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Osteoarthritis Basics: The Joint and Its Parts

A Healthy Joint

Healthy Joint

A Healthy Joint. Click for larger view.
Illustration: National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)

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.

Joints allow movement between the bones and absorb the shock from walking or other repetitive motion. Joints are made up of:

Cartilage. A hard, slippery coating on the end of each bone.

Joint capsule. A tough membrane 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.

Ligaments, tendons, and muscles. Tissues that surround the bones and joints, a llowing the joints to bend and move. Ligaments are tough, cord-like tissues that connect one bone to another. Tendons are tough fibers that connect muscles to bones. Muscles are bundles of specialized cells that, when stimulated by nerves, either relax or contract to produce movement.

Fast Facts

  • Osteoarthritis is the most common type of arthritis. More common in older people, it is sometimes called degenerative joint disease.
  • Osteoarthritis most often occurs in the hands (at the ends of the fingers and thumbs), spine (neck and lower back), knees, and hips.
  • Some 27 million Americans age 25 and older have osteoarthritis.
  • Osteoarthritis is more likely in overweight people and among those with jobs that stress particular joints.
  • Exercise is one of the best treatments for osteoarthritis.
  • Before age 45, osteoarthritis is more common in men. After 45, it is more common in women.
A Joint with severe Osteoarthritis

A Joint With Severe Osteoarthritis.
Click for larger view.
Illustration: National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)

A Joint With Severe Osteoarthritis

With osteoarthritis, the cartilage wears away. Spurs grow out from the edge of the bone, and synovial fluid increases. The joint feels stiff and sore.

Read More "Osteoarthritis" Articles

Living Better With Osteoarthritis / Osteoarthritis Basics / Symptoms, Diagnosis, Treatment / "No Pills Yet" / Research Findings

Winter 2013 Issue: Volume 7 Number 4 Page 11