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BACKGROUND: Children with cerebral palsy (CP) present altered gait patterns and electromyography (EMG) activity compared to typically developing children. To temporarily reduce muscular activity and to correct the abnormal muscle force balance, Botulinum Toxin type A (BTX-A) injections are used. RESEARCH QUESTION: What is the effect of BTX-A injections on dynamic muscle forces during gait, when calculated using an EMG-constrained approach?. METHODS: Retrospective data of ten typically developing (TD) and fourteen children with spastic diplegic CP were used for musculoskeletal modeling and dynamic simulations of gait, before and after BTX-A treatment. Individual muscle forces were calculated using an EMG-constrained optimization, in which EMG of eight muscles was used as muscle excitation signal to constrain the muscle activation patterns. Paired t-tests were used to compare average modelled muscle forces in different phases of the gait cycle pre- and post-BTX-A, summarized in the muscle profile score. Two-sample t-tests were used to determine significant differences between TD and pre- and post-BTX-A modelled muscle forces. RESULTS: For most muscles, the force was decreased in CP compared to TD children in all phases of the gait cycle, both before and after BTX-A treatment. Differences in muscle forces before and after BTX-A treatment were limited, with only few significant differences between pre- and post-BTX-A. Compared to a standard static optimization approach, imposing the EMG activity increased modelled muscle forces for most muscles. SIGNIFICANCE: Our findings indicate that BTX-A treatment has a limited effect on the muscle balance in CP children. Besides that, the use of EMG-constrained optimization is recommended when studying muscle balance in children with CP. ispartof: GAIT & POSTURE vol:82 pages:54-60 ispartof: location:England status: published

Plantar fasciitis is one of the most frequently occurring overuse injury of the foot and characterized by pain under the foot which aggravates during standing, walking and running. A frequently used treatment option for plantar fasciitis is the rocker shoe. The rocker shoe has a proximal apex position and a stiff insole. The rocker shoe is assumed to unload the plantar fascia during gait because it minimizes peak achilles tendon forces and dorsiflexion angles of the toes. However whether a proximal apex position and a stiff insole minimize the strain on the plantar fascia and how these two parameter interact has not been investigated yet. A musculoskeletal model similar to a previously published study and data from a cadaver study was used to estimate the strain of the plantar fascia in ten healthy young adults and nine patients diagnosed with plantar fasciitis. The participants walked for 60 seconds on their comfortable speed on a treadmill. Four different shoe conditions were randomly applied by varying sole stiffnes and the apex position of the shoe. Plantar fascia strain remained unaffected by shoe condition, but peak Achilles tendon force, peak MTP1 angle and peak plantarflexion moment were significantly lower when walking with with a proximal apex position and a stiff insole. Rocker shoes with a stiff insole positively affect peak dorsiflexion angles of the toes and plantar flexion moments but not PA strain during gait. Possibly more proximal apex positions should be used in patients with plantar fasciitis to minimize plantar fascia strain during gait and facilitate healing processes.

In vivo estimates of tibiotalar and the subtalar joint kinematics can unveil unique information about gait biomechanics, especially in the presence of musculoskeletal disorders affecting the foot and ankle complex. Previous literature investigated the ankle kinematics on ex vivo data sets, but little has been reported for natural walking, and even less for pathological and juvenile populations. This paper proposes an MRI-based morphological fitting methodology for the personalised definition of the tibiotalar and the subtalar joint axes during gait, and investigated its application to characterise the ankle kinematics in twenty patients affected by Juvenile Idiopathic Arthritis (JIA). The estimated joint axes were in line with in vivo and ex vivo literature data and joint kinematics variation subsequent to inter-operator variability was in the order of 1°. The model allowed to investigate, for the first time in patients with JIA, the functional response to joint impairment. The joint kinematics highlighted changes over time that were consistent with changes in the patient's clinical pattern and notably varied from patient to patient. The heterogeneous and patient-specific nature of the effects of JIA was confirmed by the absence of a correlation between a semi-quantitative MRI-based impairment score and a variety of investigated joint kinematics indexes. In conclusion, this study showed the feasibility of using MRI and morphological fitting to identify the tibiotalar and subtalar joint axes in a non-invasive patient-specific manner. The proposed methodology represents an innovative and reliable approach to the analysis of the ankle joint kinematics in pathological juvenile populations.

