@article{IgnasiakDendorferFerguson, author = {Ignasiak, Dominika and Dendorfer, Sebastian and Ferguson, Stephen J.}, title = {Thoracolumbar spine model with articulated ribcage for the prediction of dynamic spinal loading}, series = {Journal of Biomechanics}, volume = {vol. 49}, journal = {Journal of Biomechanics}, number = {6}, publisher = {Elsevier Science}, doi = {10.1016/j.jbiomech.2015.10.010}, pages = {959 -- 966}, abstract = {Musculoskeletal modeling offers an invaluable insight into the spine biomechanics. A better understanding of thoracic spine kinetics is essential for understanding disease processes and developing new prevention and treatment methods. Current models of the thoracic region are not designed for segmental load estimation, or do not include the complex construct of the ribcage, despite its potentially important role in load transmission. In this paper, we describe a numerical musculoskeletal model of the thoracolumbar spine with articulated ribcage, modeled as a system of individual vertebral segments, elastic elements and thoracic muscles, based on a previously established lumbar spine model and data from the literature. The inverse dynamics simulations of the model allow the prediction of spinal loading as well as costal joints kinetics and kinematics. The intradiscal pressure predicted by the model correlated well (R2=0.89) with reported intradiscal pressure measurements, providing a first validation of the model. The inclusion of the ribcage did not affect segmental force predictions when the thoracic spine did not perform motion. During thoracic motion tasks, the ribcage had an important influence on the predicted compressive forces and muscle activation patterns. The compressive forces were reduced by up to 32\%, or distributed more evenly between thoracic vertebrae, when compared to the predictions of the model without ribcage, for mild thoracic flexion and hyperextension tasks, respectively. The presented musculoskeletal model provides a tool for investigating thoracic spine loading and load sharing between vertebral column and ribcage during dynamic activities. Further validation for specific applications is still necessary.}, subject = {Brustwirbels{\"a}ule}, language = {en} } @article{AurbachSpickaSuessetal., author = {Aurbach, Maximilian and Spicka, Jan and S{\"u}ß, Franz and Dendorfer, Sebastian}, title = {Evaluation of musculoskeletal modelling parameters of the shoulder complex during humeral abduction above 90°}, series = {Journal of Biomechanics}, volume = {106}, journal = {Journal of Biomechanics}, number = {June}, publisher = {Elsevier}, doi = {10.1016/j.jbiomech.2020.109817}, abstract = {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.}, subject = {Schultergelenk}, language = {en} } @misc{EnglertDendorfer, author = {Englert, Carsten and Dendorfer, Sebastian}, title = {Einfluss der Rotatorenmanschette auf die glenohumerale Stabilit{\"a}t}, series = {20. Intensivkurs Schulterendoprothetik Marburg}, journal = {20. Intensivkurs Schulterendoprothetik Marburg}, address = {Marburg}, language = {de} } @inproceedings{JungtaeublSchmitzGrossetal., author = {Jungt{\"a}ubl, Dominik and Schmitz, Paul and Gross, Simon and Dendorfer, Sebastian}, title = {FEA of the transiliacal internal fixator as an osteosynthesis of pelvic ring fractures}, series = {CMBEBIH 2017, Proceedings of the International Conference on Medical and Biological Engineering 2017}, booktitle = {CMBEBIH 2017, Proceedings of the International Conference on Medical and Biological Engineering 2017}, editor = {Badnjevic, Almir}, publisher = {Springer}, address = {Singapore}, isbn = {978-981-10-4165-5}, doi = {10.1007/978-981-10-4166-2_32}, pages = {212 -- 217}, abstract = {Common Schanz screw systems can be used to stabilize pelvic ring fractures. In order to accommodate for different patient's requirements, implants can be placed in cranio-caudal direction into the os ilium (T1), or into the supraacetabular bone canal, and thus, in dorso-ventral direction (T2). Whereas both techniques are currently used, no data of the biomechanical behavior is available up to this date. The aim of this study is to analyze, whether T2 shows biomechanical advantages with respect to tissue and implant stresses due to the enlarged bone-implant interface. Forces acting on the pelvis were analyzed using motion capture data of a gait cycle obtained by the utilization of a musculoskeletal simulation program. A three dimensional finite element (FE) model of the pelvis with grayscale-based material properties was generated. The muscle and joint reaction forces at toe-off were applied to the FE model and instable pelvis fractures were implemented. The osteosynthesis systems were positioned within the model in order to enable the comparison between the two different surgical techniques. Stresses and displacements were analyzed for bone tissue, fracture zone and implant. T2 lead to approx. 30\% larger displacements in the fracture zone. Von-Mises stresses were larger for T2 in the implant (80 MPa vs. 227 MPa), whereas T1 leads to larger stresses in the bone tissue (200 MPa vs. 140 MPa). Both implantation techniques showed a good biomechanical behavior. Differences could be found with respect to tissue strains and deformations in the fracture zone. If bone quality or fracture healing are of concern, T2 or T1 should be used, respectively. However, both techniques seem to be applicable for cases with no special requirements. Further analyses aim to investigate the behavior under cyclic loading.