A Response to an Article entitled
"The Measurement of Forces to the Cervical Spine During
Gary N. Lewkovich, DC and Michael Blott, DC
We were recently sent, from several sources, an article published in May 1999 by the American Chiropractic Associationís Council on Chiropractic Orthopedics. This article is entitled "The Measurement of Forces to the Cervical Spine During Spinal Manipulation"1 (hereafter referred to as "the article"). As unthreatening as the title sounds, even a cursory analysis of the content proved otherwise.
The main point of the article, though somewhat unclear, appears to be that the forces involved in a "minor" motor vehicle accident may be less than a cervical spinal manipulation. While it seems obvious that there must be some degree of overlap in the range of forces in both types of motions, the implications of this conclusion are ripe for misuse by defense-oriented experts. A closer look at the specifics of the article revealed major flaws in its design, definitions, and conclusions. Some of these flaws were so significant, in our opinion, that we are forced to question both the motives of the author and the peer review process involved in its publication.
In the short space allotted here, it is difficult to systematically review the six pages of the article. This task is made more difficult by the fact that most people reading this review will not have read the subject of the review. (The article should be available by contacting: Jennnifer L. Martin, D.C., FACO 916-448-1700) With these limitations in mind, we have decided to selectively quote passages or summarize aspects of the article under various "fault headings" as a means of supporting our contentions.
Three basic categories of faults are outlined here. It is our opinion that all research articles must, at the vary least, avoid all of these shortcomings. Failure to achieve this standard severely compromises any studyís usefulness and acceptance. Poor research has no place in any discipline, especially when it can be misapplied in medlegal settings, thereby jeopardizing patient care.
The authorís stated goal was to measure the g forces to the cervical spine during high-velocity cervical spinal manipulation, using a lowĖg accelerometer. In this endeavor, the following occurred:
1. Eight subjects were used: This is a very limited sample size, making any generalization to the overall population highly suspect.
2. Age of subjects was not controlled: Age of subjects ranged from 15-49, with a mean age of 32.6 years. There were no subjects over 50. Obviously, both the range and average is not representative of the typical chiropractic patient population.
3. All were healthy, asymptomatic, and screened for a history of serious cervical complaints: This represents a biased sampling, which is highly atypical of the patient population coming to a chiropractic office. A typical chiropractic patient is in pain, warranting gentle spinal manipulation due to the nature of his/her condition. Manipulation to a healthy, asymptomatic patient may be more forceful because is it more easily tolerated.
4. All subjects were informed of what was to occur: Thus, each was aware that he or she was about to receive a force delivered to the neck. This is atypical of what commonly occurs in a rear-end motor vehicle collision, where there is no awareness of the impending impact. Without awareness, the muscles of the neck do not have the opportunity to protectively guard the area.2,3 Therefore, any comparison with non-aware subjects is highly suspect.
5. All subjects were tested in a well supported, supine position: When making any comparison of forces and their possible effects, it is vital to compare apples with apples. In this study, each subject was tested lying on his or her back, and each subjectís head was well supported by the adjuster. A motor vehicle accident victim rarely has the advantage of both of these factors. If a motor vehicle occupant could have a well supported head in a supine position, then the injury threshold, in terms of applied acceleration, would rise dramatically.
6. Apparently, all manipulation was performed by one person: Assuming it was the author performing the manipulation, we know almost nothing of her technique, finesse, or relative "forcefulness". Thus, any extrapolation to the chiropractic profession in general is suspect.
7. The head was placed in rotation, extension, and lateral flexion: The positioning inherent to the manipulation assures minimal stress on the soft tissue, with maximal input to releasing the dysfunction of the facets. Spinal manipulation is a precise procedure, using a precise amount of force, directed in a precise direction, and requires years of training to perfect. The motions involved in motor vehicle collision are highly variable and imprecise, with considerable stress on the soft tissues. With such inherent differences in both movements, any comparison of the likelihood of trauma resulting from even remotely similar g forces is near meaningless.
