Pressure distributions inside intervertebral discs under unilateral pedicle screw fixation in a porcine spine model

Zhao Meng,Chen Wang,Xue-Jun Zhang,Dong Guo,Yan Zou,Li-Jun Tian

doi:10.1186/s13018-018-0962-3

Abstract

BackgroundLittle data are available regarding the effects of pedicle screws on the intervertebral disc stress for different spinal segments. The aim of this study was to analyze the intervertebral disc stress in response to the placement of pedicle screws.MethodsT3–4, T11–12, T15–L1, L3–4, and L4–5 intervertebral disc segments from six porcine spine specimens were harvested. A compressive load of 200 N was applied both before and after the pedicle screw was implanted on the left side of each target segment; the resulting pressure was measured during vertical, 5° anterior flexion, 5° posterior extension, and 5° lateral bending.ResultsThe posterior intradiscal pressures of the intervertebral disc were significantly lower in the fixed group than in the unfixed group for all segments during vertical, 5° anterior flexion, and 5° posterior extension. The left pressures of the intervertebral disc were significantly lower in the fixation group for all segments. During 5° lateral bending, the left intervertebral disc pressures were significantly lower in the fixation group. Lower mean pressures were observed in the fixed group.ConclusionsUnilateral pedicle screws can effectively reduce the pressure of the fixed lateral intervertebral disc. Moreover, it can change the pressure distribution of the intervertebral disc and reduce the pressure of the entire intervertebral disc, especially the posterior side of the intervertebral disc.

Highlights

Little data are available regarding the effects of pedicle screws on the intervertebral disc stress for different spinal segments
The clinical application of unilateral pedicle screw fixation for the treatment of scoliosis in children has been established; the purpose of this study was to explore the feasibility of unilateral pedicle screw fixation for scoliosis based on bilateral pedicle screw fixation, with less interference and fewer implants to achieve the same control and orthopedic purposes
The posterior intradiscal pressures under different loading conditions When comparing the posterior intradiscal pressures of intervertebral disc (Table 1), in the unfixed group, generally, there was no significant difference among different loading conditions; the posterior intradiscal pressure under 5° posterior extension for the T3–4 segment was significantly lower than those under vertical or 5° anterior flexion conditions (P < 0.05)

Summary

Introduction

Little data are available regarding the effects of pedicle screws on the intervertebral disc stress for different spinal segments. One of the complex three-dimensional deformities of the spine, refers to a lateral curvature of the spine in the coronal plane of more than 10°. It has a high prevalence of about 1/1000 and is usually complicated with the spine rotation and change of numbers of the sagittal dorsal or anterior processes, as well as uneven rib levels, the pelvic rotation and tilt, and paraspinal ligament and muscle abnormalities [1, 2]. Pedicle screw-rod constructs have become increasingly popular in the treatment of spinal deformities, as they have excellent biomechanical properties and are suitable for the transfer and subsequent maintenance of large correction forces in all planes [7]

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