Osteoarthritis

Osteoarthritis is a form of joint disease that develops when cartilage deteriorates. Over time, the space between bones narrows and the surfaces of the bones change shape, leading eventually to friction and joint damage (see Figure 5). Osteoarthritis often affects more than one joint, and while it can affect any joint in the body, some joints are affected much more often than others. For example, osteoarthritis is quite common in the hip, knee, lower back, neck, and certain finger joints, but it is rare in the elbow.

Figure 5: Joint changes in osteoarthritis Joint changes in osteoarthritis

Osteoarthritis is the most common of all joint diseases, accounting for about half of arthritis diagnoses in the United States. It affects approximately 21 million Americans. But these numbers only hint at the impact of osteoarthritis, which can send people to pain clinics and doctors' offices, make them reach for medications, keep them home from work, and curtail leisure and everyday activities. Because the risk of developing osteoarthritis increases with age, this form of arthritis is expected to become even more prevalent as the population of the United States grows older.

About equal numbers of men and women have osteoarthritis, but it tends to affect them differently. Men typically develop symptoms before age 45, while women usually don't have symptoms until after age 55. Women more often have osteoarthritis in the hands and knees. Men are more likely to have it in the hips, knees, and spine. Women are 10 times more likely to develop Heberden's nodes, a type of osteoarthritis in which hard, bony growths form on the joint nearest the fingertip.

More than wear and tear

Osteoarthritis is virtually unheard of in children and is rare in young adults. But it's common among older people. Almost everyone over age 65 has some cartilage and bone changes typical of the disorder. For this reason, osteoarthritis was long considered a natural product of aging, reflecting everyday wear and tear on cartilage. Although this attitude still prevails among many physicians, experts now believe the cause is much more complex. External factors, such as injuries, are important initiators, but the rate of progression is probably also affected by genetic and environmental traits.

While it's true that one's risk of developing osteoarthritis symptoms increases with age, many people whose x-ray films indicate joint changes typical of osteoarthritis have no symptoms. The severity of osteoarthritis symptoms depends on many factors, including how people use their joints. That's why taking the time to protect your joints is so important (see "Joint protection strategies").

The first signs of osteoarthritis are microscopic pits and fissures in the surface of the cartilage in your joints (see Figure 5). These fissures indicate that biochemical changes are gradually making the cartilage less resilient. Cartilage cells themselves produce enzymes that damage the molecules making up the structure of the cartilage, and tiny pieces of cartilage may flake off into the joint cavity. This changes the shape of the cartilage lining the bone, causing further damage as the altered surfaces move against each other.

As cartilage degenerates, patches of exposed bone appear. Just as a damaged gasket leads to metal-on-metal contact in a machine, your bones experience mechanical friction and irritation. They try to repair themselves, but the repair is disorderly. As a result, the surface thickens and osteophytes (bone spurs) form.

Once your cartilage is damaged, the resulting abnormalities can irritate surrounding soft tissues and cause inflammation. People with severely damaged joints sometimes have episodes of joint swelling from synovitis (inflammation of the joint's lining); however, this inflammation tends to be much milder than in rheumatoid arthritis or other inflammatory joint diseases. The damaged cartilage, bone rubbing on bone, and the inflammation combine to make movement painful.

Doctors sometimes refer to osteoarthritis as noninflammatory to distinguish it from other rheumatic diseases. But many people with osteoarthritis experience low-grade inflammation. It may arise when the articular cartilage in your joint fails to recover fully from an injury. In addition, inflammation may reflect an attempt by the joint to repair damage, or it may be due to genetic or metabolic factors that predispose you to joint degeneration.

Fast fact Researchers in a biomechanics laboratory at Wake Forest University reported in 2005 that overweight and obese people with knee osteoarthritis who lost weight could literally reduce the pounding on their knees. For each pound of weight lost during the study, participants experienced a 4-pound reduction in force per step.

Possible causes of osteoarthritis

Doctors may categorize osteoarthritis as primary, meaning the principal cause is unknown. However, excess weight and genetics also contribute to predisposition. Or the disease may be categorized as secondary, originating from trauma, such as a blow or injury, or a recognizable disease process, such as hemophilia. Some scientists believe primary osteoarthritis begins with repeated minor injuries. The cartilage is able to repair itself for a time, but eventually this effort fails.

