Whenever chiropractors are asked about the benefits of spinal manipulation, and how it works, they will usually answer that the effect is 'neurological'. But what does this actually mean? What is the neurological effect that we claim to create, and does it work the same way for everyone? Furthermore, how does this 'neurological' effect benefit someone with the average musculoskeletal disorder? After all, the most common reason that someone consults a chiropractor is for a musculoskeletal condition, and our treatment of choice invariably seems to involve manipulation. But if a patient's connective tissues have been damaged then surely our treatment should somehow address the damage itself? Can manipulation do this? If not, then what are we doing?
One of the most commonly proffered explanations for the neurological benefits of manipulation is 'analgesia'. This makes sense, and has been tested repeatedly. So far, so good. However, chiropractors also look after many patients with chronic pain who do not show any immediate analgesic benefits, but there is a presumption that an accumulated benefit will occur over time. This also makes sense, based upon studies of plasticity within the pain pathways (although there is little patient data yet to support it). However, chiropractors do spend much of their time managing totally pain-free patients, for whom 'analgesia' is no longer a viable justification for their intervention. On what basis are we choosing to treat such patients?
Obviously there is more to chiropractic than the treatment of pain, but as the profession matures and we enjoy a more visible role within the health care community, we also take on the responsibilities and accountability that go with it. This means that we need to be able to explain what we do, and do so in the contemporary language of our peers. Unfortunately, as relative newcomers to the inner circle of 'mainstream' healthcare it seems that chiropractors still have a lot to prove. Indeed, it also appears that we are held to a standard of evidence that exceeds that of others operating within the same sphere. While this is not rational or 'fair', it is the way that human nature works I'm afraid. As I discussed at length in another Clinical Clarity Blog article entitled 'The Stroke Perspective' (here), we face a strong emotional resistance when promoting the chiropractic 'brand'. To put it bluntly, if someone doesn't trust the messenger, then they won't trust the message itself. But there are ways to overcome this friction if we understand its rationale, so I would recommend that you read the previously mentioned article to get some additional perspective.
Fortunately the field of modern neuroscience is vibrant and teeming with high quality research - much of which is relevant to contemporary chiropractic. Literally hundreds of new papers are published every day, but sadly the average chiropractor will never come to know of their existence. Furthermore, we all tend to view the world through a tightly focused lens that reinforces our current worldview and tries to keep out anything new that might undermine our existing 'truths'. In years gone by this was seen as a way to keep our profession 'pure' and distinct, but sadly now it only serves to marginalise us further. It seems that chiropractors also don't trust non-chiropractic messengers? I think that Moseley (1) captured the mood perfectly in a recent paper when he quoted Voltaire,
"We have long known that innovation is neither easy nor necessarily welcomed - 'Our wretched species is so made that those who walk on the well-trodden path always throw stones at those who are showing a new road.' ”
I would contend that the chiropractic profession should position itself at the forefront of contemporary spine science, wherever that may take us. We should take pride in the breadth and depth of our knowledge, and in our willingness to embrace the new. Personally, I look forward to innovative ideas that challenge my thinking and allow me to make better decisions. But this does mean that we must get to grips with a large body of scientific knowledge and then assimilate it within the context of contemporary chiropractic thinking - no easy task.
So this begs the question, what is contemporary chiropractic thinking? Why do we believe that an adjustment does something beneficial to a patient? Well, to answer this we should go back one step further and ask ourselves what it is that we think we're trying to fix? What is the problem that chiropractors are hoping to address with a spinal adjustment? Is it a neurological issue? A mechanical problem? A combination of both? And if so, how do you measure it?
THE IMPORTANCE OF LANGUAGE
Historically chiropractors have focused upon the mechanical aspects of spinal derangement and have tended to maintain a fondness for 'alignment'. Indeed, the word 'alignment' seems to carry within it connotations of an ideal that we should strive to attain for our patients. However, the language that we utilise in any situation is important, as it can take on the role of a 'forcing function'. That is, some words corral our mind into adopting additional ideas automatically, without discrimination or thought (a case of 'two for the price of one', if you like). In the case of the word 'alignment', we tend to assume a mechanistic and static understanding when we use it to describe the nature of spinal disorders.
