Biomechanical Characteristics of Chiropractic Adjustments

Christopher J. Colloca, D.C.

"There is a preoccupation with outcome and efficiency studies in chiropractic research. Although it is interesting to know that patients receiving chiropractic manipulations fare better than those receiving physiotherapy, or that chiropractic treatments are more cost-effective than back surgery, these facts describe (from a scientific point of view) irrelevant findings. For chiropractic research, a single study that could describe precisely the mechanics, physiology, and neuromuscular responses of a treatment, and that had quantified the healing effect of these responses, would be more use to chiropractic as a profession than any clinical outcome study."

- Walter Herzog, Ph.D., 2000. The Mechanical, Neuromuscular, and Physiologic Effects Produced by Spinal Manipulation. In: Herzog W. Clinical Biomechanics of Spinal Manipulation. Philadelphia: Churchill Livingstone, 2000:206.

Growing consideration has been given in the past 20 years to the biomechanical characteristics of chiropractic adjustments. Most of the interest in this field stems from the necessity of quantifying the forces produced during spinal manipulation to assure the safety of chiropractic adjustments and protect doctors of chiropractic from frivolous malpractice claims of alleged injury.

Bone Movement During Spinal Manipulation in Humans

Tony S. Keller, Ph.D., from the Department of Mechanical Engineering, University of Vermont, conducted pioneering research in the field of in vivo analysis of motions produced during spinal manipulation in human subjects with a group from the University of Göthenburg, Sweden in the early 1990's.

Using an intervertebral motion device (IMD) connected to implanted Steinmann pins in the L3-L4 or L4-L5 spinous processes, intervertebral motions were quantified using a strain gauge (Kaigle et al., 1992).

Dr. Keller and his graduate student published data (Nathan and Keller, 1994)obtained from three subjects: one normal, one patient diagnosed with L4-5 degenerative disk disease, and one patient diagnosed with L5 retrospondylolisthesis to examine differences in spinal motions in response to spinal manipulation among the groups.

Spinal thrusts were delivered to each of the spinous processes (T11-L3) using an Activator Adjusting Instrument equipped with an impedance head and intervertebral displacements were quantified using the IMD.

With this design, posteroanterior dynamic spinal stiffness measurements were obtained from impedance analysis so that correlation could be made to intervertebral motions.

The most spinal motion occurred during the spinal manipulative thrusts in the normal subject.

Thrusts applied to the L2 spinous process in the normal subject (72 +/- 9 N) produced a 1.62 +/- 1.06 mm peak-to-peak intervertebral axial displacement, 0.48 +/- 0.1 mm PA shear displacement, and 0.89 +/- 0.49 degrees FE rotation at the L3-4 spinal segment.

Thoracolumbar PA stiffness values tended to be higher for the patient with a severely degenerated disk (85-362 KN/m), whereas the patient with retrospondylolisthesis had a lower PA stiffness (32-96 KN/m).

Such in vivo kinematic measurements of the normal and pathologic human lumbar spine indicated that low force, PA impulses produce measurable segmental motions and reinforced the notion that mechanical processes play an important role in spinal manipulation and mobilization.

More recently, Dr. Keller and I designed a new study to quantify spinal motions during spinal manipulation.

Specifically, we aimed to examine different segmental contact points, vectors (lines of drive), and excursions that occur during spinal manipulation using a modified chiropractic adjusting Instrument.

In 1999, and 2002 we traveled to Antwerpen, Belgium to collect data from surgical patients with the assistance of orthpaedic spine surgeon, Robert Gunzburg, M.D., Ph.D.

Prior to our departure, Dr. Keller tested a new 6-degree-of-freedom accelerometer system that we could mount to implanted bone pins into the spinous processes to be able to more accurately quantify spinal motions during spinal manipulation.

We then designed the study to account for the variables important to chiropractic clinicians.

Flouroscopic image of special bone pins implanted into adjacent spinous processes of a functional spinal unit and accelerometers mounted in place externally.
In this research, we were able to collect data on 9 surgical patients. Bone pins were placed into the spinous processes of the levels tested using Flouroscopic guidance.

With the hardware in place, we then tested the fixation and the impedance of the pin by plucking it and measuring its inherent mechanical properties as a baseline.

Next, we began our protocol delivering spinal manipulative thrusts with varying segmental contact points, vectors, and force settings (including sham settings).

Data was simultaneously recorded on a laptop computer.

We are currently analyzing the data and preparing the abstracts and manuscripts derived from this work.

You can look forward to several conference presentations and publications in the future from this unique line of study.

Bone pin being plucked to test its fixation and mechanical properties to establish baseline measurements. Needle electromyographic leads are also visualized.

Dr. Chris Colloca delivers a thrust to the spinous process of L5 as intervertebral motions are quantified at the L3-L4 functional spinal unit.

Typical force-time profile of an Activator Adjusting Instrument thrust, and corresponding posteroanterior motion response of the adjacent lumbar vertebrae observed as acceleration profiles.

