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Session: Neuro-muscular – lower extremities 2
Session starts: Friday 25 January, 13:00
Presentation starts: 13:30
Room: Lecture room 536

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Karen Rodriguez (TU Delft)
Jurriaan H de Groot (LUMC)
Frank Baas (InteSpring BV)
Yvette Kerkum (OIM orthopedie)
Marjon Stijntjes (TU Delft)
Frans van der Helm (TU Delft)
Herman van der Kooij (TU Delft)
Winfred Mugge (TU Delft)

Abstract:
The stiffness of an Ankle-Foot-Orthosis (AFO) that aims to assist walking affects the gait biomechanics of patients with impaired gait. In patients with equinus (spastic paresis of the lower leg), impaired gait is a consequence of an increased passive ankle joint stiffness (originated from calf muscles) in combination with reduced active muscle strength. Though standard AFOs affect clinically relevant improvements of gait parameters, their designs interfere with the range of motion of the ankle joint. We hypothesize that an AFO with negative stiffness (nAFO) can compensate the patients’ increased passive ankle joint stiffness, improving the active range of motion and supporting the patients' muscle forces during gait. The first prototype of the nAFO achieved the required adjustable negative stiffness (produced with a spring-loaded CAM follower mechanism). In a preliminary study1, the nAFO revealed promising results: The nAFO was tailored to a healthy subject and showed an effective passive ankle joint stiffness compensation. During gait, Tibialis Anterior muscle forces were supported by the nAFO, as observed by a reduced electromyography signal during swing phase. A second prototype of the nAFO was developed with a modular design to fit both anatomy and stiffness of different subjects’ lower leg. We are about to start a clinical study with chronic stroke survivors that suffer from diverse equinus foot severities. The feasibility, functionality and comfort of the AFO will be tested. We will compare the active range of motion of the ankle joint at Single-joint level (foot movements only) and at Activity level (during walking) in 3 main conditions, with patients wearing: (1) no AFO, (2) their own AFO, (3) the nAFO at different compensation levels. Results of the study will contribute to improve the nAFO design and the methods to tailor the nAFO stiffness to specific patient’s needs.