Understand Your Joints: What Is Cartilage?
We explain what cartilage is and how it functions in our joints.
Most of us take for granted the smooth, painless movements we use to set a table, open a door, or walk to the mailbox. Each of these daily activities engages multiple joints in the body. Bone moves against bone in our joints as we open and close our hand, bend our elbow, and extend our leg to take a step. Usually, we have no sense of friction during these movements thanks to the cartilage in our joints. Cartilage is a flexible connective tissue that keeps joint motion fluid by coating the surfaces of the bones in our joints and by cushioning bones against impact. It is not as rigid as bone, but is stiffer and less flexible than muscle tissue.
There are three types of cartilage, and the tissue of each type has distinct qualities.
- Elastic cartilage functions to provide support and maintain the shape of flexible body parts like our ears and larynx.
- Hyaline cartilage is the most abundant type of cartilage in the body. This smooth, transparent, glassy type of cartilage coats the ends of the bone surfaces, reducing friction in the joints. It is firmly anchored to the bone, and is responsible for the fluid movement of the bones in a joint. The more common name for this type of cartilage is articular cartilage.
- Fibrocartilage is a flexible, elastic, tough form of cartilage that provides cushioning in the joints. The meniscus in the knee joint is made of half-moon-shaped fibrocartilage, and so is the ring-shaped labrum that cushions our hip and shoulder joints. Fibrocartilage tissues absorb approximately a third of joint impact load, but is not as smooth as the articular, cartilage that coats the bones themselves.
For the most part, cartilage does not contain blood vessels or nerves, and is supplied with nutrients through the compression and flexion of the tissue. The cells divide slowly, with a very low turnover rate. Because cartilage has a very limited blood supply, it cannot repair itself easily compared to other types of connective tissue.
Cartilage tissues can be damaged by injury or by wear and tear over time. Without treatment, damaged cartilage may result in progressive arthritis. Because it is not able to heal well, a number of surgical techniques are available to stimulate growth of new cartilage, relieve pain, improve function, and delay or prevent the onset of arthritis.
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