8. The acceleration forces to the center of mass of the head are assumed to be a "good barometer" of acceleration in the cervical spine: There are no references offered supporting this assumption and no rationale provided. Furthermore, the precise cradling involved in manual spinal manipulation may negate any meaningful comparison with an unsupported head. Furthermore, the acceleration alone is not the sole determinant of injury. How these forces are applied relative to the involved tissues, the physiologic state of the involved tissues, and the duration of the acceleration are all part of the injury threshold equation.4 Thus, a direct comparison to the acceleration measured in this study that reported in a totally different setting, such as a motor vehicle collision, is biomechanically of little use.
The meaning ascribed to key terms in any article determine the applicability of the researcherís conclusions. Key terms are not properly defined in the article, as outlined below:
9. From the introduction: "Trauma to cervical spine soft tissue is defined as a force that exceeds normal movement or position of the cervical spine. For trauma to be symptomatic it must surpass the elasticity or plasticity of the involved tissues, releasing chemical substances from the nociceptor." This definition appears to eliminate trauma due to blunt impact or compression injuries. As a recent study has shown, facet jamming injuries may be a major source of pain and other symptoms in an MVA.5 A properly performed chiropractic manipulation would typically release stress on the involved facets, making any comparison to the g forces of a motor vehicle near meaningless.
10.From the introduction: "The consideration of injury sustained following a significant moderate to high-speed rear-end accident is not included in this paper, as many of the presenting symptoms would contraindicate spinal manipulation." What constitutes a "moderate to high-speed" collision is not defined. The author makes reference to a low speed collision, defined by McConnell, as those impacts in which the DVís are 8 mph or less. This is only one of several definitions of what constitutes a "low impact" collision. Additionally, exactly what presenting symptoms would contraindicate spinal manipulation is not detailed. Furthermore, exactly what type of spinal manipulation would be contraindicated is not specified. Some forms of manipulation are extremely gentle and may not be contraindicated except in the most extreme of cases.
There are multiple conclusions in the article. Some apparently represent the authorís interpretation of the literature. Others are conclusions apparently based upon interpretation of the authorís research data. It is our opinion that several of these conclusions are either unsupported by the current literature or are not logical interpretations of the data presented in the article.
11. From the abstract: "Evidence is conclusive regarding physiotherapy treatment and reduction in patientís pain perception as well as decreased muscle spasm. How did the author determine the evidence was "conclusive"? There are no references to support the authorís position on the effectiveness of physiotherapy. What is meant by physiotherapy is not defined. Are all forms of mobilization included in the definition?
12.From the introduction: "Comprehensive studies regarding subjective complaints of rear-end accident victims have concluded that the height of the seatís back, predisposing physiological factors, head position, and subsequent forward movement of the vehicle all contribute to the onset of symptoms." Again, no references are provided. The list appears significantly incomplete, omitting such factors as distance from head restraint, lack of a head restraint, type of seat, use of seat belt and shoulder restraints, multiple impacts, and collisions with heavier vehicles.6 Most noticeably lacking is the factor of awareness of the impending impact.7 In fact, research subjects are almost always aware of the impending impact, making suspect any conclusions based upon such experiments.
13. From the introduction: "Nevertheless, the consensus generally agrees" (sic) "that minor-strain injury as a result of low-impact MVA is self-resolving and requires little, if any, treatment before resolution: This conclusion is highly ambiguous and is presented without a single reference. We are sure that the consensus of the chiropractic profession is not the same consensus to which the author is referring.
14. From the introduction: "The results of this study" (Szabo, et al) "conclusively outlined the lack of any injuries to the subjects following minor impacts." A single study, even under the most perfect of conditions, is not "conclusive". The study8 referred to only had 5 subjects, these subjects were nonrepresentative of the general population, and the study design was deemed inappropriate in a major study.9 But these facts aside, the author of the article has misstated the facts of the article referred to. In reality, there was transient headache and minor neck stiffness the morning after the test reported by at least one subject, representing at least 20% of the sample group.10
15. From the discussion: "Obviously, inferred through these measurements of acceleration are the forces to the structures in the cervical spine." This conclusion lacks foundational support and is highly suspect for reasons previously delineated.
