@inproceedings{GalibarovAlMunajjedDendorferetal., author = {Galibarov, Pavel E. and Al-Munajjed, Amir Andreas and Dendorfer, Sebastian and Christensen, Soeren Toerholm and Rasmussen, John}, title = {The effect of varying the stiffness of spinal fusion devices on the adjacent levels using multibody dynamics simulation}, series = {Orthopaedic Proceedings}, volume = {94-B}, booktitle = {Orthopaedic Proceedings}, number = {SUPP_XL01 Sep 2012}, pages = {2}, abstract = {INTRODUCTION Several clinical studies demonstrated long-term adjacent-level effects after implantation of spinal fusion devices[1]. These effects have been reported as adjacent joint degeneration and the development of new symptoms correlating with adjacent segment degeneration[2] and the trend has therefore gone to motion preservation devices; however, these effects have not been understood very well and have not been investigated thoroughly[3]. The aim of this study is to investigate the effect of varying the stiffness of spinal fusion devices on the adjacent vertebral levels. Disc forces, moments and facet joint forces were analyzed. METHODS The AnyBody Modeling System was used to compute the in-vivo muscle and joint reaction forces of a musculoskeletal model. The full body model used in this study consists of 188 muscle fascicles in the lumbar spine and more than 1000 individual muscle branches in total. The model has been proposed by de Zee et al.[3], validated by Rasmussen et al.[4] and by Galibarov et al.[5]. The new model[5] determines the individual motions between vertebrae based on the equilibrium between forces acting on the vertebrae from muscles and joints and the passive stiffness in disks and ligaments, figure 1a. An adult of 1.75 m and 75 kg with a spinal implant in L4L5 was modeled. This model was subjected to a flexion-extension motion using different elastic moduli to analyze and compare to a non-implanted scenario. The analyzed variables were vertebral motion, the disc reaction forces and moments, as well as facet joint forces in the treated and the adjacent levels: L2L3, L3L4, L4L5 and L5-Sacrum. RESULTS When introducing a spinal fusion device in the L4L5 joint the reaction forces and moments decreased in this joint with stiffer devices leading to lower joint loads. However, in the adjacent joints, L3L4 and L5Sacrum, an increase was observed when implanting stiffer devices. Similar trends could be found for the L2L3 joint. The loads in the facet joints showed the same trends. While introducing a spinal fusion device reduced the facet joint forces in the treated joint, the loads in the adjacent facet joints were increased according to the stiffness of the implanted device, figure 1b. DISCUSSION While the treated disc joint showed reduced motion and loads, the adjacent levels demonstrated a significant increase. In particular, the increased facet joint forces in the adjacent levels can lead to adjacent level facet pain or accelerated facet joint degeneration. Introducing a device resulted in preventing facet contact and therefore facet joint loads, even using the device with the lowest stiffness. CONCLUSION The presented model shows that clinical complications such as facet joint degeneration in adjacent levels after implantation of spinal fusion device are consistent with the change in the mechanical-stimulus distribution in the system.}, language = {en} } @inproceedings{GalibarovDendorferChristensen, author = {Galibarov, Pavel E. and Dendorfer, Sebastian and Christensen, Soeren Toerholm}, title = {On modelling spine curvature dependent on muscular and external forces in multibody dynamics system}, series = {International Society of Biomechanics (ISB), 13th congress, 2011, Brussels, Belgium}, booktitle = {International Society of Biomechanics (ISB), 13th congress, 2011, Brussels, Belgium}, pages = {2}, abstract = {This paper presents a computational approach for investigating effect of muscular and external forces on curvature of the lumbar spine. Multibody dynamics system is used to compute the lumbar spine curvature using a force-dependent kinematics facility, e.g. this method allows releasing some degrees of freedom in order to be computed based on the current load configuration.}, language = {en} } @inproceedings{RasmussenBichlerChristensenetal., author = {Rasmussen, John and Bichler, R. and Christensen, Soeren Toerholm and Wirix-Speetjens, Roel and Dendorfer, Sebastian and Renkawitz, Tobias}, title = {Subject-specific Musculoskeletal Simulation of Hip Dislocation Risk in Activities of Daily Living}, series = {Proceedings of the 2011 ORS Annual Meeting, Long Beach, CA.}, booktitle = {Proceedings of the 2011 ORS Annual Meeting, Long Beach, CA.}, number = {Paper No. 306}, language = {en} } @inproceedings{RobieDendorferRasmussenetal., author = {Robie, Bruce and Dendorfer, Sebastian and Rasmussen, John and Christensen, Soeren Toerholm}, title = {Axial Rotation Requires Greatest Load in Multifidus Muscle - Potential Association with Low Back Pain?