What's in a crack? How does joint manipulation actually work?
High-Velocity Low-Amplitude (HVLA) manipulation is a common treatment method used by osteos, chiros (usually call them “adjustments”) and manipulative physios to relieve pain and improve joint mobility. HVLA manipulation is a manual therapy technique that involves a quick, high-velocity thrust applied to a joint, followed by a short amplitude movement. The purpose of this technique is to restore normal joint movement and alleviate pain. While HVLA has been in use for many years, there is still much debate regarding the underlying mechanism of action. The “crack or pop” is the joint fluid changing pressure and forming a small gas bubble (this is called cavitation) which is thought to then be reabsorbed back into the fluid over a period of about 20 minutes and probably why immediately following manipulation that your range of movement feels so good!
Here is short video of the gas bubble forming as a joint is manipulated.
Recent research has shed light on the physiological and neurological changes that occur during and after HVLA manipulation. These changes help to explain how HVLA provides pain relief and improves joint function. One of the primary effects of HVLA manipulation is the activation of the spinal reflex arc. The spinal reflex arc is a pathway that connects the sensory receptors in muscles and joints to the spinal cord and motor neurons. The quick, high-velocity thrust of the HVLA technique stimulates the muscle spindles and Golgi tendon organs, which are sensory receptors located in the muscles and joints. This stimulation triggers a reflex response that results in the relaxation of the muscles and the release of endorphins. Endorphins are natural painkillers that help to reduce pain and promote a sense of well-being.
Another effect of HVLA manipulation is the reduction of inflammation. Inflammation is a natural response to injury or tissue damage. However, when inflammation becomes chronic, it can contribute to pain and joint dysfunction. HVLA manipulation has been shown to reduce inflammation by decreasing the levels of inflammatory cytokines, such as interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha).
Additionally, HVLA manipulation has been found to improve joint mobility and range of motion. This is thought to be due to the release of joint restrictions that can occur as a result of injury, overuse, or prolonged postural habits poor that can lead to strain.
Overall, the latest evidence suggests that HVLA manipulation provides pain relief and improves joint function through a combination of neurological, physiological, and biomechanical effects. The activation of the spinal reflex arc, the release of endorphins, the reduction of inflammation, and the restoration of normal joint movement are all important factors that contribute to the effectiveness of HVLA manipulation.
References:
Bialosky JE, Bishop MD, George SZ, Robinson ME, Zeppieri G Jr. Spinal manipulative therapy has an immediate effect on thermal pain sensitivity in people with low back pain: a randomized controlled trial. Phys Ther. 2009 Dec;89(12):1292-303.
Gross A, Langevin P, Burnie SJ, Bédard-Brochu MS, Empey B, Dugas E, Faber-Dobrescu M, Andres C, Graham N, Goldsmith CH, Brønfort G, Hoving JL, LeBlanc F. Manipulation and mobilization for neck pain contrasted against an inactive control or another active treatment. Cochrane Database Syst Rev. 2015 Sep 23;(9):CD004249.
Gonzalez-Iglesias J, Fernandez-de-Las-Penas C, Cleland JA, Gutierrez-Vega Mdel R. Thoracic spine manipulation for the management of patients with neck pain: a randomized clinical trial. J Orthop Sports Phys Ther. 2009 Apr;39(4):20