Cartilage is a tremendously strong and flexible fibrous tissue, and it takes many forms and serves multiple purposes throughout the body.
There are three types of cartilage:
- Elastic cartilage
- Hyaline cartilage
Derived from the Greek word "Hyali," which means "glass,” hyaline cartilage is smooth and shiny. It is the most common type of cartilage, found in the nose, windpipe, and most of the body's joints.
In a joint, hyaline cartilage is referred to as articular cartilage. This is because the cartilage covers bones' surfaces where they articulate, or meet to form the joint. For example, at the knee joint, the top of the tibia, the bottom of the femur, and the back of the kneecap are covered with articular cartilage.
See Knee Anatomy
The thickness of articular cartilage varies from joint to joint. For example, in the wrist, cartilage may be less than 1 mm thick 1 Pollock J, O'Toole RV, Nowicki SD, Eglseder WA. Articular cartilage thickness at the distal radius: a cadaveric study. J Hand Surg Am. 2013 Aug;38(8):1477-81. doi: 10.1016/j.jhsa.2013.04.037. Epub 2013 Jun 28. PubMed PMID: 23810572. , while in some areas of the knee the cartilage may be as thick as 6 mm. 2 Cohen ZA, McCarthy DM, Kwak SD, Legrand P, Fogarasi F, Ciaccio EJ, Ateshian GA. Knee cartilage topography, thickness, and contact areas from MRI: in-vitro calibration and in-vivo measurements. Osteoarthritis Cartilage. 1999 Jan;7(1):95-109. PubMed PMID: 10367018.
Articular cartilage has two primary purposes:
- Smooth movement. Extremely slippery, articular cartilage allows bones to glide over each other as a joint flexes and straightens.
- Shock absorption. Articular cartilage acts as a shock absorber, cushioning bones against impacting each other during a weight-bearing activity, such as walking or jogging.
Articular cartilage also stores synovial fluid, a sticky, viscous fluid that lubricates and circulates nutrients to the joint. When the joint is at rest, the synovial fluid is stored in the articular cartilage much like water is stored in a sponge. When the joint bends or bears weight, the synovial fluid is squeezed out, helping to keep the joint lubricated and healthy.
Despite its flexibility and strength, cartilage can be damaged. Problems can arise due to:
- Wear-and-tear over time that can eventually lead to osteoarthritis
- Diseases, such as rheumatoid arthritis or ankylosing spondylitis
When cartilage is damaged, the bones may rub and grind against one another at the joint, causing friction.
How does damaged cartilage cause pain?
Cartilage does not contain nerves, so damaged cartilage itself does not cause pain. However, the friction between the joint's bones and other resulting abnormalities (such as bone spurs) can cause discomfort and pain as well as inflammation.
Does damaged cartilage ever heal?
Because it does not contain blood vessels, cartilage does not heal itself well. When cartilage has become thinned or damaged, a limited amount of new cartilage may be produced, but the new cartilage cells will grow in irregular, bumpy patterns. The result is that the bones may rub and grind against one another at the joint and this can be a source of pain.
Gradual onset of stiffness, pain, and swelling in the joint can be a sign of osteoarthritis.