Dynamic Assessment of Spinal Stiffness
Christopher J. Colloca, D.C.
"An
increase in stiffness can mean a reduction in the amount of allowable
motion within the motion segment or a potentially harmful increase in
force to obtain the desired motion. This may locally result in greater
stresses due to an altered ability of the disc to distribute loads."
-
Kaigle,A.; Ekstrom,L.; Holm,S.; Rostedt,M.; Hansson,T. In vivo dynamic
stiffness of the porcine lumbar spine exposed to cyclic loading:
influence of load and degeneration. J Spinal Disord 1998; 11(1):65-70.
Introduction
Neurologically
mediated reflexogenic stability of the three-joint complex of the
functional spinal unit (FSU) is becoming increasingly understood in the
scientific literature (Gedalia et al., 1999).
Research has demonstrated that the musculature and the discoligamentous tissues of the spine function synergistically, so that the desired movement is accomplished while the stability of the spine is preserved (Panjabi, 1992)
These relationships have been of utmost interest to doctors of chiropractic in assessing the spine for dysfunction, known as vertebral subluxation.
Research has demonstrated that the musculature and the discoligamentous tissues of the spine function synergistically, so that the desired movement is accomplished while the stability of the spine is preserved (Panjabi, 1992)
These relationships have been of utmost interest to doctors of chiropractic in assessing the spine for dysfunction, known as vertebral subluxation.
Chiropractors
traditionally have relied on their kinesthetic sense during palpation
of the spine to assess for presumed intersegmental spinal mobility.
Inasmuch, qualitative assessment of the posteroanterior (PA) motion of the human spine is commonly used to attempt to assess the functional status of underlying anatomy (Lewit and Liebenson, 1993).
Such assessments are highly qualitative in nature with many studies demonstrating unreliable or inaccurate results using motion palpation (Keating et al., 1990;Mootz et al., 1989;Ross et al., 1999;Troyanovich et al., 1998).
For this reason, mechanical devices utilizing static and quasi-static oscillatory PA forces have been developed to more objectively quantify PA spine stiffness (Latimer et al., 1996;Latimer et al., 1998;Lee et al., 1997;Kawchuk and Herzog, 1996).
The reliability and validity of instruments to assess PA spine stiffness have shown favorable results (Latimer et al., 1996), (Latimer et al., 1998;Lee et al., 1997;Lee and Svensson, 1990;Viner and Lee, 1995).
Assessment of PA spinal stiffness to date however, have been primarily limited to study of asymptomatic subjects at low frequencies.
Inasmuch, qualitative assessment of the posteroanterior (PA) motion of the human spine is commonly used to attempt to assess the functional status of underlying anatomy (Lewit and Liebenson, 1993).
Such assessments are highly qualitative in nature with many studies demonstrating unreliable or inaccurate results using motion palpation (Keating et al., 1990;Mootz et al., 1989;Ross et al., 1999;Troyanovich et al., 1998).
For this reason, mechanical devices utilizing static and quasi-static oscillatory PA forces have been developed to more objectively quantify PA spine stiffness (Latimer et al., 1996;Latimer et al., 1998;Lee et al., 1997;Kawchuk and Herzog, 1996).
The reliability and validity of instruments to assess PA spine stiffness have shown favorable results (Latimer et al., 1996), (Latimer et al., 1998;Lee et al., 1997;Lee and Svensson, 1990;Viner and Lee, 1995).
Assessment of PA spinal stiffness to date however, have been primarily limited to study of asymptomatic subjects at low frequencies.
   |
Research groups from Australia, Canada, and the U.S. are currently working in the area of spinal stiffness assessment.
While lecturing in Australia in 1999, I had the pleasure of meeting Michael Lee, Ph.D. and some of his group from the University of Sydney.
They hosted us on a tour of their facility and laboratory and we had a chance to discuss ongoing projects that we are both working on.
The Australian group is most
interested in studying oscillatory motions of the spine using a load
cell to measure static stiffness.
