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 Spinal disorders frequently cause a significant and permanent

decrease in quality of life.

The presence of abnormal motion is used as an indication of possible instability in the spine.

Efforts have been made to quantify spinal motion; however, the precise assessment of complex 3-D motion remains difficult.

PREVIOUS STUDIES Spinal instability has been assessed using the following 2-

D or invasive methods:– Dynamic (flexion/extension) radiography– Roentgen stereophotogrammetry– Electrogoniometric methods

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

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 An isolated vertebra was held in various known rotated

and translated position using a custom designed apparatus.

CT images were obtained of the vertebra in 0, 5, and 20 degrees of axial rotation, lateral bending, and extension.

1.0 mm scans were taken using both axial and either sagittal or coronal planes.

512 x 512 image matrix was used with a 22.0 cm field of view providing a system resolution of 0.043 cm.

METHODS

Slider

0

5

10

15

20

25

Lever Arm

Figure 1. Diagram of accuracy testing device.

METHODS Images were analyzed using commercial software,

C-Med A region of interest function based on pixel intensity

was used to select the vertebra. A measure function provided data on area, centroid,

and moments and product of inertia for each image. 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

Eigenvalues and eigenvectors were calculated from the tensor using an IMSL subroutine.

Translations of the GC and rotations of the PA were calculated.

Geometrical and inertial properties of the vertebra were compared in various positions to assess reproducibility.

RESULTS

All major rotations were within an accuracy of 1.0 degree.

Off-axis rotational errors were found when using axial scans.

Translational accuracy was within 0.1 cm.

Table 1. Rotational values using axial CT scans.

Motion 5 Degrees 20 Degrees

AR (0.020, 4.923, 0.522) (2.176, 19.251, 0.722)

LB (0.406, 1.805, 5.264) (4.027, 6.523, 20.663)

EXT (4.205, 0.767, -0.749) (20.889, 0.032, -3.980)

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

Motion 5 Degrees 20 Degrees

AR(sag) (-0.253, 5.028, 0.240) (-0.082, 20.104, -0.292)

LB(cor) (0.030, -0.005, 4.922) (-0.450, 0.039, 19.889)

EXT(sag) (4.673, 0.021, -0.097) (19.760, 0.563, 0.036)

DISCUSSION This motion analysis system has an accuracy of 1.0

degrees in rotation and 0.1 cm in translation. 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.

Geometrical and inertial errors were higher in the axial scans where off-axis motion was predicted.

Thus, system reproducibility is affected by the number of images.

DISCUSSION It was shown that greater accuracy was achieved when

using additional scans, but it the optimal number of scans was not determined.

It is hoped that future hardware enhancements will allow thinner image thickness or the ability to scan in additional planes.

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 This is the first system capable of noninvasively

measuring 3-D motion segments.

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.

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

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 inIntervertebral Joints

Segmental Instability Low Back Pain

Previous Studies 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)

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 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)

To investigate if there are significant differences between the asymptomatic group and the symptomatic patients’ group.

General Methods Radiographs

– Dynamic flexion/extension – Comparisons with previous work

Magnetic Resonance Imaging (MRI)– T2 sagittal images – Proton density axial images of facet joints– Disc and facet grading and morphologic measurements

Computer Tomography (CT)– Five positions (neutral and rotated)– Measure translation and rotation of lumbar vertebra– In vivo, non-invasive measurement of motion

General Methods Subject Selection:

– Normal subjects (80)– Age and gender matched symptomatic patients (80)

Degenerative changes in the Intervertebral Joints– MRI (T2 sagittal and Proton density axial images)– CT– Plain radiographs

Motion Measurement– CT images to measure passive AR motion– Dynamic radiographs to measure voluntary FLX/EXT motion

Subjects to date

Age (yrs) NM NF SM SF

20-29 10 10 10 10

30-39 10 10 10 10

40-49 10 10 10 10

50-59 10 10 10 10

Total = 160Remaining = 130Remaining = 130

Currently tested subjectsSubject Number Age (yr) Weight (kg) Height (cm) Ethnicity

