Determining Optimal Foot Shape Capture Methods to Prioritize Offloading in An Accommodative Insole

About This Grant

Custom accommodative insoles are prescribed to patients with diabetes who are at risk of developing plantar ulcers. Custom insoles aim to reduce plantar pressures through an accommodating insole with a weight-bearing surface that conforms to the patient’s foot. The current standard of care (SoC) insoles are typically constructed from an EVA foam block milled to match a patient’s foot shape, captured via a foam crush box, and then covered with a uniform sheet of poron and plastazote foam. The material properties of these insoles are generic and not patient specific. We have developed insoles that not only have patient specific shape but also patient specific regions of modulated stiffness. Our insoles are more effective in reducing plantar pressure in the areas of high pressure than the current SoC insoles in a healthy population and investigation is underway with similar preliminary results in individuals at risk of developing a plantar ulcer. Our work suggests that both foot shape and plantar pressure are important factors when designing accommodative insoles and offer the clinician a new tool to better customize the insole to the patient’s specific needs. Clinically, direct foot-shape scanners are already being implemented. However, it is critical to understand if these scanners distort the shape of the foot compared to the traditional foam crush box and how reliable the various scanning methods are within and across clinicians. Evaluations of intra-rater reliability of basic measures of foot shape (i.e., length and width) have been conducted, however, more comprehensive methods evaluating the plantar surface such as arch volume and overall surface differences are critical when designing an insole, given that the insole must conform to the foot shape. Thus, the purpose of this proposal is to evaluate the methods for obtaining shape and their effects on accommodative insole design and the ability to offload high-pressure areas in people with diabetes. Additionally, plantar pressure is not incorporated into the clinical design of SoC insoles. Compared to our current in-shoe pressure capture method, barefoot walking plantar pressure is a much more practical metric for clinicians to obtain. In this project, we will also determine if designing insoles with barefoot or in-shoe plantar pressure yields similar reductions in plantar pressure. Aim 1a: Quantify the inter- and intra-clinician reliability of three methods of capturing foot shape (crush box, Tiger scanner, structure sensor). Aim 1b: Quantify the differences in foot shape obtained using three methods of capturing foot shape. Aim 2: Evaluate the ability of insoles designed using the various foot scanning methods to offload areas of high pressure in the diabetic foot. Methods: Aims 1a and b: Three clinicians will take three shape measurements of the feet of ten healthy individuals with each of the following foot shape capture devices. Standard 1-D measurements and more comprehensive methods of evaluating the plantar surface will be calculated. Inter- and intra-clinician reliability will be calculated for each of the foot-shape capture methods (Aim 1a) and differences in the overall foot shape across devices compared (Aim 1b). Aim 2: 20 individuals with diabetes and elevated plantar pressures will undergo a clinical foot exam, have foot shape captured (using the three techniques described above), and have plantar pressures recorded during barefoot and shod walking. Seven sets of insoles will be manufactured for each participant, one pair of the SoC insole and six pairs of 3D printed insoles using the various foot shape and pressure capture methods. In-shoe plantar pressure will be measured during walking while wearing the insoles. Participants will also complete a comfort and usability survey after each insole condition. Peak pressure and pressure time integral in four regions (first metatarsal head, second metatarsal head, third to fifth metatarsal head, and offloading region) of the foot will be compared. VHA currently cares for 563,000 Veterans defined by the Prevention of Amputation in Veterans Everywhere (PAVE) Program as being at high risk for ulceration and amputation. Developing custom offloading insoles that are more efficacious than the current standard of care by leveraging advances in 3D printing has the potential to reduce rates of amputation and morbidity in our Veteran population.