Vibration Diagnostic Probe for Discogenic Pain Due to a Fissure in an

Annulus Fibrosus

Jae-Cheon Kim

, Giseok Kang

, Hyoung-Ihl Kim

1,2

and Jong-Hyun Lee

1,2

Department of Medical System Engineering, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea

School of Mechatronics, Gwangju Institute of Science and Technology, Gwangju, Republic of Korea

Keywords: Discography, Vibration Probe, Low Back Pain, Discogenic Pain, Pain Stimulation, Intervertebral Disc,

Annular Fissure, Disc Degeneration, Internal Disc Derangement, Linear Motor.

Abstract: Discogenic pain is the most common cause of chronic low back pain, accounting for 39% of causes. One

possible diagnostic method to determine the cause of discogenic pain is provocative discography. However,

this method is not available to patients with severe fissures due to degenerative disc disease. In this paper,

we present a diagnostic probe in which plastic optical fiber (POF), which is located in a hole in the flexible

tube of the probe, can be steered to the vicinity of fissures in the annulus fibrosus. Then, a linear motor

placed inside the grip generates a minute axial vibration of the POF tip, which irritates the tiny pain nerves

located near fissures. The intensity of the pain thus generated is used as a guideline to determine the level of

discogenic disease. The frequency and amplitude of the vibration discography ranged from 2.5 Hz to 5.7 Hz

and 1.5 mm to 3.4 mm, respectively. The applicability of the designed probe was successfully confirmed by

testing the modified intradiscal microprobe in an ex vivo animal experiment.

1 INTRODUCTION

The intervertebral disc (or disk) is the core structure

of the vertebral column located between vertebral

bodies, lending stability of the body. In the center of

the disc lies a jelly-like structure, the nucleus

pulposus, which is composed of collagen fibers and

mucopolysaccharides. The nucleus pulposus is

surrounded by strong, thick layers of the annulus

which confines the nucleus pulposus in the center of

the disc. On one hand, discs play a key role in

absorbing the axial pressure load delivered from the

trunk and head during movement of the body. On

the other hand, discs are a common source of

chronic low back pain.

The pathological process of a disc usually starts

from the tearing of the annulus. As the lesion

deteriorates, the tears enlarge and coalesce until they

form a fissure in the annulus (internal disc

derangement: IDD), or annulus ruptures at the site of

herniation of disc materials (disc herniation).

Subsequently, low back pain is generally known to

be produced by the secretion of inflammatory

cytokines around the fissure in IDD and by

mechanical compression of the nerve root in disc

herniation (Burke et al., 2002). Although disc

herniation has been well known to the public for

some time, our understanding of the etiology of

chronic back pain has changed during the last two

decades. Major studies on chronic low back pain

have shown that discogenic pain caused by IDD is

estimated to range from 26 % to 39 %, whereas pain

cause by disc herniation ranges from 2.8 % to 3.5 %

(Schwarzer et al., 1995). Recent advances in high-

resolution diagnostic imaging techniques, such as

computed tomography (CT) and magnetic resonance

imaging (MRI), facilitate the diagnosis of disc

herniation. However, even modern imaging methods

are not sufficient to discern the internal disc

derangement.

Modern discography is a pain-provocative test

which can reproduce each patient’s unique pain.

Despite controversy regarding the accuracy and

specificity of discography, it is recognized as the

only method of proving the diagnostic standard for

discogenic pain. Discography is known to provoke

pain by pressing onto nerve structures around the

fissures through the injection of contrast media (Shin

et al., 2009). However, intradiscal pressure cannot

be increased to provoke pains because severely

degenerated discs cannot entrap contrast medium

inside the discs (Kim et al., 2009); (Adams et al.,

159

Kim J., Kang G., Kim H. and Lee J..

Vibration Diagnostic Probe for Discogenic Pain Due to a Fissure in an Annulus Fibrosus.

DOI: 10.5220/0004242201590162

In Proceedings of the International Conference on Biomedical Electronics and Devices (BIODEVICES-2013), pages 159-162

ISBN: 978-989-8565-34-1

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

1986). Therefore, discography has practical

limitations in patients with severely degenerated

discs.

Meanwhile, vibration diagnostic method of

discogenic pain was studied by stimulating lumbar

spinous process (the bony part of the spine) from

skin surface (Yrjama et al., 1994). The method,

however, also couldn’t diagnose patients with total

annular rupture because they felt no pain during the

bony vibration provocation.