NM20_01 25 88.00 180.34 East Indian/AsianNM20_02 24 76.20 177.8 East Indian/AsianNM20_03 24 74.84 185.42 WhiteNM20_04 24 72.57 182.88 East Indian/AsianNM20_05 26 88.45 180.34 WhiteNM20_06 25 61.23 168.91 WhiteNM20_07 24 92.99 187.96 WhiteNM20_08 23 81.65 172.72 WhiteNM20_10 28 104.33 177.8 WhiteNM20_11 25 70.31 171.45 East Indian/AsianNM30_01 32 86.18 180.34 WhiteNM30_02 33 88.45 182.88 WhiteNM30_03 36 81.65 177.8 WhiteNM50-01 55 104.33 177.8 White

NF20_01 25 63.50 162.56 WhiteNF20_02 26 45.36 165.1 East Indian/AsianNF20_03 26 62.60 157.48 Pacific IslanderNF20_04 25 63.50 182.88 WhiteNF20_06 24 58.97 167.64 White/East IndianNF20_07 24 49.89 154.94 AsianNF20_08 23 49.89 160.02 AsianNF20_09 26 52.16 157.48 WhiteNF30_01 37 49.89 154.94 Hispanic (White)NF30_02 35 77.11 167.64 Black NF30_03 32 81.65 167.64 Black NF30_04 38 49.89 162.56 Hispanic (White)NF40-01 40 68.04 167.64 White

Data shown in this presentation

Radiographs

Flexion Extension

NF40-01

Dynamic Flexion/Extension

Radiographic Data

Flexion Extension

Unit L1/L2 L2/L3 L3/L4 L4/L5 L5/S1mm -0.56 -1.36 -0.50 -1.01 -2.63

degrees -3.07 0.00 -6.60 -6.20 -24.70mm 1.70 0.92 0.57 2.05 1.83

degrees 3.37 7.41 13.60 13.50 39.70Y or N N N N N NY or N N N N N N

Length (mm) & Height (mm)

N N N N N

Angular Displacement (-)Posterior Translation (RO)Angular Displacement (+)

Spondylolysis?Schmorl's Nodes?

Spurs?

Measured ParameterAnterior Translation (AO)

NF40-01

MRI- Disc Grading

Grade 1Grade 1 Grade 2Grade 2 Grade 3Grade 3

Grade 4Grade 4 Grade 5Grade 5

Grade 1Grade 1 Grade 2Grade 2 Grade 3Grade 3

Grade 4Grade 4 Grade 5Grade 5

Fujiwara, et al 2000

Thompson’s Grading

Sagittal T2- NF40-01

1- Normal2- Less distinct np/af3- Crack in np or af4- Decreased height5- Collapse

Thompson’s scale

MRI- Disc Grading Data (sagittal)Intervertebral

Joint Level

Disc Degeneration

(1-5)

Disc Degeneration, alternate scale

(1-3)

Cartilage Degeneration

(1-4)

Subchondral Sclerosis (1-4)

Cartilage Degeneration

(1-4)

Subchondral Sclerosis (1-4)

Osteophyte Grade (1-4)

Posterior Bulging

(mm)

Disc Herniation? (extruded/

sequestered)

Endplate Condition

NM20-01T12/L1 2 1 1 1 1 1 1L1/L2 2 1 1 1 1 1 1L2/L3 2 1 1 1 1 1 1L3/L4 2 1 1 1 1 1 1L4/L5 2 1 1 1 1 1 1L5/S1 2 1 1 1 1 1 1

NM30-01T12/L1 2 1 1 1 1 1 1L1/L2 2 1 1 1 1 1 1L2/L3 2 1 1 1 1 1 1L3/L4 2 1 1 1 1 1 1L4/L5 4 2 1 1 1 1 1L5/S1 4 2 1 1 1 1 1

NF40-01T12/L1 2 1 1 1 1 1 1L1/L2 2 1 1 1 1 1 1L2/L3 2 1 1 1 1 1 1L3/L4 2 1 1 1 1 1 1L4/L5 2 1 1 1 1 1 1L5/S1 4 2 1 1 1 1 1 3.86 extruded

Left Facet Right Facet

1- Normal2- Radial tear (HIZ, SI, BA)3- Collapse

Alternative scale

MRI- Measurements (sagittal)

1 24

3

5 6

7

8

9

10

11

12

13

1 24

3

5 6

7

8

9

10

11

12

13

NF40-01 sagittal T2

MRI- Measurement Data

Intervertebral Level T12/L1 L1/L2 L2/L3 L3/L4 L4/L5 L5/S11 Mid-sagittal diameter 16.04 17.26 15.11 14.68 12.79 16.04

