COMPARISON OF HYDROXYAPATITE GRANULES TO AUTOGENOUS BONE-GRAFT IN FUSION CAGES IN A GOAT MODEL

BACKGROUND With the increased use of fusion cages to achieve lumbar in tervertebral fusion, the question arises as to the potential for bone ingrowth from the host bone through the entire cage. is it even necess ary to have an autogenous graft to achieve total bone incorporation? M ETHODS Nine adult male goats had fusion cages implanted into three ver tebral bodies. The design was Surgical Dynamics/Ray Fusion Cage, measu ring 21 mm x 14 mm. In each animal, one fusion cage was filled with au togenous graft, one with hydroxyapatite, porous granules, and the othe r with nonporous granules. Amount of new bone formation was determined by backscatter electron microscopy at 3 months post implantation in a ll animals. RESULTS The histologic section shows that there was total incorporation in all specimens at 3 months. There was slightly more ne w bone (43%) with the nonporous granules compared with the porous gran ules (35%). The amount of residual void space was about the same in al l specimens, indicating that the amount of new bone formation was simi lar and not statistically different in cages filled with hydroxyapatit e granules versus granules of autogenous bone. CONCLUSION This study c onfirms that total incorporation by ingrowth of new bone can be expect ed in fusion cages. The amount of ingrowth is about the same for autog enous graft versus hydroxyapatite granules. Apparently, it is not nece ssary to use bone graft to achieve successful bone incorporation if an acceptable biocompatable lattice, such as hydroxyapatite granules, is used. (C) 1998 by Elsevier Science Inc.