}, series = {Annual Meeting of the AANS/CNS Section on Disorders of the Spine and Peripheral Nerves, 2011, Phoenix, Arizona}, booktitle = {Annual Meeting of the AANS/CNS Section on Disorders of the Spine and Peripheral Nerves, 2011, Phoenix, Arizona}, language = {en} } @inproceedings{GalibarovDendorferRasmussen, author = {Galibarov, Pavel E. and Dendorfer, Sebastian and Rasmussen, John}, title = {Two Computational Models of the Lumbar Spine:}, series = {Proceedings of the 2011 ORS Annual Meeting, Long Beach, CA, vol. Marie Curie Initial Training Network "SpineFX"}, booktitle = {Proceedings of the 2011 ORS Annual Meeting, Long Beach, CA, vol. Marie Curie Initial Training Network "SpineFX"}, language = {en} } @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} } @article{BenditzAuerSpoerreretal., author = {Benditz, Achim and Auer, Simon and Sp{\"o}rrer, J.F. and Wolkerstorfer, S. and Grifka, Joachim and S{\"u}ß, Franz and Dendorfer, Sebastian}, title = {Regarding loads after spinal fusion, every level should be seen separately: a musculoskeletal analysis}, series = {European Spine Journal}, volume = {27}, journal = {European Spine Journal}, number = {8}, publisher = {Springer-Verlag}, doi = {10.1007/s00586-018-5476-5}, pages = {1905 -- 1910}, abstract = {The number of spinal fusion surgeries is steadily increasing and biomechanical consequences are still in debate. The aim of this study is to provide biomechanical insights into the sagittal balance of the spine and to compare spinal load before and after spinal fusion. METHOD: The joint reaction forces of 52 patients were analyzed in proximo-distal and antero-posterior direction from the levels T12-L1 to L5-S1 using musculoskeletal simulations. RESULTS: In 104 simulations, pre-surgical forces were equal to post-surgical. The levels L4-L5 and T12-L1, however, showed increased spinal forces compression forces with higher sagittal displacement. Improved restauration of sagittal balance was accompanied by lower spinal load. AP shear stress, interestingly decreased with sagittal imbalance. CONCLUSION: Imbalanced spines have a risk of increased compression forces at Th12-L1. L4-L5 always has increased spinal loads. These slides can be retrieved under Electronic Supplementary Material.}, subject = {Biomechanische Analyse}, language = {en} } @article{ScheerKubowitschDendorferetal., author = {Scheer, Clara and Kubowitsch, Simone and Dendorfer, Sebastian and Jansen, Petra}, title = {Happy Enough to Relax? How Positive and Negative Emotions Activate Different Muscular Regions in the Back - an Explorative Study}, series = {Frontiers in Psychology}, volume = {Volume 12}, journal = {Frontiers in Psychology}, number = {May 2021}, publisher = {Frontiers Media}, issn = {1664-1078}, doi = {10.3389/fpsyg.2021.511746}, abstract = {Embodiment theories have proposed a reciprocal relationship between emotional state and bodily reactions. Besides large body postures, recent studies have found emotions to affect rather subtle bodily expressions, such as slumped or upright sitting posture. This study investigated back muscle activity as an indication of an effect of positive and negative emotions on the sitting position. The electromyography (EMG) activity of six back muscles was recorded in 31 healthy subjects during exposure to positive and negative affective pictures. A resting period was used as a control condition. Increased muscle activity patterns in the back were found during the exposure to negative emotional stimuli, which was mainly measured in the lumbar and thorax regions. The positive emotion condition caused no elevated activity. The findings show that negative emotions lead to increased differential muscle activity in the back and thus corroborate those of previous research that emotion affects subtle bodily expressions.}, language = {en} } @inproceedings{DendorferKubowitschSuess, author = {Dendorfer, Sebastian and Kubowitsch, Simone and S{\"u}ß, Franz}, title = {How to determine the effect of working conditions on the human body}, series = {11th International Scientific Conference on Production Engineering DEVELOPMENT AND MODERNIZATION OF PRODUCTION (RIM 2017), Sarajevo, Bosnia and Herzegovina}, booktitle = {11th International Scientific Conference on Production Engineering DEVELOPMENT AND MODERNIZATION OF PRODUCTION (RIM 2017), Sarajevo, Bosnia and Herzegovina}, abstract = {Work places and conditions strains the human body, both psychologically and biomechanically. In order to analyse working conditions and in the following to improve them, detailed knowledge about the effect of the different stressors on the body is needed. This manuscript discusses methods on how to evaluate biomechanical and mental loading and its effect on the musculoskeletal system. A possible workflow for the analysis is presented.}, subject = {Arbeitsbedingungen}, 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} }