The influences of different ratios of biphasic calcium phosphate and collagen augmentation on posterior lumbar spinal fusion : a comparative study using rats' posterior lumbar fusion model

Abstract

The purpose of this study was to determine the influence of the different ratio of Hydroxyapatite (HA) / beta tricalcium phosphate (β-TCP) and collagen augmentation for posterior lumbar fusion using rat model and to find ideal composition of two materials for various fusion situation. We generated a posterior fusion model of lumbar vertebrae in 50 rats and divided it into five groups with equal number by implanting the following materials between transverse processes of vertebrae, (1) Autologous bone graft as group A, (2) 70% HA + 30% β-TCP as group B, (3) 70% HA + 30% β-TCP + Collagen as group C, (4) 30% HA + 70% β-TCP as group D, and (5) 30% HA + 70% β-TCP + Collagen as group E. Rats were euthanized at 12 weeks after surgery and fusion was assessed by manual palpation, quantitative analysis using Micro CT and histology. The score of manual palpation was significantly higher in group C than group E (3.1±1.1 vs. 1.8±0.8, respectively, p=0.033) although no significant difference was noted between group B and group D (3.2±1.3 vs. 2±1.9, respectively, p=0.164). However, in terms of Micro CT analysis, Group D showed significant higher score than group B (5.5±0.8 vs. 3.1±1.1, respectively, p=0.021) although there was no difference between group C and group E (4.8±1.1 vs. 5.4±0.8, respectively, p=0.073). According to quantitative volumetric analysis, 30% HA + 70% β-TCP groups (group D and E) showed significantly reduced fusion mass at 12 weeks after surgery (123 ± 14.2, 117 ± 46.3 vs. 151 ± 27.3, p=0.008, p=0.003, respectively). Collagen augmentation groups revealed superior results in terms of both Micro CT score and histologic grade. Given our results, 70% HA + 30% β-TCP rather than 30% HA + 70% β-TCP could be more favorable graft substitute for lumbar spinal fusion. Because appropriate HA proportion should be needed for initial stabilizing the fusion mass. There was some positive role of collagen as adjunct for spinal bone fusion process in our study. Future study should be needed to determine the exact effect of collagen on spinal bone fusion.