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Research Review By Dr. Jeff Muir© with guest commentary from Dr. Casper Glissmann Nim


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Date Posted:

February 2023

Study Title:

Pressure pain thresholds in a real world chiropractic setting: topography, changes after treatment, and clinical relevance?


Nim CG, Aspinall SL, Weibel R, Steenfelt MG & O’Neill S

Author's Affiliations:

Medical Research Unit, Spine Centre of Southern Denmark, University Hospital of Southern Denmark, Middelfart, Denmark; Department of Regional Health Research, University of Southern Denmark, Odense, Denmark; College of Science, Health, Engineering and Education, Murdoch University, Perth, Australia

Publication Information:

Chiropractic & Manual Therapies 2022; 30: 25.

Background Information:

Pressure pain threshold (PPT) is a concept within manual therapies that is proffered as a partial explanation as to why spinal manipulative therapy (SMT) is associated with decreased pain. PPT involves testing deep tissue sensitivity by determining the amount of pressure over a given area in which a steadily increasing nonpainful pressure stimulus turns into a painful pressure sensation. SMT is thought to increase the PPT in the short-term (representing a reduction in mechanical pain sensitivity) in both symptomatic and asymptomatic patients (1, 2). In this context, PPT falls under the umbrella of quantitative sensory tests (QSTs), where painful stimuli can be used to investigate the neurophysiology of pain and the effects of various interventions (3, 4). The evidence in support of SMT as a modifier of PPT is varied and relatively inconclusive, with some systematic reviews showing that PPT increases with SMT (5) and others showing no change in PPT following SMT (6).

An interesting topic within QST research is the use of topographical mapping, which provides data on responses to stimuli and/or treatment using various test sites (7). While mapping responses can improve the understanding and knowledge of pain-generating conditions, there are questions as to whether research typically performed in experimental settings offers valid and valuable information for clinicians (8). To address this, the authors sought to evaluate the effect of SMT on PPT in a real-world clinical setting.

Pertinent Results:

17 chiropractic clinics were invited to participate, of which 4 provided data. 135 patients across the participating clinics were enrolled in the study (11 chiropractors), of which 129 were able to attend for the follow-up. The majority of patients presented with low back pain of less than 12 weeks’ duration. SMT was generally targeted to the spinal area of complaint (i.e. lumbar SMT for lumbar complaints) and some received treatment to multiple regions.

Change in PPT Following SMT:
The average change in PPT was 0.14 kg (95% CI = −0.01 to 0.29 kg, p = 0.07), although the findings were relatively evenly distributed amongst patients seeing an increase in PPT and others seeing a decrease in PPT, possibly accounting for an average difference close to zero.

Distance between test site and SMT site saw a small association (−0.03 Kg (95% CI = −0.05 to −0.01 Kg, p < 0.01), although this finding is not significant, suggesting that any effect of SMT on PPT is not likely related to vertebrae or region. An opposite effect was noted when the distance between test site and nearest SMT application site was < 15 vertebrae.

When stratified based on status as a rapid responder to SMT, there was no significant difference in PPT change (0.07 Kg, 95% CI = −0.21 to 0.34 kg, p = 0.63).

Baseline PPT had a small but not significant effect on PPT change, with lower baseline PPT associated with a smaller increase in PPT (−0.04 Kg, 95% CI = −0.11 to 0.04 kg, p = 0.34).

A median of 3 SMT treatments was provided per patient, with no significant association noted between number of treatments and change in PPT (0.04 kg, 95% CI = −0.03 to 0.11 kg, p = 0.25).

When comparing regions of pain (clinical, adjacent or distant), PPTs increased more in the clinical region than the adjacent or distant regions, although this observation was not significant.

Patients who received myofascial techniques in addition to SMT saw a significant change in PPT (0.53 Kg, 95% CI = 0.08 to 0.98 kg, p < 0.01).

A post-hoc analysis stratifying patients based on the number of prior chiropractic visits was unable to discern any pattern based on prior experience with SMT.

Topographic Mapping:
Regarding site mapping, group-mean differences in PPT were significantly different when the upper cervical region was compared with any other site and the C7 region to any lumbar site (p < 0.05). The infraspinatus site had lower PPT values than other sites, save for the cervical sites. PPT values were lowest in the cervical region and increased in sites located in a caudal direction.

A post-hoc analysis used three PPT practice attempts in non-spinal regions prior to test sites; however, no significant changes were observed based on the order of test sites (− 0.02 kg, 95% CI = −0.10 to 0.06 kg).

Clinical Application & Conclusions:

This study of real-world responses to SMT did not find evidence of an increase in PPT following SMT. While PPT increased substantially in some individual patients, no predictable results based on subgroups were identified. The authors appropriately caution against extrapolating experimental results – which historically have shown an increase in PPT following SMT – to clinical settings, given the lack of response in this clinical study.

Commentary from lead author, Dr. Casper Glissmann Nim:

PPT changes following SMT have been scrutinized in numerous studies, using different equipment and populations with varying results. One question always remains, is this clinically relevant? More often than not, the populations are not similar to what clinicians see. This is why we in this study moved out of the "lab" and set up within "real-world" chiropractic clinics.

