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July 2006, Vol. 16, No. 3
Table of Contents
Autism and Glutathione • CBP® Nonprofit has 24 publications in 12 months • CBP® Research Presented at the International Spine Conference in Norway • CBP® to File Lawsuit Against Quackwatch • CCE Weathers the Storm • Chiropractic Culture • Dr Don Harrison is ICA's Chiropractor of the Year • Dr Jim Gudgel to Co-Instruct With Neuromechanical Innovations • Dr Deed Harrison Speaks at Palmer West • Experimental or Medical Necessity • Fine Tune Patient Communication • From Screening to the Value of Proper Posture • ICA at the Table • ICA's Newly Elected Board Members • Instrument Adjusting's Mechanical Advantage • It's Don's Opinion • Letters to the Editor • My New Whiplash Text is Available • Patient Expectation and Retention • Principles, Ethics and Other Bygone Ideals • Problematic Decision Spectrum • Research Corner • Triano and CCGPP's Will Give You Six Visits
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Instrument Adjusting's Mechanical Advantage
by Chris Colloca, DC
A 1995 cum laude graduate of Life College School of Chiropractic (Marietta, GA),
and a 1990 graduate of Ithaca College (Ithaca, NY), Dr. Colloca directs a full time private practice and clinical research facility in Phoenix, Arizona. Dr. Colloca holds post-graduate faculty appointments in five chiropractic colleges and is Master’s Candidate in the Department of Kinesiology at Arizona State University (Tempe, AZ) with an emphasis in biomechanics. His original research has been presented at numerous international scientific conferences and published in several biomedical and professional journals. To this extent, he has authored over 100 professional articles, over 40 journal publications, more than ten textbook chapters, and over 25 conference proceedings. He is a reviewer for the Journal of Biomechanics, Spine, and European Spine Journal, among others. Dr. Colloca received the prestigious Scott Haldeman Award (1st Prize) for the best research paper at the 7th biennial congress of the World Federation of Chiropractic (2003) and is a recipient of the Sofamor-Danek Poster Presentation Award (2002 International Society for the Study of the Lumbar Spine). He has lectured extensively throughout the United States, and around the world, providing hundreds of post-graduate educational seminars for thousands of doctors of chiropractic.
Chiropractic techniques have evolved to provide clinicians with a variety of choices in the delivery of particular forces and speeds deemed appropriate for a particular patient or condition. It should come as no surprise that instrument adjusting has risen in popularity to become the second most commonly used chiropractic technique in the U.S.1 For both the doctor and patient, the mechanical advantage of instrument adjusting equates with a less physically stressful adjusting experience.
In the new millennium, the face of instrument adjusting has changed. Traditionally popular spring-loaded mechanical adjusting instruments have been replaced with electromechanical adjusting instruments due to a number of advantages discussed herein. An understanding of the attributes and mechanical advantages of instrument adjusting puts into perspective why electromechanical adjusting instruments have become so desirable among clinicians for patient care.
Force, Speed, Frequency, and Stress
Force. In mathematical modeling of chiropractic adjusting, we have previously published data demonstrating that instrument-delivered adjustments can create similar intersegmental vertebral motions as those delivered manually.2 To understand how this is possible, basic physics can be used to demonstrate some of the mechanical advantages of instrument adjusting. Force is a vector quantity, meaning it has both a magnitude and a direction. Force, expressed in Newtons (N) equals mass times acceleration. One Newton is the amount of force required to give a 1-kg mass an acceleration of 1 m/s/s. Adjusting instruments impart high accelerations to accomplish force delivery, whereas manually delivered chiropractic adjustments (i.e. Diversified technique), utilize more mass and less acceleration to achieve a similar force. Figure 1 provides examples of force-time profiles of typical instrument- and manually-delivered forces showing the remarkable speed of instrument delivered thrusts.
