What causes the "popping" noise when you crack a joint? (Does it improve joint manipulation outcomes?)

This content was cited from the course:

• Joint Mobilization and Manipulation: Introduction
  • 3 Credit Course: Pre-approved for continuing education and the Integrated Manual Therapist (IMT) Certification

What is the "Popping Sound"

In this article, we discuss the "pop" sound that seems to arise from inside a joint after moving the joint past a restricted range of motion (ROM). These sounds are thought to be correlated with a cavitation and will be referred to as "cavitation sounds" for the rest of this article. Defining cavitation sounds in this way is intended to separate these sounds from sounds that also sound like a "pop", but may arise from structures rubbing over or past one another (e.g. a tendon snapping across a bony protuberance), or the tearing or ripping of tissues (e.g. an Achilles tendon or quadriceps tendon rupture).

What is a cavitation?

A cavitation is the formation of an empty space within a solid object or body. More specifically, the formation of bubbles in a liquid via the reduction in static pressure below a liquid's vapor pressure, leads to the formation of small vapor-filled cavities (bubbles). When subjected to higher pressures, these cavities may collapse and can result in shock waves that result in sound.

• Evidence-based Joint Cavitation Sound Hypothesis: Cavitation sounds result from the separation of joint surfaces, which results in a rapid decrease in intra-articular pressure (cavitation), which results in degassing of synovial fluid (mostly carbon dioxide), the creation of a cavitation bubble within the joint, and the sound itself is either the result of bubble collapse (e.g. shockwaves mentioned above) or bubble formation/tribonucleation (e.g. similar to removing a suction cup from a window).
  1. Separation of joint surfaces
  2. Resulting in a rapid decrease in intra-articular pressure (cavitation)
  3. Degassing of synovial fluid (mostly carbon dioxide)
  4. Creation of cavitation bubble within the joint
  5. The sound itself is either the result of bubble collapse (like popping a balloon) or bubble formation/tribonucleation (like pulling a suction cup off of a window).

Additional Manual Therapy Articles

• You Can Palpate The Psoas

Additional Joint Manipulation Courses

• Joint Mobilization and Manipulation: Palpation, Assessment, and Reliability
• Joint Mobilizations and Manipulations: Risk of Adverse Events
• Joint Manipulation: Ankle, Midfoot and Tibiofibular Joint
• Joint Manipulation: Elbow (Radial Head) and Wrist
• Joint Manipulation: Lumbar Spine, Sacroiliac Joint and Pubic Symphysis
• Joint Manipulation: Thoracic Spine
• Joint Manipulation: Cervical Spine

Caption: Visualization of joint cavitation (joint popping) - By © 2015 Kawchuk et al. - http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0119470, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=49089125

Proposed Mechanism:

Published literature suggests that the sound that accompanies manipulation has been a curiosity of researchers for more than 100 years, and research continues to debate whether bubble formation or bubble collapse produces the sound. The first evidence-based theory was likely published in a review by Roston et al. in 1947 (1), which references a German study that demonstrates gas bubble formation within joints, published by Christen, T. in 1911 (2). The review by Roston et al. begins the development of a theory that the sound results from the separation of joint surfaces, resulting in cavitation (a sudden decrease in pressure), which results in gas formation within the joint, and an audible "crack" (1). A more recent and detailed review by Unsworth et al. (3) includes mathematical modeling, high-speed imaging, gas analysis, and force data, and suggests that the sound is produced by the collapse of the cavitation bubble. Note, that this study goes into much greater detail regarding various aspects of metacarpophalangeal joint cavitation sounds (3). A study by Suja et al. supports the assertion of sound resulting from a collapsing cavitation bubble, demonstrating that metacarpophalangeal joint cavitation sounds are consistent with mathematical modeling of an acoustic signature (dominant frequency and magnitude) of a collapsing bubble. Further, the model demonstrated that only a partial collapse of the bubble was needed to replicate the acoustic signature, implying bubbles could persist following the collapse and allow for multiple cavitation sounds (4). These studies establish that the cavitation sound is correlated with the separation of joint surfaces, which results in a rapid decrease in intra-articular pressure (cavitation), and the formation of a bubble within a joint; and further, supports that the collapse of the bubble results in the cavitation sound.

