Session 44 – Spine - Hall E 130-131, Wed 8:00 AM - 10:00 AM0276 47th Annual Meeting, Orthopaedic Research Society, February 25 - 28, 2001, San Francisco, California

PROSPECTIVE COMPARISON OF COMMERCIALLY AVAILABLE DEMINERALIZED BONE MATRIX FOR SPINALFUSION

+*Wang, J C; *Davies, M R; **Kanim, L E A; *Ukatu, C J; **Dawson, E G; *Lieberman, J R+*Department of Orthopaedic Surgery, UCLA School of Medicine, Los Angeles, CA. UCLA Dept of Orthopaedic Surgery, Box 956902, Los Angeles, CA 90095-

6902, 310-206-8263, Fax: 310-206-0063, jwang@mednet.ucla.edu

INTRODUCTION: Demineralized bone matrix derived fromhuman tissues has demonstrated the ability to aid in thestimulation of an osteoinductive response allowing forimproved bone growth and fusion. In an effort to augment theavailable grafting material as well as increase fusion rates, theutilization of a demineralized bone matrix (DBM) as a graftextender or even as a graft substitute has becomecommonplace. A variety of human DBM composites arecommercially available, but no comparative studies existexamining their relative effectiveness in spinal fusion. Theathymic rat offers a unique animal model with the advantageof a non-immunogenic environment for in vivo evaluation offusion. The purpose of this study was to compare theosteoinductive ability between three commercially availablehuman DBMs to heal a spinal fusion.

METHODS: 54 mature athymic nude female rats were usedin this study (175-240 g, Harlan Sprague Dawley, IN). Threegroups of 18 rats each were implanted with one of the threeDBMs evaluated (Dynagraft putty - Gen-Sci, RegenerationLaboratories, CA, Grafton putty - Osteotech Inc. NJ, andOsteofil allograft bone paste - Regeneration Technologies,FL), and the rats were sacrificed at 2, 4, 6, and 8 weeks. Allprocedures were performed by a single surgeon through amidline incision, exposing the transverse processes.Decortication was performed on the L4 and L5 (lamina andfacet joints were left intact without decortication) and thewound was irrigated. An aliquot equal to 0.3 cc as measuredin a 1.0 cc syringe was placed into each posterolateral gutterspanning the transverse processes for a total of 0.6 cc of graftper animal. The wound was closed. High ResolutionRadiographs were obtained in vivo and after sacrifice.Explanted lumbar spines were manually tested forintersegmental motion by three independent observers blindedto the treatments. Any motion detected for either side betweenfacets or between transverse processes of L4 and L5 bymanual testing was considered a failure of fusion. Absence ofany motion was considered successful fusion. Histologicalanalysis consisted of non-decalcified sections.

RESULTS: Overall, a majority of the L4-L5 levels implantedwith Osteofil or Grafton fused compared to none of the spinesimplanted with Dynagraft (comparison at 6 weeks, P<0.0001,Fischer’s Exact Test*). Even after 8 weeks, Dynagraft did notrestrict motion and no bone formation was notedradiographically.

All spines considered fused contained a large fusion mass,whereas the spines implanted with Dynagraft, containing anequally abundant bulk as the others (Grafton and Osteofil),were easily manually flexed, and the material was minimallyincorporated, even at 8 weeks.

These data support the athymic rat as a model for effectiveevaluation of the relative efficacy of these as well as otherhuman DBMs to induce posterolateral intertransverse processfusion. Taken from a separate experiment, rats receiving ratautogenous iliac crest bone or human cortical bone graft and

sacrificed at 6 weeks (controls) did not result in spinal fusion.Non-decalcified histology confirmed the presence of apseudarthrosis and the presence of a solid fusion, and thehistology correlated with the manual testing.

CONCLUSIONS: This is the first highly controlled,prospective testing of three commercially availabledemineralized bone matrix products in a spinal fusion model.The athymic nude rat model allows for each substance to beused in its commercial, “off the shelf” form, since the rat doesnot reject the human tissue substance. Although, all theproducts claim to have significant osteoinductive potential,this study does demonstrate differences in their ability toinduce an osteoinductive response capable of healing a spinalfusion. By at least 6 weeks and as early as 4 weeks, Osteofiland Grafton alone demonstrated posterolateral fusionmanually, radiographically and histologically while Dynagraft,local human cortical bone, or autogenous rat iliac crest bonedid not.

**UCLA Comprehensive Spine Institute, Los Angeles, CA.

Test SubstanceDynagraft Grafton Osteofil

Time at Sacrifice fusions/total fusions/total fusions/total2 weeks 0/1 0/1 0/14 weeks 0/5 2/5 4/5

6 weeks* 0/7 7/7 7/88 weeks 0/4 2/4 3/4Totals 0/17 11/17 14/18