Name: precision measurements and parametric models of vertebral endplates
Uploaded: 2019-09-17T12:30:00
Description: Watch this Scientific Journal Video about Precision Measurements and Parametric Models of Vertebral Endplates at JoVE.com

This work was funded by Key Discipline Construction Project of Pudong Health Bureau of Shanghai (PWZxk2017-08) and the National Natural Science Foundation of China (81672199). The authors would like to thank Wang Lei for his help in proofreading an earlier version and Li Zhaoyang for his help in developing the parametric model.

This study was approved by the health research ethics board of the authors&#8217; 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
<ol>
	<li>Collect a dry cervical vertebra without pathologic deformation or broken parts.</li>
	<li>Place the vertebra vertically in the platform of the scanner (<stron...

<ol>
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M., Duranceau, J., Goel, V., Oxland, T., Takata, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cervical+human+vertebrae.+Quantitative+three-dimensional+anatomy+of+the+middle+and+lower+regions.">Cervical human vertebrae. Quantitative three-dimensional anatomy of the middle and lower regions.</a> Spine (Phila Pa 1976). 16, 861-869 (1991).</li><li>Panjabi, M. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thoracic+human+vertebrae.+Quantitative+three-dimensional+anatomy.">Thoracic human vertebrae. Quantitative three-dimensional anatomy.</a> Spine (Phila Pa 1976). 16, 888-901 (1991).</li><li>Ravi, B., Rampersaud, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Clinical+magnification+error+in+lateral+spinal+digital+radiographs.">Clinical magnification error in lateral spinal digital radiographs.</a> Spine (Phila Pa 1976). 33, E311-E316 (2008).</li><li>Silva, M. J., Wang, C., Keaveny, T. M., Hayes, W. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Direct+and+computed+tomography+thickness+measurements+of+the+human,+lumbar+vertebral+shell+and+endplate.">Direct and computed tomography thickness measurements of the human, lumbar vertebral shell and endplate.</a> Bone. 15, 409-414 (1994).</li><li>Langrana, N. A., Kale, S. P., Edwards, W. T., Lee, C. K., Kopacz, K. 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P., Knox, J., Bibb, R., Zhurov, A. I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+comparison+of+plaster,+digital+and+reconstructed+study+model+accuracy.">A comparison of plaster, digital and reconstructed study model accuracy.</a> Journal of Orthodontics. 35, 191-201 (2008).</li><li>Numajiri, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Designing+CAD/CAM+Surgical+Guides+for+Maxillary+Reconstruction+Using+an+In-house+Approach.">Designing CAD/CAM Surgical Guides for Maxillary Reconstruction Using an In-house Approach.</a> Journal of Visualized Experiments. , (2018).</li></ol>

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...

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 parameters of endplates are necessary for the design and amelioration of spinal implants with effective prosthesis-vertebra contact and bone ingrowth potential3. Furthermore, information on the exact shape and geometry of vertebral endplates is important for understanding the biomechanics. Although the finite element modeling allows for simulation of the real vertebrae and has been widely used to study physiological responses of the spine to various loading conditions4, this technique is patient-specific and not generalizable to all vertebrae. It has been suggested that the intrinsic variability of vertebrae geometry among the general population should be considered when developing the finite element model5. Therefore, the geometric parameters of endplates are conducive to the mesh generation and fidelity enhancement in finite element modeling.
Although the importance of the matching of endplate geometry and implant surface has been discussed in previous studies6,7,8, data on the morphology of vertebral endplates is scarce. Most previous studies have failed to reveal the 3D nature of the endplate9,10,11. A spatial analysis is required to better and fully depict endplate morphology12,13,14. In addition, most studies have employed lower precision measurement techniques10,15,16. Moreover, significant magnification has been reported when geometry parameters are measured by employing radiography or computed tomography (CT)17,18. Though magnetic resonance imaging (MRI) is considered non-invasive, it is less accurate in defining the precise margins of osseous structures11. Due to a lack of a standardized measurement protocol, there are large differences among existing geometric data.
In recent years, reverse engineering, which can digitize the existing physical parts into computerized solid models, has been increasingly applied to the field of medicine. The technique makes it feasible to develop an accurate representation of the anatomical character of sophisticated vertebrae surfaces. The reverse engineering system includes two subsystems: the instrumentation system and software system. The instrumentation system adopted in this protocol has a non-contact optical 3D range flatbed scanner, which is high-speed and highly accurate (precision 0.02 mm, 1,628 x 1,236 pixels). The scanner can efficiently (input time 3 s) capture surface morphology information of the target object and convert it into digital point cloud. The software system (i.e., reverse engineering software) is a computer application for point cloud data processing (see Table of Materials), 3D surface model reconstruction, free curve and surface editing, and data processing (see Table of Materials).
The purposes of the present report are to (1) devise a measurement protocol and algorithm to obtain quantitative parameters of vertebral endplates based on a reverse engineering technique, (2) develop a mathematical model that allows for a realistic representation of vertebral endplates without digitizing too many landmarks. These methods will be beneficial to surgical act planning and finite element modeling.

