Biomechanical studies of single segmental spinal interbody fusion with bisegment fixation for thoracolumbar burst fracture type B / 中国组织工程研究

ABSTRACT

BACKGROUND: Thoracolumbar burst fracture Dennis type B does not have significant damage in the intervertebral discs of the inferior vertebral body. To reduce fusion segment and remain normal intercalated disc, single discectomy (damaged vertebral body and supervisor vertebral body) is proposed, but because of the damage to the vertebral body, implanted screw is easy to loose following excising partial vertebral body, even cannot be fixed. However, it is still unknown whether implanted screw in the inferior vertebral body of the damaged vertebral body was stabilized using two segment discectomy with fixation.OBJECTIVE: To analyze the feasibility of single segmental spinal interbody fusion with bisegment fixation for thoracolumbar burst fracture type B.DESIGN, TIME AND SETTING: The randomized controlled in vitro study was conducted at the Laboratory of Biomechanics, Southern Medical University from June 2007 to June 2008.MATERIALS A total of 20 fresh freezing 7-9 months pig samples (T_(13)?L_3 segment) were used, comprising 10 integral samples and 10 L_1 type B thoracolumbar burst fracture samples prepared by pre-injury and weight dropping technique.METHODS: Pig fresh thoracolumbar specimens from T_(13)?L_3 were collected to create models of type B thoracolumbar burst fracture. There were 4 groups in this study. Ten of them were selected as intact group (n=10) (fresh pig T_(13)?L_3 segment). T_1 vertebral endplate pre-injury and weight dropping technique and incremental trauma approach were used. Denis' type B burst fracture was produced, and ten of them were selected as unstable group (n=10). Firstly, unstable group was decompressed by discectomy and semivertebraectomy in upper half of the vertebral body, single level was fused with iliac and U-FRONT anterior thoracolumbar system were placed between T_(14) and L_2, as single discectomy with fixation group (n=10). Then lower disc of injury vertebra discectomy and vertebraectomy, fused with iliac U-FRONT anterior thoracolumbar system were placed between T_(14) and L_2, as two segment discectomy with fixation group (n=10). The bone graft was longer 1 mm than the bone graft region.MAIN OUTCOME MEASURES: The flexion, extension, right/left lateral bending, and right/left axial rotation range of motion (ROM) of T_(14)?L_2 were measured in each group on the spinal three-motional test machine at 10 N穖.RESULTS: The flexion, extension, right/left lateral bending, and right/left axial rotation were not stable in the unstable group.ROM was significantly increased in the unstable group compared with the intact group (P< 0.01). The primary stability was significantly elevated in the single discectomy with fixation and two segment discectomy with fixation groups. The flexion, extension, right/left lateral bending, and right/left axial rotation ROM were significantly reduced in the single discectomy with fixation and two segment discectomy with fixation groups compared with the unstable group (P < 0.05). The flexion, extension, right/left lateral bending ROM was significantly decreased in the two groups compared with the intact group, but axial rotation ROM was significantly increased (P< 0.05). Axial rotation ROM was smaller in the single discectomy with fixation group compared with the two segment discectomy with fixation group (P < 0.05).CONCLUSION: Single segmental spinal interbody fusion with bisegment fixation for thoracolumbar burst fracture type B had a good immediate stability in flexion, extension, lateral bending motion. Compared with traditional partial corpectomy L_1 between the caudal and cranial endplate of the adjacent vertebrae with bisegmental fixation, it had a better immediate stability in axial rotation.