Intramedullary osseointegration: development of a rodent model and study of histology and neuropeptide changes around titanium implants.

A rodent model has been developed to explore intramedullary osseointegration and the phenomena of osseoperception. Osseointegration with endosseous titanium implants is frequently used in oral surgery. More recently, intramedullary osseointegration has been used for direct skeletal anchoring of amputation prostheses, a procedure that provides for a stable prosthesis with improved perception. Experimental, commercially pure titanium rods with threaded ends were surgically implanted in the intramedullary space of 18 rat femurs, and were left in place for 8 wk. Microscopic and immunohistochemical observation of the titanium/bone interface at this time-point indicated successful osseointegration with normal remodeled bone adjacent to the fixture. Calcitonin gene-related peptide activity was upregulated during the process of bone remodeling, and there was no significant inflammatory reaction. There was new, normal bone adjacent to and fully occupying the space between fixture threads. Innervation also appeared normal in remodeled bone, as indicated by immunohistochemical observation of small nerve fibers with the antibody Protein Gene Product 9.5 (PGP 9.5). The model will be used further to explore intramedullary osseointegration and osseoperception in connection to clinical applications.