Research Review By Jesse Awenus©

Audio:

Download MP3

Date Posted:

April 2020

Study Title:

No difference in pressure pain threshold and temporal summation after lumbar spinal manipulation compared to sham: A randomized controlled trial in adults with low back pain

Authors:

Aspinall SL, Jacques A, Lebeouf-Yde C, Etherington SJ & Walker BF

Author's Affiliations:

College of Science, Health, Engineering and Education, Murdoch University, Perth, Australia; Institute of Regional Health Research, University of Southern Denmark, Odense, Denmark.

Publication Information:

Musculoskeletal Science and Practice 2019; 43: 18-25.

Background Information:

Spinal manipulative therapy (SMT) is commonly used as a treatment modality for those suffering from low back pain (LBP) in an attempt to relieve pain and dysfunction. The exact mechanisms by which SMT may exert an analgesic effect, specifically in the spine, remain under study. One theory suggests that manipulation-induced hypoalgesia may occur via a reduction in pain sensitivity. Two commonly employed research methods through which sensitivity can be studied in the context of SMT are pressure pain threshold (PPT) and temporal summation (TS). PPT is the threshold at which gradually increasing pressure causes pain and has been shown to be decreased in a variety of musculoskeletal conditions, meaning it requires less pressure for the patient to feel pain (3, 4). PPT is normally tested with a pressure algometer. TS is a measure of how subjective pain severity changes over a series of painful stimuli repeated at intervals of 3s or less. The severity typically increases (‘summation’), and this increase appears to be heightened in multiple chronic pain conditions. TS in this study was tested using a pinprick stimulus (there are other methods as well).

The research using PPT and TS to date has mostly been of low-quality with numerous shortfalls. In musculoskeletal pain populations, there are few sham-controlled studies (none assessing TS) and most are low quality, with sham interventions that involve holding the participant in a pre-manipulative position, without actually assessing the believability or credibility of the sham (1).

The central purpose of this study was to perform a high-quality, double blinded, randomized controlled trial on a low back pain (LBP) population to investigate short-term changes in PPT and TS after lumbar SMT compared to a credible sham intervention. The intended aim of the study was to assess the time course of any changes seen with either SMT or sham SMT using repeated measures post intervention, as well as the location of any changes by measuring multiple testing sites.

The two main research questions the authors looked to answer were:
  1. Do PPT (measured at the lumbar spine, calf, and shoulder) and TS (measured at the feet and hands) change in the 30 minutes following true lumbar SMT compared to sham manipulation, in people with LBP?
  2. Do PPT and TS change from baseline to post-intervention in each group, and if so, which testing sites are affected?

Pertinent Results:

81 individuals participated in the study and received the intervention between October, 2017 and July, 2018. The average age of participants was 37 years (42 females and 39 males). There were no statistically significant differences in baseline participant characteristics. The majority (n = 51, 62.5%) reported having seen a chiropractor previously. Of the participants in the SMT and sham groups respectively, 33 (82.5%) and 25 (62.5%) believed they received a real treatment, suggesting the sham was successful (enough) at deceiving the majority of participants.

Manipulation vs Sham:
For PPT, there was a statistically significant time x group difference at the calf immediately and 15 min post-intervention. There were no significant time x group differences at the calf at 30 min, or at the lumbar spine or shoulder at any point after either intervention was carried out. For TS, there were no statistically significant time x group differences at the hands or feet at any time point.

Change over time:
The only major change noted was in the SMT group, where calf PPT actually decreased significantly from baseline to immediately post-intervention only. In the sham group, calf PPT increased significantly from baseline to all follow-up time points. The between-group difference observed in calf PPT could be explained by the significant decrease in PPT after SMT (increased sensitivity) and concurrent increase after sham (decreased sensitivity).

In both the SMT and sham groups, lumbar PPT did not change significantly over time. In both the SMT and sham groups, shoulder PPT increased significantly from baseline to immediately post-intervention only. Hand TS decreased significantly in both groups from baseline, but only at the 30 min post-intervention mark. In the SMT group, feet TS decreased significantly from baseline to all follow-up time points, and in the sham group, feet TS decreased significantly from baseline to 15- and 30-min post-intervention.

As mentioned above, the between-group differences observed in change in calf PPT appear to be explained by regression to the mean in both groups. The data otherwise indicate there is no difference in change in PPT and TS after lumbar SMT compared to sham. Any changes in PPT and TS may therefore be attributable to non-specific effects including expectations, the patient-clinician interaction, hands on contact, and positioning, rather than being unique to SMT. Without a no-treatment control group, the authors could not exclude normal variations over time or changes in response to the study protocol as potential explanations for their observations.

