INTRODUCTION

Bertolotti first described the lumbosacral transitional vertebrae in 1917 and put forward a concept of Bertolotti syndrome[1].It is believed that the unilateral or bilateral transverse process of the terminal lumbar vertebrae is enlarged and broadened due to abnormal development, and sometimes the enlarged transverse process forms pseudarthrosis or fusion with the deformity is related to chronic low back pain, lower limb pain and other is the earliest report about lumbago caused by lumbosacral transitional recent years, different scholars[2-6]reported that the incidence of lumbosacral transitional vertebrae was different in different people, but in people with lumbar pain diseases such as lumbar disc herniation, the incidence of transitional vertebrae was significantly increased, and the overall incidence was higher[7-9].Lumbar vertebrae as a whole system,the pathological changes and morphological abnormalities of any segment will lead to changes in the mechanical morphology of the whole system, and then lead to an increase in the probability of injury in a certain part, so the study of transitional vertebrae has a very important clinical significance.

For patients with lumbar sacral vertebrae, the analysis of the maximum load of each vertebral segment and the trend of mechanical changes is the basis of clinical treatment of low back pain caused by lumbar vertebrae, but at present, there are few mechanical simulation on the mechanics of lumbar pedicle in adolescent patients with transitional vertebrae are even less[10-11].In this study,the CT images of adolescent patients with lumbar sacralization were selected to obtain three-dimensional finite element models of lower lumbar vertebrae of adolescent sacral lumbar vertebrae, andtheir stress and strain distribution and mechanical characteristics were analyzed, so as to provide carrier and basis for further study of mechanical changes and bone fatigue coefficient of lower lumbar vertebrae in transitional vertebrae patients.

MATERIALS AND METHODS

Design

A three-dimensional finite element analysis.

Time and settings

The experiment was conducted in 2019 at the Digital Medical Center of Inner Mongolia Medical University.

Subjects

One patient with lumbar sacral vertebrae was selected, a 16-year-old male of Han nationality, with a body mass of 60 kg, height of 1.75 m and body mass index (19.59 kg/m2).The volunteer had no previous history of lumbar trauma and related obtain written informed consent from patient and his research was approved by the Ethics Committee of Inner Mongolia Medical University (approval number YKD) on March 5, 2018.

Methods

Acquisition of two-dimensional data

In this study, the Lightspeed dual-source 64-slice spiral CT (GE, USA)was used to scan the upper edge of the L1vertebra to the lower edge of the L5vertebra using the volume scan mode.Lie on your back with your head parameters: slice thickness 5 mm, layer spacing 5 mm, scanning field 20 cm2, matrix 512 × 512, standard algorithm the end of the scan, the data is divided into layer thickness 0.625 mm, layer spacing 0.625 mm and saved in DICOM format (Figure 1).

Figure 1｜ Mimics 21.0 software interface of lumbosacral transitional vertebrae in adolescentsNote: Import CT data into software for 3D reconstruction.

3D reconstruction of 2D data

Import the original DICOM data into (Materialise Belgium), through the steps of threshold setting, image segmentation, region growth, image filling and so on, the L4-sacrum is segmented and smoothed, and then the Mask, of each vertebra is obtained through the Calculate3D module to get the 3D image of the use the 3-matic software in software to optimize the model and export it in STL format (Figure 2).

Reconstruction of 3D solid model

Figure 2｜ Geometric reconstruction model of lumbar vertebrae of sacral vertebraeNote: The built-in 3-matic software in software to smooth, reduce noise and repair the model.

After Mimics image extraction and 3-matic model repair, the complete vertebral models of L5and sacrum were present, the appearance of each model is close to the real vertebra,with regular vertebrae, transverse process, spinous process, upper and lower articular process and other main introducing the model into Geomagicstudio (Geomagic, USA) the model unit is first selected, which is millimeter by default, and the system automatically prompts for grid doctor this processing, the polygon model of feature and smoothness balance is the sacrum model, use the plane clipping function,retain only the part of the sacrum in contact with S1, and carefully close the clipping plane, using the grid doctor to check to avoid causing the model to be unclosed (Figure 3).

Figure 3｜ L5and optimized reconstruction model of lumbar sacral vertebraeNote: Use Geomagicstudio software to simplify the sacrum model, and use the plane clipping function to retain only the part of the sacrum that is in contact with S1, thereby obtaining a polygonal model with balanced features and smoothness.