How does chiropractic work?

Recently I was engaged in a discussion on a website with a group of people who were claiming that chiropractic is “pseudoscientific bunk” and “People who believe in chiropractic are like believers in any particular religion; you can argue with them all you want, bring up science and facts, but in the end it doesn’t matter. It comes down to belief, not understanding.”

This reminded me of a quote from E. B. White: “Prejudice is a great time saver. You can form opinions without having to get the facts.”  I realized that most of these people are just poorly informed.  So, I have decided to present the “science and facts” with regard to chiropractic manipulation.

I’m going to try to explain things as clearly as I can.  In the interest of brevity I will not include references, but feel free to contact me if you have questions or if you’d like the specific peer-reviewed references I used to build this post. 

First off, I feel the need to make this point: Everybody wants to focus on spinal manipulation when it comes to chiropractic, but that’s not all we do.  In my office I perform treatments like ultrasound when appropriate, soft-tissue techniques, joint mobilization, post-isometric stretching, McKenzie protocols, athletic taping, etc.  For a lot of patients I don’t even manipulate the spine. And, I have a complete exercise rehabilitation facility where we work on everything from core strengthening to shoulder and knee injuries.

Furthermore, chiropractors are trained and licensed to diagnose. I perform complete health histories and physical exams. For example, in my headache patients I perform opthalmoscopic exams and check cranial nerves. I also perform standard orthopedic test and do things like palpation, auscultation, and percussion. I also perform pre-employment physicals. I routinely order X-rays, MRI, MRA, CT, blood work, diagnostic ultrasounds, etc. For non-musculoskeletal conditions I refer to internists or specialists. For musculoskeletal conditions that are beyond my scope or are not responding as expected I obtain orthopedic consults.

Now on to the meat of the article:  How does chiropractic manipulation work?

The “subluxation complex”:  For many years, the chiropractic profession has referred to the concept of a “subluxation”.  The definition and understanding of the “subluxation” has changed a great deal over the years but our current concept is this:  The subluxation complex is a dysfunction of the normal motion in a spinal segment.  Aberrant motion in these joints impacts the surrounding musculature and connective tissue as well as local blood vessels and nervous tissue.  Additionally, when joints are not moving normally this can lead to the development of adhesions (sort of like scar tissue) in the zygapophysial (Z) joints.  Among the ways that this can happen is by direct injury to the joint which limits its motion or via straining the surrounding musculature which causes pain and spasm that prevents the Z joint from moving normally.  This can also happen more gradually as in the case of degenerative joint disease (aka osteoarthritis).  In support of this hypothesis, several scientific studies have identified adhesions and degenerative changes in the Z joints after hypomobility.   Further, studies show that the Z joint capsule receives significant sensory innervation and between 15% and 40% of chronic low back pain is related to the Z joints.

Mechanical actions on the joint and IVF: Spinal manipulation is also sometimes referred to as HVLA (high-velocity, low-amplitude) which means that the force is generated by performing the manipulation at a high velocity but with tightly controlled amplitude.  Numerous studies have examined the specific forces involved in HVLA manipulation.  Researchers have also shown that the Z joints gap significantly during manipulation and that this allows for improved motion in the spinal segment. As the joint is gapped during HVLA, a rapid increase in joint capsule volume is associated with a corresponding drop in the capsule pressure (ideal gas law).  As pressure drops in the capsule, some of the liquid synovial fluid quickly converts into gas resulting in a “popping” sound.  This creates a bubble of gaseous synovial fluid in the joint that helps keep the joint gapped which decreases pressure in associated intravertebral foramena (IVF) as the bubble gradually dissolves back into liquid. 

Substantial evidence has demonstrated that the dorsal roots and dorsal root ganglia are susceptible to the effects of mechanical compression.   Compressive loads as low as 10 mg applied to dorsal roots can increase the discharge of incoming (afferent) nerve fibers.  Compression on the nerve root can also alter non–impulse-based mechanisms (eg, axoplasmic transport) and cause edema and hemorrhage.  So at the most basic level, spinal manipulation mechanically opens the IVF which decreases pressure on the dorsal nerve roots. 

