Joint Cavitation: Does it Matter?
Reading time: 6 minutes
Studies have shown that the audible cavitation of the joints during manipulation doesn't actually impact treatment outcomes. However, a patient’s expectations of hearing a pop can contribute positively toward improved outcomes… or negatively via a nocebo effect.
This means patient education is key. This blog will equip you with evidence-based answers to the top five questions, plus a downloadable patient infographic to help explain joint manipulation and manage patient expectations around the “pop.”
1. What causes joint cavitation?
Short answer: The science is not definitive, but probably the distraction-induced release of gasses within the joint fluid, aka “tribonucleation.” (1)
Deeper dive: The specific mechanism(s) of audible joint cavitation remain undefined.
“High-velocity, low-amplitude thrust manipulation consists of applying a rapid impulse accompanied by an audible pop sound. The exact origin of the popping sound is still unknown and under debate.” (2)
As mentioned in the What is Manipulation blog by the other guy 😏, the three leading hypotheses include:
Creation of vapor bubbles via rapid separation of joint surfaces, aka “tribonucleation.”(1,3,4) Essentially, quickly lowering the pressure on a fluid allows dissolved gasses to escape and coalesce.
The collapse of vapor bubbles (5-7)
Multiple concurrent mechanisms (8-10)
One prevailing premise suggests sound is created by “rapid separation of the joint surfaces with subsequent gas cavity formation.” (1,2,4,11)
“When sufficient distraction force overcomes the viscous attraction or adhesive forces between opposing joint surfaces, 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. This cavity persists after the popping sound is produced and therefore proposes that joint cracking is associated with cavity formation within the synovial fluid.” (11)
2. Provider beliefs: Does joint cavitation matter?
Short answer: It probably depends on how often you “pop” joints.
Deeper dive: This might be hard to imagine, but not all chiropractors agree about the significance of a “pop.” 🤯
“There is still no consensus among chiropractors on the association of an audible pop and pain outcomes in spinal manipulative therapy.” (11)
Many HVLA-oriented manual therapists believe that a popping sound is a primary differentiator between manipulation and mobilization. (11,12) Several sources suggest that an audible popping sound is a primary characteristic of successful joint manipulation. (2,13,21) In fact, many providers apply subsequent thrusts if the first (or second, or third…) attempt did not result in an audible release. (11,22)
One recent literature analysis, including five studies of 303 patients, determined that approximately three out of four (74%) manipulations resulted in audible joint cavitation. (11) Other authors have shown that the frequency of audible joint cavitation increases with experience and speed. (23,24)
Thus, the natural Pavlovian response would persuade HVLA chiropractors to mentally connect incremental improvements in audible joint cavitation and treatment success.
3. Patient beliefs: Does joint cavitation matter?
Short answer: “If it cracks, you know it has moved”
Deeper dive: Like providers, patients also have a natural Pavlovian response to relate their improvements to the most distinct aspect of care - audible joint cavitation. In fact, experienced providers will attest to many stories of patients who sighed with relief when the provider's knuckles cavitated as they motion palpated or thrust on the patient.
Multiple studies have concluded that most patients believe the absence of a popping sound equates to an ineffective thrust manipulation. (2,25,26) One study suggested that 75% of patients believe that “If it cracks, you know it has moved” and that a popping sound is essential. (26)
However, patient and provider expectations may not align with the current literature.
4. What does the research say about joint cavitation?
Short answer: The pop does not matter
Deeper dive: Multiple studies have shown no difference in range of motion, pain, or disability outcomes between thrust manipulation with and without associated audible cavitation. (27-31) One recent review of five prior studies concluded: “regardless of the area of the spine manipulated or follow-up time, there was no evidence of improved pain outcomes associated with an audible pop.” (11)
5. Do chiropractors need joint cavitation patient education?
Short answer: Yes. The nocebo effect is in play when patients expect a “pop” but don’t experience it.
The Nocebo Effect
“The opposite of the placebo effect. It describes a situation where a negative outcome occurs due to a belief that the intervention will [not work or] cause harm. Some experts state that the nocebo effect may have a larger effect on clinical outcomes than the placebo effect as negative perceptions are formed much faster than positive one.” (32)
Deeper dive: Evidence-based providers understand that a patient’s biopsychosocial perspective regarding manipulation can dramatically impact compliance, outcomes, and chronicity. (2,33)
“Inconsistency between patient beliefs for understanding the popping sound after thrust manipulation and the explanations currently provided can potentially alter patient-reported outcome changes.” (25)
Patients often mistakenly believe that their healing is dependent on the provider. (34) These same patients are subject to a potent nocebo effect if they also believe that successful therapy requires the provider to deliver a “pop.” (2,25)
“Practitioners who perform thrust manipulation should pay attention to patients' beliefs and clearly explain the aim and effectiveness of thrust manipulation using current theoretical models.” (2)
One recent study found that nearly one-third (31%) of HVLA patients did not recall receiving any information on the mechanisms or effects of manipulation. (2) Educating and preparing patients' expectations for HVLA can help mitigate the nocebo effect, leading to better outcomes and compliance. (2,34,35)
Good news for you! Your ChiroUp team has created an informative infographic to help you educate patients and avoid the nocebo effect. Subscribers can access the infographic in the Forms Library by searching “The Pop”.
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