Novel Model of Calvarial Defect in an Infected Unfavorable Wound: Reconstruction With rhBMP-2. Part II

Background: Animal models of bone reconstruction have shown recombinant human bone morphogenetic protein 2 (rhBMP-2) to be an effective therapy in the acute calvarial defect wound. The purpose of this study was to compare the effectiveness of rhBMP-2 in a rabbit model of an unfavorable scarred calvarial wound with the criterion standard of autograft. Methods: Nineteen adult New Zealand white rabbits underwent subtotal calvariectomy. After 6 weeks of healing and normal scar formation, these animals underwent reoperation for scar debridement and assignment to 1 of 4 therapeutic groups. Animals were assigned to an empty control group (no treatment, n = 3), vehicle control group (neutral buffered solution on an absorbable collagen sponge [ACS], n = 3), surgical control group (cryopreserved autograft, n = 3), or an experimental treatment group (rhBMP-2 on an ACS, n = 10). All animals underwent computed tomography imaging at 0, 2, 4, and 6 weeks after secondary reconstructive surgery. At 6 weeks, all animals were killed, and the defects were examined histologically. Percentage of healing of each defect was determined, and a 4 x 3 mixed-model analysis of variance was performed on healing as a function of time and therapy. Results: Based on measures of defect radiopacity, the treatment group (rhBMP-2/ACS) and surgical control group (autograft) were statistically equivalent with 98% and 83% healing, respectively, at 6 weeks. The empty control and vehicle control groups were inferior to the treatment group (rhBMP-2/ACS) and surgical control (autograft) groups at each timepoint (P < 0.05). Histologically, bone in the surgical control (autograft) group was less trabecular and less cellular than the bone formed in the experimental treatment group (rhBMP-2/ACS). Conclusions: Compared with historical controls, rhBMP-2 therapy was as effective in reconstructing calvarial defects in the unfavorable scarred wound as in the acute favorable calvarial wound. When compared with cryopreserved autograft, rhBMP-2-regenerated bone showed equal defect coverage and similar bone thickness with varying bony architecture.