When we view our patients through the lens of 'alignment' we see mechanical disorders that might seem best quantified through the taking of an X-ray. A crooked spine is plain to see, and it would appear logical that any physical distortion should be corrected by mechanical means. Furthermore, it's not hard to imagine the consequences if such 'alignment' issues were to go unchecked - degeneration, wearing, compression, pinching, stretching, distortion, thinning, weakening, atrophy - the list goes on. We tend to reinforce this static mindset by relying upon examination tools that measure parameters such as posture, spinal curvatures, range of motion, static palpation, leg-length measurement etc. In this mechanical worldview we remain internally consistent and therefore happy and contradiction-free.
Unfortunately, modern spine science just doesn't support such a model.
The “Miss Correct Posture” competition. Contestants pose with trophies and their X-rays at the Chicago chiropractors convention, May 1956. Images sourced from: http://www.historybyzim.com/2013/07/miss-correct-posture-1956/
Photo Credit: Wallace Kirkland/LIFE
At this point I should draw a distinction between those individuals with clear-cut pathoanatomical changes in spinal tissues (such as disc herniation with nerve root compression), and those who have no evidence of damaged neural tissue. Obviously there is a time and a place for spine surgery, and a need for decompression, and thankfully we now have the tools to allow us to quickly determine when this is actually happening. Indeed, the vast majority of our patients have no evidence of direct neural insult (particularly the younger patients). There is no compression, no stretching, no mechanical compromise - yet the nervous system is clearly unable to function normally. It's not that these things are irrelevant. It's just that the average chiropractic patient who comes in regularly for transient symptoms, general well-being, or performance enhancement is surely not obtaining their very real benefits through the mechanism of disengaging swollen nerve tissue from its neighbouring anatomy. Something else is going on. And if something else is going on, then it is important that the chiropractic profession learns to justify its approach using the latest scientific models and evidence - not those of history.
While there have been some significant trailblazers in the chiropractic research community in recent years (such as Heidi Haavik, Bernadette Murphy and Kelly Holt), our attempts to explain the neurological aspects of spinal disorders have otherwise still maintained a distinctly mechanical flavour. That is, the focus remains upon mechanical distortion of neural tissue at the macro level - impinged nerves, cord tension, 'dural torque', changes to CSF flow, IVF ligament encroachment etc. But how often do these truly occur and can they be reliably and independently measured? I think that you will be disappointed by the answer. It seems that we remain mired within the constraints of our past thinking and cannot escape the basic presumption that spinal disorders must somehow begin as a mechanical problem that then compromises nerve flow. In other words, something goes 'wrong' within the spine and this ultimately 'causes' neurological disturbances.
Interestingly, science now suggests that we may have this sequence the wrong way around...
EVEN NEUROLOGICAL PROBLEMS CAN BE MECHANICAL
Traditionally chiropractors have viewed spinal dysfunction (subluxation) as a primary cause of neurological disturbance, which was then conceived to be a cause of further illness. However, it can be just as easily argued that modern sedentary lifestyles lead to deconditioning within the human neuraxis, including the pathways responsible for maintaining postural integrity, balance and spinal segmental control. And it is this functional deconditioning that creates the vulnerability for future tissue injury, such as an acute disc herniation or facet joint strain. Essentially, this means that whatever painful tissue disorder we might find within the spine is secondary - the mechanical by-product of a neurological system that has already begun to fail. But this failure is not visible on X-ray, or CT or even on a standard MRI scan. As we shall see in the paragraphs below, the functional deficits that I am talking about occur as abnormal patterns of electrical activity throughout the neuraxis, particularly within the brain itself - a far cry from the bones of the spine that have enraptured chiropractors for so long.
Of course, I am not suggesting that tissue changes within the spine itself are completely irrelevant. Far from it. Indeed, I have written extensively on this Blog about disc herniations, facet joint lesions, Modic changes, and the proprioceptive deficits that often accompany them. However, such connective tissue failures often represent the end-point of a neurological deconditioning process that may have been years in the making.
So this again begs the main question of this article - where does the real problem lie then?
