Several types of arthritis can affect the knee joint, but by far the most common is osteoarthritis, which also is called “degenerative joint disease.”
Knee arthritis occurs when the joint-surface cartilage (also called hyaline cartilage or articular cartilage) becomes worn away, leaving the raw bone exposed. The cartilage serves as a pad or a bearing in the joint and, under normal conditions, the cartilage is even slicker than a hockey puck on ice. When the bearing wears away, the result is a roughed joint surface that causes the pain and stiffness that people associate with osteoarthritis.
Osteoarthritis can cause severe pain and disability. As a result of this condition, several hundred thousand people each year in the United States undergo knee-replacement surgery.
Most people with osteoarthritis of the knee can be managed without surgery.
The cause of osteoarthritis of the knee is not known, but risk factors include obesity, severe knee trauma and genetics.
Because other kinds of arthritis can affect the knee, and are treated differently, it is important to diagnose correctly.
Osteoarthritis of the knee usually causes pain. Other potential symptoms include swelling, stiffness, warmth and joint deformity.
The condition is not an emergency. It can flare at times, however, with increased pain and swelling. Many patients who experience a sudden flare-up will seek a doctor’s care, and for many patients an exam of the apparent acute symptoms will ultimately reveal this chronic condition.
No one knows what causes osteoarthritis of the knee. It is not contagious, nor caused by infection – though severe bacterial infections can cause post-infectious arthritis, a different type that typically feels worse than osteoarthritis.
It is not possible to predict who will get osteoarthritis of the knee. However, some risk factors that may increase the likelihood that knees will become arthritic:
Genetics: Arthritis often runs in families.
Severe trauma: Fractures (broken bones) and total removal of the supporting cartilages of the knee (meniscus) both increase the likelihood of arthritis.
By maintaining an ideal body weight and avoiding severe knee trauma, it is possible to minimize the risk of arthritis. However, many patients with osteoarthritis are slender and have never severely injured their knees, so no guarantees exist to avoid the condition.
The diagnosis of osteoarthritis of the knee is usually very straightforward, and is made in almost all cases by a qualified physician taking a thorough history, performing a physical examination, and taking X-rays with the patient standing up.
An X-ray is a simple test that helps a physician diagnose osteoarthritis of the knee with great accuracy. Very mild arthritis can be seen on a bone scan or an MRI (magnetic resonance imaging) even before it is visible on X-rays, but these tests are seldom helpful clinically for this purpose.
Osteoarthritis of the knee is a serious condition, and the most common of the more than 100 kinds of arthritis. The condition results in pain, stiffness and joint deformity, which can affect one’s ability to walk, work and enjoy life. It is a chronic disease, meaning that it takes months to years to emerge. Although it is not curable, it is readily treated with activity modifications, medications, injections and, if those interventions don’t work, knee replacement surgery. New minimally invasive approaches appear to decrease the recovery time from this operation.
Osteoarthritis of the knee is progressive, and when it becomes severe, it can severely affect one’s ability to walk, climb stairs, enter or exit a vehicle, and enjoy daily activities.
Keeping one’s body weight appropriate and choosing activities that don’t cause the arthritic pain are two things patients with osteoarthritis of the knee can do to help decrease the symptoms.
It is also important that patients with osteoarthritis of the knee avoid decreasing their activity level, so they remain physically fit. However, this often does require changing exercise programs. Running and walking programs are usually poorly tolerated by (and not recommended for) patients with osteoarthritis of the knee. Stationary bike, swimming, and water aerobics usually are well-tolerated and they are recommended.
No data suggests that diets can cure or treat osteoarthritis. However, it is important to try to avoid weight gain when one has osteoarthritis of the knee, as increased body weight is associated with worse symptoms.