Osteoconduction at porous hydroxyapatite with various pore configurations

To assess the histological response and the reinforcing effects of bone ingrowth within porous hydroxyapatite (HA) implants depending on pore geometry, four kinds of cylindrical-type with parallel linear pores (φ50, 100, 300, 500 μm), one kind of sponge-type with irregular interconnecting pores (φ250 μm) and one cross-type with crossing linear pores (φ100×120 μm) of porous HA were prepared. Eighty-four rabbits were divided into six groups, and a 5×5×7 mm sized porous HA block was inserted through the 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 implantation, the implants showed different histological changes depending on pore geometry. Active osteoconduction was also found in the φ50 μm sized cylindrical-type porous HA. Evidence of remodeling of new bone and bone marrow formation within porous HA was found in the larger cylindrical-types (φ300, 500 μm), and the sponge- and cross-types. The biomechanical test showed that the ultimate compressive strength increased significantly in the φ300 μm sized cylindrical-type, and in the sponge- and cross-types eight weeks after implantation. Porous HA with cylindrical pores could be a useful graft material due to its strength, osteoconductivity and the ease with which its pore geometry can be controlled.