Cavitation during upper cervical high-velocity, low amplitude (HVLA) thrust manipulation is significantly more likely to occur bilaterally than unilaterally, say investigators.
Indeed, they found that the popping sounds associated with C1-2 manipulation were 11 times more likely to occur bilaterally than just unilaterally.
"Therefore, for practitioners [who] wish to target a specific dysfunctional vertebral segment of the upper cervical spine, as has been traditionally taught in manual therapy, and based on the results of our study, it may be inappropriate to perform the C1-2 HVLA thrust manipulation from both sides, to maximize the likelihood that the target articulation indeed 'cracked' or 'popped," James Dunning (Alabama Physical Therapy & Acupuncture in Montgomery, USA) and team comment.
The researchers also found that most of the 19 patients receiving two upper cervical thrust manipulations to the right and left C1-2 articulation produced 3-4 pops during a single rotary HVLA thrust manipulation.
"Therefore, practitioners should expect multiple popping sounds when performing this type of manipulation of the atlanto-axial joint," say the researchers.
They add that it is unlikely, although not proven so, that the 3-4 popping sounds were from a single facet joint.
The popping sounds were recorded using skin-mounted microphones that were secured bilaterally over the transverse process of C1, from which sound wave signals were recorded.
Bilateral popping sounds were detected in 34 (91.9%) of 37 manipulations, while unilateral popping sounds were detected in just three (8.1%) manipulations. Of the 132 total cavitations, 72 occurred ipsilateral and 60 contralateral to the targeted C1-2 articulation.
This, says the team, means that "the traditional manual therapy approach of targeting a single ipsilateral or contralateral facet joint in the upper cervical spine may not be realistic."
The average number of pops per patients following both right and left C1-2 thrust manipulations was 6.95. The mean duration of a single audible pop was 5.66 ms and the mean duration of a single manipulation was 96.95 ms.
The authors conclude in BMC Musculoskeletal Disorders that their findings give practitioners a better idea of the mechanism of the cavitation sound, considered by many to be an "important indicator of the successful delivery of an HVLA thrust manipulation."
They now call for further study into the possible relationship between the number of cavitations and the degree of change in pain and disability.
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