Your joints can make a variety of sounds: popping, cracking, grinding,
and snapping. The joints that "crack" are the knuckles,
knees, ankles, back, and neck. There are different reasons why
these joints "sound off".
- Escaping gases: Scientists explain that synovial fluid
present in your joints acts as a lubricant. The fluid contains
the gases oxygen, nitrogen, and carbon dioxide. When you pop
or crack a joint, you stretch the joint capsule. Gas is rapidly
released, which forms bubbles. In order to crack the same knuckle
again, you have to wait until the gases return to the synovial
- Movement of joints, tendons and ligaments: When a joint
moves, the tendons position changes and moves slightly
out of place. You may hear a snapping sound as the tendon returns
to its original position. In addition, your ligaments may tighten
as you move your joints. This commonly occurs in your knee or
ankle, and can make a cracking sound.
- Rough surfaces: Arthritic joints make sounds caused
by the loss of smooth cartilage and the roughness of the joint
Is joint cracking harmful? If you are feeling pain when your joints
pop, then you should seek a health care professional. In terms
of knuckle cracking, some studies show that knuckle cracking does
not cause serious harm. Other studies show that repetitive knuckle
cracking can do some damage to the soft tissue of the joint. It
may also lead to a weak grip and a swelling hand.
Carol. How do we move? Austin, Tex., Raintree
Steek-Vaughn, c.1998. 32p. (Juvenile).
Christine. Bones and joints: a guide for students.
Edinburgh; New York, Church Livingstone, 1992. 186 p.
Bernard. Understanding joints: a practical guide to
their structure and function. Cheltenham, Stanley
Thornes, 2000. 240 p.
Brian. Bones and joints. New York, F. Watts, c.1991.
32 p. (Juvenile).
more print resources...
Search on "osteoarthritis," "synovial," or "bones
in the Library of Congress Online
A Healthy Joint. In a healthy joint, the bones
are encased in smooth cartilage. Together, they are protected by
a joint capsule lined with a synovial membrane that produces synovial
fluid. The capsule and fluid protect the cartilage, muscles and
An Osteoarthritic Joint. With osteoarthritis,
the cartilage becomes worn away. Spurs grow out from the edge of
the bone, and synovial fluid increases. Altogether, the joint feels
stiff and sore.
From the National
Institute of Arthritis and Musculoskeletal and Skin Diseases