Histological assessment of tissue from large human bone defects repaired with β-tricalcium phosphate

This report describes the histological characteristics of large human bone defects that were implanted with β-tricalcium phosphate (β-TCP). Samples were obtained longer after the primary operation than in the earlier studies. We assessed a total of nine biopsies taken 33-208 weeks after implantation. The tissue sections were stained with hematoxylin-eosin for general observation, with Gomori stain to visualize the reticulin fibers, and with an antibody against tartrate-resistant alkaline phosphatase (TRAP) to characterize the cells. Ongoing bone remodeling was observed even 208 weeks after implantation as determined by the presence of osteoclasts and active osteoblasts and new woven and lamellar bone. We observed multinuclear giant cells phagocytosing the biomaterial and the attachment of osteoclasts to the β-TCP. The osteoclasts showed intense TRAP positivity, while the giant cells showed variable TRAP positivity. There was a zonal pattern in the original defects: The central regions showed granules and fibrous septa, while peripheral areas showed a layer of new bone formation. These data demonstrate ongoing bone remodeling long after implantation in the peripheral regions of the original defects as well as fibrous changes in the central regions and phagocytosis of biomaterial by multinuclear giant cells.