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Item type:Publication, Access status: with files , Additive manufactured versus traditional osteosynthesis plates : a finite element analysis(Infinite Science Publishing, 2022-09-12); ; ; ; Additive Manufacturing (AM) is rapidly gaining acceptance in healthcare. Due to 3D printing of polyetheretherketone (PEEK) constructions almost any complex geometry, e. g. bio-mimicking implants or light-weight hollow implant bodies, can be produced. In this paper a direct comparison between PEEK and titanium osteosynthesis plates is achieved with a finite element analysis. By that, pros and cons of PEEK as implant material are discussed and different use cases are identified. For the comparison a generic osteosynthesis plate for diaphysis is designed. The exceeding of the yield strength even at low bending and torsional loads highlights the problems that occur when applying PEEK implants at locations which are affected by moderate mechanical loads. Since fracture stabilisation is the main function of osteosynthesis plates, stiffness is a highly relevant property of these. Therefore, a direct exchange of titanium to PEEK would increase the risk of non-union. Thus, a different structure or an improved material, e. g. carbon fibre PEEK composite, is required for loaded locations to replace metallic implants.Publicationtype: Journal Article40 60 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Biomechanical analysis of fixation methods in acetabular fractures : a systematic review of test setupsPurpose: Optimal anatomical reduction and stable fixation of acetabular fractures are important in avoiding secondary dislocation and osteoarthritis. Biomechanical studies of treatment options of acetabular fractures aim to evaluate the biomechanical properties of different fixation methods. As the setup of the biomechanical test can influence the experimental results, this review aimed to analyze the characteristics, comparability and clinical implications of studies on biomechanical test setups and finite element analyses in the fixation of acetabular fractures. Methods: A systematic literature research was conducted according to the PRISMA guidelines, using the PubMed/MEDLINE and Web of Science databases. 44 studies conducting biomechanical analyses of fixation of acetabular fractures were identified, which met the predefined inclusion and exclusion criteria and which were published in English between 2000 and April 16, 2021. The studies were analyzed with respect to distinct parameters, including fracture type, material of pelvis model, investigated fixation construct, loading direction, loading protocol, maximum loading force, outcome parameter and measurement method. Results: In summary, there was no standardized test setup within the studies on fixation constructs for acetabular fractures. It is therefore difficult to compare the studies directly, as they employ a variety of different test parameters. Furthermore, the clinical implications of the biomechanical studies should be scrutinized, since several test parameters were not based on observations of the human physiology. Conclusion: The limited comparability and restricted clinical implications should be kept in mind when interpreting the results of biomechanical studies and when designing test setups to evaluate fixation methods for acetabular fractures.Publicationtype: Journal ArticleScopus© Citations 6 82 179 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Stresses and deformations of an osteosynthesis plate in a lateral tibia plateau fracture(2022-01-01); ; ; ; This study has the aim to investigate the strain and stress in an anterolateral locking plate applied for the fixation of a lateral split fracture. To simulate a complex fracture situation, three segments were separated. With a FEM analysis, representative places for strain and stress measurement were determined. A locked osteosynthesis plate was instrumented with strain gauges and tested on a fractured and a non-fractured Saw Bone model. To simulate different loading situations, four different points of force application, from the center of the condyles to a 15 mm posterior position, were used with a medial-lateral load distribution of 60:40. The simulations as well as the biomechanical tests demonstrated that two deformations dominate the load on the plate: a bending into posterior direction and a bulging of the plate head. Shifting the point of application to the posterior direction resulted in increasing maximum stress, from 1.16 to 6.32 MPa (FEM analysis) and from 3.04 to 7.00 MPa (biomechanical study), respectively. Furthermore, the comparison of the non-fractured and fractured models showed an increase in maximum stress by the factor 2.06-2.2 (biomechanical investigation) and 1.5-3.3 (FEM analysis), respectively.Publicationtype: Journal ArticleScopus© Citations 2 47 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , An Electronic Osteosynthesis Implant for Continuous Load Monitoring using a Strain GaugeThe utilization of strain gauges for monitoring the applied mechanical load to osteosynthesis plates using electronic implants was reported several times in literature. The technique was found to provide valuable information for monitoring the fracture healing process and for improving the rehabilitation. This paper introduces