Category Archives: Neurophysiological effects of SMT

Findings from study on the mechanism of spinal manipulation: Clinical Implications? Part 2 of 2.

This is the second and final part of a blog-post where I’d like to take the opportunity to  shed some light on what the findings from my study might mean for practising clinicians by addressing questions/comments that have been directed to me that have appeared in social media. By necessity some of the questions/comments are paraphrased and I have tried hard not to misinterpret these. I’m only too happy to (try to) answer any further questions you might have as a result of reading these posts. Please post comments, especially if you disagree! (Although please be polite! It’s fine to attack methods and methodology, not people). The limitations of the study should always be kept in mind when interpreting the ‘clinical implications’ responses to each comment. I look forward to hearing from you!

Comment 3 – ‘[Would have been] more interesting/important to research cervical inter-vertebral rotation in the transverse plane’

This study investigated cervical inter-vertebral flexion-extension (angular rotation in the sagittal plane) as it is not currently possible to use quantitative fluoroscopy to measure inter-vertebral rotation (angular rotation in the transverse plane) or lateral flexion (angular rotation in the coronal plane) due to radiographic superimposition. Axial rotation motion has been measured using CT and biplanar radiography (Bogduk and Mercer 2000) but accuracy can be problematic and radiation doses are high (Anderst et al. 2011).

I agree that, based on clinical experience, it would be interesting to measure inter-vertebral motion during regional rotation. What might make this possible one day is the creation of 3-D models of patients’ spines by combining MRI data with the continuous inter-vertebral motion data provided by quantitative fluoroscopy – but this is probably a long way off! Until measurement methods improve it will not possible to measure the effects of SMT on inter-vertebral motion other than in the sagittal plane (flexion-extension).

It should also be noted that changes in passive regional cervical ROM after SMT have been found to only be short-term (Nilsson et al. 1996). It is worth also considering the other factors at play as suggested in the diagram below:

mech chainThe ‘black box’ represents the (unknown) underlying mechanisms that account for the outcome after an intervention (Howick et al. 2010). In the above black box are mechanical, neurophysiological and psychological effects (mechanisms) that may be considered to act in isolation or in concert in producing the clinical outcome. ‘Changed IV-RoM’ includes the possibility of a change (increase) in range, or change in another kinematic variable, e.g. IAR location, with or without a change in range.

 Figure 4: A suggested mechanistic chain to explain the clinical effects of spinal manipulative therapy (Branney 2015)

Clinical implications?  Current methods only allow for measurement of inter-vertebral angular rotation in the sagittal plane (flexion-extension). Other factors that can influence patient recovery, or otherwise, (Figure 4) should also be considered.

Comment 4 – ‘If there is no difference in intervertebral movement between those with and those without neck pain and we can’t palpate with reasonable certainty which joints are “locked”, and we can’t effect intervertebral ROM and movement with SMT, then why use time on this?’

Good point – doesn’t sound good when you put it like that! It should be said that the findings from my study are not definitive, mainly through it having a small sample size (29 patients, 30 healthy volunteers). Also, the patients in the study were of low/moderate disability – there might be important inter-vertebral motion differences in patients of high neck pain-related disability. Further, differences may not be detected in terms of ROM but other parameters might be important such as IAR (instantaneous axis of rotation) that future studies could measure. However, this doesn’t stop palpation being problematic with studies consistently finding this is not reliable for assessing motion alone; the presence of pain however increases reliability.

Clinical implications? In the absence of pain it is possible that inter-vertebral motion is not clinically important, or at least we are as yet unable to measure clinically important inter-vertebral motion abnormalities.

Comment 5 – ‘Perhaps it is something else than intersegmental hypomobility we palpate, but should still continue with motion palpation?’

This links with comment 4 and begs the question, if motion palpation is not reliable, what are we feeling when we palpate patients’ spines, and it feels like a joint is restricted? Could we be palpating anisotropic muscle? Might this respond favourably to SMT? We’re back to considering neurophysiological mechanisms…

In Conclusion…

I have attempted to address a number of comments that were made in social media discussions of my PhD study’s findings. I hope I have not misinterpreted any of these comments. My responses may have opened more questions than provided answers and I’d be really interested to hear from anyone who would like to add their thoughts which may include disagreement with any of the above. Any more questions regarding my PhD study are most welcome. I’d also like to point out this study would not have been possible without the fantastic support of Professor Alan Breen and that of my other supervisors, Professor Jenni Bolton and Associate Professor Sarah Hean. Thank you very much again.

An overall conclusion is that we still do not understand how SMT works but I’d like to finish on this note: despite whatever mechanism SMT works by (see Figure 4), 87% of patients in the study had clinically meaningful decreases in pain and disability, and I’m sure that’s all the patients cared about.


