[1] The most rigorous definition, based on available empirical research is that of Evans and Lucas:[2] "Separation (gapping) of opposing articular surfaces of a synovial joint, caused by a force applied perpendicularly to those articular surfaces, that results in cavitation within the synovial fluid of that joint."
Following the labelling system developed by Geoffery Maitland,[6] manipulation is synonymous with Grade V mobilization, a term commonly used by physical therapists.
Because of its distinct biomechanics (see section below), the term high velocity low amplitude (HVLA) thrust is often used interchangeably with manipulation.
[citation needed] Manipulation can be distinguished from other manual therapy interventions such as joint mobilization by its biomechanics, both kinetics and kinematics.
In particular, the rapid rate of change of force that occurs during the thrust phase when spinal joints are manipulated is not always necessary.
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.
[9] 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.
When a manipulation is performed, the applied force separates the articular surfaces of a fully encapsulated synovial joint.
Infrequent, but potentially serious side effects, include: vertebrobasilar accidents (VBA), strokes, spinal disc herniation, vertebral and rib fractures, and cauda equina syndrome.
Cassidy, DC, and co-workers concluded that the treatment of lumbar intervertebral disk herniation by side posture manipulation is "both safe and effective.
[19] The degree of serious risks associated with manipulation of the cervical spine is uncertain, with widely differing results being published.
A 2008 study in the journal "Spine", JD Cassidy, E Boyle, P Cote', Y He, et al. investigated 818 VBA strokes that were hospitalized in a population of more than 100 million person-years.
[24] Jaskoviak reported approximately 5 million cervical manipulations from 1965 to 1980 at The National College of Chiropractic Clinic in Chicago, without a single case of vertebral artery stroke or serious injury.
[25] Henderson and Cassidy performed a survey at the Canadian Memorial Chiropractic College outpatient clinic where more than a half-million treatments were given over a nine-year period, again without serious incident.
It has required only the very rare reporting of these accidents to malign a therapeutic procedure that, in experienced hands, gives beneficial results with few adverse side effects".
[30] In very rare instances, the manipulative adjustment to the cervical spine of a vulnerable patient becomes the final intrusive act which results in a very serious consequence.
"[35] The NHS Centre for Reviews and Dissemination stated that the survey had methodological problems with data collection.
In a 1995 study, chiropractic researcher Allan Terrett, DC, pointed to this problem: This error was taken into account in a 1999 review[40] of the scientific literature on the risks and benefits of manipulation of the cervical spine (MCS).
Special care was taken, whenever possible, to correctly identify all the professions involved, as well as the type of manipulation responsible for any injuries and/or deaths.