16. From the discussion: "As seen with minor MVAís, acceleration forces of 0.5 Ė 5 g forces are described; these g forces are potentially less than those following high-velocity manipulation." Common sense would dictate that there must be some degree of overlap in the range of forces involved in both motions, especially when the low end acceleration of an MVA is arbitrarily listed as "0.5" g.
The stated purpose of the article was to measure the g forces to the cervical spine during high-velocity cervical spinal manipulation, using a lowĖg accelerometer. In our review of this attempt, it is our opinion that only one conclusion can accurately be drawn from this study: acceleration forces from one chiropractorís manipulation were measured at the head in a limited number of subjects. Any extrapolation beyond this conclusion is not supported by this study. The design, definitions, and conclusions presented in the article are, in our opinion, highly questionable.
Each reader must judge for him or herself the possible motives involved in writing the article. In that pursuit, it might be of value to consider how a defense expert or insurance company might misuse or misapply just one of its unsupported conclusions.
For instance, if the forces of a spinal manipulation are assumed to be potentially greater than those experienced in a motor vehicle accident, then there are at least two misleading statements that could be made. First, that spinal manipulation is as likely to injure the neck as the force of the motor vehicle accident itself. If this were true, then the 93% success rate of spinal manipulation in whiplash patients is difficult to explain.11 Second, if a manipulation is extremely safe and the forces involved in its application are potentially greater than a whiplash, then how can a whiplash injure a neck? As we have already outlined, this reasoning is just another example of comparing apples with oranges. But while a person trained in trauma and biomechanics can easily see past all this, an untrained jury member could easily be confused.
The purpose of research is to enlighten, not to confuse. Chiropractic, like all of healthcare, should welcome more research. However, pseudo-research has no place in the profession. It is hoped that future studies will avoid the myriad of flaws displayed in the current endeavor. Additionally, it is our opinion that a scientifically accepted peer review system would have prevented the appearance of such an article in the first place.
1. Martin JL, The Measurement of Forces to the Cervical Spine During Spinal Manipulation, Orthopedic Brief of the Council on Chiropractic Orthopedics, May 1999: 1-6.
2. Chandler RF, Christian RA: "Crash Testing of Humans in Automobile Seats", Society of Automotive Engineers (SAE No. 700361), 112-132, 1970.
3. Seemann MR, Lustick LS, Frisch GD: "Mechanism for Control of Head and Neck Dynamic Response", Proceedings of the 28th Stapp Car Crash Conference (SAE No. 841669), 207-222.
4. Szabo TJ, "Comparative Activities", from Collision Reconstruction for the Medical Practitioner, Texas Engineering Extension Service, Texas A&M University, 1998:section 11, pg. 1-2.
5. Kaneoka K, Ono K, Inami S, Hayashi K, Motion Analysis of Cervical Vertebrae During Whiplash Loading, Spine 24(8):763-70.
6. Nordhoff, LS, Motor Vehicle Collision Injuries: Mechanism, Diagnosis, and Management. Gaithersburg, Maryland; Aspen Publications; 1996: 280-319.
7. Ryan GA, Moore VM, Dolinas J, Crash Severity and Neck Strain in Car Occupants, In: International Conference on the Biomechanics of Impacts, Lyon, France; 1994.
8. Szabo, TJ, et al., Human Occupant Kinematic Response to Low Speed Rear-end Impacts", Society of Automotive Engineers SP-925 (SAE No. 940532) 23-35, 1994.
9. Freeman MD, Croft AC, Rossignol AM, Weaver DS, Reiser M, A Review and Methodologic Critique of the Literature Refuting Whiplash Syndrome, Spine 24(1)86-96.
10. Davis, GC, Rear-End Impacts: Vehicle and Occupant Reponses, JMPT 21(9):634, 1998.
11. Woodword MN, Cook JCH, Gargan MF, Mannister GC, Chiropractic Treatment of Chronic Whiplash Injury, Injury: International Journal of the Care of the Injured, 27(9):643-645, 1996.
This article was peer reviewed by Michael Sackett, DC, DABCO, QME; Jeff Ross, DC, QME; and Ted Rosen, DC, QME.