Additional studies suggest a collapsing cavitation bubble resulting in the sound is an incomplete theory. A review by Brodeur et al. cites evidence that the sound is the result of a rapid "degassing" of the dissolved gases within the synovial fluid (80% carbon dioxide), and the rapid creation of a cavitation bubble produces the sound (5). Kawchuk et al (2015) used MRI before and after manipulation, and real-time MRI during manipulation, to demonstrate that the cavitation sound coincided with bubble formation and that the bubble did not collapse following the cavitation. This study asserts that cavitation is the result of tribonucleation, in which opposing surfaces resist separation until a critical point (like pulling a suction cup from a window) (6). Conversely, a study by Cascioli et al. demonstrated that no significant change in facet joint space followed by cervical manipulation with cavitation, which implies that the bubble formation hypothesis is incomplete (7). Conversely, a blinded RCT by Cramer et al. (discussed below) demonstrated that cavitation sounds during side-lying lumbar manipulations were correlated with increased gapping of facet joints (8). This may imply that MRI is not sensitive enough to reliably identify the changes in facet joint space correlated with cavitation. In summary, these studies imply that cavitation sounds result from the separation of joint surfaces, which results in a rapid decrease in intra-articular pressure (cavitation), which results in degassing of synovial fluid (mostly carbon dioxide), the creation of a cavitation bubble within the joint, and the sound itself is either the result of bubble collapse or bubble formation/tribonucleation.

Caption: Performing a lumbar manipulation to decrease excessive arthrokinematic stiffness

Position Statement:

• Research suggests that manipulations are most likely to result in cavitation sounds occurring within a few segments of the target area, result in multiple cavitation sounds, and cavitation sounds may occur on either side. Further, research demonstrates there is no correlation between manipulations producing a cavitation sound(s) and manipulations resulting in a systemic neurophysiological response or improved patient outcomes.

Summary:

• Cavitation Sounds and Manipulations:
  • Cervical Manipulations: Cervical manipulations are likely to result in multiple cavitation sounds, and cavitation sounds are equally likely to occur on either or both sides regardless of manipulation direction. Although individual studies suggest that certain techniques may increase the likelihood of cavitation sounds occurring on a particular side, the lack of agreement between studies suggests that predicting the side is not reliable .
  • Thoracic and Lumbar Manipulations: Lumbar manipulations are most likely to result in multiple cavitation sounds, from the facets on the same side as the direction of rotation, within a 3 segment range of the intended target segment, including the intended target segment, and may be followed by a refractory period (silent period) of about 60 minutes. Additionally, thoracic manipulations are likely to result in multiple cavitation sounds within a range of 3 segments, including the target segment.
  • Ankle: A single ankle joint manipulation is an insufficient intervention plan to reliably increase dorsiflexion range of motion (ROM), and the production of cavitation sounds from manipulations may have a higher likelihood of occurring in individuals with more mobile ankles.
• Cavitation Sounds and Outcomes: Research demonstrates there is no correlation between manipulations producing a cavitation sound(s) and manipulations resulting in a systemic neurophysiological response or improved patient outcomes.

Cavitation Sounds and Manipulations

Cervical Manipulation

Several studies have investigated the location and frequency of cavitation sounds during cervical spine manipulations. Dunning et al. performed both right- and left-sided, rotary cervical manipulations, intended for the C1 - C2 segment of asymptomatic individuals, resulting in bilateral cavitation sounds during 91% of manipulations, and cavitation sounds occurring with equal likelihood on either side regardless of the direction of rotation. Additionally, the average number of cavitation sounds was 3.57 per manipulation and 6.95 for both sides combined (10). Bolton et al. investigated the location of cavitation sounds during cervical manipulations intended for the C2 segment of asymptomatic individuals. When the motion during the manipulation was primarily rotation, the cavitation sounds were more likely to occur on the side opposite the direction of rotation; however, when the motion during the manipulation was primarily lateral flexion the cavitation sounds were equally likely to occur on either side (11). Conversely, Reggars et al. demonstrated that diversified rotary manipulation of the cervical spine was more likely to produce cavitation sounds on the same side as the direction of rotation, and bilateral cavitation sounds were more likely from individuals with a history of neck pain (12). In a follow-up study, Reggars et al. demonstrated that asymptomatic individuals receiving a single diversified rotary cervical manipulation most often produced multiple cavitation sounds per manipulation (82%) (contradicting the previous study). Of 50 participants, 9 (18%) produced a single cavitation sound, 22 (44%) produced 2 cavitation sounds, 10 (20%) produced 3 cavitation sounds, 7 (14%) produced 4 cavitation sounds, and 2 (4%) produced 5 cavitation sounds (13). Last, another study by Dunning et al. investigated cavitation sounds from right- and left-sided, cervicothoracic thrust manipulations targeting the T1/T2 segment of patients with upper trapezius  myalgia . The findings suggest that this technique exhibits an increased likelihood of unilateral cavitation sounds on the same side the head is rotated toward (14). These studies suggest that cervical manipulations are likely to result in multiple cavitation sounds, and cavitation sounds are equally likely to occur on either or both sides regardless of manipulation direction. Although individual studies suggest that certain techniques may increase the likelihood of cavitation sounds occurring on a particular side, the lack of agreement between studies suggests that predicting the side is not reliable .

