Clinical study on the effect of individual rod bending in internal fixation of AO-A3 thoracolumbar fractures: a retrospective clinical study

Abstract Background Spinal pedicle screw internal fixation is a mature technique for the treatment of thoracolumbar fractures. A large number of studies have shown that the bending angle of the connecting rod has a significant correlation with the postoperative spinal stability. However, there has been no study to determine a reliable method to guide the bending angle of the connecting rod during operation. The purpose of our research was to explore an individualized rod bending method and analyze its effect in AO-A3 thoracolumbar fractures. Methods The angles (angles A, B, A', B') of upper and lower motion segments before and after fracture were measured in 64 patients. By analyzing the correlations between H and angle changes(ΔA, ΔB) of the vertebra, a linear regression model was established to derive the bending angle. A total of 48 patients with fractures(AO-A3) were included and assigned to observation groups and control groups in order to measure the sagittal parameters after three years of follow-up, including LL, TK, SVA ,ASD,PT, PI and SS. Result There was a significant linear correlation between H and angle change (ΔA, ΔB) of the vertebra. The correlation coefficient was 12.24 and 8.62,respectively. The formula for guiding bending rod was 1.50×(A’+B’) + 31.29H-0.38. Compared with normal group, there were significant differences in LL, TK, PT and SS in the control group(P༜0.05), but no significant differences in the observation group(P༞0.05). The incidences of SVA > 50mm were 23.08% and 22.73% in the two group respectively and the incidences of ASD were 7.69% and 13.64%, respectively. There was significant difference identified between the two groups in ASD(P༜0.05), but not in SVA༞50mm(P༞0.05). Conclusion Using this method to guide the bending rod during the operation can well restore the sagittal angle and reconstruct the stability of the spine after operation.