This paper presents details of the study undertaken to find the effects of foot sole hardness, thickness and footwear on walking-foot pressure distribution parameters (power ratio (PR)) in diabetic neuropathy. The foot sole hardness is characterized by Shore level. PR represents the ratio of high-frequency power to the total power in the power spectrum of the walking-foot pressure image distribution obtained from the optical pedobarograph. Spatial frequency distributions in the walking-foot pressure images were analysed to calculate the PR in each of the foot sole areas at different levels of foot sole sensation loss and mechanical and geometrical properties. The results show that the increase in PR in the upper foot sole Shore ranges (30-40) is 1.2-2.5 times the corresponding increase in lower Shore ranges (20-30) for some foot sole areas, implying a higher possibility of development of plantar ulcers when combined with deterioration of foot sole sensation. Plantar ulcers are found in feet with foot sole Shore values of 30, a sensation level of 45 mN and PR of 35; for Shore values of 40, sensation levels of 100 mN, with PR 52; and for Shore values above 40, sensation level > 100 mN with PR 58. Providing microcellular rubber insole footwear based on optimum hardness and thickness was found to be helpful in healing plantar ulcers in three to four weeks. Wearing preventive footwear for six months reduced hardness of the foot sole and PR values to near-normal values.

The use of optical pedobarography is presented in this article. The limitations of the analytical methods using peak pressures as a parameter for assessment of foot at risk of plantar ulcers are indicated. A new method, which takes into consideration the actual plantar pressure distribution using the power ratio PR (the ratio of high-frequency power to the total power in the walking foot pressure image distribution)and relates it to 3 levels of sensation loss is described. PR is able to detect early loss of foot sensation characterized by a loss of sensation level of 4.5 gm. The methods available in the literature for management of foot ulcers by proper footwear design, and their limitations, are discussed. A new method of individualized footwear based on matching the softness of the footwear insole with the softness of normal foot sole soft tissue (having durometer reading of 20 degrees Shore) and optimum insole thickness (12 mm) is helpful in the prevention of plantar ulcers.

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