Arthritis and other rheumatic diseases are characterized by pain, swelling, and limited movement in joints and connective tissues in the body. According to the Centers for Disease Control and Prevention, nearly 47 million people in the US have some form of arthritis or chronic joint symptoms.

Arthritis, which literally means inflammation of a joint (where two or more bones meet), actually refers to more than 100 different diseases. Rheumatic diseases include any diseases that cause pain, stiffness, and swelling in joints or other supportive body structures, such as muscles, tendons, ligaments, and bones.

Arthritis and other rheumatic diseases are often mistakenly associated with old age, because osteoarthritis (the most common form of arthritis) occurs more often among elderly persons. However, arthritis and other rheumatic diseases affect people of all ages.

Arthritis is usually chronic, which means that it rarely changes, or it progresses slowly. Specific causes for most forms of arthritis are not yet known.

What are the parts of a joint?

Joints are the areas where two bones meet. Most joints are mobile, allowing the bones to move. Joints consist of the following:

• cartilage - a type of tissue that covers the surface of a bone at a joint. Cartilage helps reduce the friction of movement within a joint.
• synovial membrane - a tissue called the synovial membrane lines the joint and seals it into a joint capsule. The synovial membrane secretes synovial fluid (a clear, sticky fluid) around the joint to lubricate it.
• ligaments - strong ligaments (tough, elastic bands of connective tissue) surround the joint to give support and limit the joint's movement.
• tendons - tendons (another type of tough connective tissue) on each side of a joint attach to muscles that control movement of the joint.
• bursas - fluid-filled sacs, called bursas, between bones, ligaments, or other adjacent structures help cushion the friction in a joint.
• synovial fluid - a clear, sticky fluid secreted by the synovial membrane.
• femur - the thighbone.
• tibia - the shin bone.
• patella - the kneecap.
• meniscus - a curved part of cartilage in the knees and other joints.

What are the most common types of arthritis?

The three most prevalent forms of arthritis include the following:

• osteoarthritis - the most common type of arthritis. It is a chronic disease involving the joints, particularly the weight-bearing joints such as the knee, hip, and spine. Osteoarthritis is characterized by the following:
  
  
  • destruction of cartilage
  • overgrowth of bone
  • spur formation
  • impaired function

It occurs in most people as they age, but also may occur in young people as a result of injury or overuse.

• fibromyalgia - a chronic, widespread pain in muscles and soft tissues surrounding the joints throughout the body.
• rheumatoid arthritis - an inflammatory disease that involves the lining of the joint (synovium). The inflammation often affects the joints of the hands and the feet and tends to occur equally on both sides of the body.
• Other forms of arthritis, or related disorders, include the following:
  
  
  • gout - a result of a defect in body chemistry (such as uric acid in the joint fluid), this painful condition most often attacks small joints, especially the big toe. It can usually be controlled with medication and changes in diet.
  • systemic lupus erythematosus (lupus) - a very serious, chronic, autoimmune disorder characterized by periodic episodes of inflammation of and damage to the joints, tendons, other connective tissues, and organs, including the heart, lungs, blood vessels, brain, kidneys, and skin.
  • scleroderma - a very serious disease of the body's connective tissue that causes thickening and hardening of the skin.
  • ankylosing spondylitis - a disease that affects the spine, causing the bones of the spine to grow together.
  • juvenile rheumatoid arthritis (JRA) - a form of arthritis in children ages 16 or younger that causes inflammation and stiffness of joints for more than six weeks. Unlike adult rheumatoid arthritis, which is chronic and lasts a lifetime, children often outgrow juvenile rheumatoid arthritis. However, the disease can affect bone development in the growing child.

What are the symptoms of arthritis?

The following are the most common symptoms of arthritis. However, each individual may experience symptoms differently. Symptoms may include:

• pain and stiffness in the joints
• swelling in one or more joints
• continuing or recurring pain or tenderness in a joint
• difficulty using or moving a joint in a normal manner
• warmth and redness in a joint

The symptoms of arthritis may resemble other medical conditions or problems. Always consult your physician for a diagnosis.

How is arthritis diagnosed?

In addition to a complete medical history and physical examination, diagnostic procedures for arthritis may include the following:

• x-rays or other imaging procedures (to show the extent of damage to the joint)
• blood tests and other laboratory tests, including the following:
  
  
  • antinuclear antibody (ANA) test (to check levels of antibodies in the blood)
  • arthrocentesis or joint aspiration (to remove a sample of the synovial fluid to determine if crystals, bacteria, or viruses are present)
  • complete blood count (to determine if white blood cell, red blood cell, and platelet levels are normal)
  • creatinine (to monitor for underlying kidney disease)
  • erythrocyte sedimentation rate (to detect inflammation)
  • hematocrit (to measure the number of red blood cells)
  • rheumatoid factor test (to determine if rheumatoid factor is present in the blood)
  • urinalysis (to determine levels of protein, red blood cells, white blood cells, and casts)
  • white blood cell count (to determine level of white blood cells in the blood)