An investigation into the effect of customised insoles on plantar pressures in people with diabetes

Introduction High plantar pressures have been shown to be a key risk factor for foot ulceration in people with diabetes. Consequently, patients are often prescribed insoles designed to reduce pressure. New technologies, such as plantar pressure measurement devices and 3D foot scanners, have the potential to improve insole design. However, it is not clear to what extent such technologies are currently being used by clinicians, nor which other factors influence clinical decision making in the prescription of insoles. Furthermore, there has been minimal previous research designed to understand how best to use technology to improve insole design for patients with diabetes. Methods This thesis comprises four separate studies: a first qualitative study aimed at understanding the factors influencing practitioner decision making and the current role of technology. Three other quantitative studies were then performed to help understand the potential role of technology in designing insoles for medium-risk patients with diabetes and neuropathy. For each of these three studies, individually customised insoles were manufactured for every patient using CAD/CAM technology and data on both plantar pressure and foot shape. The first study investigated the reproducibility of plantar pressure collection in patients with diabetes and neuropathy while wearing the customised insoles, while the second investigated the effect of systematically varying two insole design features, metatarsal bar position and cushion material, on plantar pressures. In the final study, associations were investigated between changes in plantar pressure with different customised insole designs and specific structural and biomechanical foot characteristics of each participant. Results The findings of the qualitative study suggest that current clinical practice is based on training but that it develops in time based on practitioner’s clinical experience. Technology is not normally used because the data is considered too complex to use and interpret. However, practitioners agreed that they would use technology that is more user-friendly and focused on improving patient outcomes. The first quantitative study showed a relatively high level of pressure variability (up to 55 KPa under metatarsal heads) which we suggest is a characteristic of patients with diabetes and neuropathy. The second quantitative study showed that customised insoles which incorporate both a metatarsal bar and cushioning materials in front of the bar are effective in reducing peak pressures (PP). However, the optimum design was that which incorporated a combination of poron (cushioning material) with a metatarsal bar, located distal or on the point of PP. In the final quantitative study, specific individual characteristics which predicted PP changes were identified, such as tissue stiffness and joint range of movement (ROM). Based on these findings, some tentative recommendations for insole prescription were suggested. For example, to reduce PP under the 1st metatarsal when high tissue stiffness is present use a metatarsal bar just behind the PP combined with poron if there is a low range of movement of the 1st metatarsophalangeal joint. But if there is a high range of movement of the 1st metatarsophalangeal joint, a distal metatarsal bar with Poron should be used. Conclusion Taken together, the results of this work show that practitioners are willing to embrace more technology within their clinical practice and that it could be used to improve the efficacy of insoles designed to reduce plantar pressures for people with diabetes.