In this paper, to overcome the weakness of

conventional discography, we propose a novel

intradiscal microprobe that delivers direct

mechanical stimuli on the nerve endings around the

fissure. The microprobe, capable of steering and

vibrating, was realized for clinical trials, and its

applicability was confirmed by ex vivo animal

experiment.

2 CONFIGURATION

Fig. 1 shows the configuration of the proposed

intradiscal microprobe used to diagnose discogenic

pain. The intradiscal microprobe is composed of a

polymer tube, a plastic optical fiber (POF), a

steering lever, a steering wire, a grip, a linear motor

and a motor controller. The polymer tube has two

holes for insertion of the steering wire and the POF.

The steering wire is inserted into one hole of the

polymer tube, and then each end of the wire is fixed

to the tip of the polymer tube and the lever. Thus,

the lever bend the polymer tube in a counter

clockwise direction as the lever is driven manually.

Figure 1: Diagram of the proposed intradiscal microprobe

capable of steering and vibrational stimulus. The device is

composed of a polymer tube, a plastic optical fiber (POF),

a steering lever, a steering wire, a grip, a linear motor and

a motor controller. The steering lever enables the tip of the

polymer tube to be navigated within an annulus fibrosus.

The linear motor and motor controller are used to generate

axial vibration of the POF tip.

Meanwhile, the POF is inserted into the other

hole of polymer tube and then connected with the

moving part of the linear motor, which is located in

the grip of the microprobe. Also, the linear motor is

linked to the motor controller which enables the

reciprocation of the linear motor. Reciprocation

leads to axial vibration of the POF tip which

facilitates stimulation of the nerve endings around

the fissure.

3 OPERATION PRINCIPLE

Fig. 2 shows how the POF, which is placed in the

polymer tube of the intradiscal microprobe,

approaches the annulus fibrosus. First, the polymer

tube is introduced through a guide needle into the

nucleus pulposus (jelly-like substance inside the

disc). After that, the POF is steered to the vicinity of

the fissure in the annulus fibrosus as the lever is

pulled slowly. As shown in the inset of fig. 2, one

end of the POF comes out from the polymer tube,

facilitating navigation toward the fissure. The other

end of the POF is connected to the movable part of

the linear motor. The movable part moves back and

forth to produce the alternating motion of the

protruding POF tip which delivers a vibrational

stimulus to nerve structures near the fissures. The

frequency and amplitude of the vibrational stimulus

can be changed according to two input variables of

the linear motor. The variables are velocity and span,

which can be regulated by the motor controller.

Figure 2: Photograph of the polymer tube steered towards

the outer disc above a life-size human spine model. The

inset is a magnified view of the protruding POF tip. A

round metal plate is a fixture used to fasten the spine.

The vibration of the POF tip directly irritating

the nerve endings will cause pain, the intensity of

which is applicable as an effective indicator for the

diagnosis of discogenic pain. In addition, unlike

conventional discography, the proposed method is

valid even for patients with severely degenerated

discs where the nucleus pulposus has escaped from

the annulus fibrosus.

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4 FABRICATION

The intradiscal microprobe was fabricated by

modification of commercial steerable catheter for

drug injection. First, considering the size of the

human intervertebral disc, the polymer tube length

was designed to protrude 30 mm from the guide

needle. Next, the linear motor (PoteNit, LSA-3024)

was fixed inside the grip of the microprobe, and was

electrically coupled to the motor controller outside

of the grip. After that, one end of the wire (dia. 250

μm) was inserted into the smaller hole (dia. 300 μm)

of the polymer tube (dia. 2000 μm, and was fixed at

the tip of polymer tube. The other end was joined to

the lever. Then, the moving part of the linear motor

was connected with one end of the POF (dia. 500

μm). Finally, the fabrication of the microprobe was

completed by the insertion of a POF into the larger

hole (dia. 2000 μm) of the polymer tube.

Fig. 3 shows the process of steering the polymer

tube tip that is inserted into the guide needle. The

steering angle of the tube tip was about 10° when the

steering lever was in the middle of the operating

range as shown in fig. 3a. As the lever was fully

pulled back, the tube tip became more bent in a

counter clockwise direction as shown in figs. 3b and

3c. Meanwhile, the POF tip protruded further

outwards as the steering angle of the tube increased,

as shown in the insets of figs. 3a, 3b, and 3c.

