Insole design based on pressure distribution and foot shape under different weight bearing conditions

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Insole design based on pressure distribution and foot shape under different weight bearing conditions


Author: Tsung, Yuk-san Bonnie
Title: Insole design based on pressure distribution and foot shape under different weight bearing conditions
Degree: M.Phil.
Year: 2003
Subject: Hong Kong Polytechnic University -- Dissertations
Foot -- Mechanical properties
Foot -- Abnormalities -- Treatment
Department: Jockey Club Rehabilitation Engineering Centre
Pages: xii, 160 leaves : ill. (some col.) ; 30 cm
Language: English
InnoPac Record:
Abstract: Various types of shoe insoles are available for a range of patients and are particularly popular for the diabetes mellitus (DM) sufferers. High plantar pressure is a typical finding at ulceration sites in DM patients with peripheral neuropathy. Custom-molded insoles are often utilized for prevention and treatment of foot ulcers in subjects with DM. Previous studies indicate that properly designed insoles can help prevent neuropathic foot ulcerations by maximizing the contact area and decreasing local pressure on the foot. Because the insole can be designed based on the foot shape under different weight-bearing conditions, the resulting insole function may vary depending on the casting condition. Little information is available on what casting condition is appropriate for the needs of particular subject groups. In the present study, the plantar foot shapes of eight normal and six DM subjects were collected by an impression casting method under three weight-bearing conditions, namely, non-weight bearing, (NWB), semi-weight bearing (SWB), and full-weight bearing (FWB). The foot shapes obtained were used to quantify the 3-dimensional foot shape change with load and to design different testing insoles. The study was divided into two main parts. In the first part, quantitative comparisons of the foot shapes from three-weight bearing conditions were conducted for the whole foot and different regions of the foot. The differences in foot shape variables were then examined for different weight-bearing conditions, between left and right side, and between normal and DM subject groups. In the second part of the study, the pressure distributions were investigated by examining pressure variables in both normal and DM groups under five support conditions, namely, NWB insole, SWB insole, FWB insole, flat insole and shoe only. The pressure variables analyzed were the maximum peak pressure, the mean peak pressure, the pressure-time integral, and the mean peak contact area. Regression analysis was also used to determine the relationship between the shape of the foot cast and the resulting insole function. The results indicated that adding weight onto the foot increased the contact area, foot length and foot width, but decreased the average foot height, arch height, and arch angle. No significant differences in foot shape except the arch angle were found between the two subject groups. It was also found that customized insoles were more effective in relieving pressure than flat insoles or shoe only. The foot shape observed under the SWB condition was always an intermediate between that of the NWB and FWB conditions. Insoles cast under the SWB condition were found to be most effective for the majority of subjects. The findings may be of use in the selection of shoe size by considering the percentage change of foot shape with load. It appears that the arch angle has the strongest relationship with the regional pressure distribution, suggesting that this may be an important factor in effective insole design. The SWB casting condition is recommended for insole fabrication.

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