Influence of rhBMP-2 on the healing patterns associated with allograft interbody constructs in comparison with autograft

Study Design. A prospective, nonblinded, multicenter study. Objective. To determine the patterns of allograft incorporation and new bone formation after ALIF using stand-alone threaded cortical allograft dowels with either autograft or rhBMP-2. Summary of Background Data. Accelerated healing patterns of allograft dowels have been reported in an animal study and a small human study of ALIF with rhBMP-2 and bone dowels. Methods. We enrolled and randomly assigned 131 patients with lumbar spondylosis who were undergoing single-level ALIF with allograft dowels to either the investigational group who received rhBMP-2 (79 patients) or the control group who received autologous bone graft (52 patients). Independent radiologists used plain radiographs and computed tomography scans to evaluate fusion. Allograft incorporation was assessed using a modified Bridwell-Lenke scale, and changes in bone density within the adjacent vertebral bodies were monitored. Results. At 12 months, all investigational patients had radiographic evidence of new bone formation and incorporation of the allografts into the adjacent vertebral end-plates; there were no changes in fusion status at 24 months. Fusions were documented in 89% of patients in the control group at 12 months. The percentage declined to 81.5% at 24 months with 10% of the patients in the autograft group showing incomplete healing and 11% having no healing of the allograft dowels. On CT scans, 14 of the investigational patients (14 of 79; 18%) developed a transient, localized area of bone remodeling within the vertebral body adjacent to the allograft dowel. All were healed by 24 months. The transient appearance of these zones had no effect on clinical outcomes. No patient in the control group developed bone remodeling zones. Conclusion. We think that the use of rhBMP-2 is a promising method of facilitating allograft dowel incorporation and new bone formation in patients undergoing ALIF with allograft dowels.