For the purpose of studying bone remodeling around prostheses, a segmental replacement for the goat tibia was designed, using a conical, screw-threaded, hydroxyapatite-coated stem for fixation. Eight goats were provided with the implant, seven of which loosened within 10 days post-operatively, displaying progressive radiolucency and gross rotational motion. The eighth one also loosened radiographically, but developed a stabilizing callus bridge to prevent motion. A second design of similar shape and coating, but lacking the screw threads, was designed and also applied in eight animals. In this case, no loosening occurred in the first 6 weeks post-operatively. It is concluded that the application of screwed intramedullary stems for prosthetic fixation is not a viable concept, because the threads prevent the stem from subsiding and restabilizing when minor initial interface stress-relaxation and remodeling has occurred.

dx.doi.org/10.1016/0267-6605(92)90017-N, hdl.handle.net/1765/15381
Clinical Materials
Erasmus MC: University Medical Center Rotterdam

van Loon, P.J.M, Weinans, H.H, & Huiskes, R. (1992). Intramedullary fixation with screwed, conical stems--unsolicited results from animal experiments. Clinical Materials, 10(4), 239–242. doi:10.1016/0267-6605(92)90017-N