Development of a functional outcome prediction strategy for the design of orthoses.

Approximately 200 million European citizens suffer from a disorder to the ankle or foot, which is accompanied by a decreased functionality of and/or pain in the foot, ankle joint of knee joint. Due to the aging of the population the number of people suffering this disorder increases. Mostly ankle foot ortheses (AFO) are described in order to recover the gait function of the patients. AFOs are external aids to correct the movement of the foot. The large variety of ankle disorders call for a personalized approach. The design of these aids currently relies largely on the personal experience and knowledge of the orthopaedist, movement registration and plantar pressure measurements. This subjectivity leads to a large uncertainty in the reliability and functionality of the orthosis. Themodern computer technology would allow, in principle, a fully digital design process. This has as advantages: flexibility in production, high speed of production and consistency in quality. Gait analysis software, such as ‘OpenSim’, ‘AnyBody’ and ‘SIMM’, are used to analyze the gait pattern of patient with orthosis. The use of predictive simulations is currently strongly limited by the lack of a validated contact model, which is also computational efficient, in order to predict the contact forces between both the body and the environment (AFO/footwear/ground). This research aims at designing, implementing and validating a simulation platform that allows to define design parameters for an optimal AFO, on the basis of forward simulations which predict the effect of design changes ofthe AFO on the motion and the forces of the body.

The overall objective of this project will be achieved by improving the current simulation software. As a first operation, the force of the AFO on the body ischaracterized by means of a finite-element modeling. Then a contact model is defined, implemented and validated, which generally describes the contact between the body (foot/leg), the external fittings (shoe/AFO) and the ground. The computational efficiency is increased by the evolutionfrom this contact model to a surrogate model, where the force transmission of the AFO on the body segments are simplified by analytical expressions. Finally, this surrogate model is used in the fully predictive simulation, where the gait of patients with orthosis is simulated, starting from the experimentally measured pathological gait. This provides the necessary information to compare the different designs of orthosis quantitatively. Through optimization of an evaluation criterion, such as for example the step length or the energy cost, design parameters are defined for an optimal design of AFO, adapted to the patient's specific functional needs.