Spinal bone density following spinal fusion.

Spinal bone densities were assessed in 25 patients following lumbar fusion and bracing, in an attempt to study bone remodeling by noninvasive methods. Dual-photon densitometry was used to study specific areas of autologous bone grafts and adjacent vertebrae above the fusion mass. Measurements were made preoperatively and at 6-week intervals postoperatively. The data for the first 12 months postoperatively are reported here. In all patients there was at first a consistent loss in density in the vertebrae above the fusion mass, averaging 15.7%. This was followed by a gradual density increase such that by 1 year postoperatively, in 60% of the subjects, the density of these vertebrae was higher than the preoperative level. In the grafted areas, bone changes were cyclical, demonstrating a remodeling pattern consistent with that described in animal literature for graft healing and also consistent with modern bone remodeling theory. There was a general tendency toward a gradual increase in the density of the fusion mass.