And we did not find anything of interest; it indeed appeared as if changes in PPT were completely random, with some showing substantial increases and others very large decreases. A critique could be that the algometer used to assess PPT is unreliable. However, studies suggest that PPT is a stable measure, and we even have a paper coming out on the equipment we used in this data collection, showing that neither the time nor rater provided any significant variance. Thus, something is likely to happen following a clinical encounter that includes SMT. Still, it is unlikely to significantly contribute to the sensation of improvement, and it is not dependent on the SMT target or the patient characteristics – at least in the short term.

A limitation was that we did not solely investigate the SMT, but a clinical encounter where SMT was provided completely pragmatically. However, we would argue that if we cannot find any directional changes in PPT in a clinical setting, what is the importance of finding one in a laboratory? In reality, we actually expected to find more significant increases compared to lab testing, as we allowed for an influx of every possible contextual factor one can think of. However, this was not the case.

Despite the limitations and the cross-sectional design, we still suggest that researchers be mindful about presenting their lab results on healthy individuals as potential mechanisms for clinical pain relief in a pain population. And we can even extend this into caution about recommendations on pain relief for highly experimental lab settings that uses "patients" – and I put patients in quotations as they often are university students or social media volunteers and therefore not necessarily presenting with problems comparable to regular chiropractic patients.

Study Methods:

This study was a pre/post treatment design, in primary care chiropractic practices in Southern and Central Denmark. Patients 18 years of age or older who were able to read and write Danish and had a primary complaint of spinal pain in any region were eligible for inclusion. Patients with competing diseases that could affect the central nervous system were excluded. Convenience sampling was used. PPT was assessed immediately prior to treatment and immediately following treatment.

PPT Assessment:
8 anatomical sites were assessed: C3, C7, T3 and T7, L1 and L5, infrasp-inatus and tibialis anterior. PPT was assessed using a custom-made pressure algometer with a spherical probe head. PPT was measured by applying 0.5 kg/second of pressure to the site. If no pain was elicited by 10 kg of pressure, 10 was recorded as the PPT.

Variables of Interest:
  1. PPT: Change in PPT was calculated for each patient, with a negative PPT change indicating a decrease in PPT and a positive change indicating an increase in PPT.
  2. Patient-Reported Variables: Patient demographics, region of pain, current pain level, duration of pain and chiropractic visit information (number of visits, rapid response) were collected for each patient.
  3. Clinician-reported variables: Location of SMT, number of SMTs provided, details regarding SMT (optional) and non-SMT treatments were recorded.PPT changes are presented as 95% confidence intervals; for multilevel data, linear mixed models were used.
Topographic mapping used linear regression to create a heat map with mean differences and 95% CIs.

Study Strengths / Weaknesses:

  • This was a clinical study design, using real-world settings rather than laboratory settings used by other authors.
  • QST evaluation followed procedures used in other QST studies.
  • Post-hoc assessments were used to expand analyses.
  • Single PPT trial was used for each site assessment.
  • Convenience sample could be subject to selection bias.
  • Time lapse between SMT and PPT testing was not consistent.
  • See Dr. Nim’s comments above.

Additional References:

  1. Aspinall SL, Leboeuf-Yde C, Etherington SJ, Walker BF. Manipulation-induced hypoalgesia in musculoskeletal pain populations: a systematic critical review and meta-analysis. Chiropr Manual Ther 2019; 27(1): 7.
  2. Honoré M, Leboeuf-Yde C, Gagey O. The regional effect of spinal manipulation on the pressure pain threshold in asymptomatic subjects: a systematic literature review. Chiropr Manual Ther 2018; 26: 11.
  3. Arendt-Nielsen L, Skou ST, Nielsen TA, Petersen KK. Altered central sensitization and pain modulation in the CNS in chronic joint pain. Curr Os-teoporos Rep 2015; 13(4): 225–34.
  4. Arendt-Nielsen L, Morlion B, Perrot S, Dahan A, Dickenson A, Kress HG, et al. Assessment and manifestation of central sensitisation across different chronic pain conditions. Eur J Pain (London, England) 2018; 22(2): 216–41.
  5. Nim CG, Kawchuk GN, Schiøttz-Christensen B, O’Neill S. Changes in pain sensitivity and spinal stiffness in relation to responder status following spinal manipulative therapy in chronic low back pain: a secondary explorative analysis of a randomized trial. BMC Musculoskelet Disord 2021; 22(1): 23.
  6. Aspinall SL, Jacques A, Leboeuf-Yde C, Etherington SJ, Walker BF. No difference in pressure pain threshold and temporal summation after lumbar spinal manipulation compared to sham: a randomised controlled t. Musculoskelet Sci Pract 2019; 43: 18–25.
  7. Alburquerque-Sendín F, Madeleine P, Fernández-de-las-Peñas C, Ca-margo P, Salvini T. Spotlight on topographical pressure pain sensitivity maps: a review. J Pain Res 2018; 11: 215–25.
  8. Newell D, Lothe LR, Raven TJL. Contextually aided recovery (CARe): a scientific theory for innate healing. Chiropr Manual Ther 2017; 25: 6.

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