From the University of Calgary, Kawchuk and Herzog have also developed technology to assess static spine stiffness (Kawchuk and Herzog, 1996;Kawchuk and Herzog, 1995).
More recently, Dr. Kawchuk, as part of his Ph.D. dissertation project developed a method to assess static spinal stiffness using ultrasound (Kawchuk et al., 2000;Kawchuk and Elliott, 1998).
In this manner, an ultrasound transducer is placed on the skin overlying a prone laying subject and an image is recorded.
Next, a force is applied (similar to a preload of approximately 70 N) and another image is recorded so that the static displacement can be calculated.
While lecturing in Australia in 1999, I had the pleasure of meeting Michael Lee, Ph.D. and some of his group from the University of Sydney.
They hosted us on a tour of their facility and laboratory and we had a chance to discuss ongoing projects that we are both working on.
 Michael Lee, MbiomedE, Ph.D. from the dept. of health sciences, University of Sydney shown with a prototype of a PA spinal stiffness assessment device. |
From the University of Calgary, Kawchuk and Herzog have also developed technology to assess static spine stiffness (Kawchuk and Herzog, 1996;Kawchuk and Herzog, 1995).
More recently, Dr. Kawchuk, as part of his Ph.D. dissertation project developed a method to assess static spinal stiffness using ultrasound (Kawchuk et al., 2000;Kawchuk and Elliott, 1998).
In this manner, an ultrasound transducer is placed on the skin overlying a prone laying subject and an image is recorded.
Next, a force is applied (similar to a preload of approximately 70 N) and another image is recorded so that the static displacement can be calculated.
Dynamic vs. Static Spinal Stiffness Assessment
 A dynamic spinal stiffness assessment being conducted over the L4 spinous process using a modified spinal manipulation device. Surface EMG electodrodes are also visualized to record the back muscle response to the test. |
Limitations of the static and quasi-static (oscillatory) technologies are clear.
They combine large size and an intricate mechanical makeup with a high potential cost and unease of use that makes them only desirable in a research setting as opposed to clinical practice.
More importantly, because the spine exhibits time-dependent and frequency-dependent or viscoelastic mechanical properties, to understand the spine's stiffness, dynamic frequency response functions must be evaluated.
This is precisely what Dr. Tony Keller, professor of Mechanical Engineering at the University of Vermont has developed - technology that provides a dynamic assessment of the mechanical properties of the spine using instrumentation that can be easily used by the clinician.
They combine large size and an intricate mechanical makeup with a high potential cost and unease of use that makes them only desirable in a research setting as opposed to clinical practice.
More importantly, because the spine exhibits time-dependent and frequency-dependent or viscoelastic mechanical properties, to understand the spine's stiffness, dynamic frequency response functions must be evaluated.
This is precisely what Dr. Tony Keller, professor of Mechanical Engineering at the University of Vermont has developed - technology that provides a dynamic assessment of the mechanical properties of the spine using instrumentation that can be easily used by the clinician.
 |
Original Research of Dynamic Spinal Stiffness
Exciting
a musculoskeletal structure with an input force, and by detecting the
resulting dynamic output response during excitation allows for
assessment of an inventory of frequency response functions.
A commonly used technique to examine the mechanics of structures in engineering is called driving point mechanical impedance where force and velocity are measured at the same point.
This
differs from transfer impedance, where a force is put in at one
location, and measurements are obtained at a different location (i.e.
thusting on a patient and measuring the forces transmitted at the
table).
This method substantially differs from the previously discussed low frequency oscillatory stiffness assessment techniques in that it provides a comprehensive dynamic assessment of the spine.
In this manner it allows us to examine numerous frequencies instead of only one or a few - thus, making it a dynamic assessment.
Adapting a commonly used instrument used for spinal manipulation to include a load cell and accelerometer (impedance head), inputs are able to be put into the spine and the spine's response to such input is able to be recorded using a validated method (Keller et al., 1999).
