Knee pain is a common problem. According to Kelley's Textbook of Rheumatology, knee pain affects 20% to 52% of people 55 years of age or older. And while the condition is common, the cause is sometimes not immediately obvious. If pain persists, you'll likely need to consult with your doctor, as your medical history and a physical examination will provide important information that will lead to the correct diagnosis and appropriate treatment.
Knee arthritis is among the many conditions that can cause knee pain. There are three common types of arthritis that frequently involve the knee joint: osteoarthritis, rheumatoid arthritis, and post-traumatic arthritis. Osteoarthritis, a degenerative disease and the most common type of knee arthritis, usually affects middle-aged to older people. Rheumatoid arthritis is an inflammatory type of arthritis that affects young as well as older people, and post-traumatic arthritis develops after a joint injury, sometimes years later. In essence, post-traumatic arthritis is osteoarthritis, but it's referred to as "post-traumatic" because of its association with a prior injury.
Symptoms of Knee Arthritis
Usual signs and symptoms associated with knee arthritis include:
- Pain that usually develops gradually, although sudden onset is possible
- Joint stiffness
- Joint swelling
- Pain, stiffness, and swelling are characteristically worse in the morning or following prolonged periods of inactivity (e.g., sitting in a movie theater)
- Activity, especially weight-bearing activity such as walking and stair-climbing, can increase symptoms
- The knee can lock, pop, or feel like it's giving out
Physical Examination of the Knee
A physical examination of your knee will include an assessment of your gait, range of motion, and observation of your knee as you're standing. Your doctor will observe the musculature above and below the knee as you stand in front of him; if there are signs of atrophy of the quadricep muscle, that's usually a sign of a chronic knee condition. The doctor will also observe the knee for swelling. Significant joint effusion (swelling) may be seen as bulging from the lateral (outer) or medial (inner) aspect of the knee. Inspection of the knee from the back side allows the doctor to observe malalignment, such as varus or valgus deformities. Varus deformity, which causes a bow-legged appearance, is typically associated with osteoarthritis. Valgus deformity, which causes a knock-kneed appearance, can be seen with rheumatoid arthritis. Inspection of the knee from the back can also reveal a Baker's cyst.
After the standing examination of the knee is complete, your knee will be examined while you're lying down. The doctor will examine the knee when it's fully extended and flexed, and your knee joint will be palpated for swelling, warmth and tenderness. Also, while supporting the knee with his hand on one side, your doctor will apply stress to the other side to test the strength of the ligaments that support the knee.
Based on the findings of your physical examination, your doctor may order imaging studies (usually x-rays, but perhaps an MRI), and if necessary, blood tests or a synovial fluid analysis to help diagnose the type of arthritis you have and provide evidence of the extent of joint damage (e.g., joint space narrowing).
Differentiating Knee Osteoarthritis and Rheumatoid Arthritis of the Knee
From the patient's perspective, both knee osteoarthritis and rheumatoid arthritis of the knee cause significant pain, stiffness, limited range of motion and more. But it's important to distinguish between the two types of arthritis so that proper treatment can be prescribed.
Usually when osteoarthritis is the cause of the knee pain, one knee is involved more than the other. With rheumatoid arthritis, both knees are typically affected simultaneously, because it's a symmetric disease (i.e., affects joint on both sides of the body). Inflammatory markers, which are detected by blood tests (e.g., CRP and sedimentation rate), are typically elevated in patients with rheumatoid arthritis and normal in patients with osteoarthritis. Another significant sign of rheumatoid arthritis is knee pain that's not relieved by rest.
Treatment for Knee Arthritis
Managing knee pain and other symptoms associated with osteoarthritis initially involves conservative treatment. Activity modification, exercise, physical therapy, rest, nonsteroidal anti-inflammatory drugs, acetaminophen, and mobility aids (e.g., cane) are typically recommended for knee pain. As your condition worsens, the treatment plan becomes more aggressive. Stronger analgesic medications may be an option. As a last-resort, when conservative treatment fails, knee replacement surgery has relieved pain and restored function for many people with severe knee arthritis. Initial treatment for knee pain associated with rheumatoid arthritis is usually more aggressive.
In 2008, the American Academy of Orthopaedic Surgeons offered 22 recommendations for the treatment of knee osteoarthritis. In 2012, the American College of Rheumatology revised guidelines for treating rheumatoid arthritis that involve the use of disease-modifying anti-rheumatic drugs (DMARDs) and biologic drugs.
Hip and Knee Pain. James I. Huddleston and Stuart Goodman. Firestein: Kelley's Textbook of Rheumatology. 9th Edition.
Arthritis of the Knee. OrthoInfo. American Academy of Orthopaedic Surgeons. October 2007.
Primer on the Rheumatic Diseases. Evaluation of the Patient. The Knee. Robinson D. et al. Thirteenth Edition. Arthritis Foundation.
Update of the 2008 ACR Recommendations for Use of DMARDs and Biologics in the Treatment of Rheumatoid Arthritis. Arthritis Care & Research. pp. 625-639. Singh JA et al. May 2012.
Guideline on the Treatment of Osteoarthritis (OA) of the Knee. Richmond John MD et al. American Academy of Orthopedic Surgeons. 12/11/2008.