Well, the bad news is that there isn't ONE convenient problem that can be easily quantified. There's a myriad of different issues within our patients. The good news is that others in the world of science have not been idle, and have been diligently documenting the nature of neuromusculoskeletal disorders for years. It's just that the average chiropractor never gets to hear about it. Obviously there is a pain-centric view to the research, but this is not surprising. However, as we shall see later, there are many other non-pain-related and exciting ramifications of this research to be considered.
According to Nijs et al (2), even the topic of spinal pain can be triaged into broad categories - based upon their underlying mechanisms:
(1) Input mechanisms, including nociceptive pain and peripheral neurogenic pain;
(2) Processing mechanisms, including central pain and central sensitization and the cognitive-affective mechanisms of pain;
(3) Output mechanisms, including autonomic, motor, neuroendocrine, and immune systems.
Each of these different mechanisms may play a dominant role in maintaining symptom chronicity in our patients, possibly explaining why some individuals do better than others with different treatment modalities. However, there remains a heavy bias amongst treating practitioners to find and eradicate sources of nociception down amongst the spinal tissues themselves, presumably because they just seem closest to the action. As Moseley put it recently (1),
"Surgeons focus on removing (eg, a discectomy), anaesthetising (eg, a facet joint block), or denervating (eg, lumbar rhizotomy) a particular tissue; physiotherapists might focus on strengthening muscles of the trunk, altering biomechanics (eg, the McKenzie method), or motor control strategy; psychologists might focus on biofeedback or relaxation to reduce unwanted trunk muscle tension."
As you can see, it's not just chiropractors who steadfastly focus upon the spine itself. However, Nijs (2) goes on to make the distinction that in the case of chronic pain, we are no longer dealing with a tissue-based disorder. Rather, what was once a mechanical injury has been replaced by a neurological entity.
"Except for inflammatory pain conditions (eg, rheumatoid arthritis) or non-inflammatory sources of ongoing spinal nociception, the stage of real tissue damage or nociception has disappeared in chronic spinal pain. Within this context, there is increasing evidence that central mechanisms (ie, brain abnormalities [changes in brain structure and function] and hyperexcitability of the central nervous system [sensitization of the brain]) play a tremendous role in patients with chronic spinal pain."
ENTERING THE MATRIX
In recent years the literature has shown that patients with chronic spinal pain can exhibit neurological compromise at multiple levels within the neuraxis. Furthermore, the form that this compromise takes can be both complex and fascinating. Ultimately it seems that patients who continue to suffer from spinal pain do so because of a fundamental change in the way that their brain 'sees' their body. In essence, there is a disconnect between their brain's perception of their spine and the reality of their moving parts. Moseley (1) explains it thus,
"The brain holds multiple bodily and spatial “maps” - multisensory neural networks that subserve the regulation and protection of the body and the space around it, networks that have been collectively termed “the cortical body matrix”. The last decade has seen rapid progress in our understanding of the relationship between chronic pain and disruptions of these bodily representations."
Wallwork et al (3) described the importance of these neural networks and the cortical body matrix,
"Movement and motor performance involve highly complex interactions between the neural networks in the brain that represent our body and the space around us. For example, skilled motor performance utilises neural representations from visual, proprioceptive, spatial and tactile domains, enabling us to establish body position and alignment in relation to the external environment. Such information gets continually fed into sensory-motor loops that constantly update internal predictions about the outcome of a motor command. This continuous updating promotes smooth, efficient and accurate motor performance as well as optimal protection and functionality. Both a wide repertoire of possible motor strategies, and a precise and efficient cortical predictive modelling capacity, are considered important for high level motor commands such as those required in sport. Finely tuning such a system after injury or inactivity involves reinstating the capacity of the brain to integrate these multiple representations and rapidly run them in a constantly changing and updating sensory-motor environment. The implications of this neurological component to sports rehabilitation depends on fundamental matters of neural representations and their governance."
All this talk of brain maps and 'body schema' might seem somewhat theoretical and far-removed from the practical realities of a patient suffering from humble back pain. However, the same was probably said the first time that someone dared posit that the earth was actually round, and not the flat surface that we could all see and agree was 'reality'. Interestingly though, if we think back to the musings of our chiropractic founders, they had originally conceived of subluxation as a 'disconnect' between the brain and the body. While the details weren't quite right, some of the broad strokes were quite profound.
