Experimental Posterolateral Lumbar Spinal Fusion With a Demineralized Bone Matrix Gel

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Abstract
A controlled rabbit model of lumbar posterolateral intertransverse process arthrodesis was used to evaluate a bone graft substitute. To determine the efficacy of demineralized bone matrix gel as an autograft extender, using different ratios of demineralized bone matrix to autograft and to determine the efficacy of demineralized bone matrix as an autogenous bone graft enhancer by adding it to the usual quantity of autograft. Autogenous bone is considered the most effective bone graft material for posterolateral lumbar arthrodesis, yet nonunions occur in up to 30% of patients. In addition, donor site complications may occur in 25-30% of patients. This has prompted the search for and investigation of bone graft extenders, enhancers, and substitutes. Commercially available demineralized bone matrix gel is one possible graft extender and enhancer, which, unlike mineralized allografts, has osteoinductive properties. Although the gel is in common use, the efficacy of demineralized bone matrix when used for posterolateral spine arthrodesis has not been examined in prospective clinical studies. Furthermore, no known animal studies have tested demineralized bone matrix gel in a posterolateral arthrodesis model. Forty-seven New Zealand white rabbits underwent bilateral posterolateral spine arthrodesis at L5-L6 using autogenous iliac crest bone graft alone or in combination with demineralized bone matrix. Four groups were formed on the basis of the ratio of autograft to demineralized bone matrix: autograft alone (3 mL), 100:0 group; autograft (3 mL) and demineralized bone matrix (1.5 mL), 100:50 group; autograft (1.5 mL) and demineralized bone matrix (1.5 mL), 50:50 group; and autograft (0.75 mL) and demineralized bone matrix (2.25 mL), 25:75 group. Rabbits were killed 6 weeks after surgery. Inspection, manual palpation, radiographic film, and histologic evaluation were used to assess fusion. All groups had similar fusion rates (66-73%) based on manual palpation. Rabbits implanted with demineralized bone matrix had more mature fusion masses, evidenced by the greater trabecular bone formation seen on radiographic film and histologic study. Demineralized bone matrix was effective as a graft extender when used in up to a 3:1 ratio with autograft in a rabbit posterolateral spine fusion model. When less than the standard volume of autograft was used, the addition of demineralized bone matrix gel lead to fusion success rates comparable to those of the standard amount of autograft alone. However, demineralized bone matrix did not increase the frequency of successful fusion when added to the standard amount of autograft.

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