@article{LenichBachmeierDendorferetal., author = {Lenich, Andreas and Bachmeier, S. and Dendorfer, Sebastian and Mayr, E. and Nerlich, Michael and F{\"u}chtmeier, Bernd}, title = {Development of a test system to analyze different hip fracture osteosyntheses under simulated walking}, series = {Biomedizinische Technik. Biomedical engineering}, volume = {57}, journal = {Biomedizinische Technik. Biomedical engineering}, number = {2}, doi = {10.1515/bmt-2011-0999}, pages = {113 -- 119}, abstract = {The mechanical complications of osteosyntheses after hip fractures are previously investigated by mostly static or dynamic uniaxial loading test systems. However, the physiologic loading of the hip joint during a normal gait is a multiplanar, dynamic movement. Therefore, we constructed a system to test osteosyntheses for hip fractures under physiologic multiplanar loading representative of normal gait. To evaluate the testing system, 12 femora pairs were tested under 25,000 cycles with two standard osteosyntheses (Proximal Femoral Nail Antirotation/Gamma3 Nail). For angular movement, the varus collapse to cut out (∝CO) (∝CO=4.8°±2.1° for blade and ∝CO=7.8°±3.8° for screw) was the dominant failure mode, and only slight rotational angle shifts (∝Rot) (∝Rot=1.7°±0.4° for blade and ∝Rot=2.4°±0.3° for screw) of the femoral head around the implant axis were observed. Angular displacements in varus direction and rotation were higher in specimens reinforced with screws. Hence, the cut out model and the migration directions showed a distinction between helical blade and hip screw. However, there were no significant differences between the different implants. The new setup is able to create clinical failures and allows to give evidence about the anchorage stability of different implant types under dynamic gait motion pattern.}, subject = {H{\"u}ftgelenk}, language = {en} } @inproceedings{PutzerWeberDendorfer, author = {Putzer, Michael and Weber, Tim and Dendorfer, Sebastian}, title = {Design studies on hip prosthesis using patient specific data}, series = {Simpleware Users meeting, November 9th 2011, Bristol, UK}, booktitle = {Simpleware Users meeting, November 9th 2011, Bristol, UK}, language = {en} } @article{FoerstlSuessEnglertetal., author = {F{\"o}rstl, Nikolas and S{\"u}ß, Franz and Englert, Carsten and Dendorfer, Sebastian}, title = {Design of a reverse shoulder implant to measure shoulder stiffness during implant component positioning}, series = {Medical Engineering \& Physics}, volume = {121}, journal = {Medical Engineering \& Physics}, edition = {Journal Pre-proof}, publisher = {Elsevier}, doi = {10.1016/j.medengphy.2023.104059}, pages = {22}, abstract = {To avoid dislocation of the shoulder joint after reverse total shoulder arthroplasty, it is important to achieve sufficient shoulder stability when placing the implant components during surgery. One parameter for assessing shoulder stability can be shoulder stiffness. The aim of this research was to develop a temporary reverse shoulder implant prototype that would allow intraoperative measurement of shoulder stiffness while varying the position of the implant components. Joint angle and torque measurement techniques were developed to determine shoulder stiffness. Hall sensors were used to measure the joint angles by converting the magnetic flux densities into angles. The accuracy of the joint angle measurements was tested using a test bench. Torques were determined by using thin-film pressure sensors. Various mechanical mechanisms for variable positioning of the implant components were integrated into the prototype. The results of the joint angle measurements showed measurement errors of less than 5° in a deflection range of ±15° adduction/abduction combined with ±45° flexion/extension. The proposed design provides a first approach for intra-operative assessment of shoulder stiffness. The findings can be used as a technological basis for further developments.}, language = {en} } @misc{FoerstlSuessEnglertetal., author = {F{\"o}rstl, Nikolas and S{\"u}ß, Franz and Englert, Carsten and Dendorfer, Sebastian}, title = {Design of a reverse shoulder implant to measure shoulder stiffness during implant component positioning}, series = {Book of abstracts / ESB 2023, 28th Congress of the European Society of Biomechanics, 9-12 July 2023, Maastricht, The Netherlands.}, journal = {Book of abstracts / ESB 2023, 28th Congress of the European Society of Biomechanics, 9-12 July 2023, Maastricht, The Netherlands.}, abstract = {Introduction Dislocation of the shoulder joint is one of the more common complications after reverse total shoulder arthroplasty [1], which is often associated with malposition of the prosthetic components [2]. Therefore, achieving sufficient shoulder stability should not be neglected when positioning the implant components. One parameter for assessing shoulder stability can be shoulder stiffness. The aim of this work is to develop a reverse shoulder implant prototype that allows intraoperative measurement of shoulder stiffness while varying the position of the implant components. The measured stiffness could provide a quantitative statement regarding the optimal positioning of the implant components, which can be adjusted accordingly in the final reverse shoulder prosthesis. Methods To measure the stiffness of the shoulder joint, it is necessary to record the joint angles and the torques generated during movement. The changes in the rotation angles were measured using 3D hall sensors and magnets. The magnets were placed under the humerosocket, and the hall sensors were integrated into the glenosphere. The strength of the magnetic field was used to determine the position of the humerosocket in relation to the glenosphere. The accuracies of the angle measurements were tested using a test bench. Three thin film pressure sensors were used to record forces at different