Forces Among Chiropractic Adjusting Instruments. Being easily able to change the force output of a chiropractic adjustment is another desirable attribute of chiropractic adjusting instruments. Spring-loaded instruments, however, have been found to be quite limited in their ability to appreciably change the force from setting to setting, despite claims to the contrary by their manufacturers. In fact, research has demonstrated that despite changing the expansion control knob or numbered setting on these activation type devices, the force does not appreciably change. In the 1980’s, Duell demonstrated that the greatest force of the Activator® device is produced on its lower ring setting.3 Likewise, last year similar findings were reported in the Journal of Manipulative & Physiological Therapeutics (JMPT), for the line of Activator® devices.4 Noteworthy in this research, the latest version Activator® IV, was found to produce very similar forces on its settings 1, 2, and 3 (123 N, 121 N, and 115 N respectively), as opposed to its setting 4 which produced 212 N.4 One could say that the device essentially has two force settings, despite its four numbered settings on the device itself.
Designed to improve the force delivery characteristics of instrument adjustments, electromechanical adjusting instruments have been developed more recently and have subsequently grown in popularity in the chiropractic marketplace within the last decade. The Impulse Adjusting Instrument® (Impulse®) is one such device that has been designed to provide a greater range of forces over traditional spring-loaded mechanical adjusting instruments. Simply stated, to adjust the cervical spine, less force is required, whereas adjusting the lumbar spine requires more force.4 Thus, Impulse® was designed to impart less force than its spring-loaded counterparts on the low setting, about the same force on the medium setting, and more force on its high setting. Providing clinicians with a larger range of forces to choose from at higher speeds than spring-loaded activation devices are clear benefits of electromechanical adjusting instruments.4
Speed. Another mechanical advantage of chiropractic adjusting instruments is speed. As shown in Figure 1, manual adjusting techniques typically have a time duration of 200 milliseconds time to peak whereas chiropractic adjusting instruments can be as much as 100 times faster, with pulse durations (time to peak) of 2 milliseconds. High-speed adjustments (those with pulse durations below 10 milliseconds) are termed impulsive. The high speed of instrument-delivered adjustments enable the application of force that is faster than the body’s ability to tighten up and resist the adjustment while creating larger magnitude intersegmental vertebral accelerations.5
Frequency. In recent years, attempts have been made to improve the frequency characteristics of instrument delivered thrusts as adjustments given at the right frequency can create more bone movement with less force.2 Unfortunately, despite design changes and significant price increases in spring-loaded devices, research has demonstrated that the second, third, and fourth generation activation devices still didn’t have the desired range of forces or thrust at the desired frequency.4 Using a computer microprocessor to control the waveform, the Impulse® device creates the desired half sine wave that best simulates a manual adjustment (albeit ~100x faster). Resent research has validated these developments;4 specifically noting a broader range of forces and a superior frequency area ratio among electromechanical adjusting instruments over traditional spring-loaded activation devices specifically favoring Impulse®.
The signature of a spring-loaded (Activator® IV Adjusting Instrument) thrust is compared to the thrust of an electromechanical device (Impulse Adjusting Instrument®) in Figure 2. As apparent in the figure, and confirmed when these data were analyzed, Impulse® was found to produce a more uniform waveform and a higher frequency area ratio over the spring-loaded activation devices.4
To validate just how the improved forces, speeds, and frequencies actually affected vertebral motions, the Impulse Adjusting Instrument® was compared to two popular spring-loaded activation devices. Impulse® was found to create two to three times the vertebral accelerations as the other instruments.6 More recently, new research for the first time has recorded what happens during multiple-thrusts, and the 6 Hz frequency of the Impulse® multiple-thrust mode.7 This research reports a 25% increase in vertebral motions during multiple-impulse thrusts. In all, the new developments in instrument adjusting are exciting and on the cutting-edge of instrument adjusting.