Lumbar and Thoracic Manipulation

Studies have also investigated the location and frequency of cavitation sounds during thoracic and lumbar manipulations. Frantzis et al. investigated the accuracy of lumbar manipulations based on the location of cavitation sounds, demonstrating cavitation sounds occurred in 12 of 20 subjects (60%), 16 of 38 manipulations produced at least one cavitation sound, 8 of 16 cavitation sounds were accurate to the intended target (50%), and the mean-variance from the intended location was 5.31 cm (15). Mourad et al. demonstrated that side-lying rotatory lumbar manipulations resulted in cavitation sounds that were equally likely to occur on either side regardless of the direction of rotation, occurred on both sides 2% time, and an average of 5 cavitation sounds were recorded per manipulation (range 2-9) (16). Cramer et al. demonstrated that two lumbar side-lying manipulations in quick succession, performed by an experienced chiropractor, resulted in most cavitation sounds produced by the upside facet joints (93.5%), some joints produced multiple cavitation sounds, and cavitation sounds occurred mostly in the target area (71.7%) (8). A blinded RCT by Cramer et al. demonstrated that side-lying lumbar manipulations resulted in more cavitation sounds than side-lying positioning (96.7% vs 30%), that upside facet joints produced the majority of cavitation sounds, and the cavitation sounds correlated with increased gapping of facet joints (17). Ross et al. demonstrated that about half of the cavitation sounds from lumbar and thoracic manipulations occurred within one segment of the intended target, additional cavitation sounds occurred within a 3-segment range, and most manipulations resulted in multiple cavitation sounds including the target segment (18). Beffa et al. attempted to correlate which lumbosacral manipulation technique was used with the location of the cavitation sounds (19). Last, Bereznick et al. demonstrated that following lumbar manipulation until no audibles were present there was a refractory period (defined as a return of less than 50% of the number of cavitations) of about an hour in asymptomatic individuals. The findings demonstrated no correlation between technique and location; however, it should be mentioned that the lower lumbar spine and sacroiliac joint were the only joints monitored for cavitation sounds (20). These studies suggest that lumbar manipulations are most likely to result in multiple cavitation sounds, from the facets on the same side as the direction of rotation, within a 3 segment range of the intended target segment, including the intended target segment, and may be followed by a refractory period (silent period) of about 60 minutes. Additionally, thoracic manipulations are likely to result in multiple cavitation sounds within a range of 3 segments, including the target segment.

Ankle

Two studies were located investigating cavitation sounds and ankle manipulations. An RCT by Anderson et al. demonstrated that a single ankle manipulation did not increase dorsiflexion for individuals with a history of a lateral ligament sprain. Further, a trend (statistical significance not reached) was noted that may imply an increased likelihood of cavitation sounds occurring from individuals with more mobile ankles (21). Similarly, Fryer et al. demonstrated that a single ankle joint manipulation did not increase dorsiflexion range of motion (ROM) in asymptomatic individuals; however, this study demonstrated a correlation (statistical significance reached) between more mobile ankles and an increased likelihood of cavitation sounds produced during manipulations (22). These studies suggest that a single ankle joint manipulation is an insufficient intervention plan to reliably increase dorsiflexion range of motion (ROM), and the production of cavitation sounds from manipulations may have a higher likelihood of occurring in individuals with more mobile ankles. Author's note, individuals with the most mobile ankles are likely to benefit least from manipulations, due to manipulations most often being administered with the intent to increase joint mobility.

