Research Review By Guest Reviewer Dr. Casper Nim©


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Date Posted:

February 2022

Study Title:

Targeting SMT Application – Importance of Segmental Pain vs. Stiffness

Studies Reviewed:

  1. Nim CG, Kawchuk G, Schiøttz Christensen B & O’Neill S. The effect on clinical outcomes when targeting spinal manipulation at stiffness or pain sensitivity: a randomized trial. Nature Scientific Reports 2020; 10: 14615.
  2. Nim CG, Downie A, O’Neill S, Kawchuk G, Perle S & Leboeuf Yde C. The importance of selecting the correct site to apply spinal manipulation when treating spinal pain: Myth or reality? A systematic review. Nature Scientific Reports 2021; 11: 23415

Author's Affiliations:

Spine Centre of Southern Denmark, University Hospital of Southern Denmark; Department of Regional Health Research, University of Southern Denmark, Odense, Denmark

Background Information:

Spinal manipulative therapy (SMT) is often recommended in clinical guide-lines to treat spinal pain (1). SMT is a clinician-guided therapy attempting to reduce pain and improve disability and its efficacy appears to be on par with other guideline-recommended interventions. Interestingly though, SMT does not heavily out-perform sham SMT interventions (2), suggesting that physical touch has a potential clinical effect that is not affected by actual therapeutic input to the spine.

A likely and potential factor affecting SMT’s efficacy is where the treatment is applied or targeted (i.e. the application site). While there are numerous options for applying SMT, the two most common are the indication of: 1) a stiff or 2) a tender vertebra (3).

While this seems straightforward for most young clinicians and students, the application site has developed significantly with different guises over time. This includes vitalistic concepts of ‘life-forces’, with theological under-tones to scientific sounding, but fuzzy notions about subluxations perturbating autonomic nervous activity, thereby, affecting specific organs to, more recently, that SMT, if applied appropriately, can affect clusters of dormant neurons in the brain (4, 5). Thus, there is no good consensus on a clinically relevant application site.

Animal-based research has found biomechanical effects on the tissues and cell structures specific to the application site of SMT (6, 7). Yet, the clinical translation of such effects is not as straightforward, and there is no good evidence for selecting one area over another (8). However, suppose specific effects can be shown to be related to the application site? In that case, the clinical outcomes should differ depending on the SMT application site.

This Research Review will investigate if the clinical effects of SMT are dependent on the application site using two different methods:
  1. A randomized controlled trial (RCT) that randomly allocated pa-tients with persistent low back pain (LBP) to receive four SMT sessions at either the stiffest or most painful vertebra (most common indicators); and
  2. a systematic literature review (SR) to assess the effect of applying SMT at candidate sites (clinically-relevant sites) compared to any control site (not clinically-relevant sites).

Randomized Trial:

Study Methods: We measured stiffness using the custom-made VerteTrack device. Basically, it is two wheels that roll a weighted indenter along the lumbar spine of a prone subject. By measuring the resulting vertical displacement in the spinal tissues, tissue stiffness (N/mm) can then be determined (applied mass/displacement).

We measured the pressure pain threshold using a pressure algometer. This is a prevalent technique often used in pain research. We 3D printed a new probe to align the pressure at each side of the lumbar spine at the same positions measured by stiffness. Subjects would indicate when a continuous pressure started to be perceived as painful, indicating their threshold. These techniques resemble clinical palpation in an attempted objective manner.

We randomly allocated subjects to receive SMT at vertebrae dominated by either stiffness or pain sensitivity. Four sessions of SMT were provided at that specific vertebra over 2 weeks, and clinical follow-ups were measured after the 4th treatment and at 4-weeks follow-up.

Results: Following our attempt to allocate patients into two groups differing only on the application site of SMT (the stiffest segment or the most painful segment), we failed to find any between-group differences at any time point (up to 2 weeks).

Systematic Review:

Study Methods: We conducted a systematic review that included RCTs comparing SMT ap-plied to any candidate site to SMT applied to any non-candidate site. We searched for literature in four databases. The credibility of the included studies was based on two assessments. Quality of the study: reproducibility of the study design, experienced and qualified clinician, proper primary outcome, and reproducible statistical analyses. Risk-of-bias: we used the Cochrane risk-of-bias tool, evaluating each study included on seven different biases. Credible studies would have to be of acceptable quality, and either scored as low or moderate risk of bias. Results were reported descriptively.

