What is osteoarthritis?
Arthritis, which means "joint inflammation," causes joint pain and
swelling. There are many types of arthritis, but osteoarthritis is the most
common type. Also known as degenerative joint disease or age-related arthritis,
osteoarthritis is more likely to develop as people age. Inflammation and injury
to the joint cause a breaking down of cartilage tissues, resulting in pain,
swelling and deformity. The changes in osteoarthritis usually occur slowly over
many years, though there are occasional exceptions.
There are two main types of
osteoarthritis:
- primary: more generalized osteoarthritis
that affects the fingers,
thumbs, spine, hips, and knees
- secondary: osteoarthritis
that occurs after injury or inflammation in a joint
What is cartilage?
Cartilage is a firm, rubbery material covering the ends of bones in normal
joints (see figure 1). It is primarily composed of water and proteins whose
primary function is to reduce friction in the joints and serve as a "shock
absorber." The shock-absorbing quality of normal cartilage comes from its
ability to change shape when compressed, because of its high water content.
Although cartilage may undergo some repair when damaged, the body does not
regenerate new cartilage after injury.
Cartilage is made up of two main elements: a gel-like substance called
matrix composed primarily of water and two types of proteins – collagen and proteoglycans
- and cells known as chondrocytes that are contained within the matrix.
- Collagen is a structural protein found in many tissues such
as skin, tendons and bone, and is a key structural component of cartilage.
Collagen provides cartilage with its strength and creates a framework for the
other components of cartilage.
- Proteoglycans are complex molecules composed of protein
and sugar combinations that are interwoven in the matrix of cartilage. Their
function is to trap large amounts of water in cartilage, which allows it to
change shape when compressed and thus act as shock absorber.
- Water makes up a large part of healthy cartilage. Water
helps to form a "gel-like" matrix with the other components outlined,
allowing it to function as the "shock absorber" for the joint. In
diseases like osteoarthritis, cartilage loses a lot of its water content. This
water loss diminishes protection of the joint.
- Chondrocytes are highly complex multifunctional cartilage
cells. Functions include production of collagen, proteoglycans, and enzymes
involved in the maintenance of healthy cartilage. As cartilage forms, these
cells migrate through the different layers of cartilage, changing as they do so
by mechanisms that are not fully understood.