Again from Moseley (1),
"Regarding back pain, disrupted representations have been observed in the motor, tactile, and spatial domains. Broadly speaking, these deficits reflect a loss of precision, as evidenced in altered functional imaging data and altered performance in behavioural tasks involving the back. For example, patients are unable to voluntarily move their back without also moving their pelvis, they cannot differentiate 2 separate tactile stimuli unless they are a long way apart, and they process stimuli delivered to the affected side of the body midline more slowly than identical stimuli delivered to the healthy side, even when the stimuli are delivered to the hands held near the back, rather than to the back itself."
A recent paper in the journal SPINE by Hotz-Boendermaker et al (4) looked at cortical activity during mechanical stimulation of the lumbar spine in chronic lower back pain patients when compared with controls, using functional MRI. They wrote,
"These findings support accumulating evidence from behavioral studies that demonstrated impaired body perception in CLBP patients, with deficits in proprioception, disruption of vibrotactile stimuli processing, and poorer tactile acuity. Due to the complex relationship between perception and action, a disturbed lumbar spine representation may have important consequences, as sensory information is mandatory to select appropriate neural control strategies for stabilization and movement of the spine. Central in this process is the secondary sensory cortex (S2) that has close connections with premotor planning areas. Subsequently, cortical reorganization of the sensorimotor system may lead to maladaptive functional changes that might include impoverished motor programming, planning, and impaired postural control."
It appears that once the delicate interplay between brain and spine is lost, the default adaptive strategy tends to be one of increasing generalised stiffness. However, this is not the normal, healthy segmental stiffness that the brain directs as needed on a moment-to-moment basis - like the conductor of an well-rehearsed orchestra. Such physiological stiffness is highly refined and nuanced, and relies upon the deep intrinsic muscles of the spine (such as the multifidus), and it beautifully adapts the body to the needs of the moment and the task.
Rather, maladaptive generalised stiffness uses the longer superficial strap muscles (such as the erector spinae) to brace larger sections of the torso and neck - sacrificing fluid segmental control for gross regional stability (5). Unfortunately, this form of stabilisation is akin to a rigid tree branch that is unable to bend in the wind - it will snap if the wind becomes too strong. Such changes have been described as a 'maladaptive motor strategy' and are common in those with chronic musculoskeletal problems, as well as other neurological states such as migraine. Furthermore, this represents only one of many neurological disturbances that have been catalogued within the brains of our patients - but in this article I am trying my best to avoid diving down too many complex rabbit holes (for more intriguing neurology read this article about the concept of inhibition, and the huge range of symptoms that can occur if inhibition is compromised). My point is simply to illustrate that chiropractors are dealing with a complexity that is so much greater than a simple misaligned vertebra or a compressed nerve. Furthermore, knowing this has important ramifications for the profession as a whole.
When humankind grasped the implications of a spherical earth, it changed everything. In a similar fashion, the ideas we've discussed here are not just entertaining concepts for academics and neuroscientists. When we appreciate the role of the brain in so many seemingly mechanical disorders we can understand the need to rethink some of our approaches. Obviously manipulation is an excellent tool and continues to serve us well, in spite of the fact that the traditional theories as to how it works are quite obviously incomplete. More recent studies have started to look at some of the features that I've highlighted above, both within the spine and the brain, and shown that spinal manipulation may be an effective 'change agent'. According to Hotz-Boendermaker and colleagues (4),
"Fortunately, maladaptive reorganization appears to be reversible. Therefore, research is needed to determine whether novel therapeutic approaches such as repeated, nonpainful manual input are beneficial in activation of the mechanosensory cortices and results in the restoration of normal sensory activity of the lower back and contributes to alleviating pain levels and disability in CLBP patients."