Medial knee joint osteoarthritis (OA) is a debilitating and prevalent condition. Surgical treatment consists of redistributing the forces from the medial to the lateral compartment through osteotomy, or replacing the joint surfaces. As the mediolateral load distribution is related to the action of the musculature around the knee, the aim of this study was to devise a technique to redistribute these forces non-surgically through changes in muscle excitation. Eight healthy subjects participated in the experiment, and neuromuscular electrical stimulation was used to change the muscle forces around the knee. A musculoskeletal model was used to quantify the loading on the medial compartment of the knee, and a novel algorithm devised and implemented to simulate neuromuscular electrical stimulation. The forces and moments at the knee, ground reaction forces, walking velocity and step length were quantified before and after stimulation. Stimulation of the biceps femoris resulted in a significant decrease in the second peak of the medial knee joint loading by up to 0.17 body weight (p = 0.016). Kinematic parameters were not significantly affected. Neuromuscular electrical stimulation can decrease the peak loads on the medial compartment of the knee, and thus offers a promising therapy for medial knee joint OA.

To investigate lower-limb muscle function during sidestep cutting, prior studies have analysed electromyography (EMG) data together with three dimensional motion analysis. Such an approach does not directly quantify the biomechanical role of individual lower-limb muscles during a sidestep cut. This study recorded three dimensional motion analysis, ground reaction force (GRF) and EMG data for eight healthy males executing an unanticipated sidestep cut. Using a musculoskeletal modelling approach, muscle function was determined by computing the muscle contributions to the GRFs and lower-limb joint moments. We found that bodyweight support (vertical GRF) was primarily provided by the vasti, gluteus maximus, soleus and gastrocnemius. These same muscles, along with the hamstrings, were also primarily responsible for modulating braking and propulsion (anteroposterior GRF). The vasti, gluteus maximus and gluteus medius were the key muscles for accelerating the centre-of-mass towards the desired cutting direction by generating a medially-directed GRF. Our findings have implications for designing retraining programs to improve sidestep cutting technique.

Juvenile Idiopathic Arthritis (JIA) is a paediatric musculoskeletal disease of unknown aetiology, leading to walking alterations when the lower-limb joints are involved. Diagnosis of JIA is mostly clinical. Imaging can quantify impairments associated to inflammation and joint damage. However, treatment planning could be better supported using dynamic information, such as joint contact forces (JCFs). To this purpose, we used a musculoskeletal model to predict JCFs and investigate how JCFs varied as a result of joint impairment in eighteen children with JIA. Gait analysis data and magnetic resonance images (MRI) were used to develop patient-specific lower-limb musculoskeletal models, which were evaluated for operator-dependent variability (

Joint inflammation, with consequent cartilage damage and pain, typically reduces functionality and affects activities of daily life in a variety of musculoskeletal diseases. Since mechanical loading is an important determinant of the disease process, a possible conservative treatment is the unloading of joints. In principle, a neuromuscular rehabilitation program aimed to promote alternative muscle recruitments could reduce the loads on the lower-limb joints during walking. The extent of joint load reduction one could expect from this approach remains unknown. Furthermore, assuming significant reductions of the load on the affected joint can be achieved, it is unclear whether, and to what extent, the other joints will be overloaded. Using subject-specific musculoskeletal models of four different participants, we computed the muscle recruitment strategies that minimised the hip, knee and ankle contact force, and predicted the contact forces such strategies induced at the other joints. Significant reductions of the peak force and impulse at the knee and hip were obtained, while only a minimal effect was found at the ankle joint. Adversely, the peak force and the impulse in non-targeted joints increased when aiming to minimize the load in an adjacent joint. These results confirm the potential of alternative muscle recruitment strategies to reduce the loading at the knee and the hip, but not at the ankle. Therefore, neuromuscular rehabilitation can be targeted to reduce the loading at affected joints but must be considered carefully in patients with multiple joints affected due to the potential adverse effects in non-targeted joints.

