@article{ZellnerHierlMuelleretal., author = {Zellner, Johannes and Hierl, Katja and Mueller, Michael and Pfeifer, Christian and Berner, Arne and Dienstknecht, Thomas and Krutsch, Werner and Geis, Sebastian and Gehmert, Sebastian and Kujat, Richard and Dendorfer, Sebastian and Prantl, Lukas and Nerlich, Michael and Angele, Peter}, title = {Stem cell-based tissue-engineering for treatment of meniscal tears in the avascular zone}, series = {Journal of Biomedical Materials Research Part B Applied Biomaterials}, volume = {101}, journal = {Journal of Biomedical Materials Research Part B Applied Biomaterials}, number = {7}, editor = {Gilbert, Jeremy}, doi = {10.1002/jbm.b.32922}, pages = {1133 -- 1142}, abstract = {Meniscal tears in the avascular zone have a poor self-healing potential, however partial meniscectomy predisposes the knee for early osteoarthritis. Tissue engineering with mesenchymal stem cells and a hyaluronan collagen based scaffold is a promising approach to repair meniscal tears in the avascular zone. 4 mm longitudinal meniscal tears in the avascular zone of lateral menisci of New Zealand White Rabbits were performed. The defect was left empty, sutured with a 5-0 suture or filled with a hyaluronan/collagen composite matrix without cells, with platelet rich plasma or with autologous mesenchymal stem cells. Matrices with stem cells were in part precultured in chondrogenic medium for 14 days prior to the implantation. Menisci were harvested at 6 and 12 weeks. The developed repair tissue was analyzed macroscopically, histologically and biomechanically. Untreated defects, defects treated with suture alone, with cell-free or with platelet rich plasma seeded implants showed a muted fibrous healing response. The implantation of stem cell-matrix constructs initiated fibrocartilage-like repair tissue, with better integration and biomechanical properties in the precultured stem cell-matrix group. A hyaluronan-collagen based composite scaffold seeded with mesenchymal stem cells is more effective in the repair avascular meniscal tear with stable meniscus-like tissue and to restore the native meniscus.}, subject = {Meniskusschaden}, language = {en} } @article{AuerSchieblIversenetal., author = {Auer, Simon and Schiebl, Jonas and Iversen, Kristoffer and Subhash Chander, Divyaksh and Damsgaard, Michael and Dendorfer, Sebastian}, title = {Biomechanical assessment of the design and efficiency of occupational exoskeletons with the AnyBody Modeling System}, series = {Zeitschrift f{\"u}r Arbeitswissenschaften}, volume = {76}, journal = {Zeitschrift f{\"u}r Arbeitswissenschaften}, number = {4}, publisher = {Springer Nature}, doi = {10.1007/s41449-022-00336-4}, pages = {440 -- 449}, abstract = {Exoskeletons were invented over 100 years ago but have only become popular in the last two decades, especially in the working industry as they can decrease work-related loads significantly. The most often used exoskeletons are for the lower back and shoulder since these are commonly affected body regions. All devices have in common that their purpose is to reduce internal loads of vulnerable body regions. Nevertheless, there is still little understanding on how biomechanical loading in the human body changes when exoskeletons are used. Therefore, further analyses are needed. A promising candidate for these are musculoskeletal models, which are based on an inverse dynamics approach and can calculate external parameters such as ground reaction forces or other interaction forces as well as internal parameters such as joint reaction forces or muscle activities. The various examples in the literature show that these models are increasingly used for assessing the biomechanical effects of exoskeletons on the human body. Furthermore, musculoskeletal models can calculate biomechanical loadings of humans with and without exoskeletons for all kinds of applications and allow an evaluation of their purpose. Practical Relevance: This article highlights the possibilities of musculoskeletal models for assessing the design and efficiency of occupational exoskeletons. Several practical use cases are described along with distinct descriptions of common implications of musculoskeletal and exoskeleton modeling.}, language = {en} } @article{MelznerPfeifferSuessetal., author = {Melzner, Maximilian and Pfeiffer, Christian and Suess, Franz and Dendorfer, Sebastian}, title = {Musculoskeletal simulation of elbow stability for common injury patterns}, series = {Journal of Orthopaedic Research}, volume = {41}, journal = {Journal of Orthopaedic Research}, number = {6}, publisher = {Wiley}, issn = {1554-527X}, doi = {10.1002/jor.25460}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-54819}, pages = {1356 -- 1364}, abstract = {Elbow stability is derived from a combination of muscular, ligamentous, and bony structures. After an elbow trauma the stability of the joint is an important decision criterion for the subsequent treatment. The decision regarding non-operative/operative care depends mostly on subjective assessments of medical experts. Therefore, the aim of this study is to use musculoskeletal simulations as an objective assessment tool to investigate the extent to which failure of different stabilizers affects the elbow stability and how these observations correspond to the assessment from clinical practice. A musculoskeletal elbow simulation model was developed for this aim. To investigate the stability of the elbow, varus/valgus moments were applied under 0°, 45°and 90° flexion while the respective cubital angle was analyzed. This was performed for nine different injury scenarios, which were also evaluated for stability by clinical experts. With the results, it can be determined by which injury pattern and under which flexion angle the elbow stability is impaired regarding varus/valgus moments. The scenario with a complete failure of the medial and lateral ligaments and a fracture of the radial head was identified as having the greatest instability. The study presented a numerical determination of elbow stability against varus/valgus moments regarding clinical injury patterns, as well as a comparison of the numerical outcome with experience gained in clinical practice. The numerical predictions agree well with the assessments of the clinical specialists. Thus, the results from musculoskeletal simulation can make an important contribution to a more objective assessment of the elbow stability.