Lumbar spinal fusion using recombinant human bone morphogenetic protein in the canine. A comparison of three dosages and two carriers.

Study Design. A randomized, prospective and controlled animal study. Objective. To evaluate lumbar spinal fusion using recombinant human bone morphogenetic protein 2 in a canine model. Summary of Background Data. Spinal fusion using autogenous bone grafting is associated with donor site morbidity and a nonunion rate of 5% to 35%. The use of recombinant human bone morphogenetic protein 2 as a bone graft substitute would eliminate donor site morbidity and perhaps augment the rate of successful fusion. Methods. Mature beagles underwent bilateral paraspinal exposure at L4-L5, followed by transverse process decortication and randomization into one of six groups using differing doses of recombinant human bone morphogenetic protein 2 implanted using either a Type I collagen carrier or a polylactic acid carrier. Two control groups were used: one group without recombinant human bone morphogenetic protein 2 and another group using autogenous rib graft alone. Results. Groups treated with recombinant human bone morphogenetic protein 2 demonstrated complete fusion in all animals. Animals treated with collagen carrier alone (no recombinant human bone morphogenetic protein 2) demonstrated complete absence of fusion. Successful fusion occurred in one of three canines in the autogenous bone graft group. Fusion masses in the recombinant human bone morphogenetic protein 2 treatment groups were significantly larger in size at 3 months than in the autogenous bone graft group. The collagen carrier was more biocompatible and biodegradable because residual polylactic acid carrier was seen with adjacent multinucleated giant cells. There was no evidence of spinal canal or nerve root encroachment in the recombinant human bone morphogenetic protein 2 treatment groups. Conclusions. The use of recombinant human bone morphogenetic protein 2 implanted using a Type I collagen carrier resulted in 100% fusion without adverse effects.