Clinical Application & Conclusions:

Authors’ Conclusions:
It was found that lumbar SMT did not lead to greater short-term changes in PPT or TS compared to sham manipulation in people with low back pain. This suggests that lumbar SMT does not have a specific hypoalgesic effect on these types of quantitative sensory tests. Sham controlled studies investigating cervical and thoracic SMT may help clarify potential differences in hypoalgesic responses between spinal regions.

Clinical Application: Based on the findings of this study, it is hard to definitively explain the beneficial results of lumbar SMT as being due to changes in pressure sensitivity alone. It must however be acknowledged that many times patients will report a subjective feeling of reduced tension or an increase in mobility post-SMT, which is often assessed with no actual pain pressure testing by the clinician. Therefore, SMT may have effects that are unrelated to mechanoreceptor sensitivity, which is primarily what this study tested. It is also possible that any self-reported beneficial impact may be a mix of contextual factors such as expectation of benefit or placebo, but may also be due to physiological changes such as the stimulation of muscle spindles and Golgi tendon organs, which may not be fully captured by PPT and TS alone.

Study Methods:

Participants were recruited from the Murdoch University campus and were individuals aged 18–60 years who could say ‘yes’ to the statement “I have been bothered by lower back pain at some time in the last 12 months”. However, participants did not need to have current LBP.

Exclusion criteria: Suspected or confirmed contraindications to high-velocity low-amplitude (HVLA) lumbar SMT (e.g. recent lumbar disc herniation, active lumbar radiculopathy, osteoporosis, inflammatory arthritis, history of lumbar spine surgery); or any other condition that might affect pain sensitivity measurements (upper or lower limb sensory changes, neurological condition, fibromyalgia or chronic widespread pain, or skin conditions at any of the QST testing sites).

Participants were informed that they would receive one of two possible chiropractic treatments and were unaware that they might receive a sham manipulation. A focused LBP history and physical examination were performed by the assessor. Participants were instructed on the sensory testing procedure. The assessor marked the five sensory testing sites on the skin bilaterally. Baseline testing was then performed. All sensory testing was conducted by the same assessor, the first author, who had substantial prior experience with PPT and TS testing.

The assessor left the room to remain blind to the intervention and a treating clinician entered. Participants were randomly allocated to one of two groups:
  1. an HVLA SMT targeting the L5 segment; or
  2. a sham lumbar intervention.
Following the intervention, the assessor re-entered the room and tested sensitivity immediately, then 15 and 30 min post-intervention.

The active intervention involved a high-velocity, low-amplitude (HVLA) SMT using a side-lying technique targeting the L5 vertebra on one side. A rapid anterior thrust targeting the L5 mamillary process was delivered with the hypothenar aspect of the clinician's contact hand, in conjunction with the clinician's body drop. The sham intervention involved similar positioning to the real SMT, but with the hand contact over the upper medial gluteal musculature in a broad, non-specific manner. The participant's spine was kept relatively neutral. A slow, gentle, non-specific ‘thrust’ was delivered into the gluteal musculature in conjunction with a small ‘body drop’ from the clinician. The sham was intended to mimic the active intervention in positioning and hands-on contact, and to give the participant the perception that ‘something happened’. All clinicians were trained individually or in groups of two on the procedure, while remaining blind to the specific objectives of the study.

Study Strengths / Weaknesses:

Strengths:
  • Good blinding of clinicians and assessors, helping to decrease the risk of bias.
  • The sham SMT technique used in this study has been demonstrated to acceptably deceive participants (2).
  • This study was adequately powered, increasing the ability to generalize results to similar populations.
  • Multiple measurements of PPT and TS taken immediately, 15 min and 30 min post-intervention helping to assess effects of SMT at various points after treatment.
Weaknesses:
  • The authors did not correlate subjective pain reports with pressure sensitivity testing results post intervention. Therefore, we don’t know if pressure sensitivity testing and subjective pain reports were correlated in this study population.
  • 37.5% of the sham group believed they received a sham intervention, which may limit the usefulness of their pain pressure reports due to the fact they believed they got a “fake” treatment.
  • It would have been ideal to include a control group who got no intervention. Without a no-treatment control group, excluding normal variations over time or changes in response to the study protocol as potential explanations cannot be ruled out.
  • Generalizability maybe limited since intervention were given at a predetermined segment.

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 Man Ther 2019; 27(7).
  2. Chaibi A, Šaltytė Benth J, Bjørn Russell M. Validation of placebo in a manual therapy randomized controlled trial. Sci Rep 2015; 5: 11774.
  3. Cruz-Almeida Y, Fillingim RB. Can quantitative sensory testing move us closer to mechanism-based pain management? Pain Med 2014; 15(1): 61–72.
  4. Fischer AA. Application of pressure algometry in manual medicine. J Manag Med 1990; 5: 145–150.