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BACKGROUND: Validation and verification of multibody musculoskeletal models sEMG is a difficult process because of the reliability of sEMG data and the complex relationship of muscle force and sEMG. OBJECTIVE: This work aims at comparing experimentally recorded and simulated muscle activities considering a numerical model for crosstalk. METHODS: For providing an experimentally derived reference data set, subjects were performing elevations of the arm, where the activities of the contemplated muscle groups were measured by sEMG sensors. Computed muscle activities were further processed and transformed into an artificial electromyographical signal, which includes a numerical crosstalk model. In order to determine whether the crosstalk model provides a better agreement with the measured muscle activities, the Pearson correlation coefficient has been computed as a qualitative way of assessing the curve progression of the data sets. RESULTS: The results show an improvement in the correlation coefficient between the experimental data and the simulated muscle activities when taking crosstalk into account. CONCLUSIONS: Although the correlation coefficient increased when the crosstalk model was utilized, it is questionable if the discretization of both, the crosstalk and the musculoskeletal model, is accurate enough.
The gold standard for the analysis of human kinematics and kinetics is a camera-based motion capture system in combination with force measurement platforms. Alternatively, inertial measurement units can be utilized to obtain human kinematics, while ground reaction forces are computed from full body dynamics. This setup represents a system independent from the spatial confinement of a gait laboratory. The aim of this study is the comparison of the two methods by the investigation of lower limb kinematics and the resulting joint reaction forces within the ankle-, knee- and hip joints. For this purpose, human motion during gait was captured simultaneously by both measurement techniques. 13 trials from 8 different test subjects were evaluated in total. IMU data was processed with a quaternion based Kalman Filter. The data sets were implemented into a musculoskeletal simulation program in order to drive a virtual human body model. Each sensor was aligned to the gravitational and magnetic field vectors of the earth. The angles of flexions, extensions and rotations were analyzed to determine kinematic differences. Joint reaction forces defined kinetic dissimilarities. The overall kinematic differences of both models yielded root mean square errors of 7.62°, 6.02°, 4.95°, 2.79°, 2.38° and 3.56° for ankle flexion, subtalar eversion, knee flexion, hip external rotation, hip abduction and hip flexion, respectively. The proximo-distal differences in force peaks between the models yielded overall for the ankle, 57.33 %Bodyweight(BW) ± 46.86 %BW (16.66 %(Maximum peak to peak) ± 13.62 %) for the knee 37.09 %BW ± 29.33 %BW (17.65 % ± 15.44 %) and 32.03 %BW ± 24.33 %BW (15.6 % ± 12.54 %) for the hip. The overall outcome of this work investigated an approach independent of the common setup of the gait laboratory, thus enabling a cheaper and more flexible technology as an alternative. However, kinematic and thus kinetic differences remain rather large. Future work aims to improve the contact criterion for the calculation of the ground reaction forces and the implementation of a full-body calibration algorithm for the IMU system in order to counteract magnetic field disturbances.
Based on electromyographic data and force measurements within the shoulder joint, there is an indication that muscle and resulting joint reaction forces keep increasing over an abduction angle of 90°. In inverse dynamics models, no single parameter could be attributed to simulate this force behaviour accordingly. The aim of this work is to implement kinematic, kinetic and muscle model modifications to an existing model of the shoulder (AnyBody™) and assess their single and combined effects during abduction up to 140° humeral elevation. The kinematics and the EMG activity of 10 test subjects were measured during humeral abduction. Six modifications were implemented in the model: alternative wrapping of the virtual deltoid muscle elements, utilization of a three element Hill model, strength scaling, motion capture driven clavicle elevation/protraction, translation of the GH joint in dependency of the acting forces and an alteration of the scapula/clavicle rhythm. From the six modifications, 16 different combinations were considered. Parameter combinations with the Hill model changed the resultant GH joint reaction force and led to an increase in force during abduction of the humerus above 90°. Under the premise of muscle activities and forces within the GH joint rising after 90° of humeral abduction, we propose that the Hill type muscle model is a crucial parameter for accurately modelling the shoulder. Furthermore, the outcome of this study indicates that the Hill model induces the co-contraction of the muscles of the shoulder without the need of an additional stability criterion for an inverse dynamics approach.