2RSubarticular Sagittal Diameter

2LSubarticular Sagittal Diameter

3RThickness- Ligamentum Flavum

2.57 2.37 1.29 2.37 2.37 2.57

3LThickness- Ligamentum Flavum

2.37 1.15 1.82 4.64 2.88 2.58

4 Disc Height- Anterior 2.37 3.64 3.64 4.64 6.36 7.515 Disc Height- Midpoint 3.64 5.46 7.83 8.08 7.68 6.726 Disc Height - Posterior 3.10 2.37 3.10 3.45 3.50 2.58

7R Foraminal Height 17.32 14.97 18.94 18.46 17.17 16.218R Foraminal Width- Upper 7.72 8.50 10.76 11.64 8.81 8.249R Foraminal Width- Middle 8.02 8.77 8.56 8.06 4.75 3.69

10R Foraminal Width- Lower 6.20 6.44 7.28 6.36 2.37 3.867L Foraminal Height 14.22 17.00 17.66 16.49 18.65 14.978L Foraminal Width- Upper 7.12 7.83 7.28 7.57 9.65 7.739L Foraminal Width- Middle 8.56 7.49 7.83 7.01 3.50 6.2010L Foraminal Width- Lower 7.12 6.20 4.75 6.44 3.10 3.1011 Posterior Bulging 0.00 0.00 0.00 1.15 1.82 3.86

12Distance of osteophyte from Superior Vertebra Endplate

13Distance of osteophyte from Inferior Vertebra Endplate

NF40-01

MRI- Facet Grading

Grade IGrade I Grade IIGrade II

Grade IIIGrade III Grade IVGrade IV

Grade IGrade I Grade IIGrade II

Grade IIIGrade III Grade IVGrade IV

Fujiwara et al. 2000

1- Normal2- Erosion3- Cartilage half gone4- Absence of cartilage

Cartilage Degeneration

MRI- Subchondral Grading

Grade IGrade I Grade IIGrade II

Grade IIIGrade III Grade IVGrade IV

Grade IGrade I Grade IIGrade II

Grade IIIGrade III Grade IVGrade IV

1- Normal2- Focal thickening3- Up to 50% with thickening4- Greater than 50% with thickening

Subchondral Sclerosis

Fujiwara et al. 2000

MRI- Osteophyte Grading

Grade IGrade I Grade IIGrade II

Grade IIIGrade III Grade IVGrade IV

Grade IGrade I Grade IIGrade II

Grade IIIGrade III Grade IVGrade IV

1- None2- Possible osteophyte3- Small osteophyte4- Large osteophyte

Osteophytes

Fujiwara et al. 2000

MRI- Grading Data (axial)Intervertebral

Joint Level

Disc Degeneration

(1-5)

Disc Degeneration, alternate scale

(1-3)

Cartilage Degeneration

(1-4)

Subchondral Sclerosis (1-4)

Cartilage Degeneration

(1-4)

Subchondral Sclerosis (1-4)

Osteophyte Grade (1-4)

Posterior Bulging

(mm)

Disc Herniation? (extruded/

sequestered)

Endplate Condition

NM20-01T12/L1 2 1 1 1 1 1 1L1/L2 2 1 1 1 1 1 1L2/L3 2 1 1 1 1 1 1L3/L4 2 1 1 1 1 1 1L4/L5 2 1 1 1 1 1 1L5/S1 2 1 1 1 1 1 1

NM30-01T12/L1 2 1 1 1 1 1 1L1/L2 2 1 1 1 1 1 1L2/L3 2 1 1 1 1 1 1L3/L4 2 1 1 1 1 1 1L4/L5 4 2 1 1 1 1 1L5/S1 4 2 1 1 1 1 1

NF40-01T12/L1 2 1 1 1 1 1 1L1/L2 2 1 1 1 1 1 1L2/L3 2 1 1 1 1 1 1L3/L4 2 1 1 1 1 1 1L4/L5 2 1 1 1 1 1 1L5/S1 4 2 1 1 1 1 1 3.86 extruded

Left Facet Right Facet

MRI- Measurements (axial)

1 24

3

5 6

7

8

9

10

11

12

13

1 24

3

5 6

7

8

9

10

11

12

13

Intervertebral Level T12/L1 L1/L2 L2/L3 L3/L4 L4/L5 L5/S11 Mid-sagittal diameter 16.04 17.26 15.11 14.68 12.79 16.04

