Development of a New Zealand White Rabbit Model of Spinal Pseudarthrosis Repair and Evaluation of the Potential Role of OP-1 to Overcome Pseudarthrosis

In Brief Study Design. Posterolateral lumbar fusions were performed in nicotine-exposed, New Zealand white rabbits. Animals that developed a pseudarthrosis were then regrafted with no graft, autograft, or osteogenic protein-1 (OP-1). Objectives. To establish a model of pseudarthrosis repair and to evaluate the ability of OP-1 to induce fusion in this model. Summary of Background Data. OP-1 has been shown to have a 100% fusion rate in an established rabbit fusion model, even in the presence of nicotine, which is known to inhibit fusion. Methods. Forty-four New Zealand white rabbits underwent posterolateral lumbar fusion with iliac crest autograft. To maximize the incidence of pseudarthroses, nicotine was administered to all rabbits. At 5 weeks, the spines were explored, and all pseudarthroses were redecorticated and grafted with no graft, autograft, or OP-1. At 10 weeks, the rabbits were killed and fusions masses were assessed with manual palpation, radiography, computed tomography, and/or histology. Results. Nine rabbits (20%) were lost to complications. Thirty-four (94%) had pseudarthroses on exploration at 5 weeks. By manual palpation at 10 weeks, 1 of 10 (10%) pseudarthroses that received no graft fused, 5 of 12 (42%) pseudarthroses that received autograft fused, and 9 of 11 (82%) pseudarthroses that received OP-1 fused. Computed tomography and histology further characterized the fusion masses. Conclusions. This study establishes a model for treatment of pseudarthroses. OP-1, which has previously been shown to have 100% fusion rate in animal models, outperformed autograft and induced fusion in 82% of rabbits. The ability of different graft materials to induce fusion in nicotine-exposed New Zealand white rabbits with documented lumbar pseudarthroses was studied. After attempted autograft fusion, 94% had pseudarthrosis. After regrafting with no graft, autograft, or osteogenic protein-1 (OP-1), fusion was detected in 10%, 42%, and 82% of the rabbits, respectively.