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), sagittal vertical axis (SVA), and sacral slope (SS) were measured. The incidence of adjacent segment degeneration (ASD) 2 years after surgery was measured. Results The average values of normal sagittal Cobb* angle in each segment were − 5.196 ± 3.318° (T12), 2.279 ± 3.324° (L1), 7.222 ± 2.798° (L2), and 12.417 ± 11.962° (L3), respectively. The LL in the three groups was 35.20 ± 9.12°, 46.26 ± 9.68°, and 54.24 ± 15.31°, respectively. Compared 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 > 50 mm in group A, group B, and group C were 23.33%, 12.50%, and 19.23%, respectively. The parameter of PI in three groups was 41.36 ± 12.69, 44.53 ± 15.27, and 43.38 ± 9.85°, 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° greater than the corresponding segment sagittal Cobb* angle, the patient’s spinal sagittal stability is the best 2 years after the operation.

Biomechanical and Clinical Study of Rod Curvature in Single-Segment Posterior Lumbar Interbody Fusion

“…Wanivenhaus et al (2019) proposed that augmented reality-assisted rod bending could reduce operation duration by 20% compared with the traditional method and achieve higher accuracy of the rod bending process. Shi et al (2020) confirmed that the Cobb angle could be used as reference to guide rod bending in thoracolumbar fractures and also reported that 4 °-8 °greater than the Cobb angle as the RC achieved the best spinal sagittal balance 2 years after the operation. Moufid et al (2019) evaluated the mismatch between rod-screw and LL of the fused segment by the concept of the mismatch analysis index (MAI), which was determined by three parameters: the angle between the screw and rod, the angle between the superior endplate and screw, and the distance between the rod and posterior wall of vertebra.…”

The association of rod curvature with postoperative outcomes in patients undergoing posterior lumbar interbody fusion for spinal stenosis: a retrospective case–control study

“…To date, there are few studies about rod contouring in PLIF surgery. Shi et al reported that 4° to 8° greater than the cobb angle of fused segments was suggested as the optimal reference angle for rod contouring in patients with thoracolumbar fractures [10]. Their study emphasized that the accuracy of rod bending angle was important for spinal sagittal balance and prevention of adjacent disc degeneration.…”

“…But there is still a lack of solid evidence on the correlation between rod curvature and clinical outcomes. Moreover, the appropriate degree of rod curvature is also needed to be further evaluated, although Shi et al reported that the Cobb angle could be used as a reference for rod contouring for patients with thoracolumbar fractures [10].…”

Analysis of Influencing Factors of Vertebral Height Loss After Pedicle Screw Fixation of Thoracolumbar Fracture

“…The results of this study showed that there was no significant correlation between the number of fractured vertebrae and the loss of postoperative vertebral height. The sagittal Cobb angle is an important index to assess the biomechanical factors of the spine and the stability of the fracture 23–25 . Although univariate analysis showed that there was a certain correlation between preoperative sagittal Cobb angle and postoperative VHL, the sagittal Cobb angle varied greatly in different segments of the spine, and the results of multivariate logistic regression analysis showed that there was no significant correlation between sagittal Cobb angle and postoperative height loss of fractured vertebral body.…”