Caption: Proximal Tibiofibular Manipulation

Cavitation Sounds and Outcomes

Research suggests that cavitation sounds may not be correlated with outcomes. A prospective study by Flynn et al. demonstrated that the presence or absence of cavitation sounds during sacroiliac joint (SIJ) manipulation was not correlated with the magnitude or frequency of improvements in ROM, pain, or disability of patients with non-radicular low back pain (25). A multi-center clinical trial by Flynn et al. demonstrated that the perception of a cavitation sound during lumbar manipulation, heard by the patient or therapist, did not correlate with improved outcomes for patients with non-radicular low back pain immediately following treatment or during long-term follow-up (26). Note, that Herzog et al. demonstrated that a clinician's perception of whether cavitation occurred was very accurate (compared to accelerometry) (27). Cleland et al. investigated the relationships between cavitation sounds and outcomes following cervical manipulations, demonstrating that no correlation existed between the number of cavitation sounds and improvements in pain, disability, and/or range of motion (ROM) (28). Two additional studies demonstrate that the systemic effects resulting from manipulations are not dependent on the presence of a cavitation sound. Dunning et al. noted that a single cervical manipulation intended for the C5/C6 facets resulted in an immediate increase in resting EMG activity of the biceps brachii bilaterally, regardless of whether a cavitation sound occurred (29). And, a secondary analysis of an RCT by Sillevis et al. demonstrated that cervical manipulations resulted in similar improvements in pain and changes in autonomic response (pupil response) regardless of whether a cavitation sound occurred (20). In summary, research demonstrates there is no correlation between manipulations producing a cavitation sound(s) and manipulations resulting in a systemic neurophysiological response or improved patient outcomes.