Anderst, W. J., Baillargeon E., Donaldson, W. F., Lee, J. Y. and Kang, J. D., 2011. Validation of a noninvasive technique to precisely measure in vivo three-dimensional cervical spine movement. Spine, 36 (6), E393-E400.

Assendelft, W. J. J., Bouter, L. M. and Knipschild, P. G., 1996. Complications of spinal manipulation: A comprehensive review of the literature. The Journal of Family Practice, 42 (5), 475-480.

Bialosky, J. E., Bishop, M. D., Price, D. D., Robinson, M. E. and George, S. Z., 2009. The mechanisms of manual therapy in the treatment of musculoskeletal pain: A comprehensive model. Manual Therapy, 14, 531-538.

Bogduk, N. and Mercer, S., 2000. Biomechanics of the cervical spine, I: Normal kinematics. Clinical Biomechanics, 15, 633-648.

Branney, J. (2015) An observational study of changes in cervical inter-vertebral motion and the relationship with patient-reported outcomes in patients undergoing spinal manipulative therapy for neck pain. PhD Thesis, Bournemouth University. (not yet published)

Coronado, R. A., Gay, C. W., Bialosky, J. E., Carnaby, G. D., Bishop, M. D. and George, S. Z., 2012. Changes in pain sensitivity following spinal manipulation: A systematic review and meta-analysis. Journal of Electromyography and Kinesiology, 22 (5), 752-767.

Deitz, A. K., Breen, A. C., Mellor, F. E., Teyhen, D. S., Panjabi, M. M. and Wong, K. W. M., 2011. Kinematics of the Aging Spine: A Review of Past Knowledge and Survery of Recent Developments, with a Focus on Patient-Management Implications for the Clinical Practitioner. . In: Yue, J. J., Guyer, R. D., Johnson, J. P., Khoo, L. T., and Hochschuler, S. H., eds. The Comprehensive Treatment of the Aging Spine: Minimally Invasive and Advanced Techniques. 1. Philadelphia: Saunders, 51-62.

Howick, J., Glasziou, P. and Aronson, J. K., 2010. Evidence-based mechanistic reasoning. Journal of the Royal Society of Medicine, 103 (11), 433-441.

Kingston, L., Claydon, L. and Tumilty, S., 2014. The Effects Of Spinal Mobilizations On The Sympathetic Nervous System: A Systematic Review. Manual Therapy, 19 (4), 281-287.

Martinez-Segura, R., De-La-Llave-Rincon, A. I., Ortega-Santiago, R., Cleland, J. A. and Fernandez-De-las-Penas, C., 2012. Immediate changes in widespread pressure pain sensitivity, neck pain, and cervical range of motion after cervial or thoracic thrust manipulation in patients with bilateral chronic mechanical neck pain: A randomized clinical trial. Journal of Orthopaedic & Sports Physical Therapy, 42 (9), 806-814.

Meier, M. L., Hotz-Boendermaker, S., Boendermaker, B., Luechinger, R. and Humphreys, B. K., 2014. Neural responses of posterior to anterior movement on lumbar vertebrae: a functional magnetic resonance imaging study. Journal of Manipulative & Physiological Therapeutics, 37 (1), 32-41.

Nilsson, N., Christensen, H. W. and Hartvigsen, J., 1996. Lasting changes in passive range of motion after spinal manipulation: a randomised, blind, controlled trial. Journal of Manipulative & Physiological Therapeutics, 19 (3), 165-168.

Padayachy, K., Vawda, G. H. M., Shaik, J. and McCarthy, P. W., 2010. The immediate effect of low back manipulation on serum cortisol levels in adult males with mechanical low back pain. Clinical Chiropractic, 13 (4), 246-252.

Pickar, J. G. and Bolton, P. S., 2012. Spinal manipulative therapy and somatosensory activation. Journal of Electromyography and Kinesiology, 22, 785-794.

Song, X. J., Gan, Q., Cao, J. L., Wang, Z. B. and Rupert, R. L., 2006. Spinal manipulation reduces pain and hyperalgesia after lumbar intervertebral foramen inflammation in the rat. Journal of Manipulative & Physiological Therapeutics, 29 (1), 5-13.

Teodorczyk-Injeyan, J. A., Injeyan, H. S. and Ruegg, R., 2006. Spinal manipulative therapy reduces inflammatory cytokines but not substance P production in normal subjects. Journal of Manipulative & Physiological Therapeutics, 29 (1), 14-21.

Teodorczyk-Injeyan, J. A., Triano, J. J., McGregor, M., Woodhouse, L. and Injeyan, H. S., 2011. Elevated production of inflammatory mediators including nociceptive chemokines in patients with neck pain: a cross-sectional evaluation. Journal of Manipulative & Physiological Therapeutics, 34 (8), 498-505.

Tuchin, P. J., 1998. The effect of chiropractic spinal manipulative therapy on salivary cortisol levels. Journal of Australasian Chiropractic and Osteopathy, 7, 86-92.