Results: We located 3288 articles – of those, 46 were assessed for eligibility. Nine reported clinical outcomes in this review (1 study was included in the publication but did not report on clinical outcomes). Of those nine studies, eight were scored as credible based on overall quality and the risk of bias assessment. All the credible studies did not report any between-group differences for any clinical outcome (typically pain intensity and disability) at any reported time point. Only one study deemed as having a high risk of bias reported a statistical but not clinically significant difference – it was also the study with the smallest sample size out of all included papers.

Discussion, Clinical Application & Conclusions:

Whatever effect SMT has on patients with spinal pain is likely not mediated by the application site. We reported and found sufficient evidence to make this conclusion. Further, our results are supported by research indicating: 1) that we as clinicians have difficulty providing SMT specifically, and 2) that SMT is a specific treatment to begin with.

Can SMT be applied specifically?
Static palpation is much more difficult than anticipated by many, even experienced clinicians (9). So, even if trying to target some specific vertebra (ex. one with degenerative changes), you are more than likely to be one or two vertebral bodies away. However, the larger issue at hand is that, despite a large body of evidence, there is no clear consensus on what an SMT appropriate site is – clinicians simply cannot agree with each other on this. So, while it may be possible to locate a (congenital or acquired) block vertebra using motion palpation, it cannot distinguish between a population with or without back pain. Further, it cannot be used to indicate who has received SMT (10-12). While it may be considered important to target pain or stiffness when applying SMT, we have to acknowledge that the application site chosen is completely a subjective concept, that likely will depend on clinician-based factors (i.e. school of training, experience, and preference) rather than patient factors.

Is SMT a specific treatment?
Most clinicians consider cavitation an indicator of a successful treatment input (which empirically is a fair assumption), despite the “pop” likely not being important for patients (13). Multiple studies indicate that SMT affects multiple segments in proximity to the target and many times does not even cavitate on the actual target site (14-16). A rule-of-thumb would be that 2-3 cavitation sounds would indicate that you actually ‘hit’ (or ‘got’ or ‘released’) the intended target segment. Another important aspect for clinicians is the thrust vector or the line-of-drive. However, it is unlikely that we can ‘move’ the target in any specific direction as it appears the force is greatest at a perpendicular angle, with deviations only decreasing the force and being absorbed into the fascia, not moving the vertebra in the desired direction (17, 18). When considering this, it is possible that we (these authors) could have guessed the results from the RCT beforehand and should have used an equivalence design instead.

A new model of understanding?
We desperately need high-quality studies to determine the underlying effects of SMT. However, it appears unlikely that the answer lies within a specific vertebra or likely even a distinct region of the vertebral column. We must accept that SMT is likely a non-specific treatment for specific vertebrae and update our teaching curricula to consider this non-specificity.

While many may initially argue that this is a wrong assertion that limits ‘the art of chiropractic’, we argue that this is a good thing. Experienced clinicians who are already confident in their technique can continue to treat as they wish. But students or early graduates stumbling with palpation and ‘feeling the correct dysfunctional estimates’ could modify their approach and thinking on this. This could remove this barrier and potentially improve their therapeutic alliance with their patients. In educational settings, we could then devote time to more essential aspects for students considering SMT (ex. technique practice and psychomotor skills) as well as psychosocial assessment and long-term, reasonable management plans.

Study Strengths / Weaknesses:

Randomized Trial: The apparent limitation of this study was the experimental setup using objective measures of unknown clinical relevance to determine application sites. Potentially, palpation has benefits that outweigh this limitation, but as mentioned, palpation is not free of bias or non-reproducibility.

Systematic Review: Due to the broad inclusion criteria, we could not complete a meta-analysis. However, we actually considered this a strength of our conclusion, considering that the outcome was the same, no matter what method was applied in the included studies (i.e., different targets within the same vertebra, the same spinal region, or between spinal regions).

Again, these were primarily experimental trials, many of them only providing a single SMT session. However, when researching SMT, we have to be conscious about contextual factors potentially obscuring the research findings. We had no intentions of examining the effect of a chiropractic consultation applying SMT at one site or the other. Therefore, employing SMT as such is likely a necessity to explore potential mechanisms not related to the contextuality of the setting. Further, when we consider the remaining evidence suggesting the overall non-specificity of the SMT, we regard our conclusion as valid.

