Fusion status of allogenic bone graft in adult spinal deformity surgery: an evaluation using computed tomography
Introduction
Allograft bone is one of the major options of bone grafting in spinal fusion surgery. However, there are very few reports on the detailed fusion morphology of allografts used in adult spinal deformity (ASD) surgery. In this study, we investigated in detail how the morphological changes of grafted allograft occur on the lamina using computed tomography (CT) after posterior spinal fusion surgery in ASD.
Methods
The participants were 40 ASD patients (mean age: 69.9 years) with total 389 vertebral laminae who had undergone anteroposterior or posterior spinal fusion surgery in which allogeneic femoral heads were granulated and transplanted onto the vertebral laminae and posterior spinal fusion was performed for at least five levels. Allogenic femoral heads, which was extracted from patients performed total hip arthroplasty were provided after processing by bone bank in our institute. Plain CT scans were performed preoperatively, 1 week and 1 year postoperatively to measure and compare the cross-sectional area and CT values of the grafted bone in axial section on the T9-L2 vertebral laminae. We classified the grafted bone morphology into three groups; A: grafted bone was incorporated into lamina, B: grafted bone was separated from lamina without any contact, and C: grafted bone was completely or partially absorbed. T-test and χ2 test were used for statistics, and p value<0.05 was defined as a significant difference.
Results
The cross-sectional area of grafted bone was 406.2±174.2 mm2 just after surgery and decreased significantly to 286.3±142.8 mm2 at 1 year postoperatively. Conversely, CT values were increased into 588.8 ± 257.6 HU 1 year postoperatively compared with preoperative 430.6 ± 246.7 HU. At postoperative 1 year, morphologic classification was A: 72.0%, B: 16.5%, and C: 21.4%, respectively. There were no significant differences in age and sex among the three groups. However, the cross-sectional area of grafted bone just after surgery in group C was significantly smaller than that in the other groups.
Discussion
Japanese tissue transplant guidelines stipulate that allogeneic bone must be sterilized at a low temperature of 60 degrees for 10 hours, which is unique sterilization method worldwide. It has been reported that this method preserves bone morphogenetic proteins and biomechanical strength compared with other methods as are autoclave or gamma‐ray irradiation. However, bone absorption at 1 year was noted in over 20% of laminae, which seems inevitable. Also, there were cases in which continuity of the vertebral lamina and grafted bone obtained just after surgery was lost at postoperative 1 year. These findings suggest that a certain amount of allograft bone transplantation is mandatory to achieve the definite fusion in posterior spinal fusion for ASD patients, and sufficient preparation of lamina surface with decortication and administration of bone anabolic agents might be useful.