Osteoarthritis, or degenerative joint disease, is the most common form of arthritis in the United States, affecting 15.8 million Americans. More than 15% of women over the age of 80 have symptomatic osteoarthritis of the knee. Osteoarthritis is a leading cause of disability and thus has a significant economic impact. Although there is no cure for osteoarthritis, individualized treatment programs can limit loss of function, reduce pain, and maintain joint mobility.
Osteoarthritis results from degeneration of cartilage within joints. This cartilage provides a cushion between the two bones and forms the smooth gliding surface needed for normal joint function. Cartilage is composed of water, cells, and matrix. Seventy percent of cartilage is water. The cells make the stiff matrix that is composed of proteoglycans, collagen, and glycoproteins. Damage to cartilage is caused by multiple factors including biomechanical, metabolic, biochemical, and genetic factors that combine to produce inflammation. The main cause of osteoarthritis is repeated exposure to physical forces that injure cells within the cartilage, leading to the release of enzymes that degrade cartilage. Less commonly, defective cartilage can fail under normal joint loading. Multiple risk factors have been associated with the development of osteoarthritis, including age (over 50), gender, obesity, occupation, injuries, genetics, and others. Secondary osteoarthritis can also result from other conditions such as trauma, calcium deposition diseases, and other bone and joint disorders such as rheumatoid arthritis.
The main symptom of osteoarthritis is joint pain. Stiffness is also a common complaint and is usually worse in the morning or after periods of inactivity, but generally resolves in less than 30 min. The diagnosis is made by noting a characteristic pattern of joint involvement, characteristic appearance on x-rays, and the absence of clinical and laboratory evidence for other types of arthritis. The most commonly affected joints are the small joints of the fingers and the weight-bearing joints such as the knees, hips, and spine. On x-rays, osteoarthritis appears as joint space narrowing with formation of bone spurs near joints.
Osteoarthritis of the knee is common in patients over the age of 50 and in obese patients, and is diagnosed based on the presence of knee pain with bony tenderness and enlargement, and less than 30 min of morning stiffness. Osteoarthritis of the hands causes bony enlargement of the small finger joints as well as the joint at the base of the thumb. This form of osteoarthritis is often seen in mothers and grandmothers and is inherited as an autosomal dominant trait. When the feet are involved with osteoarthritis the joint at the base of the first toe is often affected and results in a bunion. Osteoarthritis of the hip usually produces pain in the groin area. Osteoarthritis of the spine is common in the neck and lower back. When the joints between the vertebrae are affected, nerve roots can be compressed as they exit the spine, causing nerverelated pain and weakness. Osteoarthritis of the spine can also lead to slippage of the vertebral bodies on each other and compression of the spinal cord itself.
Treatment for osteoarthritis includes medication, nondrug treatment, and surgery. Nondrug treatment includes weight loss, rest, physical therapy, bracing, and exercise. Obesity is strongly associated with the development of osteoarthritis; being obese more than doubles the risk for osteoarthritis of the knee. In one study, losing just 10 lb reduced the risk of osteoarthritis of the knee by 50%. Rest relieves pain but prolonged rest can lead to muscle weakness, so rest is recommended for only short periods of time. Physical therapy can improve flexibility and muscle strength, which is important for supporting the affected joints. By supporting more weight, strong muscles unload the joint and cartilage. Braces (e.g., to correct deformity in the knee) and knee sleeves that correct abnormal tracking of the kneecap may help pain. Exercise is important to maintain flexibility and strengthen muscles.
Pain relief is an important goal of therapy in osteoarthritis, and pain-relieving drugs are a mainstay of treatment. Acetaminophen (Tylenol) in doses of up to 4 g per day is recommended as the first treatment and has few side effects. Liver damage may occur with large doses of acetaminophen in people who also drink alcohol. Nonsteroidal anti-inflammatory drugs (NSAIDs) are useful in patients who do not respond to acetaminophen. NSAIDs such as ibuprofen, naproxen, and ketoprofen are available over the counter or by prescription. Side effects of these medications include gastrointestinal (GI) problems such as gastritis and ulcers, which occasionally can be serious. Rash and impairment of kidney, liver, and bone marrow function are rare but do occur. Newer NSAIDs called COX-2 inhibitors (celecoxib, rofecoxib, and valdecoxib) have slightly fewer GI side effects compared to other NSAIDS. Other medications such as codeine, Tramadol, and propoxyphene should be limited to short-term use only. However, these medications may be useful for some patients who are at high risk for side effects with NSAIDs (such as people with a history of stomach ulcers or allergic reactions).
When oral medications are not enough, injection of corticosteroids into the joint is usually quite effective for short periods of time (weeks to months). These injections should be limited to 3-4 times per year in the same joint. Newer hyaluronic acid derivatives (another class of medications; Synvisc and Hyalgan) may be effective in osteoarthritis of the knee in selected patients. These medications are given in a series of 3-5 weekly injections and can be repeated twice per year.
Surgery is helpful in patients with significant limitations of joint function who are not helped by other treatments. Joint replacements of the knee and hip provide marked pain relief and improve function in most patients.