Tierärztliche Hochschule Hannover / Bibliothek – University of Veterinary Medicine Hannover – Foundation / Library


Patrick Hans Wefstaedt







Hannover, Tierärztliche Hochschule, Habilitationsschrift, 2012




Total hip replacement (THR) is a routine surgical treatment for severe hip dysplasia in dogs as well as in humans. Aseptic loosening of prostheses components is one key factor influencing the long term outcome of total hip replacements. Current collaborative research between engineers and veterinary as well as medical physicians aim at the improvement of prosthetic materials, prostheses geometries and prosthetic stem alignment within the femoral canal to reduce stress shielding processes in the periprosthetic bone and implant loosening thereof. In this context, computerized modelling methods like the finite element method and multibody simulations can help to provide knowledge about bone remodeling processes in the periprosthetic bone as well as of the loading situation in the artificial joint. To set up these models accurate motion analyses in combination with measured ground reaction forces of the patients are needed. Gait analysis measurements can furthermore be used to quantify the lameness improvement in dogs after orthopaedic surgical interventions such as THRs. To validate the established computerized models and to gain a deep insight into the morphologic processes in the periprosthetic bone modern imaging analyses are necessary.

Within the current work at first the establishment of a gait analysis laboratory at the Small Animal Hospital of the University of Veterinary Medicine Hannover is described. The laboratory was validated by comparative kinematic and kinetic gait analysis of the hind limb function in dogs walking on a treadmill and force plate. As one result a lower weight bearing behaviour could be demonstrated during walk on the treadmill in comparison to the force plate measurements. In the following, gait analyses were carried out for the comparison of the functional outcome of dogs undergoing different surgical treatments of common orthopaedic hind limb diseases. Severe hip dysplasia was treated with either cemented or uncemented THR. As one main result, both groups showed similar weight bearing characteristics during a time course of four months after surgery. Gait analysis data was further used to setup and validate an MBS model for the calculation of joint forces and moments in the canine hind limb. The results of this study show that measured and simulated vertical ground reaction forces are in good accordance to each other. For that reason it can be concluded that the established MBS can be used for the computing of the loading situation of the hip joint during different movements. In this context also combined simulations between MBS and FEM are wanted to simulate the influence of different loading conditions on bone remodeling processes in the periprosthetic femur. Within the here introduced work two studies are presented dealing with the numerical simulation of periprosthetic bone remodeling processes in the canine and human femur after THR. Simulation results suggest that bone remodeling processes mainly occur in the proximal analysis regions of the femur. In addition to the results from the FEA in case of the dog quantitative measurements of the periprosthetic bone density (grayscale value) by means of postoperative radiographs were carried out to prove whether this technique is capable to allow insights into periprosthetic bone remodeling processes or not. As the results show changes in periprosthetic bone density can be sufficiently analysed for cemented as well as for uncemented prostheses by means of the established technique. Significant bone loss occurred mainly in the region of the greater trochanter of femurs implanted with the uncemented prosthetic stem. For morphologic analysis of periprosthetic bone remodeling processes in the human periprosthetic femur, DEXA analyses were carried out at different time points before and after implantation of a widely used uncemented THR system. By means of the carried out analyses the hypothesis of a proximal load transfer from the prosthesis to the periprosthetic bone with initial bone loss in the calcar region and the region of the trochanter major could be confirmed. To improve the knowledge and understanding of morphological changes in the joints and the periprosthetic bone after THR, future work will have to combine simulative and morphological analyses of the bone implant interface with functional analyses of the surgical outcome. In this context, the investigations reported here can serve as a basis for the future establishment of optimized THR systems with long term stability.



Gait analysis, imaging diagnostics, total hip replacement, Ganganalyse, bildgebende Diagnostik, Hüftgelenkstotalendoprothese