The use of recombinant human bone morphogenetic protein 2 (rhBMP-2) to promote spinal fusion in a nonhuman primate anterior interbody fusion model

Study Design. A study on the efficacy of recombinant human bone morphogenet ic protein 2 (rhBMP-2) in a nonhuman primate anterior interbody fusion mode l. Objectives. To investigate the efficacy of rhBMP-2 with an absorbable colla gen sponge carrier to promote spinal fusion in a nonhuman primate anterior interbody fusion model. Summary of Background Data. RhBMP-2 is an osteoinductive growth factor capa ble of inducing new bone formation in vivo. Although dosage studies using r hBMP-2 have been performed on species of lower phylogenetic level, they can not be extrapolated to the primate, Dosage studies on nonhuman primates are essential before proceeding with human primate application. Methods. Six female adult Macaca mulatta (rhesus macaque) monkeys underwent an anterior L7-S1 interbody lumbar fusion. All six sites were assigned ran domly to one of two fusion methods: 1) autogenous bone graft within a singl e freeze-dried smooth cortical dowel allograft cylinder (control) or 2) rhB MP-2-soaked absorbable collagen sponges within a single freeze-dried smooth cortical dowel allograft cylinder also soaked in rhBMP-2, The animals unde rwent a baseline computed tomography scan followed by 3- and 6-month postop eration scans. Anteroposterior and lateral radiographs of the lumbosacral s pine were performed monthly. After the monkeys were killed, the lumbar spin e fusion sites were evaluated. Histologic evaluation of all fusion sites wa s performed. Results. The three monkeys receiving rhBMP-2-soaked collagen sponges with a freeze-dried allograft demonstrated radiographic signs of fusion as early as 8 weeks. The control animals were slower to reveal new bone formation. T he computed tomography scans revealed extensive fusion of the L7-S1 lumbar vertebrae in the group with rhBMP-2, A pseudarthrosis was present in two of the control animals. Conclusions. This study was able to document the efficacy of rhBMP-2 with a n absorbable collagen sponge carrier and a cortical dowel allograft to prom ote anterior interbody fusion in a nonhuman primate model at a dose of 0.4 mg per implant site (1.5 mg/mL concentration). The rate of new bone formati on and fusion with the use of rhBMP-2 and cortical dowel allograft appears to be far superior to that of autogenous cancellous iliac crest graft with cortical dowel allograft.