Whelan, T. L., Dishman, J. D., Burke, J., Levine, S. and Sciotti, V., 2002. The effect of chiropractic manipulation on salivary cortisol levels. Journal of Manipulative and Physiological Therapeutics, 25 (3), 149-153.



Findings from study on the mechanism of spinal manipulation: Clinical Implications? Part 1 of 2.

Last July the main findings from my PhD study into the mechanism of spinal manipulation were published and, especially as an early career researcher, I’ve been delighted at the interest shown in the paper. Really this is testament to the benefits of open access publishing (although there are criticisms of this publishing model) where research papers are made freely accessible to anyone (with an internet connection) anywhere in the world as well as the channels for spreading the word provided by social media. Of course, as well as that, the topic of the mechanism of spinal manipulation continues to generate interest in the manual therapy professions as we continue to try (and try) to understand how it works.

I’d like to take this opportunity to shed some light on what the findings from the study might mean for practising clinicians by addressing questions/comments that have been directed to me that have appeared in social media. By necessity some of the questions/comments are paraphrased and I have tried hard not to misinterpret these. I’m only too happy to (try to) answer any further questions you might have as a result of reading these posts. Please post comments, especially if you disagree! (Although please be polite! It’s fine to attack methods and methodology, not people). The limitations of the study should always be kept in mind when interpreting the ‘clinical implications’ responses to each comment. I look forward to hearing from you! (and look out for Part 2 of this blog-post, coming soon).

Comment 1 ‘The findings of the study make sense since SMT does not lead to plastic deformation of joint and disc and therefore cannot increase movement more than anatomical range of motion (not lead to hypermobility)’.

How should hypermobility be defined within the context of inter-vertebral motion? (As distinct from say, generalised hypermobility diagnosed by the Beighton scale?). It’s standard in the biomechanics literature to define it as motion at or above the 98th percentile of the curve describing the distribution of inter-vertebral motion in the population (study sample) as illustrated in the graph below:


Figure 1: Theoretical framework for the categorisation of inter-vertebral motion (Deitz et al. 2011)

 In the study there were 20 segments that increased in range above the MDC (minimum detectable change) after four weeks of SMT; motion changes after SMT are more likely to be ‘true’ changes if larger than the MDC. (MDC = repeatability coefficient. This was calculated from the age/gender-matched healthy volunteer group who did not receive SMT. The MDC provided an estimate of how much we might expect inter-vertebral motion to vary between baseline and follow-up 95% of the time; in other words, how much inter-vertebral motion might vary in people with no neck pain not receiving SMT).  The graph below shows the angular range classification (i.e. hypomobile, normal or hypermobile) of these 20 segments at baseline (blue) and at four-week follow-up (red) after eight treatment visits for SMT.

Classification of segments at baseline and follow-up

Figure 2: Baseline and follow-up angular range classification of segments that increased in range (n=20 segments)

You might note the red column at the far right-hand side of the graph which represents seven segments (in four patients) that were classified as hypermobile (>mean +2 standard deviations) at follow-up. These segments were classed as within normal range at baseline. Since this study was observational (no randomisation or true control group) it cannot be said that the SMT caused these segments to increase beyond the normal range, but these findings open up the possibility.

Clinical Implications? – The continued use of cervical manipulation in the absence of pain, or for very low levels of pain, might not be clinically justified since there appears to be the possibility of inducing segmental hypermobility…


Comment 2 – ‘SMT works by neurophysiological mechanisms’

One might reasonably consider this, especially in light of the findings from this study (in brief, patients tended to get better whether their inter-vertebral motion increased, decreased or did not change, and only one segment that increased in range was hypomobile at baseline). However, which neurophysiological mechanism(s)? As the model proposed by Bialosky et al (2009) below suggests, answering this is not going to be straightforward:

bialoskyFigure key: The model suggests a transient, mechanical stimulus to the tissue produces a chain of neurophysiological [and psychological] effects. Solid arrows denote a direct mediating effect. Broken arrows denote an associative relationship which may include an association between a construct and its measure. Bold boxes indicate the measurement of a construct.

 Figure 3: Model of proposed mechanisms of manual therapy (Bialosky et al. 2009) (If model difficult to see please click here to see the original)

Simply put, this model proposes that a mechanical stimulus, like SMT, sets off a chain of neurophysiological responses that are ultimately responsible for the clinical outcomes. A number of the mechanisms postulated by this model have been investigated, but mostly theorised, in relation to SMT. Most investigative research has used cadavers, animal models or asymptomatic volunteers which can provide useful information to inform patient studies but the findings from such studies are in themselves not immediately clinical useful. Further, when mechanisms are explored in patients they are rarely considered in relation to symptomatic changes (one of the strengths of my PhD study) and study designs rarely include a control group (one of the weaknesses of my PhD study). I’ll briefly take each neurophysiological mechanism that has been investigated in turn:

 Descending pain inhibition?