Musculoskeletal models of the shoulder complex are valuable research aids to investigate tears of the supraspinatus and the resulting mechanical impact during abduction of the humerus. One of the major contributors to this motion is the deltoid muscle group and for this, an accurate modeling of the lines of action is indispensable. The aim of this work was to utilize a torus obstacle wrapping approach for the deltoids of an existing shoulder model and assess the feasibility of the approach during humeral abduction. The shoulder model from the AnyBody™ modeling system was used as a platform. The size of the tori is based on a magnetic resonance imaging (MRI) approach and several kinematic couplings are implemented to determine the trajectories of the tori during abduction. To assess the model behavior, the moment arms of the virtual muscle elements and the resultant glenohumeral joint reaction force (GHJF) were compared with reference data from the literature during abduction of the humerus in the range 20°–120°. The root mean square error for the anterior, lateral and posterior part between the simulated muscle elements and reference data from the literature was 3.9, 1.7 and 5.8 mm, respectively. The largest deviation occurred on the outer elements of the muscle groups, with 12.6, 10.4 and 20.5 mm, respectively. During abduction, there is no overlapping of the muscle elements and these are in continuous contact with the torus obstacles, thus enabling a continuous force transmission. This results in a rising trend of the resultant GHJF.
The torus obstacle approach as a wrapping method for the deltoid muscles provides a guided muscle pathing by simultaneously approximating the curvature of the deltoid muscle. The results from the comparison of the simulated moment arms and the resultant GHJF are in accordance with those in the literature in the range 20°–120° of abduction.
Although this study shows the strength of the torus obstacle as a wrapping approach, the method of fitting the tori according to MRI data was not suitable. A cadaver study is recommended to better validate and mathematically describe the torus approach.
BACKGROUND:
Validation and verification of multibody musculoskeletal models sEMG is a difficult process because of the reliability of sEMG data and the complex relationship of muscle force and sEMG.
OBJECTIVE:
This work aims at comparing experimentally recorded and simulated muscle activities considering a numerical model for crosstalk. METHODS:
For providing an experimentally derived reference data set, subjects were performing elevations of the arm, where the activities of the contemplated muscle groups were measured by sEMG sensors. Computed muscle activities were further processed and transformed into an artificial electromyographical signal, which includes a numerical crosstalk model. In order to determine whether the crosstalk model provides a better agreement with the measured muscle activities, the Pearson correlation coefficient has been computed as a qualitative way of assessing the curve progression of the data sets.
RESULTS:
The results show an improvement in the correlation coefficient between the experimental data and the simulated muscle activities when taking crosstalk into account.
CONCLUSIONS:
Although the correlation coefficient increased when the crosstalk model was utilized, it is questionable if the discretization of both, the crosstalk and the musculoskeletal model, is accurate enough.
Forschung 2018
(2018)
Musculoskeletal modelling of the shoulder – effects on muscle recruitment and joint reaction force
(2019)
In Rahmen der Promotion wird ein muskuloskelettales Modell der Schulter optimiert. Zwischen in-vivo gemessenen und berechneten Gelenkreaktionskräften der Schulter besteht eine Diskrepanz während der Abduktion. Verschiedene Modellparameter (z.B. Schulterrhythmus, Muskelmodell, Translation des Humerus) werden auf ihre Auswirkungen auf die Gelenkreaktionskraft getestet. Mit einem optimierten Modell werden zwei klinische Fragestellungen untersucht. Die Erste befasst sich hierbei mit den Auswirkungen verschiedener Tenodesetechniken der langen Bizepssehne auf Reaktionskräfte des Schulter- und Ellenbogengelenks. Hierbei soll untersucht werden, ob eine der angewandten Techniken unter einer biomechanischen Betrachtung potentiell zu bevorzugen ist. Die Zweite klinische Fragestellung bezieht sich auf Muskelrekrutierungsänderungen bei einer Ruptur des m. supraspinatus und vergleicht Modelle gesunder und pathologischer Probanden. Ferner werden die Reaktionskräfte im Schultergelenk miteinander verglichen.