}, subject = {Beckenbruch}, language = {en} } @inproceedings{WeberDendorferDullienetal., author = {Weber, Tim A. and Dendorfer, Sebastian and Dullien, Silvia and Grifka, Joachim and Verkerke, Gijsbertus Jacob and Renkawitz, Tobias}, title = {Measuring functional outcome after total hip replacement with subject-specific hip joint loading}, series = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, volume = {226}, booktitle = {Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine}, number = {12}, doi = {10.1177/0954411912447728}, pages = {939 -- 946}, abstract = {Total hip replacement is an often-performed orthopedic surgical procedure; the amount of procedures undertaken will increase since our life expectancy is growing. In order to optimize function, hip biomechanics should be restored to as near normal as possible. The goal of this pilot study was to determine whether or not it is feasible to compute the vectorial hip reaction force pathways on the head of the prosthesis and the force angles relative to the cup of the prosthesis that occur during gait in total hip replacement patients, serving as an objective measurement of the functional outcome following hip replacement. A three-dimensional gait analysis, measuring ground reaction forces and kinematics, was performed. The data retrieved from the gait analysis was used as the input for the musculoskeletal model to compute vectorial joint reaction forces for data processing. To evaluate the position and orientation of the joint reaction forces, the force path, as well as the force angles for the operated and non-operated joint, has been calculated during the stance phase of the specific leg. The force path for subject 2 on the non-operated side is only located in the posterior-lateral quarter, as is the force path for subject 1. In contrast to this subject, the force path for subject 2 at the operated hip joint can be found only within the anterior quarter of the head of the implant, where it is nearly equally distributed in the medio-lateral half of the prosthesis head. The force-inclination angles on the cup of subject 1, with respect to the plane of the socket face, indicates that the force vector is mainly positioned in the same quadrant when compared with subject 2 (in a cup-fixed coordinate system). The force-anteversion angle behaves similarly to the force-inclination angle, even when the effects are not as pronounced. The proposed methods in this article are aiming to define two functional outcomes of total hip replacement that are related to wear and rim loading. It is accepted that wear is not only a function of time, but a function of use. Owing to the methods listed in this article, we are able to determine a) the applied force and b) the sliding distance (force pathway) in a subject-specific manner. The computed hip-reaction force angles and the distance to the rim cup are a measurement for cup or rim loading, and occurs in the so-called safe-zones. This method may well give us insight into the biomechanical situation during gait, after receiving total hip replacement, that we need to fully understand the mechanisms acting on a hip joint and to prove a possible increase of functional outcome after receiving total hip replacement.}, subject = {H{\"u}ftgelenkprothese}, language = {en} } @article{WeberAlMunajjedVerkerkeetal., author = {Weber, Tim and Al-Munajjed, Amir Andreas and Verkerke, Gijsbertus Jacob and Dendorfer, Sebastian and Renkawitz, Tobias}, title = {Influence of minimally invasive total hip replacement on hip reaction forces and their orientations}, series = {Journal of Orthopaedic Research}, volume = {32}, journal = {Journal of Orthopaedic Research}, number = {12}, doi = {10.1002/jor.22710}, pages = {1680 -- 1687}, abstract = {Minimally invasive surgery (MIS) is becoming increasingly popular. Supporters claim that the main advantages of MIS total hip replacement (THR) are less pain and a faster rehabilitation and recovery. Critics claim that safety and efficacy of MIS are yet to be determined. We focused on a biomechanical comparison between surgical standard and MIS approaches for THR during the early recovery of patients. A validated, parameterized musculoskeletal model was set to perform a squat of a 50th percentile healthy European male. A bilateral motion was chosen to investigate effects on the contralateral side. Surgical approaches were simulated by excluding the incised muscles from the computations. Resulting hip reaction forces and their symmetry and orientation were analyzed. MIS THR seemed less influential on the symmetry index of hip reaction forces between the operated and nonoperated leg when compared to the standard lateral approach. Hip reaction forces at peak loads of the standard transgluteal approach were 24\% higher on the contralateral side when compared to MIS approaches. Our results suggest that MIS THR contributes to a greater symmetry of hip reaction forces in absolute value as well as force-orientation following THR.