Indeed, it is quite possible that spinal manipulation may be one the most effective tools available to us when faced with the challenge of a disrupted body schema. It has been theorised that such patients have a form of sensory 'neglect' (6,7), in which their brain struggles to sense and control their moving parts. Spinal manipulation creates a novel blend of rich sensory feedback that engages the brain so as to improve sensorimotor control, and this has been shown in a variety of studies. In fact, it may well be the case that the unique 'sensory signature' of spinal manipulation is the reason that it has served the profession so well for so long. I have written previously about research (8) demonstrating the effect of spinal manipulation upon the smoothness of lumbar motion, a key factor in stability and control. I have also referred extensively throughout the Clinical Clarity Blog to the impressive catalogue of work by Haavik and colleagues as they investigate the influence that spinal adjustments have upon the human brain, particularly the cortex. Indeed, some of the most interesting implications of this work are those that do not involve pain.
While pain syndromes are clearly important, and drive the majority of patients to seek out chiropractors, they are only one possible symptom amongst many. The brain relies upon sensory inputs to guide all manner of functionality beyond simply moving the spine, and studies have shown that spinal adjustments have impact upon the peripheral tissues as well. A study in the journal Brain Sciences entitled 'Impact of Spinal Manipulation on Cortical Drive to Upper and Lower Limb Muscles' (9) found,
"The results presented are consistent with previous findings that have suggested increases in strength following spinal manipulation were due to descending cortical drive and could not be explained by changes at the level of the spinal cord. Spinal manipulation may therefore be indicated for the patients who have lost tonus of their muscle and/or are recovering from muscle degrading dysfunctions such as stroke or orthopaedic operations and/or may also be of interest to sports performers. These findings should be followed up in the relevant populations."
Another recent study by Lelic et al (10) measured changes in somatosensory processing in the prefrontal cortex after a single session of spinal manipulation. They found that manipulation of the spine altered the cortical processing of any subsequent inputs from the upper limb, whereas a sham manipulation did not. This is quite profound, particularly when we pause to consider the important role of the prefrontal cortex. As Lelic explains,
"A change in prefrontal activity following chiropractic care may therefore explain and/or link some of the varied improvements in neural function previously observed in the literature, such as improved joint position sense error, reaction time, cortical processing, cortical sensorimotor integration, reflex excitability, motor control, and lower limb muscle strength."
So the idea that modern day research is only interested in manipulation as a therapy for back pain is an over-simplification. Indeed, I would strongly encourage chiropractors to step outside of their comfort zones and explore the ideas and knowledge bases of our colleagues in other disciplines, as we can learn a great deal from others. For example, in a previous article entitled "Right, Wrong or Incomplete?" (here) I discussed an interesting paper that investigated the use of acupuncture as a treatment for lower back pain. In this paper the researchers examined the effect of giving additional visual feedback to patients receiving acupuncture treatment - something they described as a form of sensory discrimination training. It was demonstrated that the simple act of providing visual data enhanced the therapeutic effect of acupuncture, perhaps as it allowed the brain to 'lock in' more precisely upon the sensory stimuli as it was being applied to the patient's lower back. They didn't just 'feel' what was happening to them, they could also 'see' it.
In a similar fashion, another experiment was published (11) in which patients with chronic lower back pain were treated with lumbar motion exercises, however, during part of the experiment the subjects were allowed to perform their routines while observing their own spinal movements in a mirror (thereby giving their brain additional visual feedback). According to the authors,
"A number of physiological responses to viewing oneself in a mirror have been reported, such as changes in the perceived location of the body part, increases in excitability of motor pathways and modification of sensory experiences; however, the exact mechanisms by which mirror visual feedback therapy (MVF) relieves pain are uncertain. A commonly offered explanation is that MVF works by restoring congruence between motor output and sensory input. It has been proposed that movement-related pain may arise if there is discordance between motor intent and sensory feedback associated with movement. When a motor command is created, the central nervous system makes predictions of the sensory consequences of the movement and monitors the congruence between predicted and actual sensory feedback. If incongruence is detected, it is hypothesized that pain may arise to warn of an error in information processing. The visual feedback afforded by the mirror may improve sensory acuity of the affected area and help reestablish congruence between sensory feedback and motor intention. This proposal is supported by data that suggest that a wide range of sensory disturbances, including pain and discomfort, can be provoked when mirrors are used to artificially induce a state of conflict between motor intent and visual feedback."
