Research Review By Dr. Michael Haneline©


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Date Posted:

November 2022

Study Title:

Impact of audible pops associated with spinal manipulation on perceived pain: a systematic review


Moorman A & Newell D

Author's Affiliations:

AECC University College, Bournemouth, United Kingdom

Publication Information:

Chiropractic & Manual Therapies 2022; 30: 42.

Background Information:

Spinal pain is very common worldwide and can have a significant negative effect on the lives of those affected as well as increased costs to society. Most people with spinal pain seek treatment, with about 75% of spinal pain patients consulting either a chiropractor, physical therapist or osteopath (1). Such clinicians commonly provide spinal manipulative therapy (SMT) and/or spinal mobilization, which are recommended as treatment options in several practice guidelines for the management of both low back pain (LBP) and neck pain (2-4).

Most chiropractic patients are accustomed to hearing a popping or cracking sound associated with SMT and the clinician delivering SMT may associate this sound with the perception of a successful intervention. In fact, some clinicians apply another thrust (or multiple additional thrusts) when the sound does not occur.

Tribonucleation is a term that describes the process which causes a joint to generate a cracking sound and occurs when sufficient distraction force overcomes the viscous attraction or adhesive forces between opposing joint surfaces (this term is now used instead of ‘cavitation’). Rapid separation of the articulation occurs with the resulting drop in synovial pressure allowing dissolved gas to come out of solution to form a cavity within the joint (5).

It is commonly understood that the objective of SMT is to restore joint function and mobility, although how this is achieved and whether SMT is responsible for proven decreases in pain and improvements in function are undetermined. It has been suggested that personal interaction and therapeutic touch by the clinician produces psychological reassurance for the patient. However, the clinical relevance of an audible pop (AP), though inextricably associated with SMT, is currently unknown.

Hence, the objective of this review was to assess and update the evidence concerning the role of the AP in producing therapeutic benefits associated with SMT, specifically if the AP plays a role in decreasing pain perception.

Pertinent Results:

Literature Search & Study Characteristics:
After reviewing the titles and abstracts of 69 studies that were found in the literature search, five were ultimately included in the review (6-10). All of them investigated the effect of an audible pop (AP) during SMT on pain outcomes, with all but 1 study investigating musculoskeletal pain. That study included healthy subjects who received an external thermal pain stimulus to assess outcomes. Only one study was an RCT, the others were prospective cohort studies. The included studies were judged by the authors to be of fair to good quality.

A total of 303 participants were included in the 5 studies, 38.7% male and 61.3% female. Four studies included participants with pain complaints, with 2 studies focusing on cervical pain and 2 studies on LBP. There were substantial differences among the five studies regarding factors such as: participants being with or without pain, having pain at differing sites and differing durations of pain.

Participants were provided SMT in a single session in all but one study in which SMT was provided over 5 sessions. SMT was described in each study as a high velocity thrust by a skilled practitioner that was directed at the participants’ pain location.

SMT was applied to the sacroiliac region in 2 studies with LBP participants, whereas thoracic SMT was used in the 2 studies with neck pain participants. All but one of the studies repeated the SMT if AP was not recorded on the first attempt with a maximum of four thrusts in total. The practitioners decided whether an AP occurred based on their perception of hearing or feeling an AP during SMT which was noted as either ‘pop’ or ‘no-pop’.

APs were perceived on 210 participants and absent on 72 participants, although no information was provided on the total number of SMT thrusts. It was unclear whether an AP occurred in 21 participants because 1 study noted over or under 3 pops where the number categorized as “under three” can mean either no pop or 1 or 2 pops.

Pain levels were measured using either the Numeric Pain Rating Scale (NPRS) or Visual Analog Scale (VAS), which were self-completed by the participants. All studies reported that there was no statistically significant association between perceived pain and the presence of an AP during SMT.

Clinical Application & Conclusions:

This review concluded that there is currently no evidence supporting a relationship between the presence of an audible pop during SMT and pain outcomes. Clinicians should, therefore, refrain from overstating the presence of a perceived AP as an indicator of successful SMT, or otherwise implying to a patient that SMT without an AP is ‘unsuccessful’.

Nevertheless, since many practitioners and patients consider an AP to be an important indicator of successful SMT, the authors suggested that further research would be helpful to understand the full meaning of this phenomenon to both patients and practitioners.

