of the walking foot pressure image obtained by optical pedobarograph), and the foot sole hardness at different levels of sensory loss. Spatial frequency distributions in the walking foot pressure images are analysed to calculate PR in each foot sole area for different levels of foot sole sensory loss and hardness. The results show that mean value of parameter PR is able to clearly distinguish the different levels of sensation loss. The increase in PR values for diabetic subjects in the upper sensation loss region (S= 7.5 to 10 gm) is 2.1 to 5.0 times the corresponding increase in lower sensation loss region (S= 3 to 4.5 gm). The high increase of PR values in the foot sole areas may be responsible for high incidence of ulcers. The analysis also shows that the increase in PR in the upper foot sole hardness or Shore levels (30-40) is 1.4 to 3.3 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. Thus, different degrees of increase of the factors, namely, sensation loss, hardness and foot pressure distribution parameter may contribute to the formation of foot sole ulcers in diabetic subject.