A NON-INVASIVE THREE-DIMENSIONAL SPINAL MOTION ANALYSIS METHOD Tae Hong Lim, Ph.D. Jason C. Eck, B.S. Howard S. An, M.D. Linda M. Mc Grady, B.S.

INTRODUCTION l Spinal disorders frequently cause a significant and permanent decrease in quality of life. l The presence of abnormal motion is used as an indication of possible instability in the spine. l Efforts have been made to quantify spinal motion; however, the precise assessment of complex 3-D motion remains difficult.

PREVIOUS STUDIES l Spinal instability has been assessed using the following 2-D or invasive methods: – Dynamic (flexion/extension) radiography – Roentgen stereophotogrammetry – Electrogoniometric methods l The concept of using principal axes of the moment of inertia tensor to monitor rigid body orientation and position has been well described for the study of the wrist.

OBJECTIVES l Establish a computer-aided system for 3-D non-invasive spinal motion analysis. – Develop software to describe the position of the geometrical center (GC) and orientation of the principal axes (PA). – Describe the 3-D motion of the vertebrae in terms of translation of the GC and rotation of the PA. – Quantify the accuracy of the system using isolated cadaveric vertebrae.

METHODS l An isolated vertebra was held in various known rotated and translated position using a custom designed apparatus. l CT images were obtained of the vertebra in 0, 5, and 20 degrees of axial rotation, lateral bending, and extension. l 1.0 mm scans were taken using both axial and either sagittal or coronal planes. l 512 x 512 image matrix was used with a 22.0 cm field of view providing a system resolution of cm.

METHODS Slider Lever Arm Figure 1. Diagram of accuracy testing device.

METHODS l Images were analyzed using commercial software, C-Med l A region of interest function based on pixel intensity was used to select the vertebra. l A measure function provided data on area, centroid, and moments and product of inertia for each image. l 2-D data from C-Med were used in custom software to calculate 3-D moment of inertia tensor using the parallel axis theorem.

METHODS Figure 2. Portion of CT image selected using region of interest function.

METHODS l Eigenvalues and eigenvectors were calculated from the tensor using an IMSL subroutine. l Translations of the GC and rotations of the PA were calculated. l Geometrical and inertial properties of the vertebra were compared in various positions to assess reproducibility.

RESULTS l All major rotations were within an accuracy of 1.0 degree. l Off-axis rotational errors were found when using axial scans. l Translational accuracy was within 0.1 cm.

Table 1. Rotational values using axial CT scans.

Table 2. Rotational values using sagittal or coronal CT scans.

DISCUSSION l This motion analysis system has an accuracy of 1.0 degrees in rotation and 0.1 cm in translation. l Off-axis errors were found when using axial scans. No errors occurred when using either sagittal or coronal scans. The only variation is in the number of scans obtained. l Geometrical and inertial errors were higher in the axial scans where off-axis motion was predicted. l Thus, system reproducibility is affected by the number of images.

DISCUSSION l It was shown that greater accuracy was achieved when using additional scans, but it the optimal number of scans was not determined. l It is hoped that future hardware enhancements will allow thinner image thickness or the ability to scan in additional planes. l Current motion data is based on an isolated cervical vertebra. When this technique is applied to the lumbar spine fewer off-axis errors are expected due to the larger vertebral height.

CONCLUSIONS l This is the first system capable of noninvasively measuring 3-D motion segments. l This project has shown the promise of using a series of parallel scans from the CT to calculate the principal axes of the moment of inertia tensor. These can be tracked to calculate 3-D spinal motion. l System accuracy is greater than current 2-D methods and similar to invasive methods.

Project 1: In Vivo Analysis of Segmental Spine Motion of the Lumbar Spine Program Project Grant External Scientific Advisory Board Meeting April 25, 2003

Long-Term Goal l Develop new methods to diagnose and treat low back pain problems resulting from both segmental instability and degenerative changes in discs and/or facets. – Comprehensive studies of the biomechanical, biological and clinical aspects of degenerative spinal disorders

Essential Information In-vivo Relationship Degenerative Changes in Intervertebral Joints Segmental InstabilityLow Back Pain

Previous Studies l In vivo studies: – In-vivo relationship among degenerative changes in the intervertebral joint (disc, facets and surrounding structures), segmental hypermobility and low-back pain remains unclear and controversial. – Limitations Inaccurate and motion measurement (2-D measurement of 3-D motion) Subjective grading of degenerative changes Lack of control in experimental protocol (voluntary motion, subject population) l In vitro study : – Established non-invasive 3-D motion analysis method using CT images – In-vitro relationship between rotational flexibility and degenerative changes in IVDs and facets Increasing hypermobility with IVD degeneration up to grade 4 Torsional flexibility is most significantly affected Segmental flexibility is affected by the facet degeneration, too.

