Osteoconduction at porous hydroxyapatite with various pore configurations

To assess the histological response and the reinforcing effects of bone ing rowth within porous hydroxyapatite (HA) implants depending on pore geometry , four kinds of cylindrical-type with parallel linear pores (phi 50, 100, 3 00, 500 mu m), one kind of sponge-type with irregular interconnecting pores (phi 250 mu m) and one cross-type with crossing linear pores (phi 100 x 12 0 mu m) of porous HA were prepared. Eighty-four rabbits were divided into s ix groups, and a 5 x 5 x 7 mm sized porous HA block was inserted through th e medial cortical window of the proximal tibia. Histomorphological changes were examined using light and scanning electron microscopy. A biomechanical compression test was performed using material test machines. After implant ation, the implants showed different histological changes depending on pore geometry. Active osteoconduction was also found in the phi 50 mu m sized c ylindrical-type porous HA. Evidence of remodeling of new bone and bone marr ow formation within porous HA was found in the larger cylindrical-types (ph i 300, 500 mu m), and the sponge- and cross-types. The biomechanical test s howed that the ultimate compressive strength increased significantly in the phi 300 mu m sized cylindrical-type, and in the sponge- and cross-types ei ght weeks after implantation. Porous HA with cylindrical pores could be a u seful graft material due to its strength, osteoconductivity and the ease wi th which its pore geometry can be controlled. (C) 2000 Elsevier Science Ltd . All rights reserved.