Thesis (PhD(Human Movement)--University of South Australia, 2019. Includes bibliographical references (pages 136-150) The central aim of this thesis was to determine the effect of THA on gait function and hip joint loading. Individual aims for the research were to: 1) Determine changes in gait function following THA 2) Investigate if statistical shape modelling produces more accurate estimates of HJC locations compared to linear scaling 3) Determine the change in hip joint loading before and after THA using personalised HJC locations from CT 4) Determine the effect of surgical positioning of the HJC on hip muscle and joint contact forces following THA.

The tibiofemoral compressive forces experienced during functional activities are believed to be important for maintaining tibiofemoral stability. Previous studies have shown that both knee-spanning and non-knee-spanning muscles contribute to tibiofemoral joint compressive forces during walking. However, healthy individuals typically engage in more vigorous activities (e.g. jumping and cutting) that provide greater challenges to tibiofemoral stability. Despite this, no previous studies have investigated how both knee-spanning and non-knee-spanning muscles contribute to tibiofemoral compressive loading during such tasks. The present study investigated how muscles contributed to the medial and lateral compartment tibiofemoral compressive forces during sidestep cutting. Three-dimensional marker trajectories, ground reaction forces and muscle electromyographic signals were collected from eight healthy males whilst they completed unanticipated sidestep cutting. OpenSim was used to perform musculoskeletal simulations to compute the contribution of each lower-limb muscle to compressive loading of each compartment of the knee. The greatest contributors to medial compartment loading were the vasti, gluteus maximus and medius, and the medial gastrocnemius. The greatest contributors to lateral compartment loading were the vasti, adductors, medial and lateral gastrocnemius, and the soleus. The soleus displayed the greatest potential for unloading the medial compartment, whereas the gluteus maximus and medius displayed the greatest potential for unloading the lateral compartment. These findings may help to inform interventions aiming to modulate compressive loading at the knee.

Objectives: Muscle force estimation could enhance clinical movement analysis by giving insight into causes of impairments and informing targeted treatments. However, muscle force estimation is not typically used in this way due to difficulties in validation and selection of clinically adequate models.[for full text, please go to the a.m. URL], Deutscher Kongress für Orthopädie und Unfallchirurgie (DKOU 2018)

Standard musculoskeletal simulation tools now offer widespread access to internal loading conditions for use in improving rehabilitation concepts or training programmes. However, despite broad reliance on their outcome, the accuracy of such loading estimations, specifically in deep knee flexion, remains generally unknown. The aim of this study was to evaluate the error of tibio-femoral joint contact force (JCF) calculations using musculoskeletal simulation compared to in vivo measured JCFs in subjects with instrumented total knee endoprostheses during squat exercises. Using the early but common “Gait2392_simbody” (OpenSim) scaled musculoskeletal models, tibio-femoral JCFs were calculated in 6 subjects for 5 repetitions of squats. Tibio-femoral JCFs of 0.8–3.2 times bodyweight (BW) were measured. While the musculoskeletal simulations underestimated the measured knee JCFs at low flexion angles, an average error of less than 20% was achieved between approximately 25°–60° knee flexion. With an average error that behaved almost linearly with knee flexion angle, an overestimation of approximately 60% was observed at deep flexion (ca. 80°), with an absolute maximum error of ca. 1.9BW. Our data indicate that loading estimations from early musculoskeletal gait models at both high and low knee joint flexion angles should be interpreted carefully., Medical Engineering & Physics, 61, ISSN:1350-4533, ISSN:1873-4030

Body segment parameters such as segment mass, centre of mass and moment of inertia, serve as important inputs for musculoskeletal modelling. These parameters are normally derived from regression tables; however, can be poorly representative of the study population with variations of up to 40% recorded between different tables. More recent methods, such as 3D scanning, present a rapid and accurate way to produce subject-specific body segment parameters for use in musculoskeletal models. An infra-red 3D scanner was used to produce full-body scans of 95 males and females. Each was put through an algorithm to calculate bespoke segment mass, centre of mass and inertial properties for each segment of the body, with results comparable to cadaveric data. These methods could be used to increase the specificity of musculoskeletal modelling outputs for individual subjects, improving the accuracy of modelling outputs in biomechanics-related research.