a new electronic osteosynthesis implant, which uses supercapacitors as an energy storage for short term autonomous operation. Moreover, a bluetooth low energy (BLE) transceiver is integrated into the system, which covers larger distances and is less sensitive to misalignment than the commonly used inductive data transmission. This improves the usability of the proposed system for the patients. The system can continuously sample and transmit strain values at a sampling rate of 5 Hz for more than 10 min without being recharged. More than 60 cm of distance in any practically relevant direction can be covered by the BLE data transmission if the implant is placed 5 cm deep in a phantom. The implant dimensions of 20 mm x 16 mm still fit on osteosynthesis plates for larger bones.Publicationtype: Conference Paper48 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Biomechanical aspects of the posteromedial split in bicondylar tibial plateau fractures—a finite-element investigationPurpose: To gain principal insight into fixation techniques of a posteromedial split fragment in bicondylar tibial plateau fractures. Methods: A computer simulation was performed, applying the finite-element method (FEM) to compare four methods of fixation of the posteromedial split fragment: lateral plate (model 1), lateral plate and kickstand screw (model 2), lateral plate and two antero-posterior lag screws (model 3), and lateral and posteromedial plate (model 4). The displacement of the fragment and material stresses in implants and bone under 2500 N axial load were analyzed. Results: Maximal displacement of the posteromedial split fragment of 2.8 mm was found with a sole lateral plate. An added kickstand screw decreased the displacement to 1.46 mm. Added lag screws improved stability by a factor 4, with a maximal displacement of 0.76 mm. The double-plate configuration revealed 0.27 mm, a decrease of the displacement by a factor 10 compared to model 1. An additional analysis of posteromedial fragment displacements with osteoporotic bone, simulated by dividing the elastic modulus of the bone by a factor 2, turned out to be of relevant impact. For model 1, the calculations did not converge. The influence of bone quality was found to be 70% in model 2, 60% in model 3, and 40% in model 4. Conclusions: The results indicate that the additional fixation of a posteromedial split fracture by plate osteosynthesis might be advantageous in bicondylar tibial plateau fractures treated with lateral plating. This might be even more important in patients with low bone quality.Publicationtype: Journal Article109 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Low-pressure micro-mechanical re-adaptation device sustainably and effectively improves locomotor recovery from complete spinal cord injury(Springer, 2018-11-26); ; ; ; Traumatic spinal cord injuries result in impairment or even complete loss of motor, sensory and autonomic functions. Recovery after complete spinal cord injury is very limited even in animal models receiving elaborate combinatorial treatments. Recently, we described an implantable microsystem (microconnector) for low-pressure re-adaption of severed spinal stumps in rat. Here we investigate the long-term structural and functional outcome following microconnector implantation after complete spinal cord transection. Re-adaptation of spinal stumps supports formation of a tissue bridge, glial and vascular cell invasion, motor axon regeneration and myelination, resulting in partial recovery of motor-evoked potentials and a thus far unmet improvement of locomotor behaviour. The recovery lasts for at least 5 months. Despite a late partial decline, motor recovery remains significantly superior to controls. Our findings demonstrate that microsystem technology can foster long-lasting functional improvement after complete spinal injury, providing a new and effective tool for combinatorial therapies.Publicationtype: Journal ArticleScopus© Citations 3 314 317 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Experimental strategies to bridge large tissue gaps in the injured spinal cord after acute and chronic lesion(2016-04-05); ; ; ; After a spinal cord injury (SCI) a scar forms in the lesion core which hinders axonal regeneration. Bridging the site of injury after an insult to the spinal cord, tumor resections, or tissue defects resulting from traumatic accidents can aid in facilitating general tissue repair as well as regenerative growth of nerve fibers into and beyond the affected area. Two experimental treatment strategies are presented: (1) implantation of a novel microconnector device into an acutely and completely transected thoracic rat spinal cord to readapt severed spinal cord tissue stumps, and (2) polyethylene glycol filling of the SCI site in chronically lesioned rats after scar resection. The chronic spinal cord lesion in this model is a complete spinal cord transection which was inflicted 5 weeks before treatment. Both methods have recently achieved very promising outcomes and promoted axonal regrowth, beneficial cellular invasion and functional improvements in rodent models of spinal cord injury. The mechanical microconnector system (mMS) is a multi-channel system composed of polymethylmethacrylate (PMMA) with an outlet tubing system to apply negative pressure to the mMS lumen thus pulling the spinal cord