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Biomechanics of joint manipulation
Until recently, force-time histories measured during spinal manipulation were described as consisting of three distinct phases: the preload (or prethrust) phase, the thrust phase, and the resolution phase. Evans and Breen added a fourth ‘orientation’ phase to describe the period during which the patient is oriented into the appropriate position in preparation for the prethrust phase.
When individual peripheral synovial joints are manipulated, the distinct force-time phases that occur during spinal manipulation are not as evident. In particular, the rapid rate of change of force that occurs during the thrust phase when spinal joints are manipulated is not always necessary. Most studies to have measured forces used to manipulate peripheral joints, such as the metacarpophalangeal (MCP) joints, show no more than gradually increasing load. This is probably because there are many more tissues restraining a spinal motion segment than an independent MCP joint.
The kinematics of a complete spinal motion segment when one of its constituent spinal joints are manipulated are much more complex than the kinematics that occur during manipulation of an independent peripheral synovial joint. Even so, the motion that occurs between the articular surfaces of any individual synovial joint during manipulation should be very similar and is described below.
Early models describing the kinematics of an individual target joint during the various phases of manipulation (notably Sandoz 1976) were based on studies that investigated joint cracking in MCP joints. The cracking was elicited by pulling the proximal phalanx away from the metacarpal bone (to separate, or 'gap' the articular surfaces of the MCP joint) with gradually increasing force until a sharp resistance, caused by the cohesive properties of synovial fluid, was met and then broken. These studies were therefore never designed to form models of therapeutic manipulation, and the models formed were erroneous in that they described the target joint as being configured at the end range of a rotation movement, during the orientation phase. The model then predicted that this end range position was maintained during the prethrust phase until the thrust phase where it was moved beyond the 'physiologic barrier' created by synovial fluid resistance; conveniently within the limits of anatomical integrity provided by restraining tissues such as the joint capsule and ligaments. This model still dominates the literature. However, after re-examining the original studies on which the kinematic models of joint manipulation were based, Evans and Breen argued that the optimal prethrust position is actually the equivalent of the neutral zone of the individual joint, which is the motion region of the joint where the passive osteoligamentous stability mechanisms exert little or no influence. This new model predicted that the physiologic barrier is only confronted when the articular surfaces of the joint are separated (gapped, rather than the rolling or sliding that usually occurs during physiological motion), and that it is more mechanically efficient to do this when the joint is near to its neutral configuration.
Joint manipulation is characteristically associated with the production of an audible 'clicking' or 'popping' sound. This sound is believed to be the result of a phenomenon known as cavitation occurring within the synovial fluid of the joint. When a manipulation is performed, the applied force separates the articular surfaces of a fully encapsulated synovial joint. This deforms the joint capsule and intra-articular tissues, which in turn creates a reduction in pressure within the joint cavity. In this low pressure environment, some of the gases that are dissolved in the synovial fluid (which are naturally found in all bodily fluids) leave solution creating a bubble or cavity, which rapidly collapses upon itself, resulting in a 'clicking' sound. The contents of this gas bubble are thought to be mainly carbon dioxide. The effects of this process will remain for a period of time termed the 'refractory period', which can range from a few minutes to more than an hour, while it is slowly reabsorbed back into the synovial fluid. There is some evidence that ligament laxity around the target joint is associated with an increased probability of cavitation.
Clinical effects and mechanisms of action
The clinical effects of joint manipulation have been shown to include:
- Temporary relief of musculoskeletal pain.
- Shortened time to recover from acute back sprains (Rand).
- Temporary increase in passive range of motion (ROM).
- Physiological effects upon the central nervous system.
- No alteration of the position of the sacroiliac joint.
Shekelle (1994) summarised the published theories for mechanism(s) of action for how joint manipulation may exert its clinical effects as the following:
- Release of entrapped synovial folds or plica
- Relaxation of hypertonic muscle
- Disruption of articular or periarticular adhesions
- Unbuckling of motion segments that have undergone disproportionate displacement
Practice of manipulation
In the context of healthcare, joint manipulation is performed by several professional groups. In North America, it is most commonly performed by chiropractors, osteopathic physicians and physical therapists. In Europe, chiropractors, osteopaths and physiotherapists most commonly provide manipulation. When applied to joints in the spine, it is referred to as spinal manipulation.
- Herzog W, Symons B. (2001). "The biomechanics of spinal manipulation.". Crit Rev Phys Rehabil Med 13 (2): 191–216.
- Evans DW, Breen AC. (2006). "A biomechanical model for mechanically efficient cavitation production during spinal manipulation: prethrust position and the neutral zone.". J Manipulative Physiol Ther 29 (1): 72–82. doi:10.1016/j.jmpt.2005.11.011. PMID 16396734.
- Brodeur R. (1995). "The audible release associated with joint manipulation.". J Manipulative Physiol Ther 18 (3): 155–64. PMID 7790795.
- Unsworth A, Dowson D, Wright V. (1971). "'Cracking joints'. A bioengineering study of cavitation in the metacarpophalangeal joint.". Ann Rheum Dis 30 (4): 348–58. doi:10.1136/ard.30.4.348. PMID 5557778.
- Fryer GA, Mudge JM, McLaughlin PA (2002). "The effect of talocrural joint manipulation on range of motion at the ankle". Journal of Manipulative and Physiological Therapeutics 25 (6): 384–90. doi:10.1067/mmt.2002.126129. PMID 12183696.
- Nilsson N, Christensen H, Hartvigsen J (1996). "Lasting changes in passive range motion after spinal manipulation: a randomized, blind, controlled trial.". J Manipulative Physiol Ther 19 (3): 165–8. PMID 8728459.
- Murphy BA, Dawson NJ, Slack JR (March 1995). "Sacroiliac joint manipulation decreases the H-reflex". Electromyography and clinical neurophysiology 35 (2): 87–94. PMID 7781578.
- Tullberg T, Blomberg S, Branth B, Johnsson R (May 1998). "Manipulation does not alter the position of the sacroiliac joint. A roentgen stereophotogrammetric analysis". Spine 23 (10): 1124–8; discussion 1129. doi:10.1097/00007632-199805150-00010. PMID 9615363. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=0362-2436&volume=23&issue=10&spage=1124. "Because the supposed positive effects are not a result of a reduction of subluxation, further studies of the effects of manipulation should focus on the soft tissue response.".
- Senstad O, Leboeuf-Yde C, Borchgrevink C (February 1997). "Frequency and characteristics of side effects of spinal manipulative therapy". Spine 22 (4): 435–40; discussion 440–1. doi:10.1097/00007632-199702150-00017. PMID 9055373. http://meta.wkhealth.com/pt/pt-core/template-journal/lwwgateway/media/landingpage.htm?issn=0362-2436&volume=22&issue=4&spage=435.
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