"In conclusion, patients reported significantly less increase in pain and recovered significantly faster when they were able to visualize their back during the performance of repeated spinal movements, than when they were not able to visualize their back. This is consistent with emerging research on the use of (MVF) in other chronic pain problems. Recent high-quality trials have reported large and sustained improvements in chronic pain patients’ clinical status with intensive MVF training programs. The current results suggest that similar lines of inquiry may be worth pursuing in the chronic nonspecific LBP population."
While such experiments might seem entertaining, they illustrate the point that we are only starting to scratch the surface of understanding the nature of neuromusculoskeletal problems. As chiropractors we need to decide where our expertise lies. Are we really 'spine doctors'? Are we 'nervous system experts'? If so, then we need to step up and embrace the science and become the experts. There is a whole world of knowledge out there and we must do the hard work to assimilate it and own it. Only then will the wider health care community take us seriously and allow us to do the best for our patients in the way that we ought to be able to.
Something to think about...
Dr Matthew D. Long BSc (Syd), M.Chiro (Macq)
References: 1. Moseley, G. L. (2017). Innovative treatments for back pain. Pain, 158 Suppl 1, S2–S10. http://doi.org/10.1097/j.pain.0000000000000772
2. Nijs, J., Meeus, M., Cagnie, B., Roussel, N. A., Dolphens, M., Van Oosterwijck, J., & Danneels, L. (2014). A modern neuroscience approach to chronic spinal pain: combining pain neuroscience education with cognition-targeted motor control training. Physical Therapy, 94(5), 730–738. http://doi.org/10.2522/ptj.20130258
3. Wallwork, S. B., Bellan, V., Catley, M. J., & Moseley, G. L. (2016). Neural representations and the cortical body matrix: implications for sports medicine and future directions. British Journal of Sports Medicine, 50(16), 990–996. http://doi.org/10.1136/bjsports-2015-095356
4. Hotz-Boendermaker, S., Marcar, V. L., Meier, M. L., Boendermaker, B., & Humphreys, B. K. (2016). Reorganization in Secondary Somatosensory Cortex in Chronic Low Back Pain Patients. Spine, 41(11), E667–73. http://doi.org/10.1097/BRS.0000000000001348
5. Tsao, H., Danneels, L. A., & Hodges, P. W. (2011). ISSLS prize winner: Smudging the motor brain in young adults with recurrent low back pain. Spine, 36(21), 1721–1727. http://doi.org/10.1097/BRS.0b013e31821c4267
6. Moseley, G. L. (2008). I can't find it! Distorted body image and tactile dysfunction in patients with chronic back pain. Pain, 140(1), 239–243. doi:10.1016/j.pain.2008.08.001
7. Moseley, G. L., Gallagher, L., & Gallace, A. (2012). Neglect-like tactile dysfunction in chronic back pain. Neurology, 79(4), 327–332. doi:10.1212/WNL.0b013e318260cba2
8. Mieritz, R. M., Hartvigsen, J., Boyle, E., Jakobsen, M. D., Aagaard, P., & Bronfort, G. (2014). Lumbar motion changes in chronic low back pain patients: a secondary analysis of data from a randomized clinical trial. The Spine Journal, 14(11), 2618–2627. http://doi.org/10.1016/j.spinee.2014.02.038
9. Haavik, H., Niazi, I., Jochumsen, M., Sherwin, D., Flavel, S., & Türker, K. (2017). Impact of Spinal Manipulation on Cortical Drive to Upper and Lower Limb Muscles. Brain Sciences, 7(1), 2–15. http://doi.org/10.3390/brainsci7010002
10. Lelic, D., Niazi, I. K., Holt, K., Jochumsen, M., Dremstrup, K., Yielder, P., et al. (2016). Manipulation of Dysfunctional Spinal Joints Affects Sensorimotor Integration in the Prefrontal Cortex: A Brain Source Localization Study. Neural Plasticity, 2016, 3704964. http://doi.org/10.1155/2016/3704964
11. Wand, B. M., Tulloch, V. M., George, P. J., Smith, A. J., Goucke, R., O'Connell, N. E., & Moseley, G. L. (2012). Seeing it helps: movement-related back pain is reduced by visualization of the back during movement. The Clinical Journal of Pain, 28(7), 602–608. http://doi.org/10.1097/AJP.0b013e31823d480c