In the past three decades, chiropractic researchers have given a great deal of attention to the audible release (1); it is known to be sometimes caused by joint cavitation, as in the metacarpophalangeal joints, for example (2, 3), and is sometimes assumed to be associated with joint cavitation during spinal manipulation therapy (SMT) (4, 5). Recently, an excellent review of the literature on the audible release associated with joint manipulation was published by Brodeur (6). In this review, Brodeur concluded:

“that the cavitation process provides a simple means for initiating the reflex actions and that without the cavitation process, it would be difficult to generate the forces in the appropriate tissue without causing muscular damage.”

This conclusion contains two basic ideas: 1) cavitation in itself initiates reflex actions; and 2) without cavitation, SMT aimed at eliciting reflex responses could cause muscular damage. In this commentary, I will address these two issues with the use of arguments based on known experimental observations.

Does the Cavitation Process Provide a Simple Means for Initiating Reflex Actions? Does Cavitation Help to Reduce the Incidence of Muscular Damage Caused by SMT?

Conclusion: Based on research of the reflex response associated with chiropractic SMT, it  seems unlikely that cavitation causes reflex responses in the spinal musculature. Furthermore, it seems unlikely that active muscular forces produced by the stretch-reflex response would ever (substantially) resist the joint distraction forces produced by high-velocity chiropractic treatments of the spine.

Reference: Walter Herzog, PhD. J Manipulative Physiol Ther.  1996 Mar-Apr;19(3):216-18.