New Spinal Model

Using original data from our work in human subjects, and the published reports of forces and speeds of other spinal manipulative or mobilization techniques by that of others, Dr. Keller has developed a new spinal model that predicts spinal motions resulting from spinal manipulation with different lines of drive.

We presented this work at the 2000 meeting of the European Society of Biomechanics in August, 2000 in Dublin, Ireland, and at the World Federation of Chiropractic Congress in May, 2001 in Paris. The manuscript from this work appears in the journal, Clinical Biomechanics (2002).

Because numerous spinal manipulation/adjustment and mobilization techniques exist, it is necessary to quantify and model the spines response to the clinician's applied force from a biomechanical standpoint so that we may begin to understand which techniques may be beneficial in different circumstances.

Model results have been compared to force measurements reported during Diversified spinal thrusts, mechanical force-manually assisted spinal thrusts, and quasi-static and oscillatory mobilization procedures that have been reported.

This model has recently been enhanced to include two additional displacement degrees of freedom, (axial displacement and rotation {flexion-extension}) and thorax and pelvis regions have been added.

(L-R )- Chris Colloca, D.C., Tony Keller, Ph.D. and Michelle Anderson, D.C. collected data on 30 patients in 2 days on a new biomechanical assessment project.
As a result, it is now possible to characterize the segmental and intersegmental, sagittal plane motion response of the lumbar spine.

As you might imagine, significant spinal coupling occurs in adjacent vertebrae to the segmental contact point producing quantifiable accompanying motions above and below.

These results are in contrast to traditional chiropractic teachings of contacting one specific bone with the pisiform and moving it from point A to B irrespective of the adjacent segments.

We also believe this work will assist in an understanding of the inherent safety of chiropractic adjustments.

View animations of spine motion response to an mechanical force, manually-assisted adjustment with an Anterior Line of Drive, Anterior-Superior Line of Drive, or an Anterior-Inferior Line of Drive.

We are more excited now than ever at the possibilities that await us in the understanding of just how chiropractic adjustments work from a biomechanical standpoint. We believe that such an understanding will assist in making chiropractic a continued leader in conservative health care.


Kaigle,A.M., Pope,M.H., Fleming,B.C., Hansson,T., 1992. A method for the intravital measurement of interspinous kinematics. J Biomech, 25,(4), 451-456.

Nathan,M. & Keller,T.S., 1994. Measurement and analysis of the in vivo posteroanterior impulse response of the human thoracolumbar spine: a feasibility study. J Manipulative Physiol Ther., 17,(7), 431-441.

For References and Abstracts of Original Research on Biomechanical Characteristics of Chiropractic Adjustments {Link to Publications}

Related Research on Biomechanical Characteristics of Chiropractic Adjustments

Cohen,E., Triano,J.J., McGregor,M., Papakyriakou,M., 1995. Biomechanical performance of spinal manipulation therapy by newly trained vs. practicing providers: does experience transfer to unfamiliar procedures? J Manipulative Physiol Ther, 18,(6), 347-352.

Colloca,C.J., Keller,T.S., Seltzer,D.E., Fuhr,A.W., 2000. Mechanical impedance of the human lower thoracic and lumbar spine exposed to in vivo posterior-anterior manipulative thrusts. Proceedings of the 12th Conference of the European Society of Biomechanics, August 10-14, 2000, Dublin.

Colloca,C.J., Keller,T.S., Fuhr,A.W., 1999. Muscular and mechanical behavior of the lumbar spine in response to dynamic posteroanterior forces. Proceedings of 25th Annual Meeting of the The International Society for the Study of the Lumbar Spine, Kona, Hawaii. Toronto: ISSLS; 1999: p.136A..

Colloca CJ, Fuhr AW. Movements of vertebrae during manipulative thrusts to unembalmed human cadavers (Letter). J Manipulative Physiol Ther 1998; 21(2):128-9. (RE: Gal J, Herzog W, Kawchuk G, Conway PJ, Zhang YT. J Manipulative Physiol Ther 1998; 20(1):30-40.)

Gal,J., Herzog,W., Kawchuk,G., Conway,P.J., Zhang,Y.T., 1997. Movements of vertebrae during manipulative thrusts to unembalmed human cadavers. J Manipulative Physiol Ther, 20(1), 30-40.

Gal,J.M., Herzog,W., Kawchuk,G.N., Conway,P.J., Zhang,Y.T., 1995. Forces and relative vertebral movements during SMT to unembalmed post- rigor human cadavers: peculiarities associated with joint cavitation. J Manipulative Physiol Ther, 18(1), 4-9.

Gudavalli,M.R. & Triano,J.J., 1999. An analytical model of lumbar motion segment in flexion. J Manipulative Physiol Ther, 22(4), 201-208.