<table>
	<tbody>
		<tr>
			<td>Catia</td>
			<td>Dassault Systemes, Paris, France</td>
			<td>https://www.3ds.com/products-services/catia/</td>
			<td>3D surface model reconstruction, free curve and surface editing and data processing</td>
		</tr>
		<tr>
			<td>Geomagic Studio</td>
			<td>Geomagic Inc., Morrisville, NC</td>
			<td>https://cn.3dsystems.com/software?utm_source=geomagic.com&#38;utm_medium=301</td>
			<td>point cloud data processing</td>
		</tr>
		<tr>
			<td>MATLAB</td>
			<td>The MathWorks Inc., Natick,USA</td>
			<td>https://www.mathworks.com/</td>
			<td>analyze data, develop algorithms, and create models</td>
		</tr>
		<tr>
			<td>Optical 3D range flatbed scanner</td>
			<td>Xi&#8217;an XinTuo 3D Optical Measurement Technology Co.Ltd., Xi&#8217;an, Shaanxi, China</td>
			<td>http://www.xtop3d.com/</td>
			<td>acquire surface geometric parameters and convert into digital points</td>
		</tr>
	</tbody>
</table>

precision measurements and parametric models of vertebral endplates

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.

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...

Watch this Scientific Journal Video about Precision Measurements and Parametric Models of Vertebral Endplates at JoVE.com

Precision Measurements and Parametric Models of Vertebral Endplates

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.

Detailed and comprehensive geometric data of vertebrae endplates is important and necessary to improve the fidelity of finite element models of the spine, ...