Body segment parameters such as segment mass, centre of mass and moment of inertia, serve as important inputs for musculoskeletal modelling. These parameters are normally derived from regression tables; however, can be poorly representative of the study population with variations of up to 40% recorded between different tables. More recent methods, such as 3D scanning, present a rapid and accurate way to produce subject-specific body segment parameters for use in musculoskeletal models. An infra-red 3D scanner was used to produce full-body scans of 95 males and females. Each was put through an algorithm to calculate bespoke segment mass, centre of mass and inertial properties for each segment of the body, with results comparable to cadaveric data. These methods could be used to increase the specificity of musculoskeletal modelling outputs for individual subjects, improving the accuracy of modelling outputs in biomechanics-related research.

BACKGROUND: In recent years, the reliability of inverse (IK) and direct kinematic (DK) models in gait analysis have been assessed intensively, but mainly for lean populations. However, obesity is a growing issue. So far, the sparse results available for the reliability of clinical gait analysis in obese populations are limited to direct kinematic models. Reliability error-margins for inverse kinematic models in obese populations have not been reported yet. RESEARCH QUESTIONS: Is there a difference in the reliability of IK models compared with a DK model in obese children? Are there any differences in the joint kinematic output between IK and DK models? METHODS: A test-retest study was conducted using three-dimensional gait analysis data from two obese female and eight obese male participants from an earlier study. Data were analyzed using a DK model and two OpenSim-based IK models. Test-retest reliability was compared by calculating the Standard Error of Measurement (SEM) along with similar absolute reliability measures. A Friedman Test was used to assess whether there were any significant differences in the reliability between the models. Kinematic output of the models was compared by using Statistical Parametric Mapping (SPM). RESULTS: No significant differences were found in the reliability between the DK and IK models. The SPM analysis indicated several significant differences between both IK models and the DK approach. Most of these differences were continuous offsets. SIGNIFICANCE: Reliability values showed clinically acceptable error-margins and were comparable between all models. Therefore, our results support the careful use of IK models in overweight or obese populations, e.g. for musculoskeletal modelling studies. The inconsistent kinematic output can mainly be explained by different model conventions and anatomical segment coordinate frame definitions. ispartof: GAIT & POSTURE vol:66 pages:201-207 ispartof: location:England status: published

This paper is the second of a three-part series that investigates the architecture of cancellous bone in the main hindlimb bones of theropod dinosaurs, and uses cancellous bone architectural patterns to infer locomotor biomechanics in extinct non-avian species. Cancellous bone is widely known to be highly sensitive to its mechanical environment, and therefore has the potential to provide insight into locomotor biomechanics in extinct tetrapod vertebrates such as dinosaurs. Here in Part II, a new biomechanical modelling approach is outlined, one which mechanistically links cancellous bone architectural patterns with three-dimensional musculoskeletal and finite element modelling of the hindlimb. In particular, the architecture of cancellous bone is used to derive a single ‘characteristic posture’ for a given species—one in which bone continuum-level principal stresses best align with cancellous bone fabric—and thereby clarify hindlimb locomotor biomechanics. The quasi-static approach was validated for an extant theropod, the chicken, and is shown to provide a good estimate of limb posture at around mid-stance. It also provides reasonable predictions of bone loading mechanics, especially for the proximal hindlimb, and also provides a broadly accurate assessment of muscle recruitment insofar as limb stabilization is concerned. In addition to being useful for better understanding locomotor biomechanics in extant species, the approach hence provides a new avenue by which to analyse, test and refine palaeobiomechanical hypotheses, not just for extinct theropods, but potentially many other extinct tetrapod groups as well.

