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

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