Neurological actions:  In muscles, there is a specific type of proprioceptor called a muscle spindle muscle spindles γ (gamma) motoneurons Spinal manipulation also helps increases joint mobility by producing a barrage of impulses in muscle spindle afferents and smaller-diameter afferents ultimately silencing facilitated as proposed by Korr http://www.jaoa.org/cgi/reprint/74/7/638.  This theory is supported by several recent studies by the Pickar lab and by findings that low back pain patients have altered proprioceptive input from muscle spindles.   Recent work has also shown that that spinal manipulation modifies the discharge of Group I and II afferents.  This has been accomplished by recording single-unit activity in muscle spindle and Golgi tendon organ afferents in an animal model during manipulation. 

Substantial evidence also shows that spinal manipulation activates paraspinal muscle reflexes and alters motoneuron excitability. These effects are still being studied and appear to differ depending on whether performed on patients in pain or pain-free subjects. Maniupulation also inhibits somatosomatic reflexes by alterating muscle spindle input. It is thought that spinal manipulation may normalize spindle biomechanics and improve muscle spindle discharge.

β-endorphin mechanisms. Studies have shown increases in β-endorphin levels after spinal manipulation but not after control interventions. This is still being debated because results have been variable and a recent study failed to show increased β-endorphins even though subjects had decreased pain.

Additional effects:  Lastly, in humans, manual therapies can decrease heart rate and blood pressure while increasing vagal afferent activity as measured by heart-rate variability. Manual therapies in rats have been shown to produce an inhibitory effect on the cardiovascular excitatory response and reduce both blood pressure and heart rate. Manual therapies such as massage have been shown to impact behavioral manifestations associated with chronic activation of the HPA axis such as anxiety and depression, while decreasing plasma, urinary, and salivary cortisol and urinary corticotropin releasing factor-like immunoreactivity (CRF-LI). Manual stimulation in rats has been shown to significantly increase glucocorticoid receptor gene expression which enhanced negative feedback inhibition of HPA activity and reduced post-stress secretion of ACTH and glucocorticoid.

Choose 'Treatment A'

Imagine that you’re a physician comparing two possible treatments for a patient: 'Treatment A' or 'Treatment B'.  You review the medical literature and find that the most current evidence from multiple trials and systemic reviews shows that 'Treatment A' is effective [1-7].  In fact, studies that have directly compared 'Treatment A' with 'Treatment B' have found that 'Treatment A' was both more effective and less costly than 'Treatment B' [5-7].  You also find studies indicating that 'Treatment A' is much safer than 'Treatment B'.  The risk of death from 'Treatment A' estimated at about 0.27 -10 per million [8-10] while the risk for death for 'Treatment B' is estimated at about 400-2800 per million [11-13].

Assuming there are no direct contraindications for either treatment, which of the following courses of action would you choose?      

1. Recommend 'Treatment A' to your patients; or, 
2. Recommend 'Treatment B' to your patients and write an article in Readers Digest and a blog post warning people that they should stay away from 'Treatment A' because it’s ineffective and risky

Let me introduce you to a physician who chose option 2, “PalMD”.  PalMD recently tweeted a link to his blog post "Stay Away from Chiropractic Neck Manipulation". In this post he was responding to a chiropractor who accused PalMD of lying when he asserted in Readers Digest that, "Over the years, a number of my patients have had strokes after chiropractic neck manipulation." In this very real example, 'Treatment A' = chiropractic manipulation and 'Treatment B' = non-steroidal anti-inflammatory medications (NSAID).

