Porous ceramics as a bone substitute in the medial condyle of the tibia. An experimental study in sheep. Long-term observations.

A recent 3-month implantation study indicated that a new porous ceramic material might be suitable as a bone substitute in regions exposed mainly to compressive forces. The porous ceramics were implanted into the medial condyle of the tibia of sheep. In the present study the implants were left for 10 months in three animals, and 12 months in two. In the two animals with 12 months' observation, the plate which had been used to stabilize the implant was removed at 10 months. The implants and the adjacent bone tissue were studied macroscopically, radiographically and by microradiography and transmitted light microscopy. All the implants were bound to the adjacent bone by ingrowth of bony tissue. The depth of the bony invasion was slightly greater than that observed at 3 months, being maximally 3-4 mm. Some signs of ossification were still seen within the pores. The bony bridges between the implants and the surrounding bone were particularly well developed in regions of maximal stress. This was interpreted as a sign of active adaption of the bone formation to the actual stress to which the shearing surfaces were exposed. It is concluded that the properties of the porous ceramic implants justify a clinical trial in man.