Objective: Musculoskeletal modeling has been used to predict the effect of functional electrical stimulation (FES) on the mechanics of the musculoskeletal system. However, validation of the resulting muscle activations due to FES is challenging as conventional electromyography (EMG) recording of signals from the stimulated muscle is affected by stimulation artefacts. A validation approach using a combination of musculoskeletal modeling and EMG was proposed, whereby the effect on nonstimulated muscles is assessed using both techniques. The aim is to quantify the effect of FES on biceps femoris long head (BFLH) and validate this directly against EMG of gluteus maximus (GMAX). The hypotheses are that GMAX activation correlates with BFLH activation; and the muscle activation during FES gait can be predicted using musculoskeletal modeling. Methods: Kinematics, kinetics, and EMG of healthy subjects were measured under four walking conditions (normal walking followed by FES walking with three levels of BFLH stimulation). Measured kinematics and kinetics served as inputs to the musculoskeletal model. Results: Strong positive correlations were found between GMAX activation and BFLH activation in early stance peak (R = 0.78, p = 0.002) and impulse (R = 0.63, p = 0.021). The modeled peak and impulse of GMAX activation increased with EMG peak (p

The aim of this study was to compare young and adult sprinters on several biomechanical parameters that were previously highlighted as performance-related and to determine the behaviour of several muscle-tendon units (MTU) in the first stance phase following a block start in sprint running. The ground reaction force (GRF) and kinematic data were collected from 16 adult and 21 young well-trained sprinters. No difference between the groups was found in some of the previously highlighted performance-related parameters (ankle joint stiffness, the range of dorsiflexion and plantar flexor moment). Interestingly, the young sprinters showed a greater maximal and mean ratio of horizontal to total GRF, which was mainly attributed to a greater horizontal GRF relative to body mass and resulted in a greater change in horizontal centre of mass (COM) velocity during the stance phase in the young compared with the adult sprinters. Results from the MTU length analyses showed that adult sprinters had more MTU shortening and higher maximal MTU shortening velocities in all plantar flexors and the rectus femoris. Although previously highlighted performance-related parameters could not explain the greater 100 m sprinting times in the adult sprinters, differences were found in the behaviour of the MTU of the plantar flexors and rectus femoris during the first stance phase. The pattern of length changes in these MTUs provides ideal conditions for the use of elastic energy storage and release for power enhancement. ispartof: ROYAL SOCIETY OPEN SCIENCE vol:5 issue:6 ispartof: location:England status: published

Recent musculoskeletal models allow the investigation of the contribution of individual musculo-tendon forces to the locomotion dynamics. However, most of the studies are based on a forward dynamics with a high computational cost and have principally investigated the contribution to the ground reaction forces and the centre of mass acceleration. The aim of this study was to apply a pseudo-inverse method to a musculoskeletal model that includes the contact, ligament and bone forces. The results replicated well the literature for the contributions of individual musculo-tendon forces to both the vertical ground reaction force and the total tibiofemoral contact force, and provide new insights for the axial compression force of the femur during normal gait.; Les modèles musculo-squelettiques récents permettent d'estimer la contribution des forces musculo-tendineuses à la dynamique de locomotion. Cependant, la plupart des études utilisent une formulation en dynamique directe avec des temps de calculs importants et se focalisent principalement sur la contribution aux forces de réaction au sol ou à l'accélération du centre de masse. L'objectif de cette étude était d'appliquer une méthode basée sur une pseudo-inverse à un modèle musculo-squelettique incluant les forces articulaires, ligamentaires et osseuses. Les résultats reproduisent bien la littérature pour la contribution des forces musculo-tendineuses à la force de réaction au sol et à la force de contact tibiofémorale et donnent un nouvel éclairage pour la force de compression du fémur pendant la marche.