A commonly used technique to examine the mechanics of structures in engineering is called driving point mechanical impedance where force and velocity are measured at the same point.
 Schematic illustration of the dynamic mechanical impedance protocol. Data is collected at a high frequency (10 KHz) and force & acceleration time domain signals are converted to the frequency domain using a Fast Fourier Transform. Acceleration is converted to velocity and the dynamic mechanical impedance was then calculated. |
This method substantially differs from the previously discussed low frequency oscillatory stiffness assessment techniques in that it provides a comprehensive dynamic assessment of the spine.
In this manner it allows us to examine numerous frequencies instead of only one or a few - thus, making it a dynamic assessment.
Adapting a commonly used instrument used for spinal manipulation to include a load cell and accelerometer (impedance head), inputs are able to be put into the spine and the spine's response to such input is able to be recorded using a validated method (Keller et al., 1999).
After
performing work to validate the assessment, Dr. Keller collected data
from the lumbar spinous processes of asymptomatic subjects (students
from the University of Vermont) and found that the dynamic
posteroanterior mechanical behavior of the human lumbar spine was
sensitive to mechanical stimulus frequency and showed significant
region specific and gender differences (Keller et al., 2000).
The next step was to investigate the dynamic spinal stiffness in actual clinically relevant patients.
The next step was to investigate the dynamic spinal stiffness in actual clinically relevant patients.
This
technology has given rise to numerous research collaborations to
investigate dynamic spinal stiffness in actual patients with an easy to
use non-invasive diagnostic tool.
In early 1998, we began testing
patients with low back and leg pain from my clinic to determine if
there were any differences in spinal stiffness in patients stratified
by a range of objective measures.
Our research protocol consists of conducting a physical exam, obtaining lumbar spine radiographs, and recording outcome assessments as we seek to determine differences in dynamic stiffness amongst patients with lumbar spinal disorders.
To understand the physiological significance of the spine's stiffness we attached surface electrodes over the paraspinal muscles to record their reflex reactions to the perturbations.
We found that patients with worsening symptom frequency were stiffer and had higher reflex thresholds, thus correlating spinal dysfunction clinically.
These findings were both exciting and promising, as they objectively characterized what chiropractors have anecdotally reported for over 100 years - the tissue changes resulting from effects of vertebral subluxation.
We presented this research at the 1999 meeting of the International Society of the Lumbar Spine (ISSLS) (Colloca et al., 1999) and the manuscript that followed was published in 2001 in the Journal of Manipulative & Physiological Therapeutics.
 Chris Colloca, D.C. performs dynamic spinal stiffness testing on a patient as Tony Keller, Ph.D. collects the data and supervises the research protocol. |
Our research protocol consists of conducting a physical exam, obtaining lumbar spine radiographs, and recording outcome assessments as we seek to determine differences in dynamic stiffness amongst patients with lumbar spinal disorders.
To understand the physiological significance of the spine's stiffness we attached surface electrodes over the paraspinal muscles to record their reflex reactions to the perturbations.
We found that patients with worsening symptom frequency were stiffer and had higher reflex thresholds, thus correlating spinal dysfunction clinically.
These findings were both exciting and promising, as they objectively characterized what chiropractors have anecdotally reported for over 100 years - the tissue changes resulting from effects of vertebral subluxation.
We presented this research at the 1999 meeting of the International Society of the Lumbar Spine (ISSLS) (Colloca et al., 1999) and the manuscript that followed was published in 2001 in the Journal of Manipulative & Physiological Therapeutics.
 |
From
the enormous amount of data that Dr. Keller and I have collected in
patients from over 2000 adjustments, we have performed several other
clinical research projects.
These include assessing the muscular contributions to spine stiffness where we tested patients in the prone resting position as compared to during a trunk extension procedure.
In
addition, we have begun to investigate the relationship between
radiological parameters such as lumbar disc height and dynamic spine
stiffness.
