3D Foot Scanning and Customized 3D-Printed Foot Orthotics to Reduce Pressure on the Feet of Healthy Adults

The number of people with diabetes mellitus worldwide is increasing rapidly and is expected to rise to 439 million by 2030, or 7.7% of the total adult world population. The complications that can arise as a result of chronic diabetes represent a major problem in terms of clinical treatment, socio-economic consequences and costs to the health care system. One of the most serious complications is a diabetic foot, which is characterized by neuropathy, ischemia and limited joint mobility and makes the foot vulnerable to foot ulcers and possible amputation. Various interventions are being investigated to prevent foot ulcers, including custom-made foot orthotics (CFOs), also known as foot orthoses. The latter allows the health professional to achieve a number of functional effects, of which the redistribution of the plantar pressure load is the most valuable, especially in patients with so-called risk feet.

The use of integrated computer-aided design and computer-aided manufacturing systems to produce CFOs has become increasingly popular over the past decade. In practice, this digital workflow comprises three different phases. First the (3D) foot shape of the patient is recorded, then the arch support is designed using special software and finally the device is made using a subtractive or additive manufacturing process (3D printing). As a result, it can be concluded that the first two phases are decisive for determining the geometric characteristics of a CFO, while the last phase is more critical for selecting the material properties.

As for the first phase, digital approaches were developed, such as 3D optical scanning that allows the researcher to scan body parts directly, providing a robust base for determining a CFO's geometrical features. The anthropometric foot parameters examined were worth investigating, but exclusively zero-dimensional in nature, providing limited insight when assessing the 3D fit of a custom made foot orthotic. Thus, current knowledge in this area remains scarce and further efforts are needed to better understand the role of 'geometrical features' in dose-response characteristics of custom orthotics.

With regard to the production phase, additive manufacturing or 3D printing is gaining more and more attention and could potentially set a new standard for manufacturing CFOs. Limited research shows that 3D printed CFOs can be used to reduce plantar pressure in healthy and diabetic populations. However, it is important to mention that these studies have not fully exploited the possible complex design options that the additive manufacturing process can provide, as their designs are very similar to those used in less polyvalent subtractive manufacturing processes. In addition, the relief properties of previously described CFOs are not or rarely driven by patient-specific plantar pressure data.

Research design Prospective monocentric observational study with a healthy, asymptomatic population.

Objectives The main aim of this study is to evaluate the pressure distribution principle of custom orthotics in asymptomatic adults.

The study consists of two parts:

• Reliability study
• Observational study

Reliability study The methodological part of the current study consists of a reliability study with the focus on scanning the human foot. Since capturing the foot shape is the first step in the manufacturing process of custom insoles, it is important to use a reliable and objective scanning technique. This study aims to test the reliability, more specifically the intra-, inter-rater and test-retest reliability, of a portable, optical 3D scanner. In addition to the traditional zero-dimensional anthropometric measurements of the foot, mainly one-dimensional outcome measures will be studied.

Observational study In the observational part, the pressure distribution mechanism of several 3D-printed CFOs on the plantar pressure in asymptomatic patients with a so-called M2-M3 (metatarsal head of the second and third toe) pressure pattern at the level of the forefoot. There is a limited amount of literature on the effect of custom 3D-printed foot orthotics on plantar pressure distribution in healthy populations. In addition, the currently available literature appears to contain heterogeneous groups of participants with different plantar pressure distribution patterns, which complicates correct interpretation and generalization of the results, as the same orthosis designs are used for different pressure distribution patterns. During this study, several custom 3D-printed insoles, differentiated in padding density, structural architecture and geometric shape, will be applied to participants with M2-M3 forefoot patterns and then documented with a pressure distribution alg. Finally, a durability study will be conducted with the custom sole that provides the best relief from the peak pressure area of the forefoot.