Consequently, the protruding POF tip could reach to

the fissures more easily and more efficiently.

Figure 3: The steering process of the polymer tube tip of

the fabricated intradiscal microprobe: (a) initial state, (b)

the lever in the middle, and (c) the lever fully pulled. The

steering angle of the tube tip ranges from 10° to 90°. The

insets show that the POF tip protrudes from the polymer

tube with bending of the polymer tube. The protruding

length ranges from 0 mm to 2 mm.

5 EXPERIMANTAL RESULTS

Fig. 4 shows the experiment set-up to evaluate the

performance of the intradiscal microprobe. The axial

reciprocation of the POF tip was expressed as a sine

wave on an oscilloscope by using a micro-

vibrometer (Nihon Kagaku Eng. MLD-211D) which

was set to a horizontal scale of 50 ms/div and a

vertical scale of 160μm/div. The sine waves were

recorded while the velocity and span, which are

input variables of the device, were increased from 12

mm/s to 24 mm/s in increments of 6 mm/s and 2 mm

to 3 mm increments of 0.5 mm, respectively. The

frequency and amplitude of the sine wave were

converted to those of the axial reciprocation of the

POF tip using the scale. The minimum values of the

measured frequency and amplitude were 2.5 Hz and

1.5 mm, respectively, and the corresponding

maximum values were 5.7 Hz and 3.4 mm,

respectively (fig. 5).

Figure 4: Photograph of the experiment set-up to evaluate

the intradical microprobe for vibration discography.

Figure 5: Measured vibration characteristics of the

intradical microprobe.

The maximum frequency obtained with currently

available micro-motor was 5.7 Hz which is smaller

than 42 Hz to 50 Hz of the bony vibrator device

(Yrjama et al., 1994). The vibration frequency of the

VibrationDiagnosticProbeforDiscogenicPainDuetoaFissureinanAnnulusFibrosus

161

present intradiscal microprobe is thought to be high

enough to provoke pains because the method

directly irritates the nerve ending, not the bone.

In addition, the preliminary experiment to

evaluate the ex vivo steering performance of the

intradiscal microprobe was implemented using C-

arm x-ray imaging. The experiment was carried out

in a pig spinal cord, instead of the nucleus pulposus,

because an x-ray image of the polymer tube would

not be visible due to the opaque vertebrae located at

top and bottom sides of the nucleus pulposus.

Considering that the mechanical properties of the

jelly-like spinal cord are similar to those of the

nucleus pulposus, this preliminary experiment is

thought to be able to provide meaningful data for

subsequent ex vivo experiment.

Prior to the ex vivo experiment, we conducted a

steering test of the polymer tube in air to compare

with the steering performance in the ex vivo spinal

cord. The protruding length of the polymer tube,

from the guide needle, was decreased to 13 mm,

because the diameter of the pig spinal cord prepared

for the experiment was only 15 mm. The maximum

steering angle of the 13 mm length of the protruding

tube in air was measured to be 42°, which is about

half that of the 30 mm protruding tube. The

reduction in the steering angle is attributed to the

shortening of the protruding tube length, which is

easily predictable.

Fig. 6 is an ex vivo x-ray image (C-arm) which

shows that the polymer tube was successfully guided

to the outer rim of the pig spinal cord. The

maximum steering angle in the spinal cord was

measured as 40°, which is in good agreement to that

in air. This indicates that there is a negligible

difference in the steering angle in air and that in the

spinal cord. Even in a case of the tube protruding 30

mm, we can infer that the steering angle and

amplitude in clinical trials will be almost the same as

the results obtained from experiments in air.

Figure 6: The C-arm picture of the polymer tube steered

towards the outer rim of the pig spinal cord.

In a further study, we will carry out an in vitro

vibration experiment using a model that has

mechanical properties similar to those of the nucleus

pulposus before clinical trials. Also, a high-

performance linear motor will be used to achieve a

wider range of vibration frequency and amplitude.

ACKNOWLEDGEMENTS

This research was supported by a grant from the

Institute of Medical System Engineering (iMSE) of

the Gwangju Institute of Science and Technology

(GIST), Republic of Korea.

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