The use of coralline hydroxyapatite with bone marrow, autogenous bone graft, or osteoinductive bone protein extract for posterolateral lumbar spine fusion

Study Design. A posterolateral lumbar arthrodesis animal model using corall ine hydroxyapatite as a bone graft substitute. Objective. To determine the effectiveness of coralline hydroxyapatite as a bone graft substitute for lumbar spine fusion when used with bone marrow, a utogenous bone graft, or an osteoinductive bone protein extract. Summary of Background Data. Coralline hydroxyapatite is commonly used as a bone graft substitute in metaphysial defects but its use in a more challeng ing healing environment such as the posterolateral spine remains controvers ial. There are no published animal studies in which the use of coralline hy droxyapatite has been evaluated in a posterolateral lumbar arthrodesis mode l. Methods. Single-level posterolateral lumbar arthrodesis was performed at L5 -L6 in 48 adult New Zealand White rabbits. Rabbits were assigned to one of three groups based on the graft material they received: 3.0 mL coralline hy droxyapatite 1.5 mL plus bone marrow; 1.5 mL coralline hydroxyapatite plus 1.5 mL autogenous iliac crest bone; and, 3.0 mL coralline hydroxyapatite pl us 500 mu g bovine-derived osteoinductive bone protein extract on each side . Rabbits were killed after 2, 5, or 10 weeks, and the spines were excised and evaluated by manual palpation, radiographs, tensile biomechanical testi ng, and nondecalcified histology. Results. Fusions were assessed by manual palpation at 5 weeks for compariso ns among the three groups of graft materials. The coralline hydroxyapatite used with bone marrow produced no solid fusions (0/14). When combined with an equal amount of autogenous iliac crest bone, coralline hydroxyapatite re sulted in solid fusion in 50% (7/14) of the rabbits (P < 0.05). When combin ed with the osteoinductive growth factor extract, the coralline hydroxyapat ite resulted in solid fusion in 100% (11/11) of the rabbits (P < 0.05). The fusion masses in the growth factor group were significantly stronger (1.8 +/- 0.2 vs. 1.3 +/- 0.1; P = 0.02) and stiffer (1.5 +/- 0.2 vs. 1.2 +/- 0.1 , P = 0.04) based on tensile testing to failure when normalized to the adja cent-unfused level. Conclusion. These data indicate that coralline hydroxyapatite with bone mar row was not an acceptable bone graft substitute for posterolateral spine fu sion. When combined with autogenous iliac crest bone graft,coralline hydrox yapatite served as a graft extender yielding results comparable to those ob tained with autograft alone. Coralline hydroxyapatite served as an excellen t carrier for the bovine osteoinductive bone protein extract yielding super ior results to those obtained with autograft or bone marrow.