Foot–ankle simulators: A tool to advance biomechanical understanding of a complex anatomical structure

Abstract

In vitro gait simulations have been available to researchers for more than two decades and have become an invaluable tool for understanding fundamental foot-ankle biomechanics. This has been realised through several incremental technological and methodological developments, such as the actuation of muscle tendons, the increase in controlled degrees of freedom and the use of advanced control schemes. Furthermore, in vitro experimentation enabled performing highly repeatable and controllable simulations of gait during simultaneous measurement of several biomechanical signals (e.g. bone kinematics, intra-articular pressure distribution, bone strain). Such signals cannot always be captured in detail using in vivo techniques, and the importance of in vitro experimentation is therefore highlighted. The information provided by in vitro gait simulations enabled researchers to answer numerous clinical questions related to pathology, injury and surgery. In this article, first an overview of the developments in design and methodology of the various foot-ankle simulators is presented. Furthermore, an overview of the conducted studies is outlined and an example of a study aiming at understanding the differences in kinematics of the hindfoot, ankle and subtalar joints after total ankle arthroplasty is presented. Finally, the limitations and future perspectives of in vitro experimentation and in particular of foot-ankle gait simulators are discussed. It is expected that the biofidelic nature of the controllers will be improved in order to make them more subject-specific and to link foot motion to the simulated behaviour of the entire missing body, providing additional information for understanding the complex anatomical structure of the foot.

Assessment of Ankle Movements Through a Game-Based Sphere: Proof of Concept

“…Thus, people usually perform a variaety of activities with one or other limb in a daily basis [1,4,5,6]. This "unconscious training" helps to develop abilities that can make a difference when performing Activities of Daily Living.…”

“…It has been observed that for a right dominat subject is easier to perform such movements (flexion/extension, supination/pronation, aduction/abduction), in clockwise direction whereas for the left-dominant subject is easier to perform the movements in anti-clockwise direction. Therefore a proposed protocol must include both feet and both directions (clockwise and anti-clockwise) [1,4,7,8] …”

“…It is well known that the nervous terminals are less for the ankle, compared to those dedicated to the fingers or wrist. Therefore it is important that the developed system translate accurately the position of the joint to coordinates x and y in a computer display [1,4].…”

3D Printing for Foot

“…They are well protected and have only minor tendon attachments and are not subjected to strong pulling forces. Near the head of the first metatarsal, on the plantar surface of the foot, are two seamed bones (a small, oval-shaped bone which develops inside a tendon, where the tendon passes over a bony prominence) they are held in place by tendons, and ligaments [11] ( Figure 1). …”