Editor’s note: The results of this study are not surprising in many ways but may seem counter-intuitive to clinicians. Ultimately, the mechanism of action of SMT responsible for relieving our patients’ pain may indeed have little to do with achieving an AP, despite the consensus that hearing the noise might be of value to the patient and indicate to the clinician that a repeat thrust is not necessary. So, the question remains – how many times do we attempt SMT in pursuit of the AP? There is no science-informed answer to this question, unfortunately. For what it’s worth, if I do not hear an AP, I normally try at least one more time, sometimes two, depending on how well I think the force of the SMT went where I had intended (also, whether the patient was properly positioned, relaxed etc.). It is a personal choice, but there are likely diminishing returns after 3 attempts, in my opinion.

Study Methods:

This was a systematic review which followed the PRISMA guidelines (Preferred Reporting Items for Systematic Reviews and Meta-Analyses). Several electronic databases were searched using the following search terms “audible release/pop”, “joint cavitation/cracking”, “spinal manipulative therapy”, “chiropractic adjustment/manipulation”, “high velocity low amplitude adjustment”, “spinal manipulation” and “pain”. The reference lists of the included studies were also screened searching for other relevant papers.

Following are the inclusion criteria that were used:
  • empirical and mixed-method studies,
  • published in the English language,
  • human, adult participants (over 18 years old),
  • symptomatic or asymptomatic participants,
  • assessed pain outcomes following the occurrence of an AP associated with SMT of cervical, thoracic, lumbar or lumbo-pelvic regions, and
  • peer reviewed.
Exclusion criteria:
  • letters, dissertations, commentaries, editorials, conference abstracts;
  • language other than English;
  • animal participants;
  • children (under 18 years old);
  • did not assess pain outcomes; and
  • extremity adjustment(s).
Retrieved papers were independently screened for inclusion by both authors with any discrepancies resolved by consensus. If a decision to include or exclude a study could not be made based on reading the abstract, the full text was reviewed.

Both authors assessed the quality of the included studies using the Downs and Black checklist, which includes 27 criteria that cover reporting quality, external and internal validity, and power. Any discrepancies were resolved through meeting/discussion.

Study Strengths / Weaknesses:

This was a well-conducted systematic review that utilized accepted methods and followed the PRISMA guidelines. However, there were several study limitations, including the following:
  • Only 69 studies were retrieved in the literature search, a low number for a typical systematic review. It is possible the search terms were too focused and did not locate studies that reported relevant results that were outside their main objective (or, there simply isn’t a ton of research in this area).
  • There were methodological problems in the included studies which are common in studies that investigate manual therapies; for instance, lack of blinded assessment.
  • This review found that an audible pop is not associated with perceived pain regardless of the area of the spine manipulated, but it is unknown if this finding is generalizable to extraspinal articulations.

Additional References:

  1. Murthy V, Sibbritt D, Adams J. An integrative review of complementary and alternative medicine use for back pain: a focus on prevalence, reasons for use, influential factors, self-perceived effectiveness and communication. Spine J. 2015; 15(8): 1870–83.
  2. National Institute for Health and Care Excellence (NICE). Low back pain and sciatica in over 16s: assessment and management NICE guideline. London: NICE. NICE guidelines NG59. 2016.
  3. Bussières A, Stewart G, Al-Zoubi F, et al. Spinal manipulative therapy and other conservative treatments for low Back pain: a guideline from the Canadian chiropractic guideline initiative. J Manipul Physiol Therap 2018; 41(4): 265–93.
  4. Blanpied P, Gross A, Elliott JM, et al. Neck pain: revision 2017. J Orthop Sports Phys Ther 2017; 47(7): A1–83.
  5. Kawchuck G, Fryer J, Jaremko J, et al. Real-Time Visualization of Joint Cavitation. PLoS ONE 2015; 10(4): e0119470.
  6. Bialosky JE, Bishop MD, Robinson ME, George SZ. The relationship of the audible pop to hypoalgesia associated with high-velocity, low-amplitude thrust manipulation: a secondary analysis of an experimental study in pain-free participants. J Manipul Physiol Ther 2010; 33(2): 117–24.
  7. Sillevis R, Cleland J. Immediate effects of the audible pop from a thoracic spine thrust manipulation on the autonomic nervous system and pain: a secondary analysis of a randomized clinical trial. J Manipul Physiol Ther 2011; 34(1): 37–45.
  8. Cleland J, Flynn T, Childs J, Eberhart S. The audible pop from thoracic spine manipulation and its relation to short term outcomes in patients with neck pain. J Man Manipul Ther 2007; 15(3): 143–54.
  9. Flynn T, Childs J, Fritz J. The audible pop from high velocity thrust manipulation and outcome in individuals with low back pain. J Manipul Physiol Ther 2006; 29(1): 40–5.
  10. Flynn T, Fritz J, Wainner R, Whitman J. 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(7): 1057–60.

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