Review written by Steve Kamper info


Several professions (including physiotherapy) have a long history of using thrust manipulation as part of their treatment repertoire for people with spinal pain. Clinical research has demonstrated small, short-lasting effects of thrust manipulation on pain compared to no treatment, but little or not effect compared to sham or other passive treatments (Rubinstein et al 2012; Leaver et al 2010).

Spinal manipulation involves application of a high velocity, low amplitude movement producing joint surface separation; this may or may not be associated with a cracking sound. Various explanatory models have been proposed to describe the mechanism of action and account for the sound. Different professions have tended to adhere to different models, and history has seen various models fall out of favour as research evidence accumulates. Over time there has been a gradual retreat away from mechanical theories, e.g. joint surfaces being realigned, towards neurological explanations (Bialosky et al 2009) and justifying manipulation as providing a ‘window of opportunity’ (Collins et al 2017). At the same time, evidence has shown that the cracking sound during manipulation is not due to hard tissue movement, but gas bubble formation within synovial joint fluid (Kawchuk et al 2015).

This study aimed to explore what people with and without experience of spinal manipulative therapy attributed the cracking sound during manipulation to.


Around three-quarters of the population appear to believe that the ‘crack’ that comes with spinal manipulation is due to mechanical realignment or bony movement between the vertebrae.


The researchers recruited subjects via the researchers’ social networks and through advertisements, and interviewed them face-to-face. Recruitment was purposeful to include people who had, and had not previously received spinal manipulation, and people with and without current back pain. Pertinent, open-ended questions included; “What is the sound usually heard during spinal manipulation (where does it come from)?”; and: “Does the sound indicate successful spinal manipulation?”.


The study included 100 participants - 40 who had previously received spinal manipulation, and 60 who had not. There were slightly more females than males, and average age was about 43. The two groups were quite similar in terms of

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