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


Janin Reifenrath


In vivo evaluation of degradable magnesium alloys as orthopedic implant material in suitable animal models





Hannover, Tierärztliche Hochschule, Habilitationsschrift, 2010




Until today, commonly used implant materials in fracture repair are permanent and need to be removed after the healing process. In the present studies, biodegradable magnesium based implant materials were tested in different animal models for the use as orthopedic implant material in weight bearing applications. Therefore, mechanical strength is required beside a good biocompatibility during the degradation process. As in vitro studies are still not able to represent the complex in vivo situation, examinations in animal models are indispensable prior to clinical studies. In this interdisciplinary collaborative research on the development of magnesium-based implant materials for loaded applications, material and engineering scientists, bio-mechanists, and orthopedic surgeons were implemented. First promising materials were carved out by the use of clinical, radiographical, (µ-) computed tomographical and histological methods as well as biomechanical approaches, predominantly in the rabbit model. These materials, especially LAE442, were afterwards evaluated in application-oriented studies as osteosynthesis system (plate-screw system and interlocked intramedullary nailing system). While the intramedullary nailing system showed an adequate biocompatibility and very slow implant degradation, the plate screw-system caused massive clinical problems with gas formation and lameness and could not be recommended for the clinical use in the current state. However, the reason for the differences in implant degradation and resultant tissue reactions in the implant surrounding could not be finally resolved. Magnesium degradation is influenced by various factors, including pretreatments which can influence the surface structure, mechanical stresses during the implantation and differences in the surrounding tissue, especially ion concentrations. Although the intramedullary nailing systems were very promising, additional finite element simulations showed that the mechanical strength is borderline for fracture fixation without an additional stabilization within the first weeks. Further studies should clarify whether positive effects (like reduced stress shielding over time) are superior to the restriction in application.

The evaluation in animal models still remains indispensable, as the degradation in vitro differs from the degradation in vivo. Until now, no system can predict the in vivo situation. Especially the rabbit is a very commonly used and suitable animal model. It combines the ease in housing and handling requirements with the possibility of application oriented testing of implant materials by the use of various imaging techniques, including µ-computed tomography as well as simple biomechanical test. Only more complex interlocked intramedullary nailing systems were tested in the sheep as large animal model. However, differences in the metabolic rate as well as differences in the bone structure always have to be taken into account, when results are extrapolated to other animals or the human medicine.

Considering the studies together, low inflammatory reactions of the tissues surrounding magnesium based implants are beneficial. If the degradation process is slow, gas which occurs during the degradation process can be resorbed without clinical problems. The use as an osteosynthesis system especially in high loaded applications has to be considered as problematic due to a borderline mechanical stability and high amounts of material. However, smaller implants or lower loaded areas are very promising applications for magnesium based implant materials.



Magnesium, Implantat, abbaubar, magnesium, implant, degradable