Improved Lumbar Vertebral Interbody Fusion Using rhOP-1: A Comparison of Autogenous Bone Graft, Bovine Hydroxylapatite (Bio-Oss), and BMP-7 (rhOP-1) in Sheep

Study Design. After disc removal and monosegmental instrumentation of the sheep lumbar spine, interbody fusion was compared for 6 months after administration of autogenous bone graft, hydroxylapatite, or rhOP-1. Objective. To determine whether the use of rhOP-1 or hydroxylapatite would improve on the intercorporal fusion achieved by autologous bone grafting. Summary of Background Data. Spinal fusion often fails or shows loss of correction despite large-scale conventional techniques using posterior and anterior access. Also, additional operations to obtain bone grafts are required, which increase morbidity and strain for the patient, but do not always provide bone with sufficient primary stability and high osteogenic potential. Methods. Vertebral fusion quality was examined by plain radiograph at 4-week intervals, by scintigraphy at 3 and 6 months, and by computed tomography scan, magnetic resonance imaging, biomechanical testing, and histologic evaluation. Results. All examination methods demonstrated superior fusion after administration of rhOP-1, with radiologic fusion apparent at 4 months. Autologous bone grafts eventually produced bony healing in most cases, albeit of a lower quality than with rhOP-1. Hydroxylapatite use led only to the formation of a tight pseudarthrosis. Conclusions. The results indicate that rhOP-1 use is an appropriate method for improving interbody fusion in the sheep spine. In addition to offering the potential for improved bone healing, rhOP-1 use may permit less invasive surgery such as transpedicular fusion and the use of cages.