}, subject = {H{\"u}ftgelenkprothese}, language = {en} } @inproceedings{AurbachWagnerSuessetal., author = {Aurbach, Maximilian and Wagner, Kilian and S{\"u}ß, Franz and Dendorfer, Sebastian}, title = {Implementation and Validation of Human Kinematics Measured Using IMUs for Musculoskeletal Simulations by the Evaluation of Joint Reaction Forces}, series = {CMBEBIH 2017, Proceedings of the International Conference on Medical and Biological Engineering 2017, Sarajevo, Bosnia and Herzegovina}, volume = {Vol. 62}, booktitle = {CMBEBIH 2017, Proceedings of the International Conference on Medical and Biological Engineering 2017, Sarajevo, Bosnia and Herzegovina}, editor = {Badnjevic, Almir}, publisher = {Springer}, address = {Singapore}, doi = {10.1007/978-981-10-4166-2_31}, pages = {205 -- 211}, abstract = {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.}, subject = {Bewegungsapparat}, language = {en} } @article{EnglertAngeleFierlbecketal., author = {Englert, Carsten and Angele, Peter and Fierlbeck, J. and Dendorfer, Sebastian and Schubert, T. and M{\"u}ller, R. and Lienhard, S. and Zellner, J. and Nerlich, Michael and Neumann, Carsten}, title = {Conductive bone substitute material with variable antibiotic delivery}, series = {Der Unfallchirurg}, volume = {110}, journal = {Der Unfallchirurg}, number = {5}, publisher = {Springer}, doi = {10.1007/s00113-007-1229-3}, pages = {408 -- 413}, abstract = {A new bone substitute, consisting of hydroxylapatite and calcium sulphate, was prepared in two formulations and analysed for its mechanical strength and antibiotic elution.The bone substitute PerOssal has osteoconductive and degradable properties. The material has a built-in capillary structure, which results in an immediate fluid uptake. Antibiotics absorbed to the bone substitute resulted in a prolonged release rate. Mechanical strength was investigated by an unconfined compression test up to failure under both wet and dry conditions for both formulations of the bone substitute. Antibiotic release was analysed microbiologically for two antibiotics, vancomycin and gentamicin, over an elution period of 10 days using the agar diffusion method.The drug release analysis resulted in a prolonged release rate of both antibiotics over 10 days. In vitro the amount of gentamicin and vancomycin eluted at day 10. From one pellet still exceeded the minimal inhibitory concentration of most aetiologically important pathogens. Formulation two of the present bone substitute is significantly harder in both wet and dry conditions when compared to formulation one. Both formulations lose strength in the wet condition relative to their performance in the dry condition. However, formulation two is as hard under wet conditions as formulation one is when dry.PerOssal is a suitable new degradable osteoconductive bone substitute that can be loaded with antibiotic solutions, which are released in effective doses over 10 days. The mechanical strength of PerOssal is sufficient to support cancellous bone defects in non-weight-bearing areas or in combination with osteosynthesis.}, subject = {Knochenersatz}, language = {en} } @article{PfeiferMuellerPrantletal., author = {Pfeifer, Christian and M{\"u}ller, Michael and Prantl, Lukas and Berner, Arne and Dendorfer, Sebastian and Englert, Carsten}, title = {Cartilage labelling for mechanical testing in T-peel configuration}, series = {International Orthopaedics}, volume = {36}, journal = {International Orthopaedics}, number = {7}, publisher = {Springer}, doi = {10.1007/s00264-011-1468-3}, pages = {1493 -- 1499}, abstract = {PURPOSE: The purpose of this study was to find a suitable method of labelling cartilage samples for the measurement of distraction distances in biomechanical testing. METHODS: Samples of bovine cartilage were labelled using five different methods: hydroquinone and silver nitrate (AgNO3), potassium permanganate (KMnO4) with sodium thiosulphate (Na2S2O3), India ink, heat, and laser energy. After the labelling, we analysed the cartilage samples with regard to cytotoxity by histochemical staining with ethidiumbromide homodimer (EthD-1) and calcein AM. Furthermore, we tested cartilages labelled with India ink and heat in a T-peel test configuration to analyse possible changes in the mechanical behaviour between marked and unlabelled samples. RESULTS: Only the labelling methods with Indian ink or a heated needle showed acceptable results in the cytotoxity test with regard to labelling persistence, accuracy, and the influence on consistency and viability of the chondrocytes. In the biomechanical T-peel configuration, heat-labelled samples collapsed significantly earlier than unlabelled samples. CONCLUSION: Labelling bovine cartilage samples with Indian ink in biomechanical testing is a reliable, accurate, inexpensive, and easy-to-perform method. This labelling method influenced neither the biomechanical behaviour nor the viability of the tissue compared to untreated bovine cartilage.