2RSubarticular Sagittal Diameter

2LSubarticular Sagittal Diameter

3RThickness- Ligamentum Flavum

2.57 2.37 1.29 2.37 2.37 2.57

3LThickness- Ligamentum Flavum

2.37 1.15 1.82 4.64 2.88 2.58

NF40-01

NF40-01Axial T2

CT

Determine torsional stability 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 Ring CT Scanner Bed

Neutral Right Full (50)

Straps to support upper body and head

CT Image Processing

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

3-D Images from Mimics Pro-Engineer 2000i2

– Centroids– Moment of Inertia Tensor

Matlab® software– Custom in-house programs– Calculate eigen vectors– Calculate rotation and translation between rigid bodies

Rigid Body Motion

I

I I I

I I I

I I I

I

I

I

Iij

xx xy xz

xy yy yz

xz yz zz

ii

11

22

33

0 0

0 0

0 0

Inertial properties of a rigid body

Moment of Inertia-Calculate the principle axes (eigen vectors)-The orientation of the principle axes does not change wrtthe rigid body

Lim 1994

NF40-01 L1

Neutral Left 30 Left Full (=50 )

CT Image Processing (con’t)

NL1 Flex/Ext X Lateral

Bending YTorsion Z X Y Z

Trace error (%)

Volume error (%)

L30 0.429 -4.761 9.085 9.038 -8.426 -6.563 0.247 -0.37LF -1.459 -6.346 18.793 22.731 -5.872 -7.538 1.783 -1.13

R30 0.284 4.610 -7.874 -3.283 -3.306 -1.974 1.961 -1.53RF -2.608 6.441 -17.696 -11.037 -7.170 -2.561 0.724 -0.24

Translation(mm)Rotation (deg)

Geometric PropertiesInertial Properties+X= Extension +Y= Left Lateral Bending +Z= Left Axial Rotation

Further CT ExamplesNL2 Flex/Ext X

Lateral Bending Y

Torsion Z X Y ZTrace error

(%)Volume error (%)

L30 -0.870 -3.532 7.797 5.317 -8.934 -6.258 0.089 -0.15LF -2.259 -5.557 17.403 16.077 -6.435 -7.823 0.319 -0.33

R30 -0.532 2.480 -5.925 -0.132 -3.461 -2.116 0.295 -0.06RF -3.069 4.343 -15.242 -4.801 -6.935 -2.941 0.507 0.26

NL3 Flex/Ext X Lateral

Bending YTorsion Z X Y Z

Trace error (%)

Volume error (%)

L30 -2.100 -1.902 6.341 2.739 -8.361 -6.104 0.303 0.10LF -4.124 -2.703 14.314 10.712 -5.920 -7.904 1.014 0.23

R30 -1.050 0.873 -4.639 1.720 -3.075 -2.195 0.921 -0.55RF -3.336 2.083 -12.599 -0.182 -6.033 -3.537 0.043 0.33

NL4 Flex/Ext X Lateral

Bending YTorsion Z X Y Z

Trace error (%)

Volume error (%)

L30 -3.058 -0.861 5.340 1.599 -6.929 -6.150 0.277 0.21LF -5.207 -2.503 13.807 6.836 -4.261 -7.877 0.071 -0.07

R30 -1.432 -0.056 -3.752 2.369 -2.525 -2.215 0.114 -0.29RF -3.276 -0.108 -11.090 2.265 -4.503 -3.975 0.490 -0.44

NL5 Flex/Ext X Lateral

Bending YTorsion Z X Y Z

Trace error (%)

Volume error (%)

L30 -3.273 0.027 4.829 1.426 -5.172 -6.099 0.176 -0.29LF -5.116 -1.093 11.799 5.444 -1.593 -7.733 1.314 -1.04

R30 -0.822 -0.182 -3.156 2.269 -1.663 -2.130 0.138 0.15RF -3.348 0.032 -9.993 2.733 -2.988 -4.105 0.768 -0.59

Rotation (deg) Translation(mm)

Rotation (deg) Translation(mm)

Rotation (deg) Translation(mm)

Rotation (deg) Translation(mm)

NF40-01

Future Plans

Continue data acquisition and processing– Start recruting low-back pain subjects

• Summer 2003

By the summer 2004, we expect to produce sufficient data for meaningful statistical analyses and publication.