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Osteoarthritis Basics The Joint And Its Parts
A joint is the point where two or more bones are connected.
With a few exceptions (in the skull and pelvis, for example), joints
are designed to allow movement between the bones and to absorb shock
from movements like walking or repetitive motions.
These movable joints are made up of the following parts:
Cartilage: a hard but slippery coating on the end of each bone.
Cartilage, which breaks down and wears away in osteoarthritis, is
described in more detail on the next page.
Joint capsule: a tough membrane sac that encloses all the bones and
other joint parts.
Synovium (sin-O-vee-um): a thin membrane inside the joint capsule that
secretes synovial fluid.
Synovial fluid: a fluid that lubricates the joint and keeps the
cartilage smooth and healthy.
A Healthy Joint
images of a healthy joint
In a healthy joint, the ends of 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 connective tissues.
A Joint With Severe Osteoarthritis
images of a joint with osteoarthritis
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.
Ligaments, tendons, and muscles are tissues that surround the bones and
joints, and allow the joints to bend and move. Ligaments are tough,
cord-like tissues that connect one bone to another. Tendons are tough,
fibrous cords that connect muscles to bones. Muscles are bundles of
specialized cells that, when stimulated by nerves, either relax or
contract to produce movement.
Cartilage: The Key to Healthy Joints
Cartilage is 65 to 80 percent water. The remaining three components - collagen, proteoglycans, and chondrocytes - are described below.
- collagen (KAHL-uh-jen): A family of fibrous proteins, collagens are the building blocks of skin, tendon, bone, and other connective tissues.
- proteoglycans (PRO-tee-uh-GLY-kanz): Made up of proteins and sugars, strands of proteoglycans interweave with collagens and form a mesh-like tissue. This allows cartilage to flex and absorb physical shock.
- chondrocytes (KAHN-druh-sytz): Found throughout the cartilage, chondrocytes are cells that produce cartilage and help it stay healthy as it grows. Sometimes, however, they release substances called enzymes that destroy collagen and other proteins. Researchers are trying to learn more about chondrocytes.
How Do You Know if You Have Osteoarthritis?
Usually, osteoarthritis comes on slowly. Early in the disease, your joints may ache after physical work or exercise. Later on, joint pain may become more persistent. You may also experience joint stiffness, particularly when you first wake up in the morning or have been in one position for a long time.
Although osteoarthritis can occur in any joint, most often it affects the hands, knees, hips, and spine (either at the neck or lower back). Different characteristics of the disease can depend on the specific joint(s) affected. For general warning signs of osteoarthritis, see the box on the next page. For information on the joints most often affected by osteoarthritis, please see the following descriptions below:
Hands: Osteoarthritis of the hands seems to have some hereditary characteristics, that is, it runs in families. If your mother or grandmother has or had osteoarthritis in their hands, you're at greater-than-average risk of having it too. Women are more likely than men to have hand involvement and, for most, it develops after menopause.
When osteoarthritis involves the hands, small, bony knobs may appear on the end joints (those closest to the nails) of the fingers. They are called Heberden's (HEBerr-denz) nodes. Similar knobs, called Bouchard's (boo-SHARDZ) nodes, can appear on the middle joints of the fingers. Fingers can become enlarged and gnarled, and they may ache or be stiff and numb. The base of the thumb joint also is commonly affected by osteoarthritis.
Knees: The knees are among the joints most commonly affected by osteoarthritis. Symptoms of knee osteoarthritis include stiffness, swelling, and pain, which make it hard to walk, climb, and get in and out of chairs and bathtubs. Osteoarthritis in the knees can lead to disability.
Hips: The hips are also common sites of osteoarthritis. As with knee osteoarthritis, symptoms of hip osteoarthritis include pain and stiffness of the joint itself. But sometimes pain is felt in the groin, inner thigh, buttocks, or even the knees. Osteoarthritis of the hip may limit moving and bending, making daily activities such as dressing and putting on shoes a challenge.
Spine: Osteoarthritis of the spine may show up as stiffness and pain in the neck or lower back. In some cases, arthritis-related changes in the spine can cause pressure on the nerves where they exit the spinal column, resulting in weakness or numbness of the arms and legs.
Cartilage: The Key to Healthy Joints
Cartilage is 65 to 80 percent water. The remaining three components - collagen, proteoglycans, and chondrocytes - are described below.
- collagen (KAHL-uh-jen): A family of fibrous proteins, collagens are the building blocks of skin, tendon, bone, and other connective tissues.
- proteoglycans (PRO-tee-uh-GLY-kanz): Made up of proteins and sugars, strands of proteoglycans interweave with collagens and form a mesh-like tissue. This allows cartilage to flex and absorb physical shock.
- chondrocytes (KAHN-druh-sytz): Found throughout the cartilage, chondrocytes are cells that produce cartilage and help it stay healthy as it grows. Sometimes, however, they release substances called enzymes that destroy collagen and other proteins. Researchers are trying to learn more about chondrocytes.
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