LUMBAR INTERTRANSVERSE-PROCESS SPINAL ARTHRODESIS WITH USE OF A BOVINE BONE-DERIVED OSTEOINDUCTIVE PROTEIN

The use of a bovine bone-derived osteoinductive protein extract as a b one-graft substitute was evaluated in a rabbit model of intertransvers e process arthrodesis of the lumbar spine. Forty-five adult New Zealan d White rabbits had arthrodesis between the fifth and sixth lumbar ver tebrae with use of one of three graft materials: autogenous iliac-cres t bone, osteoinductive protein delivered in an allogeneic demineralize d bone matrix/collagen carrier, or demineralized bone matrix/collagen carrier without osteoinductive protein. Fusion was assessed by manual palpation, radiography, biomechanical testing, and light microscopy at two and five weeks after the operation. At two weeks, light microscop ic analysis of the arthrodesis site in which osteoinductive protein ha d been used showed that most of the demineralized bone matrix was stil l present, with small amounts of membranous and endochondral bone form ation at the peripheral margins of the implant. Light microscopic anal ysis of the five-meek specimens showed increased new-bone formation an d a more homogeneous and mature fusion mass with the osteoinductive bo ne protein than with the autogenous bone graft. At five weeks, the fus ions with the osteoinductive protein extract were characterized by mor e secondary spongiosa, with formation of bone marrow centrally and a c ortical rim peripherally. Of the thirty-five rabbits that were examine d at five weeks, all ten in the group that had received osteoinductive bone protein had a solid fusion, but the rate of fusion was significa ntly less in the other two groups: eight of thirteen rabbits (p = 0.05 ) in the group that had received autogenous bone graft and two of twel ve rabbits (p = 0.0001) in the group that had received demineralized b one matrix/collagen carrier without osteoinductive bone protein. The u se of osteoinductive bone protein resulted in stronger (p = 0.02) and stiffer (p = 0.005) fusions compared with those obtained with the use of autogenous iliac-crest graft. CLINICAL RELEVANCE: This investigatio n demonstrated the feasibility of biological enhancement of spinal art hrodesis. Although these results must be reproduced in a large-animal model, the possibility that the performance of a graft substitute may be superior to that of autogenous bone is intriguing. If solid biologi cal spinal fusions can be rapidly and reliably produced, the need for internal fixation may be reduced except in cases of gross spinal insta bility or deformity. In addition, an effective bone-graft substitute w ill solve the problems of limited availability and donor-site morbidit y that are associated with the use of autogenous bone grafts. Most imp ortantly, the prevalence of nonunions of the spine may be decreased.