points under the humerosocket. To obtain a force value from the sensor signal, the sensors were calibrated using a load cell. The variation of the implant components positions was integrated into the prototype implant through different constructive mechanisms to adjust the stiffness of the shoulder joint. Results In the range of ±45° flexion/extension combined with ±15° adduction/abduction, the joint position could be determined with sufficient accuracy (error e ≤ 5°). The areas near the combined maximum deflections of ±45° flexion/extension and ±45° adduction/abduction indicate the greatest deviation from the target angle. The force values of the thin film sensors enable the calculation of moments around two axes. As variable component position parameters, the tray offset, the neck-shaft angle and the humerus version were integrated into the implant prototype. Discussion Ideally, the accuracy of the angle measurements should only depend on the amount of deflection and not on the direction of deflection. The asymmetric behavior indicates a deviation from the correct positioning of the hall sensors. The application of a calibration matrix could compensate for the measurement errors and could demonstrate the potential of the new method for joint angle measurements. The accuracy of the torque measurements and the functionality of the mechanical arresting mechanisms must be investigated in further studies. Overall, the developed measurement method can help to avoid malpositioning of the implant components in reverse total shoulder arthroplasty. References 1. Clark et al, J Shoulder and elbow surgery, 21:36-41 2012. 2. Randelli et al, J Musculoskeletal surgery, 98:15-18, 2014.}, language = {en} } @inproceedings{HammerDendorfer, author = {Hammer, Joachim and Dendorfer, Sebastian}, title = {Cyclic loading and microstructure of cancellous bone}, series = {Journal of Biomechanics}, volume = {41}, booktitle = {Journal of Biomechanics}, number = {Suppl. 1, July 2008}, doi = {10.1016/S0021-9290(08)70409-3}, pages = {S410}, 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{RoldanMoralisDendorferetal., author = {Rold{\´a}n, J.C. and Moralis, A. and Dendorfer, Sebastian and Witte, J. and Reicheneder, C.}, title = {Controlled central advancement of the midface after Le Fort III osteotomy by a 3-point skeletal anchorage}, series = {The Journal of craniofacial surgery}, volume = {22}, journal = {The Journal of craniofacial surgery}, number = {6}, doi = {10.1097/SCS.0b013e318231fc8d}, pages = {2384 -- 2386}, abstract = {A 3-point skeletal anchorage with taping screws for distraction osteogenesis after a Le Fort III osteotomy was applied for the first time in a severely mentally impaired patient where intraoral devices had to be avoided. All 3-force application points included the center of resistance, which allowed an optimal control on the resulting moment. A novel device for skeletal long-term retention into the nasal dorsum prevented a relapse, whereas adjustment of the midface position was observed. Fusioned three-dimensional computed tomography analysis revealed real movements not accessible by a conventional cephalometry.}, subject = {Mund-Kiefer-Gesichts-Chirurgie}, language = {en} } @article{DePieriAtzoriFergusonetal., author = {De Pieri, Enrico and Atzori, Federica and Ferguson, Stephen J. and Dendorfer, Sebastian and Leunig, Michael and Aepli, Martin}, title = {Contact force path in total hip arthroplasty: effect of cup medialisation in a whole-body simulation}, series = {HIP International}, volume = {31}, journal = {HIP International}, number = {5}, publisher = {Sage}, doi = {10.1177/1120700020917321}, pages = {624 -- 631}, abstract = {Background: Cup medialisation down to the true acetabular floor in total hip arthroplasty with a compensatory femoral offset increase seems to be mechanically advantageous for the abductor muscles due to the relocation of the lever arms (body weight lever arm decreased, abductor lever arm increased). However, limited information is currently available about the effects of this reconstruction type at the head cup interface, compared to an anatomical reconstruction that maintains the natural lever arms. Through a whole-body simulation analysis, we compared medialised versus anatomical reconstruction in THA to analyse the effects on: (1) contact force magnitude at the head cup interface; (2) contact force path in the cup; and (3) abductor activity. Methods: Musculoskeletal simulations were performed to calculate the above-mentioned parameters using inverse dynamics analysis. The differences between the virtually implanted THAs were calculated to compare the medialised versus anatomical reconstruction. Results: Cup medialisation with compensatory femoral offset increase led to: (1) a reduction in contact force magnitude at the head cup interface up to 6.6\%; (2) a similar contact force path in the cup in terms of sliding distance and aspect ratio; and (3) a reduction in abductor activity up to 17.2\% (gluteus medius). Conclusions: In our opinion, these potential biomechanical gains do not generally justify a fully medialised reconstruction, especially in younger patients that are more likely to undergo revision surgery in their lifetime. Cup medialisation should be performed until sufficient press fit and bony coverage of a properly sized and oriented cup can be achieved.}, subject = {H{\"u}ftgelenkprothese}, 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, Johannes 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} } @inproceedings{KubowitschSuessJansenetal., author = {Kubowitsch, Simone and S{\"u}ß, Franz and Jansen, Petra and Dendorfer, Sebastian}, title = {Comparison of dynamic muscular imbalances in back pain patients and healthy controls}, series = {World Congress Biomechanics Dublin, 2018}, booktitle = {World Congress Biomechanics Dublin, 2018}, language = {en} }