David I. Graber, DC, DACBSP
One of the more dramatic effects of a high velocity, low amplitude dynamic thrust joint adjustment is the sound that occurs as the joint fully opens. With descriptors such as “pop,” “crack,” “snap,” and “crunch,” these provide audible evidence that something was done. I personally have several patients who are quite explicit in their expectation of hearing and feeling this result of successful joint gapping. They say in good humor things such as, “I pay by the pop,” and “If it doesn’t crack, I’m not coming back.” Many doctors similarly get hooked into producing the audible sound as an indicator of a successful adjustment, nicknaming it an “applausable.”
With such a strong allegiance to this music of manipulation, let’s explore how relevant it really is.
What causes the pop?
When synovial joints are moved in particular ways, especially when using distractive forces like an adjustment, the separation of the joint surfaces undergo a process of cavitation. A negative pressure is created in the intra-articular synovial fluid forming a gas bubble that eventually cracks. The technical term for this is tribonucleation. This process was finally visualized in real-time at the metacarpal-phalangeal joint on cine-MRI in 2015 by Kawchuk (http://journals.plos.org/plosone/ article?id=10.1371/journal. pone.0119470).
Is this noise necessary to have a therapeutic effect?
Yes and no. It’s essentially undetermined, at least according to the research evidence, and highly disputed.
In the thoracic and lumbar spines and the sacro-iliac joints, manipulation that produced audible releases were no more effective at improving range of motion, reducing pain, decreasing disability, or having an effect on the autonomic nervous system than manipulations that failed to produce a sound (Cleland 2007, Sillevis 2011, Flynn 2003, 2006).
In the cervical spine and the extremities there are no good studies on the effects of manipulation producing cavitations.
Zygopophyseal spinal joints that undergo manipulations producing cavitations have shown greater joint gapping than those that don’t (Cramer 2011), and greater EMG neurological stimulation (Dunning 2008, Herzog 1996).
Which joint is cavitating in an adjustment?
In the upper cervical spine rotation manipulation produced cavitation equally on the ipsilateral and the contralateral sides (Dunning 2013).
In the mid-cervical spine, rotation and lateral manipulations mostly produced cavitations in the side contralateral side of application (Reggars and Pollard 1995, Bolton 2007). In the thoracic and lumbar spines, it was found that cavitations occurred at the intended joints at a frequency of around 50% (Ross 2004). Several studies have found that multiple joints rather than a single one cavitates during a manipulation, even when it is specific to a segment (Reggars 1996, Ross 2004, Reggars & Pollard 1995).
So, where does that leave us? Is cavitation from an adjustment clinically relevant? From a research perspective it is too early to tell. Especially since most of the studies were focused on creating cavitation in the joints, not correcting an underlying dysfunction. From a practical standpoint, the focus required to gain a specific cavitation from an adjustment, in my experience, produces a cleaner and more effective technique, and much better results. Getting a synovial symphony is secondary to good technique application.
~Originally published in The New Jersey Chiropractor, Fall, 2015
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