Knee pain usually results from overuse, poor form during physical activity, not warming up or cooling down, or inadequate stretching. Simple causes of knee pain often clear up on their own with self care. Being overweight can put you at greater risk for knee problems.

Knee pain can be caused by:

• Arthritis -- including rheumatoid, osteoarthritis, and gout
• Baker's cyst -- a fluid-filled swelling behind the knee that may accompany inflammation from other causes, like arthritis
• Bursitis -- inflammation from repeated pressure on the knee, such as kneeling for long periods of time, overuse, or injury
• Connective tissue disorders such as lupus
• Dislocation of the kneecap
• Iliotibial band syndrome -- a hip disorder related to injury of the thick band that runs from your hip to the outside of your knee
• Infection in the joint
• Knee injuries -- may cause bleeding into your knee, which worsens the pain
• Tendinitis -- a pain in the front of your knee that gets worse when going up and down stairs or inclines
• Torn cartilage (a meniscus tear) -- pain felt on the inside or outside of the knee joint
• Torn ligament (ACL tear) -- leads to pain and instability of the knee
• Strain or sprain -- minor injuries to the ligaments caused by sudden or unnatural twisting

Less common conditions that can lead to knee pain include the following:

• Bone tumors
• Osgood-Schlatter disease

Many causes of knee pain, especially those related to overuse or physical activity, respond well to self-care:

• Rest and avoid activities that aggravate the pain, especially weight bearing activities.
• Apply ice. First, apply it every hour for up to 15 minutes. After the first day, apply it at least 4 times per day.
• Keep your knee elevated as much as possible to bring any swelling down.
• Gently compress the knee by wearing an ace bandage or elastic sleeve. Either can be purchased at most pharmacies. This may reduce swelling and provide support.
• Take acetaminophen for pain or ibuprofen for pain and swelling.
• Sleep with a pillow underneath or between your knees.

Call your doctor if:

• You cannot bear weight on your knee
• You have severe pain, even when not bearing weight
• Your knee buckles, clicks, or locks
• Your knee is deformed or misshapen
• You have a fever, redness or warmth around the knee, or significant swelling
• You have pain, swelling, numbness, tingling, or bluish discoloration in the calf below the sore knee
• You still have pain after 3 days of home treatment

Your health care provider will perform a physical examination, with careful attention to your knees, hips, legs, and other joints.

To help diagnose the cause of the problem, your doctor will ask medical history questions, such as:

• When did your knee first begin to hurt?
• Have you had knee pain before? What was the cause?
• How long has this episode of knee pain lasted?
• Do you feel the pain continuously or off and on?
• Are both knees affected?
• Is the pain in your entire knee or one specific location like the kneecap, outer or inner edge, or below the knee?
• Would you say that the pain is severe?
• Does it feel bruised?
• Can you stand or walk?
• Have you had an injury or accident involving the knee?
• Have you overused the leg? Describe your usual activities and exercise routine.
• What home treatments have you tried? Have they helped?
• Do you have other symptoms, like pain in your hip, pain down your leg or calf, knee swelling, swelling in your calf or leg, fever?

The following diagnostic tests may be performed:

• Fluid drawn from the knee and analyzed
• X-ray of the knee
• MRI of the knee if a ligament or meniscus tear is suspected

Your doctor may prescribe nonsteroidal anti-inflammatory drugs (NSAIDs) that are stronger than those available over-the-counter. If those don't help, your doctor may inject a steroid to reduce pain and inflammation.

Referrals to a physical therapist (to learn stretching and strengthening exercises) and podiatrist (to be fitted for orthotics) may be necessary. These help prevent repeated problems.

In some cases, surgery is needed. For example, if arthritis is severe, a joint replacement may be recommended. Minor ligament strain will heal with home care and torn ligaments may recover with use of a knee brace. However, for significant tears or ruptures, as well as a torn meniscus, arthroscopic knee surgery is often needed.

Recovery from ligament and meniscus problems is slow. Crutches and extended physical therapy may be needed.

• Increase your activity level slowly over time. For example, when you begin exercising again, walk rather than run.
• Always warm up before exercising and cool down afterward. Stretch your quadriceps and hamstrings.
• Replace your sports shoes often. Get good advice about proper footwear for your foot shape and mechanics. For example, if you pronate (land on the outside of your heel and turn your foot inward), consider anti-pronation footwear.

Labropoulos N, Shifrin DA, Paxinos O. New insights into the development of popliteal cysts. Br J Surg. 2004; 91(10): 1313-1318.

Fithian DC. Fate of the anterior cruciate ligament-injured knee. Orthop Clin North Am. 2002; 33(4): 621-636, v.