While I can’t prove that PalMD is lying, I can certainly demonstrate that he’s at best uninformed.  PalMD states that “While I don’t recommend chiropractic treatment to my patients, for those who use it I give them this information.  I succinctly tell them that they should not let a chiropractor manipulate their neck.  It’s just not worth it.  I do the same for “mainstream” medical therapies whose risk benefit ratios are not favorable.  It’s just good medicine.” Really?  Is that so? I’m curious to know whether PalMD has ever prescribed NSAIDs for neck pain.  If not, then what treatment is he prescribing? 

Regarding effectiveness: PalMD states that “The best literature has failed to show a significant benefit of chiropractic neck manipulation vs. more conservative therapy for the treatment of neck pain.”  This is patently false:

• A literature review of quality clinical trials (scoring above 11.5 on the Amsterdam-Maastricht Scale) found that “There is moderate- to high-quality evidence that subjects with chronic neck pain not due to whiplash and without arm pain and headaches show clinically important improvements from a course of spinal manipulation or mobilization at 6, 12, and up to 104 weeks posttreatment.”[1]
• A literature (Cochrane) review from 2004 found that mobilization and/or manipulation when used with exercise are beneficial for persistent mechanical neck disorders [3]
• A literature (Cochrane) review  from 2010 found that cervical manipulation and mobilisation may provide immediate- or short-term improvement in pain and function [4]
•  A clinical trial comparing manipulation with acupuncture and medication found that: “In patients with chronic spinal pain, manipulation, if not contraindicated, results in greater short-term improvement than acupuncture or medication.” The highest proportion of early (asymptomatic status) recovery was found for manipulation (27.3%), followed by acupuncture (9.4%) and medication (5%). [5]
• In a study evaluating the long-term benefits of medication (NSAIDs), acupuncture, and spinal manipulation researchers concluded that: “In patients with chronic spinal pain syndromes, spinal manipulation, if not contraindicated, may be the only treatment modality of the assessed regimens that provides broad and significant long-term benefit.” [6]
• A review published in the British Medical Journal concluded that, “Manual therapy (spinal mobilisation) is more effective and less costly for treating neck pain than physiotherapy or care by a general practitioner.” [7]

Regarding risk:  PalMD states that “the evidence in the literature is quite clear: vertebral artery dissection (VAD), a type of stroke, is associated with chiropractic neck manipulation”.  Again, this is incorrect.  The current best evidence is the association between spinal manipulation and stroke is coincidental rather than causal. In fact, the most recent study concluded that “relying on case series or surveys of health care professionals may provide a biased view of who develops a VBA stroke” [14].  The largest population-based study to date was published in 2009 and included all vertebrobasilar artery (VBA) strokes in Ontario, Canada over a period of 9 years.  The authors concluded that “We found no evidence of excess risk of VBA stroke associated chiropractic care compared to primary care.” [15]

Even if we use PalMD’s own statistic on strokes of “perhaps 1.5/100,000 manipulations”, PalMD concedes that chiropractic is extremely safe.  However, the actual scientific literature puts the risk much lower at 0.027- 1 death per 100,000 (0.27-10 per million) [8-10]   When you compare this with the estimated risk of death from NSAIDs (400-2800 per million) [11-13], chiropractic is much, much safer than prescribing NSAIDS.    In fact, just getting your blood drawn is far more dangerous than spinal manipulation, causing roughly 40 deaths per million [16].

• A study from 2006 showed that the risk of stroke from any NSAID = 3815 per million, the risk of vascular death from any NSAID=2786 per million, and the risk of heart attack from any NSAID = 3644 per million [12].
• A 2002 review looked at severe gastrointestinal complications from NSAID use and found that risks ranged from 27,000 to 53,000 per million [13]

Let’s specifically take a look PalMD’s references.  PalMD’s first reference [17] analyzed data from a countrywide survey of 21 neurological departments at university hospitals in Germany over a three year period of time.  Over this 3 year period, 36 patients were identified who had a stroke within 2 days following cervical manipulation.  Let’s put that in perspective shall we?  The annual incidence rate of stroke in Germany is 1.34 per 1000 [18].  The population of Germany is 81,751,602.  This means that over a 3 year period we would expect approximately 109,000 strokes per year; and well over 300,000 strokes over a 3 year period.  It becomes very clear that stroke following chiropractic manipulation is exceedingly rare.  And, if we look closer at the actual data from that study we see that even in the rare instance that manipulation was related to stroke, the majority of patient outcomes were generally mild:

