Arthritis is a word derived from the Greek, "arthron" meaning joint and "itis" meaning inflammation. It is used to refer to more than one hundred different conditions that cause joint symptoms. Arthritis is a common condition affecting almost 70 million Americans.

While arthritis is often considered to be a disease associated with aging, it can affect people of all ages, including infants and children.

Arthritis is the major cause of disability in people past the age of 55. But what many people don't realize is that it can also cause internal organ damage and early death.

It is the main cause of disability among people over fifty-five years of age in industrialized countries.

In order to understand what arthritis does to joints it's helpful to understand basic joint anatomy.

A joint is where one bone interacts with another bone. The ends of the bones are covered by a thin layer of a gristle-like material called cartilage. Cartilage serves as a gliding surface and also helps with shock absorption.

Multiple soft tissue structures such as ligaments, tendons and muscles hold the joint together.

A capsule encloses the joint. The space within the joint - the joint cavity - has a small amount of synovial fluid. Synovial fluid nourishes and lubricates the joint and the cartilage. Synovial fluid is produced by the synovium (synovial membrane) which lines the joint cavity.

Arthritis develops when abnormalities occur within the cartilage, synovium, or surrounding soft tissue structures. While there are more than 100 different types of arthritis, some are more common than others.

For example:

Osteoarthritis is the most common type of arthritis and is the one often associated with aging. In this disease, the cartilage loses its elasticity and pliability. In addition, the synovium becomes inflamed and the underlying bone becomes hardened and develops spurs. The articulating cartilage begins to wear away as a result of degradation caused by destructive enzymes. The joint becomes mechanically unstable. The end result is pain and loss of function.

Rheumatoid arthritis is a very different form of arthritis because it is an autoimmune condition where antibodies attack the joint lining as well as internal organs. The synovial membrane (synovium) becomes inflamed as a result of the autoimmune reaction. The inflammation causes rapid destruction of cartilage, synovium, bone, and soft tissue structures.

Significant deformity is the end result. And because it's a systemic disease, rheumatoid arthritis also shortens life span.

Psoriatic arthritis is a common form of arthritis that occurs in patients with psoriasis. While it attacks the skin and joints, psoriatic arthritis also attacks the enthesis, the attachment of tendons into bone. Like rheumatoid arthritis, psoriatic arthritis has systemic features and may also cause inflammation in the eyes and bowels.

Gouty arthritis is a type of arthritis due to the deposition of monosodium urate crystals (uric acid) in joints. This causes an intensely painful form of inflammatory arthritis. Early on it presents as discrete attacks of inflammatory arthritis. Over time the attacks become more frequent.

While more common in men than women, it can affect women quite commonly after the menopause. Gout attacks usually start in the feet but may spread quickly to involve multiple joints. It causes deposits of uric acid to form under the skin. These deposits are called "tophi." Gout also affects kidney function. It is associated with other medical conditions such as diabetes, obesity, elevated blood lipids, and hypertension.

Juvenile arthritis affects children of almost any age. There are at least three variants of the condition but they all have an autoimmune component as well as a genetic component. This type of arthritis, if not diagnosed quickly and treated aggressively, can be devastating. Juvenile arthritis has many patterns as far as joints involved. Most types cause eye inflammation as well.

Polymyalgia rheumatica is a common form of arthritis that affects people usually past the age of 50. It is characterized by diffuse aching, pain, and stiffness in the morning. The neck, shoulder, and hips are the areas most commonly involved. Laboratory testing shows the erythrocyte sedimentation rate to be very elevated. The major concern here is that about 15 per cent of patients with polymyalgia rheumatica also have another condition called giant cell arteritis. This is an inflammatory condition that affects blood vessels and which can lead to blindness.