Recombinant Human Bone Morphogenetic Protein–2 Improves Spine Fusion in a Vitamin D–Deficient Rat Model

Micro–computed tomography images show representative coronal and sagittal views of spines for rats in vitamin D Sufficient (A, B), Deficient (C, D), and Rescue (E, F) groups. Transverse views spanning each lower lumbar fusion (L5-6, marked with +) showed robust bone formation with recombinant human bone morphogenetic protein–2 treatment (A, C, E), but not in the presence of allograft (B, D, F).

Bone microarchitecture outcomes from trabecular bone within intact L5 vertebral bodies to assess influence of dietary vitamin D are plotted as a box-and-whisker plot. Two-way ANOVA (α = .05) demonstrated an effect of diet but no effect of graft (eg, recombinant human bone morphogenetic protein–2 versus allograft), and post-hoc Tukey tests (α = .05) revealed a consistent improvement with vitamin D sufficiency but not the rescue treatment. All differences are highly significant (P < .0001) and are noted as connecting bars between groups. BV/TV indicates bone volume fraction; Tb.Th, trabecular thickness; Tb.Sp, trabecular spacing.

Montaged images (×5 magnification) showing regions of fused bone (pink) at L5-6 for Sufficient, Deficient, and Rescue groups are presented. Recombinant human bone morphogenetic protein–2 fusions are denoted by a thin cortical bone-like shell surrounding thin trabeculated bone and marrow (light blue); the partially decorticated spinous process is retained in some samples. Allograft fusions reveal discontinuous bone formation with allograft both forming continuous bone structures with fusion bone as well as allograft fragments surrounded entirely by blue-stained connective tissue.