Improvement of vertebral body fracture reduction utilizing a posterior reduction tool: a single-center experience

Abstract

Background: Extensive research regarding instabilities and prevention of kyphotic malalignment in the thoracolumbar spine exists. Keystones of this treatment are posterior instrumentation and anterior vertebral height restoration. Anterior column reduction via a single-stage procedure seems to be advantageous regarding complication, blood loss, and OR-time. Mechanical elevation of the anterior cortex of the vertebra may prevent the necessity of additional anterior stabilization or vertebral body replacement. The purpose of this study was to examine (1) if increased bony reduction in the anterior vertebral cortex could be achieved by utilization of an additional reduction tool, (2) if postoperative loss of vertebral height could be reduced, and (3) if anterior column reduction is related to clinical outcome.

Methods: From one level I trauma center, 173 patients underwent posterior stabilization for fractures of the thoracolumbar region between 2015 and 2020. Reduction in the vertebral body was performed via intraoperative lordotic positioning or by utilization of an additional reduction tool (Nforce, Medtronic). The reduction tool was mounted onto the pedicle screws and removed after tightening of the locking screws. To assess bony reduction, the sagittal index (SI) and vertebral kyphosis angle (VKA) were measured on X-rays and CT images at different time points ((1) preoperative, (2) postoperative, (3) ≥ 3 months postoperative). Clinical outcome was assessed utilizing the Ostwestry Disability Index (ODI).

Results: Bisegmental stabilization of AO/OTA type A3/A4 vertebral fractures was performed in 77 patients. Thereof, reduction was performed in 44 patients (females 34%) via intraoperative positioning alone (control group), whereas 33 patients (females 33%) underwent additional reduction utilizing a mechanical reduction tool (instrumentation group). Mean age was 41 ± 13 years in the instrumentation group (IG) and 52 ± 12 years in the control group (CG) (p < 0.001). No differences in terms of gender and comorbidities were found between the two groups. Preoperatively, the sagittal index (SI) was 0.69 in IG compared to 0.74 in CG (p = 0.039), resulting in a vertebral kyphosis angle (VKA) of 15.0° vs. 11.7° (p = 0.004). Intraoperatively, a significantly greater correction of the kyphotic deformity was achieved in the IG (p < 0.001), resulting in a compensation of the initially more severe kyphotic malalignment. The SI was corrected by 0.20-0.88 postoperatively, resulting in an improvement of the VKA by 8.7°-6.3°. In the CG, the SI could be corrected by 0.12-0.86 and the VKA by 5.1°-6.6°. The amount of correction was influenced by the initial deformity (p < 0.001). Postoperatively, both groups showed a loss of correction, resulting in a gain of 0.08 for the SI and 4.1° in IG and 0.03 and 2.0°, respectively. The best results were observed in younger patients with initially severe kyphotic deformity. Considering various influencing factors, clinical outcome determined by the ODI showed no significant differences between both groups.

Conclusion: Utilization of the investigated reduction tool during posterior stabilization of vertebral body fractures in a suitable collective of young patients with good bone quality and severe fracture deformity may lead to better reduction in the ventral column of the fractured vertebral body and angle correction. Therefore, additional anterior stabilization or vertebral body replacement may be prevented.

Keywords: Posterior surgical treatment; Reduction tool; Thoracolumbar spine; Vertebral fracture.

Fig. 1

Bilaterally mounted NForce® reduction tool a before reduction and b after approximation of the lever arms

Fig. 2

Th12 fracture AOSpine type A3 with kyphotic angulation. a intraoperative fluoroscopic view after positioning. b vertebral height after positioning of pedicle screws. c gain of anterior cortex height via mounted reduction tool. d + e lateral and ap view of bisegmental posterior instrumentation

Fig. 3

Radiological parameters. a vertebral kyphosis angle and b sagittal index

Fig. 4

Course of the SI over the three measurement time points. Initially, the SI was corrected by surgery in both groups. Postoperatively, however, there was a loss of correction. In four patients (three of the IG and one of the CG), the anterior cortex was slightly over-distracted compared to the posterior cortex, resulting in an SI > 1

Fig. 5

Course of the VKA over the three measurement times. Physiologically, a VKA is around 0°. Positive signs mean a kyphotic position of the vertebra, and negative signs mean a lordotic position of the vertebra

Fig. 6

ODI score in percent (%)