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What is osteoarthritis?

Osteoarthritis (OA), also known as degenerative joint disease, is the most common form of arthritis. It is a painful condition that occurs when cartilage inside a joint wears down over time. Most often, this wear results from a lifetime of use, and people get it when they reach advanced age. However, younger people may get the condition early as a result of an injury to the joint.

Osteoarthritis is different from the less common but often more serious form of arthritis known as inflammatory arthritis. This is a group of autoimmune diseases such as rheumatoid arthritis and gout. Inflammatory arthritis is caused by a problem with the immune system, and it usually causes inflammation in many joints throughout the body at the same time. Osteoarthritis, on the other hand, is usually isolated to a single joint.

Video: Overview of osteoarthritis and when to see your doctor

Cartilage degeneration

Cartilage is the spongy tissue that coats the ends of bones where they meet to form joints. In joints such as elbows, knees, shoulders, ankles and knuckles, cartilage acts as a shock absorber, cushioning the bones and preventing their ends from touching during body movement. This allows a person to twist, bend, turn and have a broad range of motion. The older we get, the more our cartilage deteriorates – especially in joints that we use most frequently. When cartilage degrades, the bones are not properly cushioned and the joint becomes damaged. This results in pain, stiffness and reduced range of motion.

Osteoarthritis is most common in large weightbearing joints such as the hips or knees. With this type of arthritis, pain usually increases during activity and decreases with rest. Symptoms are often worse toward the end of the day.

What are the symptoms of osteoarthritis?

Pain is the most common symptom. Pain usually occurs when the joint is being moved, rather than when it is at rest. However, in the morning or after other long periods of inactivity, some people with OA may experience a feeling of stiffness. This symptom (known as "gel phenomenon" or "gelling phenomenon") usually lasts for less than 20 minutes in the affected joint. It is caused by a temporary thickening (or "gelling") of natural fluids inside the joint.

Pain felt during movement of the joint is often accompanied by a crackling or grinding sound called "crepitus." Some people with OA may feel little or no pain for unknown reasons. The level of pain each person with OA experiences can depend on many factors including: the stage of the disease, the way a person's brain processes pain messages, cultural, gender and psychological differences.

The joints most commonly affected by osteoarthritis are:

  • The hip
  • The knee
  • The last and middle joint in the fingers
  • The joint between the thumb to the wrist
  • The neck (joints of the cervical spine)
  • The lower back (joints of the lumbar spine)

Osteoarthritis is not associated with the following symptoms. If you have these are symptoms, you have some form of inflammatory arthritis:

  • swelling, redness or warmth in the joints where you feel pain
  • fevers
  • unexplained weight loss
  • severe muscle atrophy (weakening)
  • symptoms on both sides of the body (both knees or hips, etc.)

What puts me at risk for osteoarthritis?

  • Age: The longer a person uses their joints, the more likely they are to get OA.
  • Genetics: Some osteoarthritis may run in families.
  • Hormones: The reduction of estrogen in women after menopause may accelerate OA. Hormone replacement therapy may help protect women from developing osteoarthritis.
  • Trauma (acute injury) – especially injuries of the knee: For example, injuries to the anterior cruciate ligament (ACL) and/or meniscus increases the likelihood of osteoarthritis later in life.
  • Repetitive stress injury: Workers who use certain joints repetitively may have a greater risk. Examples include jackhammer operators (wrists, hands and elbows), coal miners (knees), cotton pickers (fingers) and farmers (hips).
  • Obesity or being overweight: This is especially true in hip and knee osteoarthritis, since the extra weight puts strain on these weightbearing joints over time.
  • Nutrition and vitamin aborption problems: In people who are in the early stages of osteoarthritis and have a vitamin D deficiency, the disease may progress more quickly.

Video – Supplements for Osteoarthritis: What Should I Know?

Can I prevent getting osteoarthritis?

There is no magic formula for avoiding joint degeneration. However, for osteoarthritis that affects the knees and hips (which are the two joints most commonly affected) maintaining an ideal weight or losing excess weight may help prevent osteoarthritis in these areas or decrease its rate of progression.

How do I know if I have osteoarthritis?

There are three key elements to getting an accurate diagnosis for osteoarthritis:

  • a complete evaluation and physical examination by a doctor
  • radiological examinations (X-rays and/or other imaging)
  • laboratory tests

The physical examination

Your physician will talk with you to learn your medical history and symptoms, and then to a physical exam to assess:

  • pain levels
  • joint range of motion
  • muscle strength in the affected region
  • presence of any swelling or tenderness of the joint
  • gait (the way you walk) if the disease is in the hip or knee

Radiological examinations

When the physical exam suggests a person may have osteoarthritis, dfferent forms of imaging may be necessary to confirm the diagnosis and determine the severity of the joint degeneration.

