Implant fixation enhanced by intermittent treatment with parathyroid hormone

The intermittent administration of parathyroid hormone (PTH) increases the formation of bone by stimulating osteoblastic activity. Our study evaluates the possibility that intermittent treatment with PTH (1-34) may also enhan ce the implant-bone fixation of stainless-steel screws, Twenty-eight rats r eceived one screw in either one (n = 8) or in both (n = 20) proximal tibiae . We administered either PTH (1-34) in a dosage of 60 mug/kg/day (n = 14) o r vehicle (n = 14) over a period of four weeks. At the end of this time, th e degree of fixation was assessed by measuring the removal torque on one sc rew in each rat (n = 28) and the pull-oat strength on the contralateral scr ew (n = 20), PTH increased the mean removal torque from 1.1 to 3.5 Ncm (p = 0.001) and the mean pull-out strength from 66 to 145 N (p = 0.002), No sig nificant differences in body-weight or ash weight of the femora were seen. Histological examination showed that both groups had areas of soft tissue a t the implant-bone interface, but these appeared less in the PTH group. The se results indicate that intermittent treatment with PTH may enhance the ea rly fixation of orthopaedic implants.