Kinetic analysis of human motion with a multi-segment musculoskeletal foot model requires the distribution of loading applied to the modeled foot segments to be determined. This work thus examines the existence of any correlation between intersegmental foot kinematics, foot morphology, and the distribution of vertical loading in a multi-segment foot model. Gait analysis trials were performed by 20 healthy subjects at a self-selected speed with intersegmental foot joint angles and the distribution of vertical loading measured for a multi-segment foot model. A statistical relationship between the sagittal plane foot kinematics and loads applied to each foot sub-area was sought using multiple regression analyses. The sub-segmental loading of the normal and abnormal morphological groups was also compared. No meaningful relationships between sagittal plane foot kinematics and sub-segment foot loading were found (max. R2 = 0.36). Statistically significant relationships between foot morphology classification and sub-area foot loading were however identified, particularly for feet exhibiting hallux valgus. Significant variation in inter-subject foot sub-segmental loading indicates that an appropriate technique for determining this load distribution must be determined before effective kinetic analyses are performed with multi-segment musculoskeletal foot models. The results of this study suggest that foot morphology is a better indicator of sub-area loading than sagittal plane kinematics and warrants further investigation.\ud \ud

Motivation: Knochen ist ein einzigartiges, lebendes Material, das sich an ��u��ere Belastungen anpassen kann. Die durch t��gliche Aktivit��ten einwirkende Lasten pr��gen daher sowohl die Form als auch interne Struktur des Knochens. In der Vergangenheit hat sich die Forschung haupts��chlich mit der Vorhersage von Knochenadaption im Zuge von ver��nderten Lasten oder Krankheiten besch��ftigt. Dabei blieb jedoch eine weiterer, spannender Nutzen der Knochenadaption au��er Acht: Ausgehend von einem gut adaptierten Knochen sollte es theoretisch m��glich sein, Lasten, die in der Vergangenheit auf ihn gewirkt haben, r��ckzurechnen und schlussendlich sogar R��ckschl��sse auf allt��gliche Aktivit��ten des entsprechenden Individuums zu ziehen. Ziele: Das prim��re Ziel dieser Dissertation war es, die Machbarkeit der Rekonstruktion von allt��glichen Aktivit��ten allein aus der Architektur eines Knochens (also seiner Form und internen Struktur) zu untersuchen. Unter der Annahme, dass Knochenlasten das Bindeglied zwischen Knochenarchitektur und Aktivit��ten bilden, wurden zwei Unterziele definiert: (1) Die Untersuchung der M��glichkeit, Knochenlasten aus der Knochenarchitektur vorherzusagen und (2) die Untersuchung der M��glichkeit, Knochenlasten mit spezifischen Aktivit��ten zu assoziieren. Methodischer Ansatz: Die Machbarkeit der Rekonstruktion von Aktivit��ten allein aus der Knochenarchitektur wurde in dieser Arbeit am Beispiel manueller Aktivit��ten von Menschen und Menschenaffen (Manipulation/Werkzeugverwendung, Klettern, Kn��chelgang) untersucht, die aus der Architektur eines Mittelhandknochens vorhergesagt werden sollen. Zwei biomechanische Methoden wurden hierbei verwendet, um die beiden Unterziele zu erf��llen: (1) Ein mikro-finite elemente-basierter inverser Remodellierungs-algorithmus wurde eingesetzt, um die Knochenlasten aus der Knochenarchitektur zu berechnen. Dieser Algorithmus wurde zuerst an humanen proximalen Femora getestet, um die Robustheit und Plausibilit��t der Vorhersagen zu untersuchen, und danach auf Mittelhandknochen angewendet um aktivit��ts-bezogene Unterschiede von Gelenklasten zu identifizieren. (2) Muskuloskeletale Modelle vom Finger eines Menschen und eines Bonobos wurden dann verwendet, um den Bezug zwischen Knochenlasten und Aktivit��ten zu untersuchen. Die Modelle wurden zuerst implementiert und anhand in vitro experimenteller Daten adaptiert und danach eingesetzt um anhand in vivo experimenteller Daten Unterschiede der auf den Mittelhandknochen wirkenden Gelenklasten zu bestimmen. Hauptergebnisse: (1) Die Anwendung des inversen Remodellierungs-algorithmus auf die proximalen Femora zeigte, dass die Vorhersagen der Gelenklasten grob aber plausibel sind und robust genug f��r einen Vergleich gro��er Lastunterschiede, wie sie bei Aktivit��ten unterschiedlicher Spezies zu erwarten sind. Die Anwendung auf Mittelhandknochen von Menschen und Menschenaffen konnte zeigen, dass der Algorithmus sensitiv genug ist, um aktivit��ts-bezogene Unterschiede von Gelenklasten zu identifizieren; allerdings waren die Unterschiede geringer als erwartet. (2) Die