Imgaing for diagnosing advanced osteoarthritis

X-rays are very helpful in diagnosing advanced osteoarthritis because the affected joint will have specific characteristics:

  • Bones that are closer to each other than they should be: As cartilage wears away, the joint space can narrow.
  • Cysts: As the body responds to cartilage destruction and attempts to stabilize the joint, cysts or fluid-filled cavities can form in the bone.
  • Increased bone density or uneven joints: When bones are no longer cushioned by cartilage, they can rub against one another, creating friction. The body responds by laying down more bone in response, increasing bone density. Increased bone creates uneven joint surfaces and osteophytes (bone spurs) around the joint margins.

X-ray view of the hip joint showing osteoarthritis and joint space narrowing.
X-ray view of the hip joint showing osteoarthritis and joint space narrowing between the femur (thighbone) and pelvis.

X-ray view of the hip joint showing severe joint space narrowing and large osteophytes.
X-ray view of the hip joint showing severe joint space narrowing and large osteophytes


Imaging for diagnosing early-stage osteoarthritis

Confirming early onset osteoarthritis is more complicated, because the signs are far more subtle. Hospital for Special Surgery has developed special X-ray views that increase the sensitivity of conventional X-rays, allowing detection of early changes in the joint before they are evident on routine X-rays.

In some cases, X-rays alone are not sufficient to show the smaller differences associated with early onset arthritis. When this is the case, other specialized diagnostic imaging technologies are used. These include:

  • CT scan (computed tomography, sometimes called a "CAT scan"): A CT exam is excellent for showing the formation of osteophytes (bone spurs) and how they affect the surrounding soft tissues of the joint.
  • Ultrasound: This sensitive imaging technology is useful for identifying synovial cysts that can form in association with osteoarthritis. Ultrasound can also be used to image articular cartilage in patients who cannot have an MRI exam because of certain medical conditions.
  • Nuclear medicine imaging, such as radionuclide bone scans: Bone scans are very sensitive and may show abnormalities in the bones and joints not yet visible on X-rays. They can also be used to image the entire skeleton in one examination to demonstrate whether a patient has osteoarthritis in multiple parts of the body.
  • MRI (magnetic resonance imaging): An MRI is very good at revealing subtle changes in both bony and soft tissues of the musculoskeletal system. MRI can demonstrate reactive bone edema or soft tissue swelling as well as small cartilage or bone fragments in the joint. At HSS, specific computer programs are used to identify early evidence of cartilage degeneration. When there is objective evidence of cartilage wear, appropriate treatment can be initiated to prevent or delay progression.

X-ray image showing normal cartilage in a knee at left and damaged cartilage and an osteophyte in a knee at right.
MRI of the knee showing normal cartilage on one side and cartilage loss and on osteophyte on the other

MRI of the hip demonstrating osteoarthritis with large osteophytes around the femoral head.


In some cases, when osteoarthritis is suspected, but X-rays appear normal, a special MRI process called quantitative T2 mapping can detect the subtle cartilage differences to confirm the diagnosis.

Knee cartilage without osteoarthritis
Normal knee cartilage
Knee cartilage with osteoarthritis
Knee with osteoarthritis

What tests are done for osteoarthritis?

Laboratory tests are helpful for diagnosing osteoarthritis, because they are used to rule out forms of inflammatory arthritis. In other words, if you have joint pain and your lab results are normal, it would confirm a diagnosis of OA. These tests include:

  • complete blood counts
  • urinalysis
  • sedimentation rate
  • rheumatoid factor (to detect rheumatoid arthritis)
  • antinuclear antibody (ANA) titer tests

When these tests return normal or negative results, this usually indicates that your arthritis is osteoarthritis. It should be noted, however, that as people age, they sometimes develop a low-level positive rheumatoid factor, ANA titer and/or elevated sedimentation rate without experiencing any obvious illness. This is why doctors do not rely on laboratory tests alone, but rather to confirm a suspected diagnosis for osteoarthritis.

Another lab test that may help confirm the diagnosis is the extraction and analysis of synovial fluid from the joint. Synovial fluid is a liquid normally found within the joints. It helps nourish and lubricate them and is usually present in only very small amounts. However, when certain forms of arthritis are present, synovial fluid will change.

In osteoarthritis, white blood cell count (“pus cells”) is usually normal and the fluid is clear (like water). Higher white cell counts should suggest inflammatory arthritis or infection, rather than osteoarthritis. In this way, extracting synovial fluid can help to confirm the diagnosis. It can also reduce pain and swelling if the fluid is contributing to inflammation.

