Implementation of the "loaded implant" model in the rat using a miniaturized setup - description of the method and first results

Objective To miniaturize the loaded implant model to permit its application to small rodents. In this model, two titanium implants are placed 8 mm apart with their heads protruding from the skin and are forced together by a dedicated actuator. To assess the effect of (i) the post-implantation healing period and the duration of stimulation and (ii) the intratissular strain level on the microtomographical bone parameters BV/TV, Tb.N., Tb.Th. and BIC. Materials and methods Implants, 1 x 8 mm, were machined, inserted into the tibiae of rats and activated. A total of 123 animals were used. In series 1, the implants were left to heal for 2/4 weeks and then loaded to generate intratissular strains of 1125 +/- 5% mu e for 4/8 weeks. Series 2 had their implants loaded to 750, 1500 and 2250 +/- 5% mu e, respectively. Results Bone to implant contact increased upon loading. In series 1, no difference was observed regarding the duration of healing or the stimulation period. In series 2, at 750 mu e, the bone parameters did not differ from baseline. At 1500 mu e, all four parameters increased. At 2250 mu e, three of four parameters decreased relative to 1500 mu e. Conclusions (i) The loaded implant model can be miniaturized to the millimeter range; (ii) in the present model, implant activation beyond 4 weeks did not affect the bone parameters; (iii) mechanical stimulation increased bone to implant contact by up to 20%; (iv) the results obtained are consistent with the concept of an anabolic effect from 750 to 1500 mu e and deleterious effects at strains in the 2250 mu e range; and (v) strains at 2250 mu e did not lead to implant dis-integration.