}, language = {en} } @article{ReinkerDendorfer, author = {Reinker, Lukas and Dendorfer, Sebastian}, title = {Evaluation of acceleration patterns during high-impact jumping exercises}, series = {Gait \& Posture}, volume = {100}, journal = {Gait \& Posture}, number = {Supplement 1, March}, publisher = {Elsevier}, address = {Amsterdam [u.a.]}, doi = {10.1016/j.gaitpost.2022.11.051}, pages = {93 -- 94}, language = {en} } @article{ReinkerBlaesingBierletal., author = {Reinker, Lukas and Bl{\"a}sing, Dominic and Bierl, Rudolf and Ulbricht, Sabina and Dendorfer, Sebastian}, title = {Correlation of Acceleration Curves in Gravitational Direction for Different Body Segments during High-Impact Jumping Exercises}, series = {sensors}, volume = {23}, journal = {sensors}, number = {4}, publisher = {MDPI}, address = {Basel}, doi = {10.3390/s23042276}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-58217}, abstract = {Osteoporosis is a common disease of old age. However, in many cases, it can be very well prevented and counteracted with physical activity, especially high-impact exercises. Wearables have the potential to provide data that can help with continuous monitoring of patients during therapy phases or preventive exercise programs in everyday life. This study aimed to determine the accuracy and reliability of measured acceleration data at different body positions compared to accelerations at the pelvis during different jumping exercises. Accelerations at the hips have been investigated in previous studies with regard to osteoporosis prevention. Data were collected using an IMU-based motion capture system (Xsens) consisting of 17 sensors. Forty-nine subjects were included in this study. The analysis shows the correlation between impacts and the corresponding drop height, which are dependent on the respective exercise. Very high correlations (0.83-0.94) were found between accelerations at the pelvis and the other measured segments at the upper body. The foot sensors provided very weak correlations (0.20-0.27). Accelerations measured at the pelvis during jumping exercises can be tracked very well on the upper body and upper extremities, including locations where smart devices are typically worn, which gives possibilities for remote and continuous monitoring of programs.}, language = {en} } @article{MuehlingSandriesserDendorferetal., author = {M{\"u}hling, Mischa and Sandriesser, Sabrina and Dendorfer, Sebastian and Augat, Peter}, title = {Assessment of implant internal stresses under physiological femoral loading: Translation to a simplified bending load model}, series = {Journal of Biomechanics}, journal = {Journal of Biomechanics}, number = {112229}, publisher = {Elsevier}, issn = {1873-2380}, doi = {10.1016/j.jbiomech.2024.112229}, pages = {17}, abstract = {The success of surgical treatment for fractures hinges on various factors, notably accurate surgical indication. The process of developing and certifying a new osteosynthesis device is a lengthy and costly process that requires multiple cycles of review and validation. Current methods, however, often rely on predecessor standards rather than physiological loads in specific anatomical locations. This study aimed to determine actual loads experienced by an osteosynthesis plate, exemplified by a standard locking plate for the femoral shaft, utilizing finite elements analysis (FEA) and to obtain the bending moments for implant development standard tests. A protocol was developed, involving the creation and validation of a fractured femur model fixed with a locking plate, mechanical testing, and FEA. The model's validation demonstrated exceptional accuracy in predicting deformations, and the FEA revealed peak stresses in the fracture bridging zone. Results of a parametric analysis indicate that larger fracture gaps significantly impact implant mechanical behavior, potentially compromising stability. This study underscores the critical need for realistic physiological conditions in implant evaluations, providing an innovative translational approach to identify internal loads and optimize implant designs. In conclusion, this research contributes to enhancing the understanding of implant performance under physiological conditions, promoting improved designs and evaluations in fracture treatments.}, language = {en} } @article{RusavyCechovaDendorferetal., author = {Rusavy, Zdenek and Cechova, Hana and Dendorfer, Sebastian and Kalis, Vladimir and Ismail, Khaled M.