Excess weight

By now, everyone has heard that carrying excess body fat can lead to problems with the heart and other organs. Here's another reason to slim down: Overweight people are much more likely to develop osteoarthritis of the knee. These weight-bearing joints just don't hold up well under the continued strain of extra pounds — and extra pounding.

An ongoing study of people living in Framingham, Mass., found that overweight young adults were more likely to develop knee osteoarthritis in their 30s and 40s than were their slimmer counterparts. Women who were the heaviest were twice as likely as thinner women to get osteoarthritis and had three times the risk for severe knee osteoarthritis. Losing weight can reduce risk. Researchers who analyzed the Framingham data found that women who lost 11 pounds cut their risk of developing osteoarthritis of the knee by half.

Genetic factors

Consensus is growing that genetic factors likely control the manifestations and progression of osteoarthritis. Studies in identical twins — who share the same genes and thus offer insight into the relative importance of genetic and environmental factors — have shown that roughly half the risk of developing osteoarthritis can be attributed to genetic factors. Multiple genes are thought to be involved, and to complicate matters further, the genes may have different effects depending on the joint affected and whether someone is male or female.

Genetic studies of a disease like osteoarthritis are hampered by several factors. First, the sheer number of people with the disorder makes it impossible to discount the influence of external factors. Second, scientists must establish that a certain gene is present in most people with the disease, but is absent in those who are healthy.

Hormones

Osteoarthritis is common among postmenopausal women. One study found that women who were taking estrogen replacement therapy appeared to have a lower risk of developing the disease, suggesting that estrogen may have a protective effect on cartilage in much the same way that it protects bones from osteoporosis. However, these findings remain controversial: Estrogen has many, and in some cases conflicting, effects on connective tissue and bone, making the association between estrogen and arthritis difficult to sort out.

Postmenopausal women tend to have either osteoarthritis or osteoporosis, but not both. This may be because the bones of thinner people are less dense and more susceptible to osteoporosis; heavier people, who have higher bone density, are less prone to osteoporosis but more susceptible to arthritis from greater stress on joints.

Joint injury

Injury to a joint, either because of repeated use or trauma, may also cause osteoarthritis. As many athletes know, severe knee trauma disrupts the normal mechanics of joint function. Nearly all tissues heal by scarring, leaving irregularities on their surfaces. Because bones, joints, or muscles that are damaged rarely heal perfectly, joint injuries can create unusual mechanical stresses that lead to abnormal wear. People in certain occupations are prone to develop osteoarthritis in those joints subjected to the most stress. For example, osteoarthritis may affect the hips, ankles, and feet of ballet dancers, the knees of soccer players, the hips of farmers, the elbows of riveters, and the hands and wrists of pneumatic tool operators. The cause is thought to be repetitive stress leading to bone fatigue, microscopic fractures, and eventually cartilage breakdown.

Even those who are sedentary can develop occupational osteoarthritis when repetitive stress is sustained for several hours a day. Perhaps surprisingly, people who spend a lot of time using a keyboard aren't more likely to develop osteoarthritis of the hands, because typing puts very little mechanical stress on the joints.

Other diseases

Osteoarthritis can also develop in a joint damaged by a related disease, such as rheumatoid arthritis, infectious arthritis, or gout. Or osteoarthritis may develop because of hemophilia, growth abnormalities, or hereditary metabolic diseases. Hemophilia can produce osteoarthritis as a result of bleeding in the joint.

Growth abnormalities that can lead to osteoarthritis include acromegaly and slipped femoral epiphysis. Acromegaly is characterized by the irregular overgrowth of bone and cartilage due to abnormal production of growth hormone. Slipped femoral epiphysis involves displacement of the growth plate at the end of the femur, the bone that extends from hip to knee. Osteoarthritis can also arise from hereditary metabolic diseases, such as hemochromatosis (the harmful accumulation of iron in tissues).

Symptoms of osteoarthritis

The symptoms of osteoarthritis usually develop over many years. Often, people first experience pain after engaging in strenuous activity or overusing a joint. The joint may be stiff in the morning, but after a few minutes of movement, it loosens up. Gradually, this stiffness becomes a routine part of waking up.