About Dr. Casper Nim:

Dr. Casper Nim is a chiropractor (2016) and received his PhD in 2021 from the University a Southern Denmark. He is currently employed at the Spine Centre of Southern Denmark as a senior researcher and the University of Southern Denmark as an assistant professor, investigating 1) spinal ma-nipulation and specificity, 2) pain trajectories for patients with low back pain, and 3) is currently running a feasibility trial geared towards a large RCT investigating multidisciplinary long-term care for persistent secondary-care patients with low back pain.

“I was headed towards a research career from early on. As a master's student, I initially discussed this with Jan Hartvigsen (as all Danish chiropractors would). But, instead of going the epidemiologic way, I went the experimental way – in a collaboration with Søren O'Neill. Then, Greg Kawchuk got involved, and we designed this SMT study and, towards the end, decided on doing the systematic review. In fact, we began this work 3 months before I had to submit my Ph.D. It was an amazing team effort to have it wrapped up and published in just over a year. We have more papers in the pipeline investigating the aspect of specificity and SMT.”

Additional References:

  1. Corp N et al. Evidence‐based treatment recommendations for neck and low back pain across Europe: A systematic review of guidelines. Eur J Pain 2021; 25: 275–295.
  2. Rubinstein SM et al. Benefits and harms of spinal manipulative therapy for the treatment of chronic low back pain: Systematic review and meta-analysis of randomised controlled trials. BMJ 2019; 364.
  3. Triano JJ et al. Review of methods used by chiropractors to determine the site for applying manipulation. Chiropr Man Therap 2013; 21: 36.
  4. Hynes RJR & Callender AK. Technique in the Classroom at Palmer College of Chiropractic: A History in the Art of Chiropractic. J Chiropr Humanities 2008; 15: 55–66.
  5. Meyer AL, Amorim MA, Schubert M et al. Unravelling functional neurology: Does spinal manipulation have an effect on the brain? - a systematic literature review. Chiropr Man Therap 2019; 27.
  6. Edgecombe TL, Kawchuk GN, Long CR & Pickar JG. The effect of application site of spinal manipulative therapy (SMT) on spinal stiffness. Spine J 2015; 15: 1332–1338.
  7. Reed WR, Long CR, Kawchuk GN & Pickar JG. Neural responses to the mechanical characteristics of high velocity, low amplitude spinal manipulation: Effect of specific contact site. Man Ther 2015; 20: 797–804.
  8. Stolz M, Piekartz H, Hall T et al. Evidence and recommendations for the use of segmental motion testing for patients with LBP - A systematic re-view. Musculoskelet Sci Practice 2020; 45: 102076.
  9. Tanaka K, Irikoma S & Kokubo S. Identification of the Lumbar Interspinous Spaces by Palpation and Verified by X-rays. Braz J Anesthesiol 2013; 63: 245–248.
  10. Leboeuf-Yde C et al. Motion palpation findings and self-reported low back pain in a population-based study sample. J Manip Physiol Ther 2002; 25: 80–87.
  11. Humphreys BK, Delahaye M & Peterson CK. An investigation into the validity of cervical spine motion palpation using subjects with congenital block vertebrae as a ’gold standard’. BMC Musculoskelet Dis 2004; 5: 19.
  12. Hansen BE, Simonsen T & Leboeuf-Yde C. Motion palpation of the lumbar spine–a problem with the test or the tester? J Manip Physiol Ther 2006; 29: 208–212.
  13. Flynn TW, Fritz JM, Wainner RS & Whitman JM. The audible pop is not necessary for successful spinal high-velocity thrust manipulation in individuals with low back pain. Arch Phys Med Rehabil 2003; 84: 1057–1060.
  14. Beffa R & Mathews R. Does the adjustment cavitate the targeted joint? An investigation into the location of cavitation sounds. J Manip Physiol Ther 2004; 27: 118–122.
  15. Ross JK, Bereznick DE & McGill SM. Determining Cavitation Location During Lumbar and Thoracic Spinal Manipulation: Is Spinal Manipulation Accurate and Specific? Spine 2004; 29: 1452–1457.
  16. Dunning J et al. Bilateral and multiple cavitation sounds during upper cervical thrust manipulation. BMC Musculoskelet Dis 2013; 14: 24.
  17. Herzog W, Kats M & Symons B. The effective forces transmitted by high-speed, low-amplitude thoracic manipulation. Spine 2001; 26: 2105-2110.
  18. Bereznick DE, Ross JK & McGill SM. The frictional properties at the thoracic skin–fascia interface: Implications in spine manipulation. Clin Biomech 2002; 17: 297–303.

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