Tissue reaction of bone inductive hydroxyapatite cement and its clinical opplication.

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1. We implanted hydroxyapatite(HA) cement into the diaphysis of tibia of 20 rabbits. Five rabbits were killed 1, 3, 6 and 12 weeks after the operation, and a series of three undecalsified specimens of tibia was made. The specimens were stained with toluidine blue and observed under a light microscopy. Quantitative evaluation for newly developed bony tissue was performed with the semiautomatic machine for histomorphometry (Affinity Index). In all specimens after 3 weeks, new bone bonded to the surface of the HA cement was observed. Affinity Index was higher in later groups. Taken together, good osteoconductivity was observed around HA cement. Hereafter, we intend to evaluate in long term examination.2. Opening wedge high tibial osteotomy was performed in 9 knees using Hydroxyapatite block until 1998, and we investigated results of these cases in this study. Clinical sympton was significantly improved, and macroscopic fracture of hydroxyapatite block was not observed in radiograms. Femorotibial angle remained same angle corrected in operation. However, longer term follow up study should be required to determine the result of this procedure. Undecalcified sections were prepared from specimens taken from the surface of implants at removal of internal fixation performed 1 year after operation. Histological appearance showed no inflammatory reaction, and direct bone-implant incorporation without fibrous tissue encapsulation was observed. Bone ingrowth was observed in the pores of the hydroxyapatite block, and the results should be compared with that of specimens taken 2 or 3 years after operation.