Cartilage is insensitive to pain, but the soft tissue in the joints is not. As more cartilage is worn away, soft tissue becomes increasingly irritated, even by slight movement. Some people have continual joint pain that interferes with sleep. Or the joint may be mildly tender, and movement may produce crepitus, a sensation of crackling or grating. In addition, gradual joint enlargement may interfere with normal mobility. Swelling may also occur as synovial tissues become irritated, or when inflammation develops. Although inflammation is not a cardinal feature of osteoarthritis, it does sometimes occur. Pain usually occurs in the affected joint, although it may extend elsewhere.

When osteoarthritis affects the knee, the result is pain, swelling, and stiffness of that joint. What starts out as some discomfort after a period of disuse can progress to difficulty walking, climbing, bathing, and getting in and out of bed.

Osteoarthritis of the hand often starts with stiffness and soreness of the joint at the base of the thumb, particularly in the morning. You may find it becomes harder to pinch, and your joints crackle when moved. As the condition worsens, the pain at the base of your thumb can become more of a problem, and your ability to pinch decreases even further. The entire area may seem unstable. People with osteoarthritis of the hand may eventually find it impossible to open jars, turn a key, write, or type. Many people with osteoarthritis of the hand find that, with age, their hands thicken and become stiff. Stiffness is gradually followed by pain or instability. In other people, the pain and stiffness of hand osteoarthritis may subside over time, despite marked bony enlargement typical of the disease.

Radiating pain is often the most striking feature of hip and spine osteoarthritis. When osteoarthritis affects your hip, you may feel pain in the groin or down the inside thigh, or pain may radiate to your buttocks or knee. Osteoarthritis of the cervical spine (neck) may cause pain in your shoulders and arms. In the lower spine, osteophytes may impinge on adjacent nerves and send pain radiating to your buttocks or legs.

For most people, osteoarthritis develops gradually. Pain and stiffness in affected joints may slowly worsen, but most people are able to lead normal lives.

Symptoms of osteoarthritis joint pain and swelling after activity joint stiffness in the morning grinding sensation when joint is used

Diagnosing osteoarthritis

Diagnosis is usually straightforward and is based on a person's symptoms and medical history (see "Diagnosing arthritis"). When symptoms don't fit the usual pattern for osteoarthritis, further investigation, often by x-ray or other imaging techniques, may be necessary. Such atypical examples may involve arthritis of joints that are usually spared, such as the elbow, shoulder, or ankle, or swelling of the synovium, a condition known as synovitis.

Drug treatment for osteoarthritis

Although no drug exists that will cure or reverse the progression of osteoarthritis, it is usually possible to alleviate pain and inflammation. Medications form the basis of treatment for osteoarthritis, but are best used in conjunction with other pain relief strategies, such as exercising to build your muscles and protecting your joints from injury or overuse (see "Slowing the progression of osteoarthritis").

Topical analgesics

Topical analgesics, which are applied to the skin, offer one alternative for mild pain relief. You can use these alone or in combination with one of the medications described below. Creams containing salicylate, such as Aspercreme or Bengay, and others containing capsaicin, such as Zostrix, are available over the counter. However, it's important to avoid touching any mucous membrane (for example, around the mouth, nose, or eyes) after applying the cream, to avoid irritation.

Mild pain relievers (analgesics)

To relieve the pain and stiffness of osteoarthritis, the first step is usually an over-the-counter pain reliever. Doctors often recommend acetaminophen (Tylenol) first because it's often effective for mild pain and easy on the stomach. But remember that acetaminophen, like any drug, has its own risks — especially for the liver.

A 2005 study in Hepatology concluded that acetaminophen was to blame for 42% of the cases of acute liver failure seen at hospitals during the study period. Many of these poisonings were accidental and occurred in people taking the drug regularly for pain relief.

To avoid an accidental poisoning, don't exceed the recommended maximum per day — generally set at 4 grams (4,000 milligrams), the equivalent of eight extra-strength Tylenol tablets. Remember that acetaminophen is often included in combination formulas, so it's important to read all medication labels carefully. If you drink more than a moderate amount of alcohol on a regular basis (more than two drinks a day for men, and one drink a day for women), it is wise to stay well below the maximum daily dose or avoid acetaminophen altogether, because your threshold for toxicity may be lower than it is for other people.

