Experimental spinal fusion using sintered bovine bone coated with type I collagen and recombinant human bone morphogenetic protein-2

Study Design. Posterolateral lumbar transverse process fusion using recombi nant human bone morphogenetic protein (rhBMP)-2 carried by sintered bovine bone and Type I collagen complex was compared with fusion achieved using au togenous bone graft or sintered bovine bone alone. Objectives. This study examined the efficacy of sintered bovine bone coated with Type I collagen as a carrier of rhBMP-2 for lumbar intertransverse pr ocess arthrodesis. Summary of Background Data. Posterolateral intertransverse process arthrode sis using osteoinductive growth factors is performed experimentally in the lumbar spine. The previous studies revealed the efficacy of osteoinductive factors applied to carriers having no bony structures, such as collagen she et or polylactic acid polymer, for the spinal fusion. However, in their stu dies, a large amount of osteoinductive proteins have been applied for the s pinal fusion. We used the sintered bovine bone "True Bone Ceramics" (TBC; K oken Co., Tokyo, Japan) coated with type I collagen as the carrier. True Bo ne Ceramics is the only biomaterial possessing a natural trabecular structu re and an organized crystal of bone minerals. Methods. Twenty-two adult rabbits underwent bilateral lumbar intertransvers e process arthrodesis at L4-L5. The animals were divided into four groups a nd had materials implanted as follows: autologous bone group, grafted autol ogous corticocancellous bone harvested from the posterior iliac crest; impl anted TBC group; TBC collagen group, implanted TBC coated with Type I colla gen infiltrating into the porous space; and BMP group, implanted sintered b ovine bone coated with Type I collagen infiltrated with 100 mu g of rhBMP-2 . Spinal fusion was evaluated by radiographic analysis, manual palpation, b iomechanical testing, and histologic examination 6 weeks after surgery. Results. Two rabbits were killed because of infection and lumbar plexus pal sy. Radiographs of the BMP group showed a homogeneous fusion mass at the in tertransverse area, and stability was confirmed by dynamic radiographs at 3 and 6 weeks after surgery. In the BMP group, a bony mass in the intertrans verse a rea was more prominent than in the other groups. The BMP group had a higher fusion rate based on manual palpation than the-other groups, and B MP fusions showed significantly higher tensile strength and stiffer fusion. The histologic findings in the BMP group demonstrated membranous bone and endochondral bone formations between the transverse process and the fusion mass. In the other groups, continuous trabecular bone formation was observe d in the:area surrounding the transverse process, but gaps between grafted fragments and less mature bone formation were present in the intertransvers e area. Conclusions. Sintered bovine bone coated with Type-1 collagen and rhBMP-2 r esulted in a higher fusion rate than the autograft and can be used as a car rier for rh-BMP-2 in spinal fusion.