In the field of orthopaedics and traumatology, a whole series of problems appear related to fracture fixation by means of various types of plates. Appropriate application of the plate is the difficult task that a doctor needs to deal with in the operating room. Regarding mechanics, the number of screws and their spacing have a major impact on the healing process. If there are too many screws or lack of them, the fracture does not heal properly. This can lead to implant failure. This work deals with stress-strain analysis of screws and bone tissue with a fracture fixed by LCP. It deals with the influence of different geometrical configurations of the screws on the stress, deformation and strain of the system. For this purpose, the computational modelling was used by means of the finite element method. Two computational models have been created, on which different screw arrangement was analysed. The first computational model represents diaphysis of the femur that is at the beginning of the healing process. For the four load models and eleven geometric configurations and number of the screws, a total of 44 computations were performed. The second computational model represents the distal part of the femur. Femoral geometry model was created based on CT (computed tomography) examination, geometric model of the plate was created by 3D scanning. Deformations and stresses were compared in the three geometric configurations of the screws during the healing process.

[Truncated abstract] Renewed interest in the fixation of fractures using plates has been stimulated by an improved understanding of the biology of fracture healing and a drive towards minimally invasive surgery. This has led to a change in the way we use plates nowadays and the way in which we build the bone-plate construct, as well as the development of new implants better suited to these techniques. As a result of this, we have now the potential to safely expand the indications for plate fixation especially in the management of fractures in osteopenic bone. This thesis provides scientific evidence allowing for better formulation of the optimum way to use the modern plating systems in the clinical setting. Biological fracture repair with conventional plates, in terms of a less rigid construct to enhance fracture healing, is becoming increasingly popular. By omitting screws the construct becomes more flexible with a risk of fixation failure. It was the aim of the first paper to investigate in an experimental model the construct strength of different conventional plate lengths and number / position of the screws, and if an oblique screw at the plate end could increase the fixation strength. Our data suggest that the plate length is the most important factor in withstanding forces in cantilever bending. Longer plates with an equal number of screws require greater peak loads to failure than short plates with more screws. Furthermore, an oblique screw at the plate end produces an increased strength of fixation in all different test setups. However, the difference is more significant in shorter plates and in constructs with no screw omission adjacent to the fracture site. ... Following cyclic loading, however, locking plates can better retain fracture reduction compared to compression plates. On the other hand, under torsional load the compression plate appears to be biomechanical superior to the locking system. In supracondylar comminuted femur fractures, combining the two principles results in less plastic deformation, and a higher load to failure compared to their single application. The last two papers examine the behaviour of locking plates in osteopenic bone. In cadaveric intra-articular calcaneal fractures, the locking plate showed a significantly lower irreversible deformation during cyclic loading and a significantly higher load to failure. In dorsal and volar fixed angle distal radius constructs in a cadaveric model, all constructs showed adequate stability with minimal deformation on fatigue testing under physiological conditions in good bone quality. In osteoporotic bone, however, dorsal fixed angle constructs are stiffer and stronger than volar constructs. The addition of a styloid plate to a volar plate does not significantly improve stability.

Bei der internen, extramedullären Osteosynthese des distalen Femurs, auf die sich diese Arbeit fokussiert, haben sich in den letzten Jahren interessante Entwicklungen vollzogen. Ausgehend von unzufriedenstellenden Komplikationsraten wurden neue Wege in der Versorgung dieser schwierigen Frakturen gesucht. Osteosynthesematerialien, Repositionstechniken, die Technik der Implantatplatzierung und die Implantate selbst, bei denen die Entwicklung zu winkelstabilen Systemen gegangen ist, haben sich grundlegend geändert. Die vorliegende Arbeit analysiert in einer retrospektiven Studie distale Femurfrakturen, die zwischen dem 1.1.1995 und 31.9.2000 entweder mit einem Fixateur interne (LISS) oder mit der konventionellen Plattenosteosynthese versorgt wurden. In die Studie konnten 51 Patienten mit 54 distalen Femurfrakturen eingeschlossen werden. Die Infektionsrate war in der LISS-Gruppe (0% versus 11,1%) nichtsignifikant geringer, die Rate der verzögerten Frakturheilungen war nichtsignifikant höher. Die einzige verzögerte Frakturheilung (LISS-Gruppe), die einer sekundären chirurgischen Intervention bedurfte, wurde bei einer Patientin mit einem großen Knochendefekt gesehen, der ohne primäre Spongiosaplastik therapiert worden war. Pseudarthrosen traten in beiden Gruppen nicht auf. Die Rate des Materialversagens unterschied sich nicht signifikant. Beim LISS kam es nicht, wie bei den konventionellen Implantaten zu sekundären Repositionsverlusten, es wurden aber im Anfang der klinischen Einführung proximale Schraubenausrisse aufgrund einer Fehlplatzierung gesehen. Es konnte gezeigt werden, dass es durch die Verwendung des LISS und die indirekten Repositionstechniken zu keiner Zunahme der Achsfehlstellungen oder der Operationszeit kam. Die funktionellen Einzelergebnisse und die Punktzahl der erhobenen Scores (Neer-Score und Lysholm-Score) unterschieden sich nicht signifikant. / Internal, extramedullary osteosynthesis of distal femoral fractures which are focussed on in this study has been influenced by interesting developments in recent years. Driven by unsatisfying complication rates new fracture treatments have been looked for. Osteosynthesis materials, reduction techniques, techniques of implant placement and implants themselves - where development went to angular stable systems - have changed decisively. This study analyzes in a retrospective setting distal femoral fractures which were treated between 1.1.1995 and 31.9.2000 either with an internal fixator (LISS) or with conventional plate osteosynthesis. In this study 51 patients with 54 distal femoral fractures could be included. The Infection rate was non significantly lower in the LISS group (0% versus 11,1%), the rate of delayed union was non significantly higher. The only delayed union in the LISS group which needed secondary surgical intervention was seen in a patient with considerate bone loss which was not treated by primary bone grafting. Non-unions were not seen in either group. The rate of implant failure did not differ significantly. In the LISS group no secondary loss of reduction (like in the group with conventional plate osteosyntesis) was seen but proximal screw pull out due to malplacement was reported in the beginning of clinical introduction. It could be demonstrated the LISS and indirect reduction leading not to a higher rate of malalignement nor to prolonged theatre times. Functional results and the point score of the Neer Score and the Lysholm Score showed no significant difference.