Gradual onset of knee pain, stiffness and swelling are typical symptoms of knee osteoarthritis. Arthritis of the knee comes in several forms. Osteoarthritis is by far the most common form, followed by some forms of inflammatory arthritis, such as rheumatoid arthritis and gout.

See 6 Types of Arthritis that Affect the Knee

Knee osteoarthritis is a condition where cartilage in the knee degenerates, or breaks down.
Knee Osteoarthritis Video

While there are many similarities in the symptoms and treatments of knee pain from various types of arthritis, this article focuses on osteoarthritis.

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Osteoarthritis involves two primary processes:

  • The cartilage in the joints breaks down
  • Abnormal bony growths develop, called osteophytes or bone spurs.

See What Is Cartilage?

Lateral view of the bones in the knee joint. Due to osteoarthritis, the cartilage has degenerated and bony growths have developed.

This degenerative process can lead to abnormal joint function, pain and stiffness. The osteoarthritic process is gradual, with symptoms that may come and go and eventually worsen over a number of years. One of the primary symptoms of persons with knee osteoarthritis is pain. This pain may follow a pattern, for example:

  • Knee pain that comes and goes, possibly with a chronic low level of pain, punctuated by intermittent more intense flare-ups;
  • Pain with certain activities, such as bending, kneeling, squatting, or stair climbing;
  • Knee pain and stiffness that is worse after prolonged inactivity or rest, such as getting out of bed in the morning.

There are several risk factors that make one more likely to develop the condition. The primary risk factors are advanced age (over age 45), prior knee injury, and excess weight.

This article provides an in-depth review of the symptoms, causes and risk factors, diagnostic process, and surgical and nonsurgical treatments for osteoarthritis of the knee.

How Knee Osteoarthritis Causes Pain

The knee is a flexible, weight-bearing joint especially prone to wear-and-tear and therefore likely to be affected by osteoarthritis. According to the Centers for Disease Control and Prevention (CDC), nearly half of Americans may experience the symptoms of knee osteoarthritis at some point during their lives, and it is a leading cause of disability in people over age 50.1

An arthritic knee has thinned, damaged or missing cartilage in the joint. The damaged cartilage is not in and of itself a source of pain or other symptoms. Instead, the damaged or missing cartilage causes friction between bones and other knee problems, which in turn cause knee pain and related symptoms.

Knee Joint Anatomy and Osteoarthritis

Other than some sort of trauma or acute injury, the most common source of pain in the knee joint is arthritis, usually osteoarthritis. Inflammatory arthritis, such as rheumatoid arthritis or gout, are less common.

In an osteoarthritic knee, the articular cartilage is thinned, damaged or entirely worn away. When the knee cartilage has deteriorated in such a manner, the following process ensues:

  • New cartilage may be produced, but the new cartilage cells may grow in irregular, bumpy patterns rather than the original smooth form of cartilage. The result is that the femur (thigh) and tibia (shin) bones rub and grind against one another in the knee joint. The patella (knee cap) may also lose cartilage, but osteoarthritis of the knee most commonly begins with the deterioration of the cartilage between the femur and tibia.
  • To compensate for the deteriorated or missing cartilage, the bones in the joint may produce small bony growths called osteophytes, or bone spurs. In turn, the bone spurs can create even more friction in the knee joint.
  • As the body attempts to compensate for abnormal function of the knee joint, the associate tendons and ligaments can also be stretched or otherwise compromised, leading to further loss of stability and function in the knee.

It is important to note that cartilage does not contain nerves, so damaged cartilage is not the primary source of pain in knee osteoarthritis. Likewise, bone spurs are a normal sign of aging and the presence of bone spurs alone are not a cause for concern. However, the friction between bones and other resulting abnormalities in the knee can cause discomfort and pain.

Chronic knee discomfort and/or minor pain may warrant evaluation, since an appropriate treatment program can encourage healthy joint function and minimize or halt the progression of symptoms. As a general rule, if the osteoarthritis is diagnosed and treated early in the disease process, health care professionals believe that the outcome will be better for the patient in terms of less pain and fewer complications.


  1. Centers for Disease Control and Prevention, "Osteoarthritis Basics,", updated June 25, 2010, accessed June 2011.