}, subject = {Knorpel}, language = {en} } @article{MelznerSuessDendorfer, author = {Melzner, Maximilian and Suess, Franz and Dendorfer, Sebastian}, title = {The impact of anatomical uncertainties on the predictions of a musculoskeletal hand model - a sensitivity study}, series = {Computer Methods in Biomechanics and Biomedical Engineering}, volume = {25}, journal = {Computer Methods in Biomechanics and Biomedical Engineering}, number = {2}, publisher = {Taylor \& Francis}, issn = {1476-8259}, doi = {10.1080/10255842.2021.1940974}, pages = {156 -- 164}, abstract = {Outputs of musculoskeletal models should be considered probabilistic rather than deterministic as they are affected by inaccuracies and estimations associated with the development of the model. One of these uncertainties being critical for modeling arises from the determination of the muscles' line of action and the physiological cross-sectional area. Therefore, the aim of this study was to evaluate the outcome sensitivity of model predictions from a musculoskeletal hand model in comparison to the uncertainty of these input parameters. For this purpose, the kinematics and muscle activities of different hand movements (abduction of the fingers, abduction of the thumb, and flexion of the thumb) were recorded. One thousand simulations were calculated for each movement using the Latin hypercube sampling method with a corresponding variation of the muscle origin/insertion points and the cross-sectional area. Comparing the standard hand to simulations incorporating uncertainties of input parameters shows no major deviations in on- and off-set time point of muscle activities. About 60\% of simulations are located within a ± 30\% interval around the standard model concerning joint reaction forces. The comparison with the variation of the input data leads to the conclusion that the standard hand model is able to provide not over-scattered outcomes and, therefore, can be considered relatively stable. These results are of practical importance to the personalization of a musculoskeletal model with subject-specific bone geometries and hence changed muscle line of action.}, subject = {Biomechanik}, language = {en} } @article{AuerKubowitschDendorfer, author = {Auer, Simon and Kubowitsch, Simone and Dendorfer, Sebastian}, title = {Kombinierter Einfluss von psychologischen und biomechanischen Faktoren auf die muskul{\"a}ren Belastungen beim Fußballspielen}, series = {Die Orthop{\"a}die}, volume = {52}, journal = {Die Orthop{\"a}die}, number = {11}, publisher = {Springer}, doi = {10.1007/s00132-023-04437-8}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-65113}, pages = {1 -- 6}, abstract = {When mental stress and musculoskeletal loading interact, the risk for injury increases due to altered body kinematics and increased muscle tension. These changes can be detected with musculoskeletal models, and mental loading and stress must be analyzed at emotional, cognitive, and behavioral levels. To investigate these kinematic and loading changes under stress, competitive athletes were subjected to mental stress during highly dynamic movements, and musculoskeletal models were used to analyze the biomechanical loading. It was shown that under mental stress, independent of the subjective perception, a strong change in muscle forces can occur. Accordingly, competitive athletes should undergo screenings to assess individual movement patterns and promote general stress resilience.}, language = {de} } @article{MelznerEngelhardtSimonetal., author = {Melzner, Maximilian and Engelhardt, Lucas and Simon, Ulrich and Dendorfer, Sebastian}, title = {Electromyography-Based Validation of a Musculoskeletal Hand Model}, series = {Journal of Biomechanical Engineering}, volume = {144}, journal = {Journal of Biomechanical Engineering}, number = {2}, publisher = {American Society of Mechanical Engineers, ASME}, doi = {10.1115/1.4052115}, pages = {8}, abstract = {Regarding the prevention of injuries and rehabilitation of the human hand, musculoskeletal simulations using an inverse dynamics approach allow for insights of the muscle recruitment and thus acting forces on the hand. Currently, several hand models from various research groups are in use, which are mainly validated by the comparison of numerical and anatomical moment arms. In contrast to this validation and model-building technique by cadaver studies, the aim of this study is to further validate a recently published hand model [1] by analyzing numerically calculated muscle activities in comparison to experimentally measured electromyographical signals of the muscles. Therefore, the electromyographical signals of 10 hand muscles of five test subjects performing seven different hand movements were measured. The kinematics of these tasks were used as input for the hand model, and the numerical muscle activities were computed. To analyze the relationship between simulated and measured activities, the time difference of the muscle on- and off-set points was calculated, which resulted in a mean on- and off-set time difference of 0.58 s between the experimental data and the model. The largest differences were detected for movements that mainly addressed the wrist. One major issue comparing simulated and measured muscle activities of the hand is cross-talk. Nevertheless, the results show that the hand model fits the experiment quite accurately despite some limitations and is a further step toward patient-specific modeling of the upper extremity.}, subject = {Elektromyographie}, language = {en} }