stumps into the honeycomb-structured holes. After its implantation into the 1 mm tissue gap the tissue is sucked into the device. Furthermore, the inner walls of the mMS are microstructured for better tissue adhesion. In the case of the chronic spinal cord injury approach, spinal cord tissue - including the scar-filled lesion area - is resected over an area of 4 mm in length. After the microsurgical scar resection the resulting cavity is filled with polyethylene glycol (PEG 600) which was found to provide an excellent substratum for cellular invasion, revascularization, axonal regeneration and even compact remyelination in vivo.Publicationtype: Journal Article88 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Intelligente Implantate für das Monitoring der Knochenheilung(Springer, 2013-11-30); ; ; ; Background: Monitoring of fracture healing is a complex problem. Radiographs solely enable the estimation of calcification. Telemetric determination of bone healing: A telemetric system to mechanically assess bone healing was developed. The system consists of an electronic unit applied to a locked plate, an external reader and a ground sensor to measure externally applied loads. By correlating the externally applied load and deformation in the implant, the elasticity of the osteosynthesis is calculated. Elasticity decreases with ongoing consolidation of a fracture or nonunion and is appropriate to monitor the course of bone healing. Clinical application: Clinical application was performed in 56 patients suffering nonunions or a fracture of the femur; in 47 cases treatment was completed. In 46 of 47 patients, consolidation was achieved. Different types of healing curves could be differentiated (fast healing, slow healing, plateau with following fast healing, nonhealing). Conclusion: The system proved to be valuable for the judgement of bone healing in difficult healing situations. Routine cost-effective manufacturing is possible, because the used electronic components are derived from mass products.Publicationtype: Journal Article94 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A mechanical microconnector system for restoration of tissue continuity and long-term drug application into the injured spinal cord(Elsevier, 2013-10-03); ; ; ; Complete transection of the spinal cord leaves a gap of several mm which fills with fibrous scar tissue. Several approaches in rodent models have used tubes, foams, matrices or tissue implants to bridge this gap. Here, we describe a mechanical microconnector system (mMS) to re-adjust the retracted spinal cord stumps. The mMS is a multi-channel system of polymethylmethacrylate (PMMA), designed to fit into the spinal cord tissue gap after transection, with an outlet tubing system to apply negative pressure to the mMS thus sucking the spinal cord stumps into the honeycomb-structured holes. The stumps adhere to the microstructure of the mMS walls and remain in the mMS after removal of the vacuum. We show that the mMS preserves tissue integrity and allows axonal regrowth at 2, 5 and 19 weeks post lesion with no adverse tissue effects like in-bleeding or cyst formation. Preliminary assessment of locomotor function in the open field suggested beneficial effects of the mMS. Additional inner micro-channels enable local substance delivery into the lesion center via an attached osmotic minipump. We suggest that the mMS is a suitable device to adapt and stabilize the injured spinal cord after surgical resection of scar tissue (e.g., for chronic patients) or traumatic injuries with large tissue and bone damages.Publicationtype: Journal Article89 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Rückenmarkadaptation : bioresorbierbares Mikrosystem, Medikamentenapplikation, Stammzellen(Springer, 2013-09-05); ; ; ; Background. The idea behind the research project on neuroregeneration after spinal cord injury currently funded by the Deutsche Gesetzliche Unfallversicherung (DGUV) is to combine known drug and cell therapeutic approaches with a surgical procedure. Technique. Damaged spinal cord tissue is resected followed by a tension-free adaptation of the uninjured tissue. For this purpose, a connector element (mMS, mechanical micro-connector system) was developed based on microsystem technologies. The mMS additionally allows the administration of drugs via microchannels Animal trials. In a key experiment in rats, the fixation of the spinal cord tissue, regenerative axon growth through the mMS, and improvement of locomotor function was shown. Currently, further therapeutic combination strategies include the use of substances to reduce fibrotic scar formation, to digest proteoglycans that inhibit axonal growth, stem cells to stimulate axonal growth as well as the chemokine SDF1. Discussion. In order to enable a tension-free adaptation of healthy tissue, depending on the extent of the damage, a shortening of the corresponding spine segment may be necessary. This can be achieved by total vertebral resection. It is known from the literature that total removal of spine segments is technically possible. However, shortening the spine in the course of the treatment of spinal cord damage is new. By combining cellular pharmaceutical treatments with surgical mechanical procedures the neuroregenerative therapy of spinal cord injury seems possible.Publicationtype: Journal Article86