Musculoskeletal modelling of the shoulder complex and its application for EMG assessed pathologies
(2020)
Die Kernaspekte der vorliegenden Dissertation fokussieren sich auf die muskuloskeletalle Modellierung und Simulation von Pathologien des menschlichen Schulterkomplexes. Die Arbeit adressiert innerhalb dieses Kontextes drei spezifische Forschungsfragen. Auf der Simulationsebene wurde die Muskelrekrutierung des Schulterkomplexes und die Kraftentwicklung innerhalb des Glenohumeralgelenks bei der Abduktion des Humerus untersucht. In-vivo Messungen basierend auf instrumentalisierten Endoprothesen des Humeruskopfes zeigen einen kontinuierlichen Anstieg der resultierenden Reaktionskraft im Glenohumeralgelenk bis zu 150° Abduktion. Eine hohe Aktivierung der involvierten Muskulatur bei der Abduktion über 90° wird ebenfalls durch elektromyographische Messungen bestätigt. Muskuloskelettale Modelle der Schulter, welche auf einem inversdynamischen Ansatz beruhen, berechnen jedoch zumeist sinkende Muskelaktivitäten und damit verbunden erniedrigte Gelenkreaktionskräfte. Um dieser Diskrepanz nachzugehen, wurden mehrere kinematische, kinetische und Muskelmodell Parameter auf ihre Auswirkung bezüglich Muskelaktivität und Gelenkreaktionskraft evaluiert und mit experimentellen elektromyographischen Messungen und der Literatur verglichen. Ferner wurde der Muskelfaserverlauf der anterioren, lateralen und posterioren Deltoiden mittels virtueller Torus-Objekte innerhalb des verwendeten Schultermodelles für die Abduktion optimiert. Die erste der beiden klinischen Fragestellungen der dargelegten Arbeit bezieht sich auf eine Transposition der langen Bizepssehne. Mehrere verschiedene tenodese Techniken oder eine Tenotomie finden hierbei im klinischen Alltag Anwendung. Eine Untersuchung bezüglich biomechanischer Aspekte der unterschiedlichen Techniken ermöglicht hierbei Einblicke, welche am ehesten dem Normalzustand im Bezug auf Gelenkskraftentwicklung entspricht. Zwei tenodese Techniken und die Tenotomy wurden hierbei während der Ellbogenflexion, Pronation und einer kombinierten Bewegung simuliert, wobei die Reaktionskräfte undMomente im Schulter und Ellenbogengelenk mit einem intakten Modell verglichen wurden. Die zweite klinische Anwendung betrifft eine Ruptur des m. supraspinatus. Die Kinematik und Muskelaktivität gesunder und pathologischer Probanden wurden hierbei experimentell bei 6 verschiedenen Bewegungen gemessen. Die Probanden wurden in Simulationsmodellen mit und ohne Riss des m. supraspinatus nachgebildet. Hierbei sollte ermittelt werden, ob ein generisches Modell Muskelrekrutierungsänderungen aufgrund eine Ruptur adäquat abbilden kann. Auf Simulationsebene konnte die Arbeit die mechanischen Eigenschaften des Hill Muskelmodelles als mögliche physiologische Ursache und Erklärung für die steigenden Reaktionskräfte im Glenohumeralgelenk bei Abduktion >90° identifizieren. Im Bezug auf die biomechanischen Auswirkungen verschiedener tenodese Techniken der langen Bizepssehne scheint eine Verankerung an der Bicipitalrille aus mechanischer Sicht am ehesten die Kräfte des gesunden Modelles zu erzeugen. Dies liegt an der Präservation der generellen Richtung des Hebelarmes des langen Bizeps. Der Vergleich zwischen modellierten Aktivitäten mit und ohne Ruptur des m. supraspinatus konnte keine Übereinstimmung der simulierten und experimentellen Unterschiede bei symptomatischen Patienten zeigen. Dies wird auf eine eventuelle Veränderung der Kinematik der Scapula zurückgeführt, welche nicht im verwendeten Modell Berücksichtigt wird. Die Erkenntnisse könnten jedoch für asymptomatische Rupturen gültig sein. Hierbei ist die Aussage, das die Änderung in der Muskelrekrutierung nur geringfügig ist, jedoch die Kumulative Erhöhung signifikante Auswirkung auf die Gelenkreaktionskraft hat.
