Use of the Sagittal Cobb* Angle to Guide the Rod Bending in the Treatment of Thoracolumbar Fractures：A Retrospective Clinical Study

Abstract

Background: Pedicle screw fixation is a well-established technique for thoracolumbar fracture. 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, no studies have confirmed an objective indicator to guide the bending angle of the connecting rod during the operation. Our study aims to define a sagittal Cobb* angle to guide the bending angle of the connecting rod during surgery.Methods: The frontal and lateral X-ray films in 150 cases of normal thoracolumbar spine were included to measure the normal spinal sagittal Cobb* angle in each segment. The patients who underwent single segment thoracolumbar fractures and pedicle screw internal fixation surgery were included. The radiological parameters included lumbar lordosis (LL), thoracic kyphosis (TK), pelvic tilt (PT), pelvic incidence (PI) and sacral slope (SS) were measured. The incidence of adjacent segment degeneration（ASD）two years after surgery were measured.Results: The average values of normal sagittal Cobb* angle in each segment were -5.196±3.318 degrees (T12), 2.279±3.324 degrees (L1), 7.222±2.798 degrees (L2) and 12.417±11.962 degrees (L3) respectively. The LL in the three groups was 35.20±9.12 degrees，46.26±9.68 degrees and 54.24±15.3 degrees, respectively. Comparing with the normal group, there were significant differences in group A and group C respectively (P< 0.05). The results were similar in the parameters of TL, PT and SS. The incidences of SVA>50mm in group A, group B and group C were 23.33%,12.50% and 19.23%, respectively. The parameter of PI in three groups were 41.36±12.69, 44.53±15.27 and 43.38±9.85 degrees，respectively. The incidences of ASD in group A, group B and group C 2 years after surgery were 21.67%，13.75% and 17.95%, respectively.Conclusions: The study confirmed that the sagittal Cobb* angle can be used as a reference angle for bending rods. When the bending angle of the connecting rod is 4 to 8 degrees greater than the corresponding segment sagittal Cobb* angle, the patient's spinal sagittal stability is the best two years after the operation.