Precision Measurements and Parametric Models of Vertebral Endplates

Summary

A reverse engineering system is employed to record and obtain detailed and comprehensive geometry data of vertebral endplates. Parametric models of vertebral endplate are then developed, which are beneficial to designing personalized spinal implants, making clinical diagnoses, and developing accurate finite element models.

Abstract

Detailed and comprehensive geometric data of vertebrae endplates is important and necessary to improve the fidelity of finite element models of the spine, design and ameliorate spinal implants, and understand degenerative changes and biomechanics. In this protocol, a high-speed and highly accurate scanner is employed to convert morphology data of endplate surfaces into a digital point cloud. In the software system, the point cloud is further processed and reconstructed into three dimensions. Then, a measurement protocol is performed, involving a 3D coordinate system defined to make each point a 3D coordinate, three sagittal and three frontal surface curves that are symmetrically fitted on the endplate surface, and 11 equidistant points that are selected in each curve. Measurement and spatial analyses are finally performed to obtain geometric data of the endplates. Parametric equations representing the morphology of curves and surfaces are fitted based on the characteristic points. The suggested protocol, which is modular, provides an accurate and reproducible method to obtain geometric data of vertebral endplates and may assist in more sophisticated morphological studies in the future. It will also contribute to designing personalized spinal implants, planning surgical acts, making clinical diagnoses, and developing accurate finite element models.

Introduction

A vertebral endplate is the superior or inferior shell of the vertebral body and serves as a mechanical interface to transfer stress between the disc and vertebral body¹. It consists of the epiphyseal rim, which is a strong and solid bony labrum surrounding the outer rim of the vertebral body, and the central endplate, which is thin and porous².

The spine is subject to a wide array of degenerative, traumatic, and neoplastic disorders, which may warrant surgical intervention. Recently, spinal devices such as artificial discs and cages have been widely used. Accurate and detailed morphometric pa....

Protocol

This study was approved by the health research ethics board of the authors’ institute. As cervical vertebral bones have more intricate shapes¹⁹, the protocol uses the cervical vertebrae as an illustration to facilitate relevant research.

1. Preparation of materials, scanning, and image processing

1. Collect a dry cervical vertebra without pathologic deformation or broken parts.
2. Place the vertebra vertically in the platform of the scanner (Figure 1, see Table of Materials), with the endplate facing the camera lens. Use the active light source of t....

Results

Using the highly accurate optical 3D range flatbed scanner, the endplates were converted into more than 45,000 digital points, which adequately characterize the morphology (Figure 2A,B).

In the measurement protocol, the spatial analysis of endplate surfaces was conducted. Representative curves were fitted and quantified on the surface to characterize morphology (Figure 4B). The line.......

Discussion

Reverse engineering has been increasingly and successfully applied to the field of medicine, such as cranioplasty²⁰, oral²¹, and maxillofacial implants²¹. Reverse engineering measurements, namely product surface digitization, refers to the conversion of surface information into point cloud data employing specific measuring equipment and methods. On the basis of such data, complex surface modeling, evaluation, improvements, and manufacturing can be pe.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Catia	Dassault Systemes, Paris, France	https://www.3ds.com/products-services/catia/	3D surface model reconstruction, free curve and surface editing and data processing
Geomagic Studio	Geomagic Inc., Morrisville, NC	https://cn.3dsystems.com/software?utm_source=geomagic.com&utm_medium=301	point cloud data processing
MATLAB	The MathWorks Inc., Natick,USA	https://www.mathworks.com/	analyze data, develop algorithms, and create models
Optical 3D range flatbed scanner	Xi’an XinTuo 3D Optical Measurement Technology Co.Ltd., Xi’an, Shaanxi, China	http://www.xtop3d.com/	acquire surface geometric parameters and convert into digital points