7th Dutch Bio-Medical Engineering Conference
January 24th & 25th 2019, Egmond aan Zee, the Netherlands
13:00   Neuro-muscular – lower extremities 2
Chair: Alfred Schouten
15 mins
A Retrospective Look at the Design of the Symbitron Modular Exoskeleton
Victor Sluiter, Cor Meijneke, Gijs van Oort
Abstract: Current commercial exoskeletons are developed for people with a complete spinal cord injury (SCI). These devices consist of a rigid structure where motors provide walking trajectories, mostly actuating knee flexion and hip flexion. Although these devices can greatly help the people that need them, the concept behind these exoskeletons neglects the needs of the larger group of people with an incomplete SCI. This group still has partial motor control and / or sensory input. A full exoskeleton neglects the functions this group of patients still has. Within the EU Symbitron project an exoskeleton was designed to explore the options to restore gait for patients with a variety of lesion levels and medical scores. Our exoskeleton was designed with modularity as one of the key concepts to make it personizable. This enabled making an Active Knee Ankle Foot Orthosis (AKAFO) for those SCI patients that still have hip function, and making a full exoskeleton by adding a hip module. Modularity was also taken into consideration in the mechanical design, electronics design and low level controller to facilitate re-use and replacement of parts during development. The exoskeleton was built by a collaboration of the University of Twente and TU Delft, and the exoskeleton was tested by Fondazione Santa Lucia in Rome, a clinic for people with SCI. Innovative ideas were applied, such as a very compact series elastic drive design, a small form factor EtherCAT based motor driver with high sensor count, disturbance observers for the low level control and the use of neuromuscular controllers for high level control. Designing a modular exoskeleton over multiple locations and with a very high level of integration was a large challenge. This talk will describe the challenges we faced, the lessons we learned from it and our vision on exoskeleton design.
15 mins
Continous Dynamic Ultrasound Skeletal Muscle Thickness Measurement During Walking Exercise
Cristina Caresio
Abstract: Ultrasound (US) skeletal muscle measurement is a fundamental procedure in muscle functionality assessment. Dynamic contraction implies muscle anatomical deformation, which depends on exercise type and intensity. Muscle thickness reflects the potential to generate force and has therefore been investigated in adaptations occurring with training, disuse, pain/injury and pathological conditions. Although previous works have examined the muscle thickness change during dynamic exercise, the information on deformation in realistic long-lasting non-isometric walking conditions are insufficient. No continuous thickness measurement has been proposed in literature, due to the unfeasibility of manual measurements and the lack of US probe fixation systems. In a pilot study, the feasibility and reproducibility of continuous dynamic US muscle thickness measurement during walking exercise are evaluated. 8 healthy subjects (age: 24.5 ± 1.9 y, BMI: 22.8 ± 3.0 kg/m2) are asked to walk at 4 km/h on a treadmill (LifeFitness, Illinois, USA), performing a 2-minutes’walk with a slope of 0 degrees and a 1-minute walk with a slope of 10 degrees. US videos of the medial gastrocnemius are recorded at 20 Hz with a MyLab70 ultrasound device equipped with a linear LA523 transducer (Esaote, Maastricht, The Netherlands) and fixated on the calf using a Probefix Dynamic (USONO, Eindhoven, The Netherlands). Dynamic US images are analysed on two disjoined 10-seconds intervals per exercise with an automated algorithm for the continuous thickness measurement, namely the distance between the muscle aponeuroses and calculated with the Centerline distance metric. The percentage of incorrect muscle aponeuroses detection is below 0.1%. The averaged muscle thickness at 0 degrees slope is 15.4 ± 0.2 mm, ranging between 9.6 - 21.5 mm and 15.5 ± 0.4 mm between 9.9 – 21.6 mm at 10 degrees slope. No significant difference has been detected in paired comparisons of 10-seconds intervals within the same exercise. The proposed method shows that continuous US skeletal muscle thickness measurement is feasible and reproducible during different walking exercises and time intervals. In the future, a validation with manual measurements will be performed to complete the study. These preliminary results will provide understanding on the applicability of the proposed methods for continuous muscle measurement in clinical practice.
15 mins
Passive Ankle Joint Stiffness Compensation by a Novel Ankle-Foot-Orthosis: Improving Spastic Paretic Ankle Motor Control after Stroke
Karen Rodriguez, Jurriaan H de Groot, Frank Baas, Yvette Kerkum, Marjon Stijntjes, Frans van der Helm, Herman van der Kooij, Winfred Mugge
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.
15 mins
A Novel Design for Decoupling the Energy Storage and Release in Passive Ankle Foot Prostheses: a Redesign of the VSPA Foot
Hashim Quraishi
Abstract: Conventional passive prosthetic feet cannot provide net positive mechanical energy, meaning a strong reduction in push-off work. This will decrease the comfortable walking speed and increase the metabolic cost of walking in amputees, as more than half of the positive work performed during gait is by means of the plantar flexion at the ankle joint. A possible contribution to enhance push-off power is to utilize passive prostheses that can store and release energy by means of springs. This restores the push-off partially, enabling a higher self-selected walking speed and a lower metabolic cost Effective energy release at push-off is not just a matter of higher energy storage, but it also needs to be well timed. Controlling the release rate of energy in current passive prosthetic feet is often constrained due to the unnatural ankle joint mechanics caused by simple spring behavior. The Variable Stiffness Prosthetic Ankle-Foot (VSPA-Foot) of Shepherd and Rouse (2017) tackles this problem by using a cam and follower transmission to decouple the leaf spring mechanics from the mechanics of the ankle joint. The cam profile determines the mechanics of the ankle joint, whereas the stiffness of the spring determines the energy stored for a particular deflection. Despite achieving this control of ankle mechanics, the VSPA still acts ‘spring-like’. This means that energy is stored and released in the exact same manner. The purpose of this study was to decouple the energy storage and release characteristics. A prototype was build that uses two cam-profiles in order to do so. These cam profiles can differ in the way they store and release energy, as long as the total energy stored or released is at most equal (thereby not violating the laws of thermodynamics). By using multiple cam profiles, energy can be stored in the initial part of the stance phase. Rather than returning this energy instantaneously, it is released during late stance to enhance the push-off. This is a continuous approach to the ‘energy recycling’ concept originally proposed by Collins and Kuo (2010).
