Ultrastructure of the bone-cement and the bone-metal interface.

A review is given of the methods used to demonstrate the bone-implant interface by transmission electron microscopy (TEM). Neither method is yet refined enough to permit demonstration without artifacts of the contact between implant, cells, and organic and inorganic matrix. Published studies on certain metallic implants and bone cement demonstrate a direct contact between bone matrix and implant, without a continuous interposed layer of cells. The 1000 nm closest to the implant surface show a variable structure, the interpretation of which is unknown. The degree of mineralization within this distance of the implant has not yet been adequately studied. Without completely reliable analytic methods and comparable implantation protocols, the gradation of implant biocompatibility, based on the TEM appearance of the interface, should be performed with great caution.