Porous tantalum trabecular metal scaffolds in combination with a novel marrow processing technique to replace autograft.

INTRODUCTION Interbody fusion requires a structural member to carry load while the autograft or osteoinductive agent stimulates bone formation. In the present study, we evaluated the potential use of extracted nucleated cells from bone marrow mixed in hyaluronic acid gel as an osteoinductive agent, in comparison to Collagraft loaded with nucleated cells or rhBMP-2 in the porous tantalum ring, in an anterior lumbar interbody fusion (ALIF) in pigs. METHODS Four 3-month-old female Danish landrace pigs were employed in the current study. Bone marrow was collected by means of aspiration, from the medullary cavity of the proximal tibia. The nucleated cells were isolated with a Ficoll step gradient centrifugation. The cell adhered rate after 24 hours of cultivation and ALP activity in the osteogenic medium following 4 days of cultivation were measured. Cell numbers in the porous tantalum discs were assessed by CyQuant measurement, and fluorescent live/dead cell staining in the porous tantalum discs was performed after periods of 24 hours and 7 days of cultivation. The nucleated cells mixed in hyaluronic acid gel were cultivated on slides for 24 hours, 7 days and 21 days. The live/dead cell staining, ALP staining or osteocalcin staining, were performed. A porous tantalum ring was loaded with nucleated cells in hyaluronic acid gel or packed with Collagraft strips also with nucleated cells or rhBMP-2. Immediately after preparation, one of three implants was inserted into L2-3, L4-5 or L6-7 respectively. The pigs were killed 3 months postoperatively. The lumbar spine specimens were prepared for histological evaluation. RESULTS The adhered rate, of the nucleated cells, was 2.26+/-0.56%. ALP activity was no different in the osteogenic culture compared to DMEM/10%FBS alone. Cell numbers and live/dead cells showed no difference in the porous tantalum discs. Histological appearance showed that nucleated cells mixed with hyaluronic acid gel, had more mature bone in the central hole of the porous tantalum ring, compared to Collagraft strips with nucleated cells or rhBMP-2. Bone volume fraction did not differ within the three porous tantalum rings; however, more marrow space in the central hole of the porous tantalum ring was present when nucleated cells mixed with hyaluronic acid gel (57.4%) compared to Collagraft strips with rhBMP-2 (29.7%). CONCLUSION In the current study, we demonstrate that nucleated cells, which were isolated from bone marrow intraoperatively, could be used to replace autograft if nucleated cells mixed with hyaluronic acid gel or with Collagraft strips packed into the porous tantalum ring in the pig ALIF model.