• 6 of the 36 patients had no neurological deficit when they were admitted
• 10 of the remaining 30 patients were discharged within 2 days with zero clinical neurological deficits. 
• In total, 21 of the 36 patients identified in this study had either zero neurological impairment, or “no significant disability”
• Of the remaining 15 patients who had some disability, 6 of those had only mild disability and were “able to look after own affairs without assistance”

This means that over a 3 year period in a country with a population of more than 81 million people, only 1 patient died following chiropractic manipulation and 8 patients were discharged with moderate to severe impairment.  

Let’s look at another of PalMD’s references.  In the Rothwell study, they looked at hospitalization records to identify VBA stroke patients in Ontario, Canada over a 5 year period [10].  Here is a direct quote from the authors: “VBA is a rare form of stroke. Despite the popularity of chiropractic therapy, the association with stroke is exceedingly difficult to study. Even in this population-based study the small number of events was problematic. Of the 582 VBA cases, only 9 had a cervical manipulation within 1 week of their VBA.”  That’s 9 patients in 5 years!  This is a very tiny number by any measure.  The authors go on to state: “VBAs are rare events with potentially dire consequences. When they occur in otherwise healthy young adults, the natural tendency to seek explanation (recall or rumination bias) may exaggerate the apparent association with use of chiropractic services.” 

Another of PalMD’s references [19] is more than a decade old and studied VBA stroke 74 patients in Canada over the course of a year.  The data from this study showed that in 68% of these stroke cases the patient had not seen a chiropractor.  In the majority of cases, the stroke occurred after such activities as: ”vigorous game of volleyball” or “mild exertion such as lifting a pet dog or during a bout of coughing.”

I certainly feel for patients who suffer a stroke for any reason and I take every precaution in my office to screen for risk factors.  I also understand that there are some patients who have suffered a stroke following chiropractic manipulation.  The fact remains that any medical intervention carries with it some risk, however small.  I completely agree with PalMD that physicians should weigh the “risk benefit ratios” of treatments.  I think it’s clear that the preponderance of evidence shows that 'Treatment A' far surpasses 'Treatment B' in this regard. 

Unfortunately, physicians like PalMD continue to perpetuate an irrational fear of chiropractic while they repeatedly prescribe the poorer 'Treatment B'.  These are often the same doctors bleating about “evidence-based medicine.”  Personally, I’d like to believe that PalMD isn't a bad guy and that he's truly interested in the scientific evidence and in his patients’ health.  Perhaps he was simply uninformed and didn’t actually read the references he provided.  If that’s the case, I’m certain PalMD will begin referring appropriate patients for the far safer, more effective 'Treatment A' - chiropractic manipulation.

1.         Vernon, H., K. Humphreys, and C. Hagino, Chronic Mechanical Neck Pain in Adults Treated by Manual Therapy: A Systematic Review of Change Scores in Randomized Clinical Trials. Journal of manipulative and physiological therapeutics, 2007. 30(3): p. 215-227.

2.         Martinez-Segura, R., et al., Immediate Effects on Neck Pain and Active Range of Motion After a Single Cervical High-Velocity Low-Amplitude Manipulation in Subjects Presenting with Mechanical Neck Pain: A Randomized Controlled Trial. Journal of manipulative and physiological therapeutics, 2006. 29(7): p. 511-517.

3.         Gross, A.R., et al., A Cochrane Review of Manipulation and Mobilization for Mechanical Neck Disorders. Spine, 2004. 29(14): p. 1541-1548 10.1097/01.BRS.0000131218.35875.ED.

