Fusion Performance of Low-Dose Recombinant Human Bone Morphogenetic Protein 2 and Bone Marrow-Derived Multipotent Stromal Cells in Biodegradable Scaffolds A Comparative Study in a Large Animal Model of Anterior Lumbar Interbody Fusion

Study Design. A large animal study comparing interbody fusion of a bioresorbable scaffold loaded with either low-dose recombinant human bone morphogenetic protein 2 (rhBMP-2) or bone marrow-derived multipotent stromal cells (BMSCs). Objective. To compare the quality of fusion resulting from implantation of medical grade poly (epsilon-caprolactone)-20% tricalcium phosphate (mPCL/TCP) scaffolds and two different bone growth stimulating agents. Summary of Background Data. Nondegradable cages have been used for interbody fusion with good results. However, the overall advantage of lifelong implantation of a nondegradable device remains a subject of ongoing debate. The use of bioresorbable scaffolds might offer superior alternatives. In this study, we evaluated the quality of fusion obtained with two potential bone graft substitutes. Methods. Eleven Yorkshire pigs underwent a bisegmental (L2/L3; L4/L5) anterior lumbar interbody fusion (ALIF) in four groups, namely: (1) mPCL/TCP + 0.6mg rhBMP-2; (2) mPCL/TCP + BMSCs; (3) mPCL/TCP (negative control); and (4) autologous bone grafts (positive control). Results. The mean radiographic scores at 9 months were 3.0, 1.7, 1.0, and 1.8 for groups 1 to 4, respectively. The bone volume fraction of group 1 was two-folds higher than group 2. Histology, micro-computed tomographic scanning and biomechanical evaluation demonstrated solid and comparable fusion between groups 1 and 4. However, group 2 showed inferior quality of fusion when compared with groups 1 and 4 while group 3 showed no fusion even at 9 months. In addition, there was no evidence of implant rejection, chronic inflammation or any other complications. Conclusion. mPCL/TCP scaffolds loaded with low-dose rhBMP-2 is comparable to autograft bone as a bone graft substitute in this large animal ALIF model. Although BMSCs lagged behind autograft bone and rhBMP-2, evidence of bone ingrowth in this group warrants further investigation. Our results suggest that mPCL/TCP scaffolds loaded with rhBMP-2 or BMSCs may be a viable alternative to conventional cages and autograft bone.