NSAIDs

It has become clear that nonsteroidal anti-inflammatory drugs (NSAIDs) may be more effective than acetaminophen in treating osteoarthritis because they not only relieve pain, but also reduce inflammation that contributes to pain, swelling, and stiffness.

The arsenal of NSAIDs has grown over the years to include about 20 different drugs. Among them are such well-known medications as aspirin, ibuprofen (Advil, Motrin, others), and naproxen (Aleve, Naprosyn, others). These drugs reduce pain and inflammation by blocking the production of prostaglandins, leukotrienes, and other chemical mediators. For many people, they are slightly more effective than Tylenol, especially during flare-ups of pain.

The most common side effects of these medications are stomach problems, including gastrointestinal bleeding and ulcers, often occurring without warning. That is because NSAIDs work by inhibiting both the COX-1 enzyme, which helps protect the stomach lining from the corrosive effects of stomach acids and digestive enzymes, and the COX-2 enzyme, which causes pain and inflammation. One widely quoted paper, published in the New England Journal of Medicine in 1999, estimated that each year these drugs contribute to at least 16,500 deaths and more than 100,000 hospitalizations in the United States. A study of people in Spain concluded that roughly one in three hospitalizations or deaths due to gastrointestinal bleeding could be attributed to NSAIDs. It is possible in many cases to avoid such complications — but first you and your doctor must work together to determine your risk of experiencing them.

The older you are, the higher your risk of developing bleeding and ulcers. Others at risk include people who have had ulcers in the past, people with rheumatoid arthritis, and people who are also taking a blood thinner or corticosteroids. Prolonged use and higher doses of NSAIDs also increase the risk. And some NSAIDs are more prone than others to causing ulcers; for example, aspirin (Anacin, Bayer, others) and indomethacin (Indocin) appear to have the highest risk.

If you are in a high-risk group, you should probably try to avoid NSAIDs if at all possible, and try other pain relief strategies. A COX-2 inhibitor is safer, but the risk isn't zero. If you're in a high-risk group and find that these other strategies don't work, then talk with your doctor about stomach-protecting drugs to take along with the NSAID. These include histamine blockers such as cimetidine (Tagamet) and ranitidine hydrochloride (Zantac), and proton pump inhibitors such as esomeprazole (Nexium), lansoprazole (Prevacid), and omeprazole (Prilosec). Another option is taking misoprostol (Cytotec) with the NSAID. Some medicines (such as Arthrotec or Prevacid NapraPAC) combine a medication that protects the stomach with an NSAID.

If taking NSAIDs produces stomach upset but not a bleeding ulcer, good initial strategies are to reduce the dose of the NSAID you're taking, try an entirely different pain reliever (such as acetaminophen), or switch to a drug that is more selective for COX-2. For example, celecoxib (Celebrex) is a COX-2 selective agent and might be better tolerated than indomethacin. Nabumetone (Relafen), although not officially a COX-2 selective agent, is also relatively selective for COX-2 and would be a better choice than indomethacin if stomach upset is a limiting factor. Other more selective medications to consider, as they may be more easily tolerated, are meloxicam (Mobic) and diclofenac (Voltaren).

No matter what your risk profile, to be on the safe side, use NSAIDs only under the supervision of your doctor, and do not combine NSAIDs with other medications without talking to your doctor first. Also take time at each doctor's visit to reassess the medications you are taking for your arthritis and to evaluate your symptoms. All too often, people are taking more medication than they really need. Other pain relief strategies might be used in combination with the drugs so you can lower the dose.

COX-2 inhibitors

In 1998, the FDA approved the first of a new generation of NSAIDs. Known as COX-2 inhibitors, these prescription drugs were designed to be more selective in their effects than traditional NSAIDs. COX-2 inhibitors, as their name implies, inhibit only the COX-2 enzyme involved in pain and inflammation, while sparing the COX-1 enzyme that protects the stomach lining. As such, they were able to relieve pain as well as the strongest NSAIDs, while causing less stomach irritation (although the risk of this side effect isn't eliminated).

Eventually the FDA approved three COX-2 inhibitors: celecoxib (Celebrex), rofecoxib (Vioxx), and valdecoxib (Bextra). But today only Celebrex is available in the United States, and it comes with a warning. The manufacturers took Vioxx and Bextra off the market after the FDA warned that these drugs could increase the risk of stroke and heart attack.

