Arthritis is inflammation of a joint - the point where two or more bones meet. There are more than 100 different diseases that are classified as arthritis - all of which may cause pain, swelling, and limited movement in joints and connective tissues in the body.

In some types of arthritis, inflammation occurs in the damaged area of a joint. Damage may be caused by any number of conditions, including trauma, infection, nerve damage, metabolic disturbances, or unknown reasons. Symptoms of inflammation include redness and warmth in the area of the injury, swelling, and pain. In other forms of arthritis, inflammation arises in normal joints and causes damage.

Arthritis is usually chronic, which means that it rarely remits. Most arthritis syndromes progress slowly. Specific causes for most forms of arthritis are not yet known.

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

cartilage - Bones adjacent to the joint are covered with cartilage (a connective tissue), which is made up of cells and fibers and is wear-resistant. Cartilage helps reduce the friction of movement and cushions force (weight-bearing) across the joint.

• synovial membrane - a tissue called the synovial membrane lines the joint. The synovial membrane secretes synovial fluid (a clear, sticky fluid) to lubricate and nourish cartilage within the joint.
  
  
• ligaments - strong ligaments (tough, elastic bands of connective tissue) surround the joint to give support and limit the joint's movement to prevent dislocation.
  
  
• tendons - tendons (another type of tough connective tissue) on each side of a joint attach to muscles that control movement of the joint.
  
  
• bursa - fluid-filled sacs, called bursa, lie between bones, ligaments, and tendons to help reduce the friction between joints, muscles and other connective tissues.
  
  
• synovial fluid - a clear, sticky fluid secreted by the synovial membrane. It carries nourishment to cartilage.
  
  
• femur - the thighbone.
  
  
• tibia - the shin bone.
  
  
• patella - the kneecap.
  
  
• meniscus - a curved part of cartilage in the knees which adds cushioning.

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. Osteoarthritis is also called degenerative joint tissue or "wear and tear" arthritis.
  
  

• 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. It is progressive, destructive and disabling if untreated.
  
  
• seronegative spondyloarthropathies - this group of arthritis syndromes is characterized by joint inflammation similar to rheumatoid arthritis, however, the distribution of arthritis favors the large joints and the axial skeleton (including the spine, hips and shoulders). The seronegative spondyloarthropathies are also associated with other diseases including psoriasis, inflammatory bowel disease (including Cohn's disease), and severe acne.
  
  
• Other forms of arthritis, or related disorders, include the following:
  
  
  • gout - an inflammatory arthritis caused by the deposit of excess uric acid into joints or bursa. It can usually be controlled with medication and changes in diet.
    
    
  • systemic lupus erythematosus (lupus) - an 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, and abnormalities of blood vessels, lung tissue, and gut motility.
    
    
  • ankylosing spondylitis - one of the seronegative spondyloarthropathies, this disease affects the spine, causing the bones of the spine to fuse 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.

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.

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 or creatine protein (to detect inflammation)
    
    
  • rheumatoid factor (to determine if rheumatoid factor is present in the blood)
    
    
  • urinalysis (to determine levels of protein, red blood cells, white blood cells, and casts)