Osteoarthritis is the most common form of arthritis affecting more than twenty to twenty-five thousand people in the United States. That figure is expected to increase dramatically with the ballooning of the baby boomer demographic.

Osteoarthritis is associated with a high cost not only to society but to the individual as well. These costs include visits to the doctor, medications, surgical intervention, time lost from work, as well as costs associated with the loss of independence, and the inability to keep up with the activities of daily living.

While osteoarthritis was initially thought to be a disease of just wear and tear of cartilage, it is quite clear now that osteoarthritis affects the entire joint including the underlying bone as well as the lining of the joint, which is called the synovium.

There is increasing evidence that inflammation occurs and is triggered by, and perpetuated by, chemical messengers that are called cytokines and metalloproteinases.

These inflammatory chemicals are released into the joint and produce more damage to the underlying cartilage.

Osteoarthritis affects primarily weight-bearing joints such as the neck, the low back, hips, knees, and feet.

A variety of osteoarthritis may also affect the hands including what are called the distal interphalangeal joints or DIP joints and proximal interphalangeal joints, the PIP joints of the hands.

When cartilage is viewed through a microscope there is evidence of small areas of ulceration which leads to cartilage loss. In addition, the underlying bone, subchondral bone, also will be affected. As a result, spurs, called osteophytes, grow And become an important factor in producing symptoms.

While osteoarthritis is typically considered a disease of aging, it is clear, from recent evidence, that osteoarthritis begins to develop at a much earlier age.

The disease is equally common among men and women between the ages of 45 to 55. However, after the age of 55, osteoarthritis is more common in women than men.

The most common symptom for which people with osteoarthritis seek medical attention is pain. Pain initially occurs with activity and is relieved by rest. Stiffness with inactivity as well as stiffness in the morning is another prominent symptom.

There are many reasons for pain to occur in osteoarthritis. These include stretching of the joint capsule due to inflammation as well as fluid buildup.

Another source of pain is increased pressure within the underlying bone. Also, inflammatory changes affecting the bursae, the fluid-filled sacks that cushion the joint, may occur. Muscle spasm around the point around the joint may also contribute to pain.

With progression, as joints become mechanically unstable, osteoarthritis becomes worse and pain becomes a more prominent symptom.

On examination, patients with osteoarthritis may present with joint swelling due to inflammation of the joint capsule. There is swelling also due to bony overgrowth as well as fluid buildup. The fluid is produced by the synovium and is called an "effusion." As the disease progresses, misalignment of the joint can develop.

In addition, there may be evidence of limited range of motion as well as muscle atrophy.

Another sign that may be detected on physical examination is "crepitus." This is a crunchy, sandy, type of sensation that the physician can feel when the joint is moved. Sometimes patients will complain that they both hear it as well as feel it.

Risk factors for osteoarthritis include, as mentioned earlier, increasing age, female gender, family history, trauma, and other factors.

Osteoarthritis develops in three distinct stages. The first stage occurs when the cartilage metabolism is affected and destructive enzymes are produced, leading to wearing away of the cartilage matrix.

The second stage involves the erosion of cartilage leading to what is called "fibrillation."

The third stage is when there is chronic inflammation within the lining of the joint, the synovium.

Various chemical inflammatory messengers such as tumor necrosis factor, metalloproteinases, and interleukin one are produced.

The cytokines lead to destruction of tissue and they also lead to the production of more destructive cytokines.

The end result is joint destruction due to cartilage wear as well as bony overgrowth and inflammation affecting the synovium.

In future articles I'll discuss other features of this disease including diagnostic measures as well as treatment.