}, title = {Is the Finnish grip tight enough? A manometric study of two manual perineal protection techniques}, series = {Acta Obstetricia et Gynecologica Scandinavica}, journal = {Acta Obstetricia et Gynecologica Scandinavica}, edition = {Early view}, publisher = {Wiley}, doi = {10.1111/aogs.15033}, language = {en} } @article{SchaefferHerrmannSchratzenstalleretal., author = {Schaeffer, Leon and Herrmann, David and Schratzenstaller, Thomas and Dendorfer, Sebastian and B{\"o}hm, Valter}, title = {Preliminary theoretical considerations on the stiffness characteristics of a tensegrity joint for the use in dynamic orthoses}, series = {Journal of Medical Robotics Research}, journal = {Journal of Medical Robotics Research}, publisher = {World Scientific}, doi = {10.1142/S2424905X23400081}, abstract = {Early motion therapy plays an important role for effective long-term healing of joint injuries. In many cases, conventional dynamic orthoses fail to address the intricate movement possibilities of the underlying joints, limited by their simplistic joint representations, often represented by revolute joints, enabling rotations by only one axis. In this paper, a two-dimensional compliant tensegrity joint for use in biomedical applications is investigated. It consists of two compressed members and five compliant tensioned members. Relative movement possibilities are realized by the intrinsic compliance of the structure. In the development of these systems, the first step is the determination of the static stable equilibrium. This analysis is conducted in this paper by considering the potential energy approach or by using the geometric nonlinear finite element method. The mechanical behavior of the structure is assessed with a specific emphasis on its mechanical compliance. The primary objective of this study is the investigation of the influence of structural parameters on the overall stiffness and movability of the structure. The results underscore the significant effect of member parameters on the stiffness and movability of the compliant tensegrity joint, particularly under varying load magnitudes. These findings provide insights for optimizing the joint's performance, contributing to its potential application in advanced orthotic and exoskeleton devices.}, language = {en} } @article{SchmitzNeumannNeumannetal., author = {Schmitz, Paul and Neumann, Christoph Cornelius and Neumann, Carsten and Nerlich, Michael and Dendorfer, Sebastian}, title = {Biomechanical analysis of iliac crest loading following cortico-cancellous bone harvesting}, series = {Journal of Orthopaedic Surgery and Research}, volume = {13}, journal = {Journal of Orthopaedic Surgery and Research}, number = {108}, publisher = {Springer Nature}, doi = {10.1186/s13018-018-0822-1}, pages = {1 -- 8}, abstract = {Background Iliac crest bone harvesting is a frequently performed surgical procedure widely used to treat bone defects. The objective of this study is to assess the biomechanical quantities related to risk for pelvic fracture after harvesting an autologous bone graft at the anterior iliac crest. Methods Finite element models with a simulated harvest site (sized 15 × 20 mm, 15 × 35 mm, 30 × 20 mm and 30 × 35 mm) in the iliac wing are created. The relevant loading case is when the ipsilateral leg is lifted off the ground. Musculoskeletal analysis is utilized to compute the muscle and joint forces involved in this motion. These forces are used as boundary conditions for the finite element analyses. Bone tissue stress is analyzed. Results Critical stress peaks are located between the anterior superior iliac spine (ASIS) and the anterior edge of the harvest site. Irrespective of the graft size, the iliac wing does not show any significant stress peaks with the harvest site being 20 to 25 mm posterior to the ASIS. The harvest area itself inhibits the distribution of the forces applied on the ASIS to extend to the posterior iliac wing. This leads to a lack of stress posterior to the harvest site. A balanced stress distribution with no stress peaks appears when the bone graft is taken below the iliac crest. Conclusion A harvest site located at least 20 to 25 mm posterior to the ASIS should be preferred to minimize the risk of iliac fatigue fracture.}, subject = {Beckenkammknochen}, language = {en} } @article{VoellnerWeberWeberetal., author = {V{\"o}llner, Florian and Weber, Tim A. and Weber, Markus and Renkawitz, Tobias and Dendorfer, Sebastian and Grifka, Joachim and Craiovan, Benjamin}, title = {A simple method for determining ligament stiffness during total knee arthroplasty in vivo}, series = {Scientific Reports}, volume = {9}, journal = {Scientific Reports}, publisher = {Nature}, doi = {10.1038/s41598-019-41732-x}, pages = {1 -- 8}, abstract = {A key requirement in both native knee joints and total knee arthroplasty is a stable capsular ligament complex. However, knee stability is highly individual and ranges from clinically loose to tight. So far, hardly any in vivo data on the intrinsic mechanical of the knee are available. This study investigated if stiffness of the native ligament complex may be determined in vivo using a standard knee balancer. Measurements were obtained with a commercially available knee balancer, which was initially calibrated in vitro. 5 patients underwent reconstruction of the force-displacement curves of the ligament complex. Stiffness of the medial and lateral compartments were calculated to measure the stability of the capsular ligament complex. All force-displacement curves consisted of a non-linear section at the beginning and of a linear section from about 80 N onwards. The medial compartment showed values of 28.4 ± 1.2 N/mm for minimum stiffness and of 39.9 ± 1.1 N/mm for maximum stiffness; the respective values for the lateral compartment were 19.9 ± 0.9 N/mm and 46.6 ± 0.8 N/mm. A commercially available knee balancer may be calibrated for measuring stiffness of knee ligament complex in vivo, which may contribute to a better understanding of the intrinsic mechanical behaviour of knee joints.}, subject = {Biomechanische Analyse}, language = {en} }