Parathyroid hormone for bone repair and implant fixation - Experiment in rats

Abstract: Intermittently administered PTH is known to increase bone mass in osteoporosis models. We studied its effects in bone repair and implant fixation, using histological and mechanical techniques in rats. In a bone chamber, PTH substantially increased the density of the new-formed bone, whereas there was only a minor effect on the pre-existing bone in the L5 vertebra or femur. Considering that PTH increased bone density especially at a site of regeneration, we evaluated the possibility of enhancing bone-implant fixation using PTH. Rats received a screw in each proximal tibia. PTH increased the removal torque three-fold at 4 weeks and doubled the pull-out strength. A similar effect was seen also at 2 weeks, and at 1 week histology showed that PTH increased the fraction of the metal surface having contact with bone without an intervening soft tissue layer from half to two thirds. A detachment test determine how PTH administration influences the bone-cement interfacial tensile strength. We used unloaded cement surfaces, which could be detached from the bone. PTH increased the median pull-away strength five-fold at 4 weeks. In conclusion, intermittent PTH treatment has a potential for enhancing the fixation of uncemented and cemented orthopedic implants due to its ability to increase bone density, especially at sites undergoing repair or regeneration.