EXPERIMENTAL POSTEROLATERAL LUMBAR SPINAL-FUSION WITH A DEMINERALIZEDBONE-MATRIX GEL

Study Design, A controlled rabbit model of lumbar posterolateral inter transverse process arthrodesis was used to evaluate a bone graft subst itute. Objective. To determine the efficacy of demineralized bone matr ix gel as an autograft extender, using different ratios of demineraliz ed bone matrix to autograft and to determine the efficacy of demineral ized bone matrix as an autogenous bone graft enhancer by adding it to the usual quantity of autograft, Summary of Background Data. Autogenou s bone is considered the most effective bone graft material for poster olateral lumbar arthrodesis, yet nonunions occur in up to 30% of patie nts. In addition, donor site complications may occur in 25-30% of pati ents. This has prompted the search for and investigation of bone graft extenders, enhancers, and substitutes. Commercially available deminer alized bone matrix gel is one possible graft extender and enhancer, wh ich, unlike mineralized allografts, has osteoinductive properties. Alt hough the gel is in common use, the efficacy of demineralized bone mat rix when used for posterolateral spine arthrodesis has not been examin ed in prospective clinical studies. Furthermore, no known animal studi es have tested demineralized bone matrix gel in a posterolateral arthr odesis model. Methods, 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 autograf t to demineralized bone matrix: autograft alone (3 mL), 100:0 group; a utograft (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, manua l palpation, radiographic film, and histologic evaluation were used to assess fusion. Results. All groups had similar fusion rates (66-73%) based on manual palpation. Rabbits implanted with demineralized bone m atrix had more mature fusion masses, evidenced by the greater trabecul ar bone formation seen on radiographic film and histologic study. Conc lusions. Demineralized bone matrix was effective as a graft extender w hen used in up to a 3:1 ratio with autograft in a rabbit posterolatera l 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 frequen cy of successful fusion when added to the standard amount of autograft .