Adaption der muskuloskeletalen Fingermodelle an die Daten der in vitro Experimente offenbarte die Parametersensitivit��t der Modelle und best��tigte die Notwendigkeit einer Modelloptimierung. Die Anwendung der in vivo Daten zeigte, dass die Unterschiede der Gelenklasten zwischen den hier untersuchten Aktivit��ten zwar deutlich sind, aber geringer ausfallen als Gelenkstellung und externe Fingerlasten es vermuten lie��en. Schlussfolgerungen: Insgesamt legen die in dieser Dissertation erhaltenen Ergebnisse nahe, dass die Rekonstruktion von Aktivit��ten allein aus der Knochenarchitektur prinzipiell m��glich ist; allerdings nur wenn die Unterschiede der aus den untersuchten Aktivit��ten resultierenden, tats��chlichen Knochenlasten ausreichend gro�� sind (hier beispielsweise zwischen Werkzeugverwendung und Kn��chelgang). Die Tatsache, dass die tats��chlichen Knochenlasten von den Erwartungen basierend auf Gelenkstellung und externen Lasten abweichen k��nnen, rechtfertigt hierbei die Verwendung von muskuloskeletalen Modellen zur korrekten funktionellen Interpretation von Knochenlasten., Motivation: Bone is a remarkable, living material which has the ability to adapt to its mechanical environment. As a result, the characteristic loading patterns of habitual activities shape the bone both externally and internally. While a lot of research focuses on predicting changes of bone architecture (i.e. external shape and internal structure) due to altered loading conditions or diseases, little was so far done to make use of the process of bone adaptation in a different way: Given a well-adapted bone architecture, it might be feasible to estimate its loading history and, ultimately, to make inferences about habitual activities of the respective individual. Goals: The primary goal of this thesis was to investigate the feasibility of predicting habitual activities from bone architecture using a biomechanical approach. Considering bone loads as the intermediate link between activity and bone architecture, the subgoals were to investigate (1) the possibility of predicting bone loads from bone architecture and (2) the possibility of associating predicted bone loads with specific habitual activities. Methodological approach: The feasibility of predicting activities from bone architecture was tested by predicting habitual manual activities of humans and non-human primates (manipulation/tool use, climbing/suspension, knuckle-walking) from metacarpal bone architecture. Two biomechanical methods were used to fulfil the subgoals of this thesis: (1) A micro-finite element-based inverse remodelling algorithm was used to predict bone loads from bone architecture. The algorithm was first tested on human proximal femora to investigate its plausibility and robustness and then applied to primate metacarpal bones to detect activity-related differences of joint loads. (2) Musculoskeletal models of a human and bonobo finger were used to investigate the relation of habitual activities to bone loading. The models were first implemented and adjusted to in vitro experimental data and then used to predict differences of joint loads acting on the metacarpal bone by applying in vivo experimental data collected during various habitual activities. Main results: (1) Application to the proximal femora showed that the inverse remodelling algorithm delivers coarse but plausible estimates of joint loads that are robust enough for inter-species comparisons. Application to the metacarpal bones revealed that the algorithm is sufficiently sensitive to detect activity-related differences of joint loads, although these differences were smaller than expected. (2) The adjustment of the human and bonobo musculoskeletal finger models to in vitro experimental data highlighted both the models parameter sensitivity and the need for model optimization to obtain accurate predictions. The application of in vivo data showed that differences of the magnitude and direction of joint loads acting on the metacarpal bone during the investigated habitual activities are evident but smaller than external loading and finger posture would suggest. Conclusions: Taken together, the results suggest that the prediction of habitual activities from bone architecture is feasible with this biomechanical approach only if the respective differences of actual bone loads are large enough (e.g. knuckle-walking vs. manipulation/tool use activities). The fact that actual bone loads might deviate from expectations based on observations of external loading and posture warrants the use of musculoskeletal models for accurate functional interpretations of bone loads.

