The compatibility of implanted ceramic materials with autogenous bone, and the subsequently noted influence of the ceramic on the rate of new bone formation, were investigated to evaluate such materials for use in orthopedic implants. Three ceramic materials, aluminum oxide (A1203), zirconium oxide (ZrO,), and calcium aluminate (yCaO.xA1203) were tested. These were placed in the femurs of rhesus monkeys for periods of 50, 100, and 350 days. Definite cornpatability between the autogenous bone and the materials was exhibited for the implant time periods evaluated. No toxicogenic activity was noted in any of the biochemical, biomedical, and ceramographic evolutions. An added benefit resulted from the calcium aluminate composition, which was fabricated as a two-phase oxide material to make it slightly soluble in the body fluids. In the 50-and 100day implants, the bone penetrated the ceramic for distances up to 100 p while the ceramic dissolved and the pores enlarged. In addition, the mineralization in the area of the calcium aluminate was greater than that found around the other ceramics. Radiographs over the entire 350-day implant period confirmed the increased callus formation around all of the materials with no signs of rejection evident in the surrounding osseous or soft tissues. After 350 days the entire pore area of the calcium aluminate ceramic was infiltrated with a columnar substance which on the basis of scanning electron microscope procedures was considered to be mineralized osteoid

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The purpose of the investigation was to show the ability of two calcium aluminate ceramic compositions to act as suitable implants for partial replacements of long bones. It was anticipated from previous studies that the ceramic would be well tolerated by the autogenous bone and surrounding soft tissue while the ceramic was slowly dissolving in the body fluids, allowing new osseous tissue t o penetrate the resulting pore structure. It was expected that after a period of time the ceramic would no longer exist as a separate entity but would be completely infiltrated with mineralized osseous tissue and ultimately be completely replaced by bone. Two ceramic implants were prepared by slightly different techniques and CaO to A$03 ratios. The result was a polyphase ceramic and a nearly single phase ceramic. The polyphase material, after implantation in the test subject for 32 weeks, was completely impregnated with connective tissue while undergoing considerable alteration in microstructure. The single-phase material was not altered significantly in any way. This implant could not be fully evaluated for its ability to allow for osseous tissue formation on its surface, or within its open pore structure, due to sllght variations in the original fixation of the implant and resulting attempts to correct the problems.