This is because both the COX-1 and COX-2 enzymes also exert effects on the arteries. The COX-1 enzyme narrows arteries and makes blood platelets sticky, while the COX-2 enzyme widens arteries. When just COX-2 is blocked, the "widen" signal is lost and the resulting combination of narrowed arteries and stickier platelets can lead to blood clots that block an artery in the heart, causing a heart attack, or one in the brain, causing a stroke.

For this reason, most people now choose to try other pain relief alternatives before taking the remaining COX-2 inhibitor on the market, celecoxib. If you do take this medication, talk with your doctor about how to take it safely, especially if you already have an increased risk of heart attack or stroke.

Corticosteroid injections

When osteoarthritis is accompanied by inflammation, as indicated by warmth and an accumulation of fluid in the joint, your doctor may remove a small amount of joint fluid and then inject a corticosteroid. This procedure can relieve inflammation quickly, but usually only for a short time. It is used almost exclusively for severe symptoms associated with these signs of inflammation, especially for osteoarthritis of the knee. This approach is usually used infrequently — up to three or four times per year — and only when absolutely necessary, because more frequent injections of these drugs may increase the risk of infection and can damage the joints.

Dietary supplements

The dietary supplements glucosamine sulfate and chondroitin sulfate are over-the-counter agents that may provide pain relief to people with moderate to severe pain from osteoarthritis (see "Glucosamine and chondroitin").

Hyaluronate injections

Injections of hyaluronate (Hyalgan, Synvisc) may provide mild relief of symptoms of knee osteoarthritis in some people. In its natural form, hyaluronate lubricates the joint and supplies it with nutrients. Synthesized forms of this chemical can be injected directly into an osteoarthritic knee once a week for three to five weeks. But the jury is still out on this approach: Some doctors do not believe the modest benefits are worth the risk and discomfort of the injections.

Surgical treatment for osteoarthritis

Sometimes surgical intervention is necessary to relieve extremely painful or badly misaligned joints. The option your doctor recommends will depend on your age, activity level, and overall health. Surgical options are usually recommended only when drug therapies and other strategies have failed.

Arthroscopy

Arthroscopy is considered minor surgery because the surgical incisions are small and the procedure generally does not require an overnight stay in the hospital. An arthroscope is an instrument with a tiny light, a camera, and a variety of surgical attachments. The surgeon inserts the instrument into the joint and performs minor surgery using the attachments. The camera enables the surgeon to see and smooth over any ragged joint edges and to locate and remove debris and loose material. Depending on the condition of the joint, this can result in mild to moderate improvement that may last several months or perhaps a few years. However, for someone with severe osteoarthritis, this approach is unlikely to offer much benefit. Studies have called into question whether this type of surgery should be routinely employed. Unless there is a specific finding or abnormality that can be addressed with this technique (such as a tear in the cartilage), arthroscopy for osteoarthritis may not be helpful.

Joint reconstruction or replacement

Doctors recommend joint reconstruction or replacement in cases of severe osteoarthritis in which the joint shows significant deterioration. Surgery can be used to correct joint deformity, to reconstruct a diseased joint, or to completely replace a diseased joint with a prosthetic device. This surgery is most often recommended for osteoarthritis of the hip or knee, because severe disease of these joints can impede movement.

Hip replacement and knee replacement are among the most common surgeries performed in the United States. A replaced joint will last an average of 10 to 15 years (or even longer, because such estimates are based on operations performed at least 10 years ago). But joint replacement is not an option for everyone; the ideal surgical candidate is in good general health and not overweight. However, as surgical and anesthesia techniques have improved, more and more people are becoming good candidates for surgery. Surgeons may encourage young, physically active people to delay joint replacement because artificial joints usually need to be replaced after a decade or two. The younger the patient, the more the joints are used, and the greater the number of replacements that may be necessary.

It's also important to have realistic expectations about what joint replacement surgery can and cannot do. Joint replacement doesn't guarantee that you will be able to move or use the joint in a normal way. Still, many people do experience great functional improvement. The major consistent benefit is substantial relief from pain. To maximize the chances of good results, it's important to participate in physical therapy after surgery.