The fluid may also be examined for the presence of uric acid crystals (seen in gout) or calcium pyrophosphate crystals (seen in pseudogout or chondrocalcinosis). The measurement of other biological markers is still experimental.

How is osteoarthritis treated?

Your doctor will develop an individualized treatment program especially for you based on several factors, including:

  • How severe your disease is
  • Which joints are affected
  • The nature of your symptoms
  • Any other conditions you have and medications you take
  • Your age, occupation and everyday work activities

What nonsurgical treatments are available for osteoarthritis?

If the osteoarthritis is not severe, it is usually first treated conservatively (nonsurgically) with physical and occupational therapy. It is wise to maintain good nutrition and a healthy weight. This will put less pressure on your joints. (Learn about the weight management program at HSS.) In the case of osteoarthritis of the knee, it is especially important to exercise and strengthen your thigh muscles, which can reduce pain and improve function.

Weight management, diet and nutrition for managing osteoarthritis

Video – Osteoarthritis: Diet and Nutrition

Staying active is essential

For people with osteoarthritis, it is important to maintaining an active lifestyle and avoid becoming sedentary. Movement can help lessen pain and prevent it from getting worse. But the correct and safe types of activity vary from patient to patient. As with any treatment, getting a proper “movement prescription” requires having a pinpoint diagnosis and an understanding of each patient's unique condition.

If these conservative measures do not work, anti-inflammatory medications may be recommended. These may be:

  • NSAIDs (nonsteroidal anti-inflammatory drugs)
  • corticosteriod injections into the joint itself

Video – Osteoarthritis treatment

When should I consider surgery?

When the conservative measures above are not enough and pain in a specific joint makes it difficult for you to move, then joint replacement surgery can restore your comfort and help you to return to normal activity. Hip replacement surgery and knee replacement surgery have become trusted treatments for restoring mobility and easing pain.

You are generally a good candidate for surgery if conservative treatment hasn't worked and you experience a significant interruption in some activity of daily life – for example, if you can't walk more than a city block or if you awaken from sleep with pain in the affected joint. In such cases, surgery should provide outstanding results, because you will become pain-free in the affected joint. The exact type of surgery you have will depend on your age, activity level, and the specific joint that is affected.

Osteoarthritis research at HSS

The scientists and doctors at Hospital for Special Surgery keep you informed on HSS.edu about their specific and ongoing studies and trials on all musculoskeletal conditions, treatments, and issues. Besides each Division’s research overview (linked below) the biography page of each HSS doctor and scientist links to their research, as well as their articles in noted professional journals.

You can also sign-up for the free HSS eNewsletter that brings a convenient monthly update on the latest news at the hospital right to your email inbox.

Hospital for Special Surgery’s pace-setting musculoskeletal research is organized into five main programs. And every program contributes essential knowledge to OA research:

  • Arthritis and Tissue Degeneration Program: HSS investigations of the intricate cellular and molecular mechanisms of tissue destruction in all musculoskeletal conditions help reveal the cellular processes of cartilage loss in osteoarthritis. When a new important step of cellular interaction is discovered, it becomes a potential target for therapies that could prevent, slow, or even stop cartilage degeneration in OA.
  • Autoimmunity and Inflammation Program: In-depth knowledge from HSS studies of how cells communicate and interact in inflammatory reactions in autoimmune diseases can be integrated with cellular studies of how inflammation is triggered – and then continues to impact – the joints in OA.
  • Department of Biomechanics: The mechanics of the body’s movement, function, and ability to carry weight are affected by every stage of osteoarthritis. Biomechanical research uses principles of engineering, materials science, physical and computer modeling, and advanced statistical analysis to study how OA impacts the body’s function and gait. The department also continually researches innovations in the design and materials of joint replacements, surgical instrumentation, and orthopedic devices.
  • Musculoskeletal Integrity Program: Using advanced technology not often available at one research center, HSS scientists unlock the understanding of the cellular nature of living bone: how it thrives, how it degenerates, how it interacts with soft tissue like cartilage and tendons, as well as orthopedic devices like implants.
  • Tissue Engineering, Regeneration, and Repair Program: Cartilage does not heal itself. Yet, when injured, other soft tissues – like tendons and ligaments – can. Our ongoing studies of the cellular mechanisms of soft tissue degradation and regeneration can help uncover ways to slow and prevent cartilage loss. Understanding the cellular nature of soft tissues also informs the science of tissue engineering. Interdisciplinary studies at HSS are developing new biologic and synthetic tissues that can help damaged joints regain function and mobility.

Overview articles

Learn more about the basics of osteoarthritis from HSS expert physicians.

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Learn more about how doctors diagnose osteoarthritis.

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