One paper that was referred to in social media when discussing the findings from my study was the systematic review and meta-analysis by Coronado et al. (2012) presumably since the authors of the review concluded that SMT had a greater effect on increasing pressure-pain thresholds (PPT) compared to other interventions, suggesting an influence on central descending pain inhibition (Coronado et al. 2012). However, the conclusions of this review need to be interpreted with the following in mind: most of the studies included had been carried out on asymptomatic participants, there was a lack of studies linking changes in pain sensitivity to changes in clinical outcomes, and most studies only assessed short-term or immediate PPT changes (Coronado et al. 2012). Finally, this systematic review appears not to have taken account of the MDC (minimum detectable change) in assessing changes in PPT – if changes are not greater than MDC, it is difficult to be sure they are true changes.

In a study that assessed immediate changes in patients with neck pain after cervical or thoracic manipulation, while pain and PPT improved significantly, changes in PPT did not exceed the MDC (Martinez-Segura et al. 2012).

Somatosensory activation?

A review paper on SMT somatosensory activation reveals that this is an area of investigation that is still at the experimental stage (Pickar and Bolton 2012) so no firm conclusions can yet be drawn.

Effects on sympathetic nervous system?

A recent systematic review of research into the effects of spinal mobilisation on the sympathetic nervous system found seven randomised controlled trials that the authors rated as high quality. These studies found consistent increases in sympathetic nervous system activity across all outcome measures, indicative of sympathetic excitation, irrespective of the segments mobilised (Kingston et al. 2014). However, only one study evaluated changes in a symptomatic population and, since changes were not linked to outcomes, the clinical utility of changes in skin conductance, decrease in skin temperature, and especially of increases in respiratory rate, blood pressure and heart rate, are unknown and questionable (Kingston et al. 2014).

Effects on endocrine system?

Despite the role it plays in pain modulation, there has been little research of the effects of SMT on the endocrine system. In a small prospective case series (n=9, assumed to be asymptomatic) serum cortisol levels were not significantly different after four treatment visits for SMT (region of spine not stated) (Tuchin 1998). A second study compared salivary cortisol levels in a cervical SMT group, a sham group and a control group before and after treatment, and found no differences in cortisol changes between the (asymptomatic) groups (Whelan et al. 2002). Finally, despite the author’s tenuous claims to the contrary, Padayachy et al (2010) similarly found no differences in serum cortisol levels five minutes after lumbar manipulation in 30 asymptomatics (Padayachy et al. 2010).

Effect on inflammation?

In a cross-sectional study patients (n=27) with chronic and recurrent neck pain were found to have significantly higher levels of serum inflammatory mediators compared to controls with no neck pain (Teodorczyk-Injeyan et al. 2011). The presence of an inflamed joint is generally considered a contra-indication to manipulation, at least in the case of spondyloarthopathies (Assendelft et al. 1996). However, in an earlier study the same research group found that a single thoracic manipulation was associated with a greater decrease in inflammatory cytokines compared to sham or venepuncture controls (Teodorczyk-Injeyan et al. 2006). While experiments with an animal model suggest SMT might decrease inflammation associated with the inter-vertebral foramen (Song et al. 2006), the mechanism behind these decreases in inflammation, the duration of action and the importance of this in mediating patients’ clinical outcomes in neck pain or any other condition remains unknown.

Effects on the brain?

The use of functional MRI to monitor brain changes in response to lumbar mobilisation has been investigated recently (Meier et al. 2014). This appears to be feasible and might be a more promising avenue for investigating the neurophysiological effects of SMT. A promising future?

Clinical Implications? – SMT might work via neurophysiological mechanisms, but we don’t yet know which one(s) are most important i.e. those that lead to clinical outcomes. More research is required, using more robust methodology and in patient populations.

“Findings from study on the mechanism of spinal manipulation: Clinical Implications? Part 2” coming soon!


An interesting post with some useful links at the end for those interested in the physiological effects of manual therapy. Dare you listen, via the link, to find out how the Piddingtons were able to do their trick…?

Keith's Korner

I recently listened to a segment of Radiolab, titled, ‘You Are The Judge.” It featured the story of Sydney and Lelsy Piddington. Apparently, they were a big deal on British radio 60 years ago.

The Piddingtons purported to be mentalists: he would be on stage somewhere in front of a live audience while she was somewhere else altogther. A call would be placed to Lesley by an operator and she would read Syndey’s mind. You will need to listen to the podcast to appreciate the drama and mystery of their trick.

It was produced incredibly well and there are 2 episodes of their show that have survived. In one episode, Sydney was able silently convey to his wife the full line of text of a book randomly selected by an audience member from a pile of random books on stage – while she was in a building miles…

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