Histological reaction to titanium alloy and hydroxyapatite particles in the rabbit tibia

The interfacial membrane harvested from failed joint replacements contains particulate debris from the materials used for the implant. To define the tissue response to particulate titanium alloy and hydroxyapatite (HA) alone, 16 mature New Zealand white rabbits were divided into 2 groups of 8 rabbits. Using sterile technique, a drill hole was placed anteromedially in the tibia, 1 cm distal to the knee joint bilaterally. The marrow was scooped out and 0.25 mg of either titanium alloy particles or HA particles were inserted in the right tibia. The titanium alloy particles had a diameter averaging 4.0 +/- 4.4 microns (mean +/- standard deviation) and an aspect ratio (the ratio of the maximum length divided by the maximum width) of 1.84. The HA particles had a diameter of 4.4 +/- 3.3 microns and an aspect ratio of 1.76. The left leg was prepared in a similar fashion, but no biomaterial was implanted. The animals were killed after 16 wk. The harvested tibiae were processed with decalcification and the plastic-embedded sections were subjected to histomorphological analysis. Black titanium alloy particles were present within the bone marrow fat between haematopoietic cells, and within scattered macrophages. The surrounding bone appeared to be unaffected. Within the spongiosa, the HA particles were surrounded by small numbers of mononuclear histiocytes or encased within a shell of new appositional bone. Where HA deposits were exposed to the endosteal aspect of bone, there was scalloping of the surface of the HA in a pattern suggestive of resorption or dissolution of the HA particles.(ABSTRACT TRUNCATED AT 250 WORDS)