View Full Version : Re: "Cracking Joints"

Partap S. Khalsa
04-03-1997, 09:59 AM
David Clarke wrote:
> Dear biomch-l readers:
> The following is for my own interest. I frequently "crack" my knuckles,
> knees, ankles, elbows, etc. The "school-yard" explanation that I've
> heard is that I'm releasing nitrogen gas from the blood. Any truth to
> that? Does anyone know the mechanism behind this?
> Incidently, I find that if I don't "crack" my knees frequently (4 or more
> times per hour), then I find flexion/extension to be a very odd
> sensation. Not painful, just a little stiff.
> Can I develop arthritus year from now because I continue to do this to my
> body? I've heard both yes and no.
> Any insight would be appreciated.
> Thanks,
> David Clarke
> Engineering Student
> Memorial University of Newfoundland
> St. John's, NF
> Canada

The phenomenon you describe has been of considerable interest to the
chiropractic, osteopathic, and physical medicine professions. In
particular, what is the cause of the "cracking" sound that commonly is
produced during spinal manipulations/adjustments. Please see the
following discussion written by R. Brodeur of the Dept. of Biomechanics,
Michican State Univ. ("The audible release associated with joint
manipulation". Journal of Manipulative & Physiological Therapeutics.
18(3):155-64, 1995 Mar-Apr. )

------------------- begin Abstract -------------------------------------

OBJECTIVE: The objective of this paper is to review the literature on
the audible release associated with manipulation.

DATA SOURCES: Bibliographic information in pertinent articles and papers
located in the MEDLINE database containing the

keywords: joint, joints, cartilage, crack, cracking, cavitation,
crepitus and noise.

STUDY SELECTION: All articles relevant to the objectives were selected.
DATA EXTRACTION: All available data was used.
DATA SYNTHESIS: The audible release is caused by a cavitation process
whereby a sudden decrease in intracapsular pressure causes dissolved
gasses in the synovial fluid to be released into the joint cavity. Once
a joint undergoes cavitation, the force-displacement curve changes and
the range of motion of the joint increases. The gasses released from the
synovial fluid make up about 15% of the joint volume and consist of
approximately 80% carbon dioxide. Habitual joint cracking does not
correlate with arthritic changes, but does correlate with loss of grip
strength and soft-tissue swelling. During the "crack" associated with a
joint manipulation, there is a sudden joint distraction that occurs in
less time than that required to complete the stretch reflexes of
periarticular muscles. Theories on the cavitation mechanism were
reviewed and new information on the cavitation process is introduced. In
this paper, it is proposed that the cavitation process is generated by
an elastic recoil of the synovial capsule as it "snaps back" from the
capsule/synovial fluid interface.

CONCLUSIONS: Because the sudden joint distraction during a manipulation
occurs in a shorter time period than that required to complete the
stretch reflexes of the periarticular muscles, there is likely to be a
high impulse acting on the ligaments and muscles associated with the
joint. This is an important conclusion, because others have proposed
that reflex actions from high threshold periarticular receptors are
associated with the many beneficial results of manipulation. This
suggests 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.
[References: 40]

-----------------------end of abstract

Hope you have found this informative.


Partap S. Khalsa, D.C., Ph.D.
Associate Research Scientist
Yale University School of Medicine