What Is Rheumatoid Arthritis of the Knee?

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Rheumatoid arthritis (RA) is one of the most common forms of arthritis, affecting more than 1.3 million people in the United States. It is an autoimmune disease in which your body attacks healthy cells by mistake. In rheumatoid arthritis, the immune system targets the joints, usually many joints at the same time. This inflammatory condition affects the knee joint in up to 30% of RA patients.

Rheumatoid arthritis of the knee causes swelling of the synovial membrane that lines the knee joint, which results in pain and stiffness. Research has found that RA of the knee damages not only the articular cartilage but the menisci of the knee as well.

Prolonged periods of sitting can cause stiffness to your joints

Charday Penn / Getty Images

Symptoms 

Symptoms of rheumatoid arthritis of the knee vary from person to person, but those with RA all share some common symptoms.

Pain

When the body accidentally attacks the synovium, it can result in inflammation, causing pain and swelling in the knee joint. Most people experience a gradual onset, which is usually most noticeable upon waking up in the morning; others may have a sharp increase in pain over a short period of time.

Rheumatoid arthritis can result in much discomfort, stiffness, and even deformity due to damage to the bones and cartilage.

RA is a symmetrical disease, and as such, rheumatoid arthritis of the knee usually causes symptoms in both knees. In contrast, the pain of osteoarthritis (OA) is typically not symmetrical.

Rheumatoid arthritis is a disease that flares, meaning there are periods when symptoms become worse. Life stress or physical trauma can trigger a flare.

Systemic Symptoms

Systemic symptoms refer to symptoms that affect the entire body. RA does not just impact the joints, but other parts of the body as well. For example, RA may impact the heart and eyes.

Systemic symptoms that may occur include:

  • Unexplained weight loss, which can be due to a loss of muscle mass from decreased exercise as a result of tiredness, fatigue, or joint pain. Weight loss has been identified as a clinical sign associated with extra-articular elements of RA, such as nodules.
  • Fever. The inflammation involved in rheumatoid arthritis may cause an elevated temperature.
  • Fatigue, tiredness, and weakness.

Causes

The exact cause of rheumatoid arthritis is unknown, but scientists have identified several risk factors that increase a person's likelihood of developing the disease, including:

  • Age (RA is most common in people over 60)
  • Female sex (new cases of RA are two or three times higher in women than in men)
  • Having the human leukocyte antigen (HLA) gene
  • Smoking
  • No history of live births (women who have never given birth are at higher risk of having RA)
  • Early life exposures, such as to smoking as a child
  • Obesity

A fully functional immune system is predicated upon your body's capacity to differentiate normal from abnormal cells or foreign threats. In autoimmune diseases, autoantibodies are generated that mistakenly attack your own normal cells. There are more than 80 autoimmune diseases, with the more common being type 1 diabetes, lupus, and inflammatory bowel disease.

Diagnosis

Rheumatoid arthritis is diagnosed by a rheumatologist. The process for diagnosing RA of the knee involves:

  • Examining the knee joints
  • Assessing symptoms
  • Checking for inflammation markers

There is no one test that confirms or rules out RA in all patients. Clinical context is key in evaluating and making the appropriate diagnosis for patients with RA. And early diagnosis is key to improving long-term outlook.

Physical Examination

A joint count may be performed, where your provider checks your joints for tenderness, swelling, warmth, deformity, bumps under the skin, and limited range of motion.

Part of your assessment plan may also involve physiotherapy. Your doctor will monitor your gait (walking, running) and range of motion of the knee joints, perform a strength test of the knees, or use isokinetics, an assessment of your posture and evaluation of breathing.

Your provider will also ask you about the duration and intensity of your symptoms, what actions make them better or worse, and whether anyone in your family has RA.

Lab Tests

Blood tests are performed to check the levels of erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP). A high level of these inflammatory markers, combined with other clues, can help your doctor make a diagnosis of RA.

What Are Antibodies?

Your body generates a special kind of protein, called an antibody, to stave off infections. After contracting an illness, your body generates antibodies to protect you from the illness if you encounter a second exposure. These antibodies can take some time to develop, and do not guarantee you will be immune.