Many artificial joints are attached to bone with pins and acrylic cement (see Figure 6). Over time, these components may loosen or break, requiring repairs. Researchers believe some design improvements that have been made may make the implants last longer. For example, cementless components are now widely used. Their metallic surfaces are roughened until they become semi-porous, allowing bone to grow into the surfaces, which may reduce the likelihood of loosening. However, such designs must be tested for 10–20 years to determine how well they perform. These components haven't yet been shown to perform significantly better than a well-cemented pin.

Figure 6: Artificial hip joint Artificial hip joint Artificial hip joints have metal shafts that are inserted into bone and anchored. At weight-bearing points, slick, high-density polyethylene is used to reduce friction (like cartilage in natural joints). Cement fastens the artificial joint to the skeleton in many joint replacement operations. Cementless implants have a porous surface that bone tissue penetrates, thereby holding the prosthesis in place.

Cartilage transplant

Cartilage transplant is a method to replace damaged cartilage with healthy cartilage transplanted from elsewhere in the body or from donated tissue from someone who has died. Cartilage cells may be removed from a joint or some other area and grown outside the body to form a biological patch. The patch is then inserted in an area of damaged or missing cartilage with an arthroscope. So far, these approaches have been used primarily in young people with small, sports-related cartilage injuries in the knee. But many experts believe that the time is coming when cartilage transplant will be a more common treatment for osteoarthritis.

Slowing the progression of osteoarthritis

Osteoarthritis is a disease that progresses slowly over many years (see "More than wear or tear"). If you've already been diagnosed with osteoarthritis, you can take steps to slow its progression and reduce your discomfort. These measures are most effective if you begin them in the earlier stages of your condition. But no matter how far your osteoarthritis has progressed, you can benefit from the following.

Stay active

For people with osteoarthritis, regular exercise has been shown to reduce pain and stiffness and to improve balance. Exercise helps people perform such basic activities as walking. It also helps build or maintain muscle tone, which is necessary for joint stability.

There are three types of exercise beneficial for someone coping with osteoarthritis. Range-of-motion exercises can maintain or improve flexibility. Strengthening exercises with weights can build muscles to support affected joints. And aerobic exercises can help improve endurance and prevent weight gain. (See "Exercise" for more information about all of these.)

One study that compared walking and weight training suggests that exercise may help prevent disability. People with knee osteoarthritis who exercised regularly were less likely to need help with daily activities such as getting out of bed, bathing, using the toilet, or getting dressed. The improvements most likely reflected a general improvement in health and functioning, rather than a change in the arthritis itself. The reported improvements were nonetheless substantial.

Try to work your way up to 30 minutes of aerobic exercise — slow walking, biking, or swimming — at least four times a week. Add in some resistance or weight-training exercises three times a week.

Protect your joints

When exercising, protect yourself from joint injury. For example, if you have osteoarthritis of the hip, knee, foot, or ankle, don't run, especially on roads. Walking is a much gentler form of exercise, although it, too, puts full, weight-bearing stress on some joints. Other good alternatives are non-impact aerobic activities such as swimming or biking.

Invest in a good pair of exercise shoes, which will absorb some of the impact. Avoid repetitive, weight-bearing motion. If you can't avoid such joint stress altogether, take frequent breaks. Remember to bend your knees when lifting heavy objects. Use the largest, strongest joint to complete a task. For example, open a jar with the palm of your hand instead of with your fingers (see "Joint protection strategies").

Control your weight

Osteoarthritis and excess pounds often go hand in hand. For one thing, arthritis promotes inactivity. For another, it affects older people, who tend to be less active. But studies have shown that weight loss reduces osteoarthritis pain. It does so by taking some of the pressure off your joints, especially the weight-bearing joints such as the knees and hips. Losing weight also allows greater ease of movement.

Exercise is the first step toward weight loss. A healthy, well-balanced diet is another. Concentrate on replacing empty calories from desserts and junk food with nutrition-packed calories from whole grains, lean proteins, and fruits and vegetables. Also be sure to control portion sizes. Most experts now agree that virtually any diet program is effective for losing weight when it encourages people to reduce their calorie intake and increase calories burned. Whatever diet strategy you choose, the bottom line is that to lose weight, you have to consume fewer calories than you burn.