Stress. In physics, stress is a measure of the internal distribution of force per unit area. Applying considerations of stress to chiropractic adjustments, imagine blotting your thenar eminence on an ink pad prior to applying your pisiform contact to a patient. The area over which manual forces is applied is quite large, when compared to blotting a 1 cm2 adjusting instrument stylus used to deliver instrument adjustment forces. Because stress equals force divided by area (_ = F/A), smaller segmental contact point areas (such as instrument stylus tips) can localize the force administration, thereby increasing stresses to the target vertebra. Forces, speeds, and stresses are all ways in which chiropractic adjusting instruments utilize mechanical advantages in accomplishing the chiropractic adjustment.
Evidence For Adjusting Instruments
A number of basic science studies have reported vertebral motions, neuromuscular and neurophysiological responses following administration of instrument adjustments.8 Building upon this research, we have begun to validate the benefits of improved speed and frequency input with electromechanical adjusting instruments in an animal model (Figure 3).
Figure 3 (Right). Dr. Chris Colloca applies the Impulse Adjusting Instrument® while 3-D intersegmental vertebral accelerations and needle EMG are measured to study how forces, speeds, and frequencies influence vertebral motions and neuromuscular responses.
Ultimately, understanding how much force at what speed, frequency, and thrusting rate relates to improved clinical outcomes are our basic objectives. Until then, clinical research has continued to demonstrate that patients with back or neck pain seem to improve just as well receiving instrument delivered adjustments as compared to Diversified type spinal manipulation.9-12
References
1. Christensen MG, et al. Job Analysis of Chiropractic 2000. Greeley, CO: National Board of Chiropractic Examiners, 2000.
2. Keller TS, Colloca CJ, Beliveau JG. Force-deformation response of the lumbar spine: a sagittal plane model of posteroanterior manipulation and mobilization. Clin Biomech 2002;17:185-96.
3. Duell M. The Force of the Activator(r) Adjusting Instrument. Digest of Chiropractic Economics 1984;27:17-9.
4. Colloca CJ, Keller TS, Black P, Normand MC, Harrison DE, Harrison DD. Comparison of mechanical force of manually assisted chiropractic adjusting instruments. J Manipulative Physiol Ther 2005;28:414-22.
5. Colloca CJ, Keller TS, Harrison DE, Moore RJ, Gunzburg R, Harrison DD. Spinal manipulation force and duration affect vertebral movement and neuromuscular responses. Clin Biomech 2006;21:254-62.
6. Keller TS, Colloca CJ, Moore RJ, Gunzburg R, Harrison DE, Harrison DD. Three-dimensional intersegmental motion validation of mechanical force spinal manipulation. J Manip Physiol Ther 2006;in press.
7. Keller TS, Colloca CJ, Moore RJ, Gunzburg R, Harrison DE. Increased multiaxial lumbar motion responses during multiple-impulse mechanical force manually assisted spinal manipulation. Chiropr Osteopat 2006;14:6.
8. Colloca CJ, Keller TS, Gunzburg R. Biomechanical and neurophysiological responses to spinal manipulation in patients with lumbar radiculopathy. J Manipulative Physiol Ther 2004;27:1-15.
9. Gemmell HA, Jacobson BH. The immediate effect of Activator vs. Meric adjustment on acute low back pain: a randomized controlled trial. J Manipulative Physiol Ther 1995;18:453-6.
10. Yurkiw D, Mior S. Comparison of two chiropractic techniques on pain and lateral flexion in neck pain patients: a pilot study. Chiropr Tech 1996;8:155-62.
11. Wood TG, Colloca CJ, Matthews R. A pilot randomized clinical trial on the relative effect of instrumental (MFMA) versus manual (HVLA) manipulation in the treatment of cervical spine dysfunction. J Manipulative Physiol Ther 2001;24:260-71.
12. Shearar KA, Colloca CJ, White HL. A randomized clinical trial of manual versus mechanical force manipulation in the treatment of sacroiliac joint syndrome. J Manipulative Physiol Ther 2005;28:493-501.
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