Haas,M. & Nyiendo,J., 1992. Lumbar motion trends and correlation with low back pain. Part II. A roentgenological evaluation of quantitative segmental motion in lateral bending. J Manipulative Physiol Ther, 15(4), 224-234.

Herzog,W., 1993. The physics of spinal manipulation: work-energy and impulse-momentum principles. J Manipulative Physiol Ther, 16(1), 51-54.

Herzog,W., 1996. Mechanical, Physiologic, and Neuromuscular Considerations of Chiropractic Treatments. In: Lawrence,D.J., Cassidy,J.D., McGregor,M., Meeker,W.C., Vernon,H.T. (Eds.), Advances in Chiropractic, pp. 269-285. Mosby-Year Book, Inc., St. Louis.

Herzog,W., 1996. On sounds and reflexes. J Manipulative Physiol Ther, 19(3), 216-218.

Herzog,W., 1998. Movements of vertebrae during manipulative thrusts to unembalmed human cadavers [letter; comment]. J Manipulative Physiol Ther, 21(5), 373-374.

Herzog,W., 2000. The Mechanical, Neuromuscular, and Physiologic Effects Produced by Spinal Manipulation. In: Herzog,W. (Ed.), Clinical Biomechanics of Spinal Manipulation, pp. 191-207. Churchill Livingstone, Philadelphia.

Herzog,W., Conway,P.J., Kawchuk,G.N., Zhang,Y., Hasler,E.M., 1993b. Forces exerted during spinal manipulative therapy. Spine, 18(9), 1206-1212.

Herzog,W., Zhang,Y.T., Conway,P.J., Kawchuk,G.N., 1993a. Cavitation sounds during spinal manipulative treatments. J Manipulative Physiol Ther, 16(8), 523-526.

Hessell,B.W., Herzog,W., Conway,P.J., McEwen,M.C., 1990. Experimental measurement of the force exerted during spinal manipulation using the Thompson technique. J Manipulative Physiol Ther, 13(8), 448-453.

Kawchuk,G.N. & Herzog,W., 1993. Biomechanical characterization (fingerprinting) of five novel methods of cervical spine manipulation. J Manipulative Physiol Ther, 16(9), 573-577.

Kawchuk,G.N., Herzog,W., Hasler,E.M., 1992. Forces generated during spinal manipulative therapy of the cervical spine: a pilot study. J Manipulative Physiol Ther, 15(5), 275-278.

Keller,T.S., Colloca,C.J., 2000. Dynamic response of the human lumbar spine: a 5 degree-of-freedom lumped parameter time and frequency domain model. Proceedings of the 12th Conference of the European Society of Biomechanics. Trinity College, Dublin, Ireland, August 27-30, 2000: 395.

Keller,T.S. & Colloca,C.J., 2000. Mechanical force spinal manipulation increases trunk muscle strength assessed by electromyography: A comparative clinical trial. J Manipulative Physiol Ther. In press.

Keller,T.S., Colloca,C.J., 2000. Mechanical force spinal manipulation increases trunk muscle strength assessed by electromyography: A comparative controlled clinical trial. Proceedings of the 27th Annual Meeting of the International Society for the Study of the Lumbar Spine, Adelaide, Australia, April 9-13, 2000.

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.

Kirstukas,S.J. & Backman,J.A., 1999. Physician-applied contact pressure and table force response during unilateral thoracic manipulation. J Manipulative Physiol Ther, 22(5), 269-279.

Lee,M., Latimer,J., Maher,C., 1993. Manipulation: investigation of a proposed mechanism. Clin Biomech, 8(6), 302-306.

Nathan,M. & Keller,T.S., 1994. Measurement and analysis of the in vivo posteroanterior impulse response of the human thoracolumbar spine: a feasibility study. J Manipulative Physiol Ther, 17(7), 431-441.

Solinger,A.B., 1996. Oscillations of the vertebrae in spinal manipulative therapy. J Manipulative Physiol Ther, 19(4), 238-243.

Solinger,A.B., 2000. Theory of small vertebral motions: an analytical model compared to data. Clin Biomech, 15(2), 87-94.

Triano,J., 2000. The Mechanics of Spinal Manipulation. In: Herzog,W. (Ed.), Clinical Biomechanics of Spinal Manipulation, pp. 92-190. Churchill Livingstone, Philadelphia.

Triano,J.J., 1992. Studies on the biomechanical effect of a spinal adjustment. J Manipulative.Physiol Ther, 15(1), 71-75.

Triano,J.J. & Schultz,A.B., 1994. Motions of the head and thorax during neck manipulations. J Manipulative Physiol Ther, 17(9), 573-583.

Triano,J.J. & Schultz,A.B., 1997. Loads transmitted during lumbosacral spinal manipulative therapy. Spine, 22, 1955-1964.

Vicenzino,B., Neal,R., Collins,D., Wright,A., 1999. The displacement, velocity and frequency profile of the frontal plane motion produced by the cervical lateral glide treatment technique. Clin Biomech, 14(8), 515-521.

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