Pore diameter of more than 100 μm is not requisite for bone ingrowth in rabbits

The optimal pore size for bone ingrowth is claimed to be 100-400 mum. With the use of a highly standardized experimental model, the present study reevaluated whether a pore size of 100 mum is the threshold value for bone ingrowth into porous structures under non-load-bearing conditions. Titanium triangle-shaped plates 250 or 500 mum thick were perforated with the use of a laser in order to create standard-sized holes (circle divide 50, 75, 100, and 125 mum) in multiple rows. The amount of bone ingrowth through the implant holes was studied in the cancellous bone of the distal rabbit femur. Twelve weeks after implantation, detailed analysis of bone ingrowth was performed with computerized image analysis of backscattered electron imaging techniques of scanning electron microscopy. The results showed that the amount of ingrown new bone was independent of the pore size and implant thickness. The median value for bone ingrowth varied between 64 and 78%. A striking feature was the formation of secondary osteonal structures even in the smallest holes. Based on these results, there is no threshold value for new bone ingrowth in pore sizes ranging from 50 to 125 mum under non-load-bearing conditions. (C) 2001 John Wiley & Sons, Inc.