Your doctor will also check for the rheumatoid factor (RF) and antibodies to cyclic citrullinated peptide (CCPs). RF is an antibody found in about 80% of people with RA, while CCPs are found in 60% to 70% of people with RA. Not every patient with RA has high levels of CCP antibodies, and the whole clinical picture is considered when making a diagnosis of RA.

Imaging

X-rays can be used to check for bone erosions in RA, but these erosions can only be seen on X-ray one to two years after disease onset. Magnetic resonance imaging (MRI) and ultrasound, however, can reveal early, non-bony signs of RA that X-ray can't detect. These two imaging tests are also more sensitive than X-ray in identifying bone erosions.

MRI allows detection of all relevant pathologies, such as synovitis, tenosynovitis, bone marrow edema (osteitis), and cartilage damage. It has also been found to be more sensitive than clinical exam for monitoring inflammation and more sensitive than X-rays and ultrasound for monitoring joint destruction.

Treatment

The goal of RA treatment is to alleviate symptoms, put the disease in remission, prevent joint and organ damage, and reduce long-term complications. There are a few ways people with RA can keep their condition and symptoms from interfering with their daily lives.

Pain Management

Pain management for rheumatoid arthritis of the knee often includes nonsteroidal anti-inflammatory drugs (NSAIDs) and topical therapies such as capsaicin cream. In a small study of three RA patients, capsaicin cream was reported to offer pain relief. Capsaicin works to deplete stores of a chemical involved in transmitting pain signals to the brain, and thus when sensory nerve fibers of the knee involved in RA are triggered, fewer pain signals are sent to the brain and less pain is experienced.

Disease-Modifying Anti-Rheumatic Drugs

Disease-modifying anti-rheumatic drugs (DMARDs) are the first-line treatment for rheumatoid arthritis. DMARDs are drugs that are immunosuppressive and immunomodulatory, meaning they suppress or change certain aspects of the body's immune system. Because rheumatoid arthritis is an autoimmune disease in which the body accidentally attacks normal cells, immunosuppressive and immunomodulatory agents can help to mitigate the impact of these attacks. Though they are all different, each DMARD has its own way of interfering with the mechanism of action in pathways related to inflammation.

Emerging research on microRNA alterations that occur in cases of RA has introduced new biomarkers that can possibly be used in the diagnosis and treatment of RA. A biomarker can be used to diagnose a condition and monitor its activity.

Exercise Therapy

A systematic literature review of six randomized trials that looked at exercise therapy in RA found that there was a positive relationship between dynamic exercise therapy and physical strength in RA patients.

Surgery

Knee arthroplasty, also known as joint replacement, has been demonstrated to improve functionality of the damaged knee joint and reduce pain and inflammation. In a study in which 17 RA patients' knees were treated with knee arthroplasty, 45.7% achieved clinical remission within 36 months of surgery. The study concluded that surgical intervention via knee arthroplasty is a safe procedure that involves only a short hospital stay and can reduce inflammation related to RA of the knee.

Coping

Rest is key, particularly when managing a flare. Set reasonable goals. Tell your doctor if your symptoms change, because they will make adjustments to your medications that can help alleviate the symptoms. With RA of the knee, you may need to create extra time in your day for commuting or ask a loved one to help with your errands.

It is normal to feel frustrated if you have been diagnosed with rheumatoid arthritis of the knee, particularly if you are very active and engage in a sport that can be hard on the knees, such as long-distance running.

Self-care is important, particularly when you have a chronic illness. Setting up a plan early is a good way to take charge of your health.

A Word From Verywell

Rheumatoid arthritis of the knee can be a painful and frustrating condition. The pain and swelling may feel limiting, but with early diagnosis and treatment, you can still have an active and enjoyable life. Although you may need to compromise on some activities, don't let RA stop you from trying new things and staying active. As with many conditions, risks of RA and symptoms of RA are increased by tobacco smoking. Reducing or stopping your usage of tobacco cigarettes may help reduce your symptoms.

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