EVALUATION OF RHBMP-2 WITH AN OPLA CARRIER IN A CANINE POSTEROLATERAL(TRANSVERSE PROCESS) SPINAL-FUSION MODEL

Study Design, Posterolateral L4-L5 transverse process fusions were don e on 14 adult beagles. Six were implanted with recombinant human bone morphogenetic protein-2 carried by open-cell polylactic acid polymer d elivery vehicle. Six received autogenous iliac bone graft. Two receive d carrier alone. Eleven were killed 3 months after implantation. One i n each group was maintained for 8 months. Objectives. To compare recom binant human bone morphogenetic protein-2 and open-cell polylactic aci d polymer with autogenous iliac bone for inducing transverse process f usion in the canine by 3 months and to determine whether transverse pr ocess decortication and implantation of carrier alone causes spontaneo us transverse process fusion in the canine. Summary of Background Data . Recombinant human bone morphogenetic proteins have healed segmental long bone defects in several models. They have induced interlaminar an d facet fusions in canines. Interlaminar and facet fusions have occurr ed after ham decortications in canines. Recombinant human bone morphog enetic protein-2 has not been evaluated for transverse process fusion in canines. Transverse process fusion is a preferred clinical method f or achieving posterior lumbar fusion. Methods. Fusion sites were evalu ated by serial computed tomography scans. After the dogs were killed, explanted spines were subjected to manual testing, mechanical testing, high resolution radiography, and histologic analysis. Results. One hu ndred percent of recombinant human bone morphogenetic protein-2-implan ted sites had solid transverse process fusion by 3 months according to all measures. No autografted sites were fused at this interval. Osseo us bridging of posterolateral gutters occurred in the recombinant huma n bone morphogenetic protein-2-implanted sites after 2 months, the ear liest radiographic measure. None of the carrier-only sites showed bone formation. Conclusions. Recombinant bone morphogenetic protein-2 carr ied by open-cell polylactic acid polymer is superior to autogenous ili ac bone for producing radiographically and mechanically solid transver se process fusions in canines by 3 months. Spontaneous transverse proc ess fusion does not occur in canines after decortication and open-cell polylactic acid polymer implantation.