Specific Aims of Project 1 l To establish the in-vivo relationship between segmental flexibility and degenerative changes in IVDs, facets and surrounding structures: – Normal asymptomatic subjects – Symptomatic back-pain patients (age and gender matched) l To investigate if there are significant differences between the asymptomatic group and the symptomatic patients’ group.

General Methods l Radiographs – Dynamic flexion/extension – Comparisons with previous work l Magnetic Resonance Imaging (MRI) – T2 sagittal images – Proton density axial images of facet joints – Disc and facet grading and morphologic measurements l Computer Tomography (CT) – Five positions (neutral and rotated) – Measure translation and rotation of lumbar vertebra – In vivo, non-invasive measurement of motion

General Methods l Subject Selection: – Normal subjects (80) – Age and gender matched symptomatic patients (80) l Degenerative changes in the Intervertebral Joints – MRI (T2 sagittal and Proton density axial images) – CT – Plain radiographs l Motion Measurement – CT images to measure passive AR motion – Dynamic radiographs to measure voluntary FLX/EXT motion

Subjects to date Age (yrs)NMNFSMSF Total = 160 Remaining = 130

Currently tested subjects Data shown in this presentation

Radiographs FlexionExtension NF40-01 Dynamic Flexion/Extension

Radiographic Data Flexion Extension NF40-01

MRI- Disc Grading Fujiwara, et al 2000 Thompson’s Grading Sagittal T2- NF Normal 2- Less distinct np/af 3- Crack in np or af 4- Decreased height 5- Collapse Thompson’s scale

MRI- Disc Grading Data (sagittal) 1- Normal 2- Radial tear (HIZ, SI, BA) 3- Collapse Alternative scale

MRI- Measurements (sagittal) NF40-01 sagittal T2

MRI- Measurement Data

MRI- Facet Grading Fujiwara et al Normal 2- Erosion 3- Cartilage half gone 4- Absence of cartilage Cartilage Degeneration

MRI- Subchondral Grading 1- Normal 2- Focal thickening 3- Up to 50% with thickening 4- Greater than 50% with thickening Subchondral Sclerosis Fujiwara et al. 2000

MRI- Osteophyte Grading 1- None 2- Possible osteophyte 3- Small osteophyte 4- Large osteophyte Osteophytes Fujiwara et al. 2000

MRI- Grading Data (axial)

MRI- Measurements (axial) NF40-01 Axial T2

CT l Determine torsional stability l Scan subjects – Using Torso Rotation Control Apparatus (TRCA) – 5 Positions Neutral (supine) Rotate Left and Right 30  Rotate Left and Right Full (up to 50  )

Torso Rotation Control Apparatus TRCA Rotation Ring TRCA (upper section) CT Scanner RingCT Scanner Bed Neutral Right Full (50  ) Straps to support upper body and head

CT Image Processing l Individual CT slices – Use Mimics software to: Threshold for cortical shell definition Hand colored to define vertebrae Create solid model

CT Solid Model from Mimics NF40-01 Neutral

CT Solid Models (con’t) Neutral Left 30  Left FullRight Full Right 30  Data from NF40-01

CT Image Processing l 3-D Images from Mimics l Pro-Engineer 2000i 2 – Centroids – Moment of Inertia Tensor l Matlab® software – Custom in-house programs – Calculate eigen vectors – Calculate rotation and translation between rigid bodies

Rigid Body Motion Inertial properties of a rigid body Moment of Inertia -Calculate the principle axes (eigen vectors) -The orientation of the principle axes does not change wrt the rigid body Lim 1994

CT Image Processing (con’t) Geometric PropertiesInertial Properties +X= Extension +Y= Left Lateral Bending +Z= Left Axial Rotation

Further CT Examples NF40-01

Future Plans l Continue data acquisition and processing – Start recruting low-back pain subjects Summer 2003 l By the summer 2004, we expect to produce sufficient data for meaningful statistical analyses and publication.