Dr. Terry Peterson (Mesa, AZ) digitized over 700 points on the lumbar spine radiographs of the research subjects and read the films for the presence of spondylosis, tropism, transitional segment, and other spinal disorders and categorized several parameters for us to investigate.
Both of these projects were presented at the 2000 meeting of the International Conference on Spinal Manipulation (ICSM) in Bloomington, MN in September (Colloca et al., 2000a;Colloca et al., 2000b).
These include assessing the muscular contributions to spine stiffness where we tested patients in the prone resting position as compared to during a trunk extension procedure.
 Radiographic images of lumbar disc height have been compared to dynamic stiffness assessments obtained over the spinous processes of the respected vertebrae. In this manner we can assess normal (A) and degenerated (B) disc heights for differences in spinal stiffness. |
Dr. Terry Peterson (Mesa, AZ) digitized over 700 points on the lumbar spine radiographs of the research subjects and read the films for the presence of spondylosis, tropism, transitional segment, and other spinal disorders and categorized several parameters for us to investigate.
Both of these projects were presented at the 2000 meeting of the International Conference on Spinal Manipulation (ICSM) in Bloomington, MN in September (Colloca et al., 2000a;Colloca et al., 2000b).
 |
Our
research team continues to investigate objective measures to more
accurately characterize spinal function from a biomechanical standpoint.
Our current research interests in this area include the continued effort to characterize full spine dynamic spinal stiffness as well as numerous other parameters such as the postural effects upon spinal stiffness.
We
believe that the development of new measures to objectively measure
biomechanical characteristics of the spine will not only serve to allow
us to better care for patients but to validate and advance our great
profession as well.
We will continue to update you on the projects that we are conducting and be sure to check our publications list frequently to be advised of the most recent publications.
Our current research interests in this area include the continued effort to characterize full spine dynamic spinal stiffness as well as numerous other parameters such as the postural effects upon spinal stiffness.
 |
We will continue to update you on the projects that we are conducting and be sure to check our publications list frequently to be advised of the most recent publications.
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Ekstrom,L., Holm,S., Rostedt,M., Hansson,T., 1998. In vivo dynamic
stiffness of the porcine lumbar spine exposed to cyclic loading:
influence of load and degeneration. J Spinal Disord, 11(1), 65-70.
Kawchuk,G.
& Herzog,W., 1995. The reliability and accuracy of a standard
method of tissue compliance assessment. J Manipulative Physiol Ther,
18(5), 298-301.
Kawchuk,G. & Herzog,W., 1996. A new
technique of tissue stiffness (compliance) assessment: its reliability,
accuracy and comparison with an existing method. J Manipulative Physiol
Ther, 19(1), 13-18.
Kawchuk,G.N. & Elliott,P.D.,
1998. Validation of displacement measurements obtained from ultrasonic
images during indentation testing. Ultrasound Med Biol, 24(1), 105-111.
Kawchuk,G.N., Fauvel,O.R., Dmowski,J., 2000. Ultrasonic
quantification of osseous displacements resulting from skin surface
indentation loading of bovine para-spinal tissue. Clin Biomech, 15(4),
228-233.
Keller,T.S., Colloca,C.J., Fuhr,A.W., 1999.
Validation of the force and frequency characteristics of the activator
adjusting instrument: effectiveness as a mechanical impedance
measurement tool. J Manipulative Physiol Ther, 22(2), 75-86.
Keller,T.S.,
Colloca,C.J., Fuhr,A.W., 2000. In Vivo Transient Vibration Analysis of
the Normal Human Thoracolumbar Spine. J Manipulative Physiol Ther,
23(8), 521-530.
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device for measuring responses to posteroanterior forces in a patient
population, Part 1: Reliability testing. Phys Ther, 76(2), 158-165.
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relationship between low back pain and lumbar posteroanterior
stiffness. J Manipulative Physiol Ther, 19(9), 587-591.
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Lee,M., Adams,R.D., 1998. The effects of high and low loading forces on
measured values of lumbar stiffness. J Manipulative Physiol Ther,
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