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.
While there are many similarities in the symptoms and treatments of knee pain from various types of arthritis, this article focuses on osteoarthritis.
Osteoarthritis involves two primary processes:
- The cartilage in the joints breaks down
- Abnormal bony growths develop, called osteophytes or bone spurs
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
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
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.
Below is a list of common signs and symptoms of knee osteoarthritis. Early recognition of symptoms and appropriate treatment can dramatically slow or eliminate progression of osteoarthritis symptoms.
Pain is the most commonly reported symptom of knee osteoarthritis. The description of the pain will depend on the patient’s condition and situation. For example, the pain may come and go or there may be a chronic low level of pain with intermittent flare-ups of more intense pain. The pain may be experienced as dull and aching or as sharp and intense, and it is usually worse with certain activities that place additional strain on the joint, such as when bending down or walking up stairs. Typically, the knee pain can be lessened with rest and an ice compress.
Bone friction and swelling in the knee joint makes the knee stiff and less flexible. Knee range of motion can become more limited. A person with moderate to advanced knee osteoarthritis may find it is difficult to straighten out his or her knee. Some people may only experience stiffness in the knee in the morning or after sitting for a long period. Stiffness may or may not be accompanied by swelling.
Stiffness and swelling may be a sign of Knee Bursitis
Inactivity makes it worse. Knees can become stiff after sleeping or sitting for a long period of time. People with knee osteoarthritis often find stiffness and pain are most noticeable when they try to get out of bed in the morning or out of a chair after a long period of sitting.
When knee cartilage wears away, the femur and tibia (and sometimes patella) bones can rub together, resulting in irritation and swelling of the knee (i.e. fluid in the knee). A swollen knee may be accompanied by a sensation of warmth, which can range from warm to burning. The knee may even be red and warm to the touch.
Knee Buckling or Locking Up
Some patients with moderate to advanced knee osteoarthritis feel a sensation of their knees giving way or buckling, especially when stepping down stairs. This can occur if uneven grooves or flaps in the degenerated cartilage catch or if a piece of cartilage breaks off and becomes lodged in the joint, producing sensation of knee buckling or of the knee locking up. These episodes are unpredictable, but tend to occur when strain is placed on the knee, such as when descending stairs or getting up from a sitting position.
In most but not all cases, the symptoms of knee osteoarthritis come and go, becoming worse and more frequent over months or years. Knee osteoarthritis pain may flare up after high intensity activities, such as jogging or tennis, or simple weight-bearing activities that add strain to the knee joint, such as squatting or stair climbing.
Two chief risk factors for developing knee osteoarthritis are advanced age and obesity:
- Advanced age. While adults of any age may develop knee osteoarthritis, the prevalence of symptomatic knee osteoarthritis increases rapidly starting at age 45 and continues to increase thereafter. The prevalence increases with age because with age the knee joints experience wear and tear and cartilage thins and becomes less flexible, making it more prone to osteoarthritis. The degeneration of the joints that is characteristic of osteoarthritis is why the condition is also called “degenerative joint disease”.
- Excess weight / obesity. Knees are weight-bearing joints and a person who is overweight or obese is significantly more likely to develop knee osteoarthritis.
- Nearly 2 out of 3 people who are obese are likely to develop knee osteoarthritis
- Losing even a few pounds can significantly reduce the risk. One study showed that losing as little as 11 pounds reduced the risk of developing knee osteoarthritis among women by 50%
In addition to the above, other risk factors for developing knee osteoarthritis include:
A broken bone, serious injury or surgery may cause damage to the knee joint that eventually leads to knee osteoarthritis, although symptoms may not appear until many years later. Osteoarthritis that develops as a result of previous injury is usually termed Traumatic Arthritis, or Post-traumatic Arthritis.
Similar to height and hair color, the likelihood of a person developing knee osteoarthritis is influenced by genetics; a woman whose mother has knee osteoarthritis is more likely to develop the disease than another woman whose mother did not have the knee osteoarthritis. While the exact extent of genetic factors is not known, the CDC estimates between 20 to 35 percent of incidences of knee arthritis may be inherited.
Congenital Defect or Illness
Episodes of gout or septic arthritis as well as metabolic disorders, poor bone alignment and other congenital conditions can increase the risk of developing osteoarthritis of the knee.
Joint Stress and Chronic Injury
People whose regular activities or jobs require spending a lot of time on their feet, doing heavy lifting while standing, squatting or crawling (e.g. installing carpets) can experience “mini-traumas” in their knee joints and are more likely to develop osteoarthritis. Athletes who participate in high impact sports (e.g. tennis, football) may also be more prone to developing knee osteoarthritis.
Women are more likely than men to develop osteoarthritis in the knee. For adults over the age of 45:
- 18.7% of women have knee osteoarthritis
- 13.5% of men have knee osteoarthritis
While the above risks factors predispose certain individuals to osteoarthritis, they are not absolutely causative: people without the above risk factors may develop the condition and people with all of the above characteristics may never develop it.
If knee pain comes on suddenly, it is more likely to be caused by trauma or another condition, not by knee osteoarthritis. If the knee feels hot or the skin around the joint turns red, then a diagnosis other than osteoarthritis may be the culprit. This could indicate an infection, and an infected knee joint requires immediate medical attention.