Archive for category Cavitation

Clinical scenario

A 24-year-old female presented to the chiropractic clinic with low back pain and neck pain. During the chiropractic treatment, the patient enquired about the significance of the “crack” that accompanied the adjustment. The audible release is a phenomenon that is familiar to chiropractors. Although it is widely accepted that this “cracking” sound is generated by a cavitation mechanism, there are a number of opinions regarding the significance of the audible release to a chiropractic adjustment. The author wonders if there is any evidence to suggest that an audible release is a necessary component to a successful adjustment.

Three part question

For [a chiropractic adjustment] does [an audible release] improve [outcome]?

Search strategy

A computerised literature search was conducted on the following databases: Allied and Complementary Medicine Allied (AMED), Index to Chiropractic Literature (ICL), Manual, Alternative and Natural Therapy (MANTIS) and Medline (Pub Med). In addition the Journal of Manipulative and Physiological Therapeutics (JMPT), Spine, and the Archives of Physical Medicine and Rehabilitation where searched. The following terms where used for the search: cavitation AND (sound OR sounds) OR audible AND (release OR pop) OR joint AND (crack OR cracks OR cracking). Results where limited to English language. Results older than 20 years where not included.

Search outcome

82 articles where found, of which 7 were relevant.

Comment

There is some evidence to suggest that a cavitation is required during an adjustment to achieve the forces in the appropriate periarticular tissues without causing muscular damage. It is suggested that a chiropractor can accurately detect a cavitation. However, during a manipulation it is impossible to be certain which joint underwent the cavitation process based solely on the sound. Therefore, the sound of an audible release does not necessarily indicate that the appropriate reflexes were stimulated.

Possibly the greatest therapeutic benefit of the audible release may not be physiological in nature but rather psychological. The joint crack may have a powerful placebo effect on both the patient and practitioner. It is not unreasonable to assume that the patient expects to hear a cracking sound during the treatment and interprets this sound as a sign of a successful adjustment. When the expectations of the patient are not fulfilled this may have a negative affect on the clinical outcome. If an audible release is achieved, especially with reinforcement from the practitioner, then a powerful placebo effect may be expected.

Clinical bottom line

There is no direct evidence for the physiological therapeutic benefit of the audible release associated with the chiropractic adjustment. Furthermore, repeating the adjustment shortly after the joint has cavitated without an audible release, aiming to “get an audible”, may even cause damage as the joint is potentially stretched beyond its anatomical range of movement.

To conclude, an audible release may improve the outcome of a chiropractic adjustment, but therapeutic benefits of the audible release are likely to be psychological, and not physiological.


 J Can Chiropr Assoc. 2004 Sep; 48(3): 237–239. [PMCID: PMC1769448]

Author information: Mischa Bakker, AECC student and Joyce Miller, BSc, DC, DABCO, Senior Clinical Tutor, AECC.

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COMMENTARY:

In the past three decades, chiropractic researchers have given a great deal of attention to the audible release (1); it is known to be sometimes caused by joint cavitation, as in the metacarpophalangeal joints, for example (2, 3), and is sometimes assumed to be associated with joint cavitation during spinal manipulation therapy (SMT) (4, 5). Recently, an excellent review of the literature on the audible release associated with joint manipulation was published by Brodeur (6). In this review, Brodeur concluded:

“that the cavitation process provides a simple means for initiating the reflex actions and that without the cavitation process, it would be difficult to generate the forces in the appropriate tissue without causing muscular damage.”

This conclusion contains two basic ideas: 1) cavitation in itself initiates reflex actions; and 2) without cavitation, SMT aimed at eliciting reflex responses could cause muscular damage. In this commentary, I will address these two issues with the use of arguments based on known experimental observations.

Does the Cavitation Process Provide a Simple Means for Initiating Reflex Actions? Does Cavitation Help to Reduce the Incidence of Muscular Damage Caused by SMT?

Conclusion: Based on research of the reflex response associated with chiropractic SMT, it  seems unlikely that cavitation causes reflex responses in the spinal musculature. Furthermore, it seems unlikely that active muscular forces produced by the stretch-reflex response would ever (substantially) resist the joint distraction forces produced by high-velocity chiropractic treatments of the spine.


Reference: Walter Herzog, PhD. J Manipulative Physiol Ther.  1996 Mar-Apr;19(3):216-18.

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Abstract

OBJECTIVE:

The objective of this paper is to review the literature on the audible release associated with manipulation.

DATA SOURCES:

Bibliographic information in pertinent articles and papers located in the MEDLINE database containing the keywords joint, joints, cartilage, crack, cracking, cavitation, crepitus and noise.

STUDY SELECTION:

All articles relevant to the objectives were selected.

DATA EXTRACTION:

All available data was used.

DATA SYNTHESIS:

The audible release is caused by a cavitation process whereby a sudden decrease in intracapsular pressure causes dissolved gasses in the synovial fluid to be released into the joint cavity. Once a joint undergoes cavitation, the force-displacement curve changes and the range of motion of the joint increases. The gasses released from the synovial fluid make up about 15% of the joint volume and consist of approximately 80% carbon dioxide. Habitual joint cracking does not correlate with arthritic changes, but does correlate with loss of grip strength and soft-tissue swelling. During the “crack” associated with a joint manipulation, there is a sudden joint distraction that occurs in less time than that required to complete the stretch reflexes of periarticular muscles. Theories on the cavitation mechanism were reviewed and new information on the cavitation process is introduced. In this paper, it is proposed that the cavitation process is generated by an elastic recoil of the synovial capsule as it “snaps back” from the capsule/synovial fluid interface.

CONCLUSIONS:

Because the sudden joint distraction during a manipulation occurs in a shorter time period than that required to complete the stretch reflexes of the periarticular muscles, there is likely to be a high impulse acting on the ligaments and muscles associated with the joint. This is an important conclusion, because others have proposed that reflex actions from high threshold periarticular receptors are associated with the many beneficial results of manipulation. This suggests that the cavitation process provides a simple means for initiating the reflex actions and that without the cavitation process, it would be difficult to generate the forces in the appropriate tissue without causing muscular damage.


J Manipulative Physiol Ther. 1995 Mar-Apr;18(3):155-64.  [PMID:7790795]

Author information: Brodeur R. Department of Biomechanics, Michigan State University, East Lansing 48824, USA.

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