A prospective comparative study of radiological outcomes after instrumented posterolateral fusion mass using autologous local bone or a mixture of beta-tcp and autologous local bone in the same patient

Abstract

We previously reported a retrospective analysis of radiographic changes in instrumented posterolateral fusion mass (PLF) established using a mixture of local autologous bone and beta tricalcium phosphate (b-TCP) in lumbar spinal fusion surgery. Here, we report a prospective study to compare the use of local bone and a mixture of local bone and b-TCP in PLF in degenerative spinal surgery. Radiological changes in the PLF mass in 42 patients were analyzed for 12 months. All patients had degenerative lumbar spinal disease and underwent instrumented fusion. Local autologous bone was used for PLF on the left side, and a mixture of local autologous bone and b-TCP was used for PLF on the right side. Lumbar spinal anterior-posterior (AP) images were performed immediately postoperative and at 1, 3, 6, and 12 months. Computed tomography (CT) was also done immediately postoperative and at 12 months. Fusion rate, radiodensity, and the dimensions of the PLF mass bilaterally on the AP X-ray were compared. The change in volume in both fusion bridges in the CT image was also compared. The overall fusion rates were 31/42 (73.8 %) and 24/42 (57.1 %) on the left and right sides, respectively. The decrease in radiodensity at 1 month postoperative was significantly greater on the left side than on the right side (from 0.79 to 0.74 versus from 0.81 to 0.78; p = 0.002). The mean immediate postoperative volume on the left side measured with CT was 5.1 cc (95 % CI, 4.94-5.34) and on the right side was 5.2 cc (95 % CI, 4.97-5.37). The mean volume at 12 months had decreased to 2.2 cc (95 % CI, 1.85-2.64) on the left side and 1.87 cc (95 % CI, 1.48-2.67) on the right side. The volume decrease on the right side was statistically greater than on the left side (p = 0.048). Based on the changes in radiodensity and fusion rate during follow-up, local bone seems to undergo earlier resorption and stabilization than the mixture of local bone and b-TCP..