42ème congrès de la Société de Biomécanique, REIMS, FRANCE, 02-/11/2017 - 03/11/2017; To better understand the mechanisms underlying the dynamics of gait, it is important to investigate how individual muscles contribute to the ground reaction force and to the acceleration of the centre of mass (i.e. progression, balance, and support). This was analysed in numerous studies using forward dynamics and perturbation analysis (e.g. Arnold et al. 2007; Allen and Neptune 2012; Correa and Pandy 2013). Only one study (Moissenet et al. 2017) investigated how individual muscles contribute to ground reaction force and moment using inverse dynamics (Moissenet et al. 2014) and pseudo-inverse (Lin et al. 2011) methods. Still, only the contributions to the vertical component of the ground reaction moment were analysed (Moissenet et al. 2017) while knowing all the components of the ground reaction force and moment opened the way to the further analysis of the position of the centre of pressure (CoP). The objective of the present study is, therefore, to investigate the individual muscle contributions to the position of the CoP. The results of this study may give access to a deeper understanding of the impacts of motor impairments on CoP and on the dynamic balance during gait in a pathological context.

Diabetic foot is one of the most debilitating complications of diabetes and may lead to plantar ulcers. In the last decade, gait analysis, musculoskeletal modelling (MSM) and finite element modelling (FEM) have shown their ability to contribute to diabetic foot prevention and suggested that the origin of the plantar ulcers is in deeper tissue layers rather than on the plantar surface. Hence the aim of the current work is to develop a methodology that improves FEM-derived foot internal stresses prediction, for diabetic foot prevention applications. A 3D foot FEM was combined with MSM derived force to predict the sites of excessive internal stresses on the foot. In vivo gait analysis data, and an MRI scan of a foot from a healthy subject were acquired and used to develop a six degrees of freedom (6 DOF) foot MSM and a 3D subject-specific foot FEM. Ankle kinematics were applied as boundary conditions to the FEM together with: 1. only Ground Reaction Forces (GRFs); 2. OpenSim derived extrinsic muscles forces estimated with a standard OpenSim MSM; 3. extrinsic muscle forces derived through the (6 DOF) foot MSM; 4. intrinsic and extrinsic muscles forces derived through the 6 DOF foot MSM. For model validation purposes, simulated peak pressures were extracted and compared with those measured experimentally. The importance of foot muscles in controlling plantar pressure distribution and internal stresses is confirmed by the improved accuracy in the estimation of the peak pressures obtained with the inclusion of intrinsic and extrinsic muscle forces.

Altered neural control of movement and musculoskeletal deficiencies are common in children with spastic cerebral palsy (SCP), with muscle weakness and contracture commonly experienced. Both neural and musculoskeletal deficiencies are likely to contribute to abnormal gait, such as equinus gait (toe-walking), in children with SCP. However, it is not known whether the musculoskeletal deficiencies prevent normal gait or if neural control could be altered to achieve normal gait. This study examined the effect of simulated muscle weakness and contracture of the major plantarflexor/dorsiflexor muscles on the neuromuscular requirements for achieving normal walking gait in children. Initial muscle-driven simulations of walking with normal musculoskeletal properties by typically developing children were undertaken. Additional simulations with altered musculoskeletal properties were then undertaken; with muscle weakness and contracture simulated by reducing the maximum isometric force and tendon slack length, respectively, of selected muscles. Muscle activations and forces required across all simulations were then compared via waveform analysis. Maintenance of normal gait appeared robust to muscle weakness in isolation, with increased activation of weakened muscles the major compensatory strategy. With muscle contracture, reduced activation of the plantarflexors was required across the mid-portion of stance suggesting a greater contribution from passive forces. Increased activation and force during swing was also required from the tibialis anterior to counteract the increased passive forces from the simulated dorsiflexor muscle contracture. Improvements in plantarflexor and dorsiflexor motor function and muscle strength, concomitant with reductions in plantarflexor muscle stiffness may target the deficits associated with SCP that limit normal gait.