Arthritis
Arthritis, an inflammation of any joint, is the most common and best known of the joint disorders, affecting 10% of the world's population. There are more than 100 different types of arthritis.
Classification is often based on the cause and progress of the arthritis. Causes include infectious agents, metabolic disorders, trauma, and immune disorders. Mild exercise retards joint degeneration and enhances mobility. Swimming and walking are recommended for people with arthritis; but running, tennis, and aerobics are not recommended. Therapy depends on the type of arthritis, but includes anti-inflammatory drugs. Current research is focusing on the possible development of antibodies against the cells that initiate the inflammatory response in the joints or against cell surface markers on those cells.
Osteoarthritis (OA) is the most common type of arthritis, affecting 16 million people in the United States. OA may begin as a molecular abnormality in articular cartilage, with heredity and normal "wear and tear" of the joint important contributing factors. Slowed metabolic rates with increased age also seem to contribute to OA. Inflammation is usually secondary in this disorder. It tends to occur in the weight-bearing joints such as the knees and is more common in overweight individuals.
Rheumatoid arthritis (RA) is the second most common type of arthritis. It affects about 3% of all women and about 1% of all men in the United States. It is a general connective tissue disorder that affects the skin, vessels, lungs, and other organs, but it is most pronounced in the joints. It is severely disabling and most commonly destroys small joints such as those in the hands and feet. The initial cause is unknown but may involve a transient infection or an autoimmune disease (an immune reaction to one's own tissues that develops against collagen. There may also be a genetic predisposition. Whatever the cause, the ultimate course appears to be immunological. People with classic RA have a protein, rheumatoid factor, in their blood. In RA the synovial fluid and associated connective tissue cells proliferate, forming a pannus (clothlike layer), which causes the joint capsule to become thickened and which destroys the articular cartilage. In advanced stages, opposing joint surfaces can become fused. Juvenile rheumatoid arthritis is similar to the adult type in many ways, but no rheumatoid factor is found in the serum.
Lyme Disease
Lyme disease is the result of a bacterial infection transmitted to humans by a tick vector, which affects the brain, nerves, eyes, heart, and joints. Chronic arthritis and central nervous system dysfunction are severely disabling but rarely fatal. The disease is named for an epidemic of childhood arthritis occurring in Lyme, Connecticut in 1975 and associated with a tick-transmitted bacterial infection. It has probably existed in Europe for many years and in North America before the first European colonization but was unrecognized. Humans and domestic animals are only incidental hosts to the ticks that normally infect wild mammals and birds. Deer are of particular concern. The northeastern United States was greatly deforested during the 18th and 19th centuries, and deer and other wildlife populations declined dramatically. The more recent abandonment and reforestation of farms in New England has lead to an increase in the deer and tick populations, with a resurgence of the associated joint and nervous system disease in an era when diagnosis can be made. There were 7624 cases of Lyme disease reported in the United States in 1993. Although the disease is most common in the northeastern United States, cases have been reported in the north central states, along the West Coast, and scattered throughout the eastern and central states. Early manifestations of the disease include flulike symptoms, with localized skin rash. If untreated, the bacterium can spread to the nervous system, heart, and joints within a few weeks to months. A human vaccine against Lyme disease is currently being tested.
Suppurative arthritis (pus-forming) may result from number of infectious agents. These joint infections may be transferred from some other infected site in the body or may be systemic (that is, throughout the body). Usually only one joint, normally one of the larger joints, is affected, and the course of suppurative arthritis, if treated early, is transitory. However, with prolonged infection the articular surfaces may degenerate. Tuberculous arthritis can occur as a secondary infection from pulmonary tuberculosis and is more damaging than typical suppurative arthritis. It usually affects the spine or large joints and causes ulceration of the articular cartilages and even erosion of the underlying bone. Transient arthritis of multiple joints is a common symptom of rheumatic fever, but permanent damage seldom occurs in joints with this disorder.
Hemophilia arthritis may result from bleeding into the joint cavity caused by hemophilia, a disease characterized by a deficient clotting mechanism in the blood. There is some evidence that the iron in the blood is toxic to the chondrocytes, resulting in degeneration of the articular cartilage.
Gout
Gout is a group of metabolic disorders in which joints are involved. These disorders are largely idiopathic (of unknown cause), although some cases of gout seem to be familial (occur in families and therefore probably genetic). Gout is more common in males than in females. The ultimate problem in gout patients is an increase in uric acid in the blood because of too much synthesis or decreased removal through the kidneys. The limited solubility of uric acid salts in the body results in precipitation of monosodium urate crystals in various tissues, including the kidneys and joint capsules.
The earliest symptom of gout is transient arthritis resulting from urate crystal accumulation and irritation in the synovial fluid. This irritation can ultimately lead to an inflammatory response in the joints, and both the crystal deposition and inflammation can become chronic. Normally only one or two joints are affected. The most commonly affected joints (85% of the cases) are the base of the great toe and other foot and leg joints to a lesser extent. Any joint may ultimately be involved, and damage to the kidney from crystal formation occurs in almost all advanced cases. Kidney failure may occur in untreated cases. With modern medications, these complications seldom occur. Weight control and reduced alcohol consumption can help prevent gout.
Pseudogout is a disorder that causes pain and swelling similar to that seen in gout, but it is characterized by calcium hypophosphate crystal deposits in joints.
Hallux Valgus and Bunion
In people who wear pointed shoes, the great toe can be deformed and displaced laterally, a condition called hallux valgus. Bunions are often associated with hallux valgus. A bunion is a bursitis that develops over the first metatarsophalangeal joint because of pressure and rubbing by shoes.
Joint Replacement
As a result of recent advancements in biomedical technology, many joints of the body can now be replaced by artificial joints. Joint replacement, called arthroplasty, was first developed in the the late 1950s. One of the major reasons for its use is to eliminate unbearable pain in patients averaging 55 to 60 years of age with joint disorders. Osteoarthritis is the leading disease requiring joint replacement, accounting for two thirds of the patients. Rheumatoid arthritis accounts for more than half of the remaining cases.
The major objectives in the design of joint prostheses (artificial replacements) include the development of stable articulations, low friction, solid fixation of the bone, and normal range of motion. New synthetic replacement materials are being designed by biomedical engineers to accomplish these objectives. Prosthetic joints usually are composed of metal, such as stainless steel, titanium alloys, or cobalt-chrome alloys, in combination with modern plastics, such as high-density polyethylene, silastic, or elastomer. The bone of the articular area is removed on one side, called hemireplacement, or both sides, called total replacement of the joint, and the artificial articular areas are glued to the bone with a synthetic adhesive, such as methylmethacrylate. The smooth metal surface rubbing against the smooth plastic surface provides a low-friction contact with a range of movement that depends on the design.
The success of joint replacement depends on the joint replaced, the age and condition of the patient, and the state of the technology. Most reports are based on examination of patients 2 to 10 years after joint replacement. The technology is improving constantly, so current reports do not adequately reflect the effect of the most recent improvements. Still, the current reports indicate a success rate of 80% to 90% in hip replacements and 60% or more in ankle and elbow replacements. The major reason for failure of prosthetic joints is loosening of the artificial joint from the bone to which it is attached. New prostheses with porous surfaces help to overcome this problem.