This accurate and reproducible method can be used to obtain detailed and comprehensive geometry data from vertebral endplates and to develop a parametrical model without digitizing too many landmarks. This reverse engineering system can be used to efficiently develop an accurate representation of the anatomical character of sophisticated vertebrae surfaces with good reliability and reproducibility. This protocol can contribute to the design of personalized spinal implants, surgical planning, clinical diagnoses, and the development of accurate finite element models.The method can be used for the sophisticated morphological studies and the parametric model can apply to other imaging modalities such as computed tomography and MRI. Although a beginner may need extra time to complete the procedure, the technique requires a short learning curve overall, to master. Demonstrating the procedure will be Hang Feng, a clinician from my laboratory.Before beginning the procedure, place a dry cervical vertebra, without pathologic deformation or broken parts, vertically onto the platform of the scanner, with the endplate facing the camera lens. Start the scanning process to obtain CloudPoint data and open the software for processing point clouds. Click Import to import the point cloud data and generate a digital graphic of the vertebra.Click Wrap to package the imaging data into a STL format file, to transform the point cloud into Mesh, which will convert a point object into a polygon object and open an appropriate 3D reconstruction and data processing software program. Under the New sub-menu, Click File and select Part in the list of types. Click Start and Shape and Digitized Shape Editor.Then click the Import icon, select the STL format file and click Apply and Okay. To define the endplate 3D co-ordinate system, Mark one anatomic landmark on each of the left and right endpoints of the epiphysial rim and mark landmark on anterior median point. Click the Line icon and select the two trailing edge endpoints to define a posterior frontal line.Click the Plane icon to set the plane type to be normal to the curve and select the posterior frontal line in anterior median point to define the midsagittal plane. Click Start, Shape, and Quick Surface Reconstruction. To generate an intersecting curve, Click the Planar Section icon enter 1 in the number option and select the end plate image and midsagittal plane.Click Curve from the Scan icon and select the intersection of the intersecting curve and posterior epiphysial rim, defining the intersection as the as the posterior median point. Click the Point icon, Points and Planes Repetition. Then, select the midsagittal diameter and enter 1 in the Instances option, to define of the midpoint of the midsagittal diameter.Click the Axis System icon and select the midpoint of the midsagittal diameter, as the origin. The line parallel to the posterior frontal line as the x-axis, the midsagittal diameter as the y-axis and the line pointing forward and perpendicular to the X-Y plane as the z-axis The appropriateness of the coordinate system can be determined according to whether the intersection of the defined midsagittal plane line and the coronal plane is perpendicular to the endplate section. To fit the characteristic curves, and points on the endplate surface, select the midsagittal diameter and enter 3 in the Instances option to divide the midsagittal diameter equally into four parts.Click the Planar Section icon, enter 1 in the number option, and select the endplate image and the X-Z plane to generate an intersecting curve. Click Curve from the Scan icon, and select the two intersections of the X-Z plane and epiphyseal rim. Define the line between the two intersections as the mid frontal diameter and divide the mid frontal diameter equally into four parts.To measure the length of a quarter of the midsagittal diameter, click the Measure Between icon. To generate two fitting curves, on one side of the frontal part, click the Planar Section icon, enter 2 in the number option, and enter the measured value in the Step option, and select the endplate image and X-Z plane. Then, click Swap to generate two fitting curves on the other side.Next, select 11 equidistant points in each curve, and obtain nine fitting curves on the endplate surface, as demonstrated. Then, click Curve from the Scan icon and select the intersection of the fitting curves and the midsagittal curve, to obtain a total of 66 points on each endplate. To measure the length of the line parameter that is the distance between two measured points, click the Measure Between icon.To measure the concavity parameters, click Start, Shape, and Generative Shape Design, and click the Sketch icon and the X-Y plane. Click the Circle icon and origin and drag the cursor of the mouse to an appropriate distance before clicking. Then, click the Exit Workbench icon.Click the Offset icon, select the filled plane, and enter an appropriate value in the offset option, until it is tangent to the most concave part. Zoom in and click Start, Shape and Quick Surface Reconstruction, followed by the 3D Curve icon, to find and create the most concave point. Then, click the Measure Between icon, and select the most concave point and X-Y plane, to measure the whole endplate concavity depth.To quantify the surface area parameters, click the Measure Inertia icon, and click endplate surface, to measure the surface area. To determine the fit order of the parametric equation, open the data analysis and visualization software, and input X the corresponding data in the command window. Click Enter and input Z the corresponding data.Then input the code as indicated. For parameter equation fitting, input cftool"and click Enter to bring up the curve fitting tool. Then, input the co-ordinates of a curve in the command window as demonstrated.Select Polynomial and enter the fit order to gain the parametric equation of the endplate surface. To obtain the geometric data, input the X and Y co-ordinate values of any point on the endplate in the command window, and input the parameters of the equation that have been fitted, using the Polynomial tool. Then, input the equation and click Enter to obtain the result.To obtain the 3D simulation graphics, enter the polynomial parameters into the command window, and input the code as indicated. Input the indicated code and equation. Then, enter the indicated code.Using a highly accurate optical 3D range flatbed scanner, as demonstrated, these representative endplates were converted into more than 4500 digital points, to adequately characterize their morphology. Using the measurement protocol as demonstrated, a spatial analysis of the endplate surfaces was conducted, and representative curves were fitted and quantified on the surface to characterize each endplate morphology. The measurements included the concavity depth and concavity apex location in the midsagittal plane.In addition to those of the whole endplate concavity and any specific sections of interest. Next, the components of the endplates, epiphyseal rim, and central endplate were separated and their lengths and areas were obtained. The parametric equation of each curve was then deduced, based on the co-ordinates of 11 points.Defining a 3D co-ordinated system for each endplate, is critical for the success of the protocol. The uncovertebral joint can be distinguished from the endplate by defining a best-fit plane, in terms of the anterior-most and posterior-most points of the bilateral uncinate processes. This protocol provides an accurate and reproducible method for performing a morphological study of complex surfaces.

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