4.         Gross, A., et al., Manipulation or Mobilisation for Neck Pain. . Cochrane Database of Systematic Reviews, 2010. Reviews 2010(1).

5.         Giles, L.G.F. and R. Muller, Chronic Spinal Pain: A Randomized Clinical Trial Comparing Medication, Acupuncture, and Spinal Manipulation. Spine, 2003. 28(14): p. 1490-1502.

6.         Muller, R. and L.G.F. Giles, Long-Term Follow-up of a Randomized Clinical Trial Assessing the Efficacy of Medication, Acupuncture, and Spinal Manipulation for Chronic Mechanical Spinal Pain Syndromes. Journal of manipulative and physiological therapeutics, 2005. 28(1): p. 3-11.

7.         Korthals-de Bos, I.B.C., et al., / Cost effectiveness of physiotherapy, manual therapy, and general practitioner care for neck pain: economic evaluation alongside a randomised controlled trial / Commentary: Bootstrapping simplifies appreciation of statistical inferences. BMJ, 2003. 326(7395): p. 911-914.

8.         Hurwitz, E.L., et al., Manipulation and Mobilization of the Cervical Spine: A Systematic Review of the Literature. Spine, 1996. 21(15): p. 1746-1759.

9.         Haldeman, S., et al., Arterial Dissections Following Cervical Manipulation: The Chiropractic Experience. Canadian Medical Association Journal 2001. 165(7): p. 905-906.

10.       Rothwell, D.M., et al., Chiropractic Manipulation and Stroke : A Population-Based Case-Control Study. Stroke, 2001. 32(5): p. 1054-1060.

11.        Dabbs, V. and W. Lauretti, A Risk Assessment of Cervical Manipulation vs. NSAIDs for the Treatment of Neck Pain. J Manipulative Physiol Ther, 1995. 18(8): p. 530-536.

12.       Kearney, P.M., et al., Do selective cyclo-oxygenase-2 inhibitors and traditional non-steroidal anti-inflammatory drugs increase the risk of atherothrombosis? Meta-analysis of randomised trials. BMJ, 2006. 332(7553): p. 1302-1308.

13.       Ofman, J.J., et al., A metaanalysis of severe upper gastrointestinal complications of nonsteroidal antiinflammatory drugs. The Journal of Rheumatology, 2002. 29(4): p. 804-812.

14.       Choi, S., et al., A Population-Based Case-Series of Ontario Patients Who Develop a Vertebrobasilar Artery Stroke After Seeing a Chiropractor. Journal of manipulative and physiological therapeutics, 2011. 34(1): p. 15-22.

15.       Cassidy, J.D., et al., Risk of Vertebrobasilar Stroke and Chiropractic Care: Results of a Population-Based Case-Control and Case-Crossover Study. Journal of manipulative and physiological therapeutics, 2009. 32(2): p. S201-S208.

16.       Horowitz, S., Peripheral Nerve Injury and Causalgia Secondary to Routine Venipuncture. Neurology, 1994 (May). 44(5): p. 962-964.

17.       Reuter, U., et al., Vertebral artery dissections after chiropractic neck manipulation in Germany over three years. Journal of Neurology, 2006. 253(6): p. 724-730.

18.       Kolominsky-Rabas, P.L., et al., A Prospective Community-Based Study of Stroke in Germany—The Erlangen Stroke Project (ESPro) : Incidence and Case Fatality at 1, 3, and 12 Months. Stroke, 1998. 29(12): p. 2501-2506.

19.       Norris, J.W., et al., Sudden neck movement and cervical artery dissection. Canadian Medical Association Journal, 2000. 163(1): p. 38-40.

When to ignore your MRI results

I can't tell you how many times a patient has come to my office and told me "My doctor ordered an MRI and I have a disc bulge at so-and-so level, so that's where my pain is coming from." Or they say "I had an MRI years ago and it showed disc degeneration at L4/L5 so I know my back will never really be fixed." However, when I perform an examination I very often find that the disc is not the cause of their pain. When I try to explain this to them they're usually nonplussed.