15 mins
Validation of an Online Reflex Activity Measure
Eline Flux, Ronald van 't Veld, Marjolein van der Krogt
Abstract: Introduction Many people with neurological impairments experience increased resistance in joints, which is caused by velocity dependent stretch hyperreflexia (increased reflex activity), increased background muscle activity and/or altered tissue properties [1]. Measures of quantifying components of joint resistance are important for clinical decision making and could be used for training focused on decreasing hyperreflexia (e.g. [2]-[3]). Ludvig et al. [4] developed an online system identification (SI) method which can be used to separate components of joint resistance and to quantify reflex activity. An adapted version of this method [5] has been validated by comparing SI outcomes to EMG outcomes for various activation levels. Our study aims to supplement the validation of this SI method to determine the possibilities of implementing this method in clinical decision making and training. Methods Twelve healthy adults (7 male, 21.3±2.0y) participated in this study. Participants were seated in a chair, the Dyno 2.0, with their right foot connected to a single axis actuator by means of a footplate. Perturbations were applied around the ankle joint (±0.0175 rad, maximum 2.74 rad/s). Participants were exposed to a control condition and two experimental conditions known to facilitate reflexes: experienced pain induced by a cold pressor task and the Jendrassik maneuver (JM [6]). Reflex activity was measured [5] and averaged over a 90 second periods. EMG reflex activity was measured using the ensemble average of 150 perturbations of the gastrocnemius EMG signal as described previously [5]. Results Reflexes were significantly higher during experienced pain and JM compared to control, both according to SI and EMG measures. Furthermore, good correlations were found (r=0.75-0.89) between SI and EMG measures during all conditions, further supporting the validity. Conclusions The online SI method as developed by Ludvig et al. [4] and modified by van ‘t Veld et al. [5] appears a valid measure to use in training. Further research should study the distinctive probabilities of the method between reflex activity and tissue properties, for example by including conditions which influence tissue properties. Furthermore, a generalizability study should be performed (e.g. [7]) to assess reliability, before implementation in clinical decision making. [1] Van den Noort, Eur J Neurol 24-7 (2017) 981-38. [2] Thompson, Front Integr Neurosci 8 (2014) 25. [3] Ludvig, Exp Brain Res 183-2 (2007) 201–213. [4] Ludvig, IEEE Trans Biomed Eng 54-10 (2007) 1875–1884. [5] Van 't Veld, BioRob proceedings. [6] Dowman, Exp Neurol 101-2 (1988) 288-302. [7] Roebroeck, Phys Ther 73-6 (1993) 386-395.
15 mins
The Effects of Electromyography-Assisted Modelling in Estimating Musculotendon Forces During Gait in Children with Cerebral Palsy
Kirsten Veerkamp, Wouter Schallig, Jaap Harlaar, Claudio Pizzolato, Christopher Carty, David Lloyd, Marjolein van der Krogt
Abstract: Cerebral palsy (CP) is one of the most common motor disorders among children, often resulting in problems with gait [1]. Neuro-musculoskeletal modelling can provide insight into the aberrant muscle function during gait in these patients. When estimating muscle activations and forces, static optimization approaches are commonly used to solve for the redundancy of the system, combined with a generic model (e.g. [2]). However, these generic approaches do not account for disturbed motor control and muscle weakness in CP. The aim of this study was to evaluate different forms of neuro-musculoskeletal model personalization and optimization to estimate musculotendon forces during gait in children with CP. Nine children with CP (GMFCS I-II) and nine typically developing (TD) children participated. Data collection included 3D-kinematics, ground reaction forces, and electromyography (EMG) of eight lower limb muscles. Four different methods were used to estimate muscle activations and musculotendon forces of a scaled-generic musculoskeletal model for each child, i.e. I) static optimization that minimized activation squared (SO), II) SO with maximum isometric muscle forces scaled to body mass (SO_MIF), III) an EMG-assisted approach using optimization to minimize summed-activation squared while reducing tracking errors of experimental EMG-linear envelopes and inverse dynamics joint moments ([3, 4], EA), and IV) EA with musculotendon model parameters first personalised by calibration ([4, 5], EA_CAL). Model performance was assessed by comparing each model’s estimated activations and joint moments to the corresponding experimental measures. All models’ agreements with EMG were significantly worse for CP than for TD, possibly due to the aberrant motor control in CP. SO and SO_MIF showed the poorest agreement with EMG in both pattern and amplitude. Compared to SO and SO_MIF, EA had substantially higher agreement with EMG, especially with CP, with only minor decrement in joint moments predictions. Overall, EA_CAL performed best. It is expected that a model more consistent with experimental measures is more likely to yield more physiologically results. Hence, this study highlights the added value of calibrated EMG-assisted modelling, in TD children and even more so in children with CP. References [1] Graham et al., Nature Reviews Disease Primers (2016) [2] Steele et al., Gait & Posture (2012) [3] Pizzolato et al., Journal of Biomechanics (2015) [4] Sartori et al, Journal of Biomechanics (2014) [5] Lloyd & Besier, Journal of Biomechanics (2003)