Caption: Thoracic Thrust Manipulation, also known as Thoracic Screw Manipulation

Bibliography

Cavitation Sounds

1. Roston, J. B., & Haines, R. W. (1947). Cracking in the metacarpophalangeal joint. Journal of anatomy, 81(Pt 2), 165.
2. Fick, R. (1911). Zum Streit um den Gelenkdruck. Anatomische Hefte, 43(2), 397-414.
3. Unsworth, A., Dowson, D., & Wright, V. (1971). 'Cracking joints'. A bioengineering study of cavitation in the metacarpophalangeal joint. Annals of the rheumatic diseases, 30(4), 348.
4. Suja, V. C., & Barakat, A. I. (2018). A mathematical model for the sounds produced by knuckle cracking. Scientific reports, 8(1), 1-9.
5. Brodeur, R. (1995). The audible release associated with joint manipulation. Journal of Manipulative and Physiological Therapeutics, 18(3), 155-164.
6. Kawchuk, G. N., Fryer, J., Jaremko, J. L., Zeng, H., Rowe, L., & Thompson, R. (2015). Real-time visualization of joint cavitation. PloS one, 10(4), e0119470.
7. Cascioli, V., Corr, P., & Till, A. G. (2003). An investigation into the production of intra-articular gas bubbles and increase in joint space in the zygapophyseal joints of the cervical spine in asymptomatic subjects after spinal manipulation. Journal of manipulative and physiological therapeutics, 26(6), 356-364.
8. Cramer, G. D., Ross, K., Raju, P. K., Cambron, J., Cantu, J. A., Bora, P., ... & Pocius, J. D. (2012). Quantification of cavitation and gapping of lumbar zygapophyseal joints during spinal manipulative therapy. Journal of manipulative and physiological therapeutics, 35(8), 614-621.
9. Demoulin, C., Baeri, D., Toussaint, G., Cagnie, B., Beernaert, A., Kaux, J. F., & Vanderthommen, M. (2018). Beliefs in the population about cracking sounds produced during spinal manipulation. Joint Bone Spine, 85(2), 239-242.
   • Cavitation Sounds and Manipulations: Cervical
10. Dunning, J., Mourad, F., Barbero, M., Leoni, D., Cescon, C., & Butts, R. (2013). Bilateral and multiple cavitation sounds during upper cervical thrust manipulation. BMC musculoskeletal disorders, 14(1), 1-12.
11. Bolton, A., Moran, R. W., & Standen, C. (2007). An investigation into the side of joint cavitation associated with cervical spine manipulation. International journal of osteopathic medicine, 10(4), 88-96.
12. Reggars, J. W., & Pollard, H. P. (1995). Analysis of zygapophyseal joint cracking during chiropractic manipulation. Journal of manipulative and physiological therapeutics, 18(2), 65-71.
13. Reggars, J. W. (1996). THE MANIPULATIVE CRACK: Frequency Analysis. Australasian chiropractic & osteopathy, 5(2), 39.
14. Dunning, J., Mourad, F., Zingoni, A., Iorio, R., Perreault, T., Zacharko, N., ... & Cleland, J. A. (2017). Cavitation sounds during cervicothoracic spinal manipulation. International Journal of Sports Physical Therapy, 12(4), 642.
    • Cavitation Sounds and Manipulations: Thoracic and Lumbar
15. Frantzis, E., Druelle, P., Ross, K., & McGill, S. (2015). The accuracy of osteopathic manipulations of the lumbar Spine: A Pilot study. International Journal of Osteopathic Medicine, 18(1), 33-39.
16. Mourad, F., Dunning, J., Zingoni, A., Iorio, R., Butts, R., Zacharko, N., & Fernández-de-las-Peñas, C. (2019). Unilateral and Multiple Cavitation Sounds During Lumbosacral Spinal Manipulation. Journal of Manipulative and Physiological Therapeutics, 42(1), 12-22.
17. Cramer, G. D., Ross, J. K., Raju, P. K., Cambron, J. A., Dexheimer, J. M., Bora, P., ... & Habeck, A. R. (2011). Distribution of cavitations as identified with accelerometry during lumbar spinal manipulation. Journal of manipulative and physiological therapeutics, 34(9), 572-583.
18. Ross, J. K., Bereznick, D. E., & McGill, S. M. (2004). Determining cavitation location during lumbar and thoracic spinal manipulation: is spinal manipulation accurate and specific?. Spine, 29(13), 1452-1457.
19. Beffa, R., & Mathews, R. (2004). Does the adjustment cavitate the targeted joint? An investigation into the location of cavitation sounds. Journal of manipulative and physiological therapeutics, 27(2), 118-122.
20. Bereznick, D. E., Pecora, C. G., Ross, J. K., & McGill, S. M. (2008). The refractory period of the audible “crack” after lumbar manipulation: a preliminary study. Journal of manipulative and physiological therapeutics, 31(3), 199-203.
    • Cavitation Sounds and Manipulations: Ankle
21. Andersen, S., Fryer, G. A., & McLaughlin, P. (2003). The effect of talo-crural joint manipulation on range of motion at the ankle joint in subjects with a history of ankle injury. Australasian Chiropractic & Osteopathy, 11(2), 57.
22. Fryer, G. A., Mudge, J. M., & McLaughlin, P. A. (2002). The effect of talocrural joint manipulation on range of motion at the ankle. Journal of manipulative and Physiological Therapeutics, 25(6), 384-390.
    • Cavitation Sounds and Manipulations: Technique
23. Van Geyt, B., Dugailly, P. M., Klein, P., Lepers, Y., Beyer, B., & Feipel, V. (2017). Assessment of in vivo 3D kinematics of cervical spine manipulation: Influence of practitioner experience and occurrence of cavitation noise. Musculoskeletal Science and Practice, 28, 18-24.
24. Conway, P. J. W., Herzog, W., Zhang, Y., Hasler, E. M., & Ladly, K. (1993). Forces required to cause cavitation during spinal manipulation of the thoracic spine. Clinical Biomechanics, 8(4), 210-214.
    • Cavitation Sound and Outcomes
25. Flynn, T. W., Fritz, J. M., Wainner, R. S., & Whitman, J. M. (2003). The audible pop is not necessary for successful spinal high-velocity thrust manipulation in individuals with low back pain. Archives of physical medicine and rehabilitation, 84(7), 1057-1060.
26. Flynn, T. W., Childs, J. D., & Fritz, J. M. (2006). The audible pop from high-velocity thrust manipulation and outcome in individuals with low back pain. Journal of manipulative and physiological therapeutics, 29(1), 40-45.
27. Herzog, W., Zhang, Y. T., Conway, P. J., & Kawchuk, G. N. (1993). Cavitation sounds during spinal manipulative treatments. Journal of manipulative and physiological therapeutics, 16(8), 523.
28. Cleland, J. A., Flynn, T. W., Childs, J. D., & Eberhart, S. (2007). The audible pop from thoracic spine thrust manipulation and its relation to short-term outcomes in patients with neck pain. Journal of manual & manipulative therapy, 15(3), 143-154.
29. Dunning, J., & Rushton, A. (2009). The effects of cervical high-velocity low-amplitude thrust manipulation on resting electromyographic activity of the biceps brachii muscle. Manual therapy, 14(5), 508-513.
30. Sillevis, R., & Cleland, J. (2011). 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. Journal of manipulative and physiological therapeutics, 34(1), 37-45.
31. Meal, G. M., & Scott, R. A. (1986). Analysis of the joint crack by simultaneous recording of sound and tension. Journal of manipulative and physiological therapeutics, 9(3), 189-195.

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