In my opinion we need to stop taking so many MRIs on patients with back pain. Why? For the vast majority of low back pain cases MRIs do more harm than good. "How is that possible?” you might ask, "Don't you want as much information as you can get?"

While diagnostic studies like MRI can be helpful in making a diagnosis, they need to be placed in context with the rest of the clinical picture. A detailed history and physical examination are extremely important in determining the cause of a patient's pain and often reveal that the MRI findings are not clinically relevant.

Consider for instance a New England Journal of Medicine study entitled “Magnetic resonance imaging of the lumbar spine in people without back pain” which took MRIs on 98 asymptomatic people and found that “52 percent of the subjects had a bulge at at least one level.” In fact, this study concluded “On MRI examination of the lumbar spine, many people without back pain have disk bulges or protrusions but not extrusions. Given the high prevalence of these findings and of back pain, the discovery by MRI of bulges or protrusions in people with low back pain may frequently be coincidental.”

An earlier study was performed on sixty-seven individuals who had never had low-back pain or sciatica in their lives. Disc degeneration or bulging was found on MRI in 35 per cent of the subjects under the age of 40 and disc degeneration or bulging was present in all but one of the sixty to eighty-year-old subjects. In a more recent study, MRIs were taken on 1043 volunteers between 18 to 55 years of age. Forty percent of the individuals under age 30 had lumbar disc degeneration and over 90% of the individuals 50 to 55 years of age had lumbar disc degeneration. In other words, lumbar disc degeneration and disc herniations are extremely common, even in patients who have never had back pain.

So what’s the big deal? Why not get an MRI anyway?

First of all, even when examination findings do support the diagnosis of disc herniation, MRIs do not improve patient outcomes. A study published in the journal Lancet demonstrated that X-rays and MRI for low-back pain do not improve clinical outcomes. And, a study in the Journal of Bone and Joint Surgery indicated that "findings on magnetic resonance scans were not predictive of the development or duration of low-back pain. Individuals with the longest duration of low-back pain did not have the greatest degree of anatomical abnormality..."

Second, I believe that a positive MRI finding often leads to a pattern of learned helplessness wherein these patients believe that their backs are “broken”. I think this might be the reason that patients receiving MRI in the Lancet study actually responded marginally WORSE to treatment than patients who didn’t get MRI. Patients who have a disc herniation that shows up on MRI often think that there’s no hope for them living a life free from low back pain. These patients come to believe that they “just have a bad back” and they can’t do anything about their “bulging discs” unless they have surgery. These patients need to understand that almost everyone eventually develops some degree of degenerative disc disease and yet most people are not living a life of pain. Doctors need to empower these patients to improve their overall health, work on their flexibility, and improve their core strength.

Lastly, in my experience doctors often focus far too much on MRI results. Disc herniations often become a “red herring” wherein doctors place such importance on the MRI results that they miss the real cause of a patient’s pain. Doctors often overlook common causes of back and leg pain such as: pseudosciatica from myofascial pain in the gluteus minimus, low back pain referred from the iliopsoias, or lumbar facet syndrome. A thorough examination that includes range of motion, standard orthopedic tests, and (most importantly) detailed palpation of spine and deep hip musculature is critical in determining the cause of a patient’s pain. When the specific structures causing the pain are identified, an appropriate treatment plan along with patient education can be very effective.

I genuinely believe that patient outcomes can be significantly improved if doctors ordered fewer MRIs and spent a little more time performing a thorough examination. Therefore, I agree with guidelines outlined in the Annals of Internal Medicine which recommend that for adults less than 50 years of age with no red flags for serious spinal pathology, no X-rays or MRI is necessary. For patients over age 50, X-rays and simple laboratory tests can almost completely rule out underlying systemic diseases. And finally, MRIs should be reserved for patients who are considering surgery or those in whom systemic disease is strongly suspected.