Symptoms

The location and severity of knee pain may vary, depending on the cause of the problem. Signs and symptoms that sometimes accompany knee pain include:

• Swelling and stiffness
• Redness and warmth to the touch
• Weakness or instability
• Popping or crunching noises
• "Locking," or inability to fully straighten the knee

When to see a doctor
Call your doctor if you:

• Can't bear weight on your knee
• Have marked knee swelling
• Are unable to fully extend or flex your knee
• See an obvious deformity in your leg or knee
• Have a fever, in addition to redness, pain and swelling in your knee
• Fall because your knee "gives out"

Causes

Knee pain can be caused by injuries, mechanical problems, types of arthritis and other problems.

Injuries
A knee injury can affect any of the ligaments, tendons or fluid-filled sacs (bursae) that surround your knee joint as well as the bones, cartilage and ligaments that form the joint itself. Some of the more common knee injuries include:

• ACL injury. An ACL injury is the tearing of the anterior cruciate ligament (ACL) — one of four ligaments that connect your shinbone to your thighbone. An ACL injury is particularly common in people who play basketball or go downhill skiing, because it's linked to sudden changes in direction.
• Torn meniscus. The meniscus is formed of tough, rubbery cartilage and acts as a shock absorber between your shinbone and thighbone. It can be torn if you suddenly twist your knee while bearing weight on it.
• Knee bursitis. Some knee injuries cause inflammation in the bursae, the small sacs of fluid that cushion the outside of your knee joint so that tendons and ligaments glide smoothly over the joint.
• Patellar tendinitis. Tendinitis is irritation and inflammation of one or more tendons — the thick, fibrous cords that attach muscles to bones. Runners, skiers and cyclists are prone to develop inflammation in the patellar tendon, which connects the quadriceps muscle on the front of the thigh to the shinbone.

Mechanical problems

• Loose body. Sometimes injury or degeneration of bone or cartilage can cause a piece of bone or cartilage to break off and float in the joint space. This may not create any problems unless the loose body interferes with knee joint movement — the effect is something like a pencil caught in a door hinge.
• Knee 'locking.' This can occur from a cartilage tear. When a portion of cartilage from the tear flips inside the knee joint, you may not be able to fully straighten your knee.
• Dislocated kneecap. This occurs when the triangular bone (patella) that covers the front of your knee slips out of place, usually to the outside of your knee. You'll be able to see the dislocation, and your kneecap is likely to move excessively from side to side.
• Hip or foot pain. If you have hip or foot pain, you may change the way you walk to spare these painful joints. But this altered gait can interfere with the alignment of your kneecap and place more stress on your knee joint. In some cases, problems in the hip or foot can refer pain to the knee.

Types of arthritis

• Osteoarthritis. Sometimes called degenerative arthritis, osteoarthritis is the most common type of arthritis. It's a wear-and-tear condition that occurs when the cartilage in your knee deteriorates with use and age.
• Rheumatoid arthritis. The most debilitating form of arthritis, rheumatoid arthritis is an autoimmune condition that can affect almost any joint in your body, including your knees. Although rheumatoid arthritis is a chronic disease, it tends to vary in severity and may even come and go.
• Gout. This type of arthritis occurs when uric acid crystals build up in the joint. While gout most commonly affects the big toe, it can also occur in the knee.
• Pseudogout. Often mistaken for gout, pseudogout is caused by calcium pyrophosphate crystals that develop in the joint fluid. Knees are the most common joint affected by pseudogout.
• Septic arthritis. Sometimes your knee joint can become infected, leading to swelling, pain and redness. There's usually no trauma before the onset of pain. Septic arthritis often occurs with a fever.

Other problems

• Iliotibial band syndrome. This occurs when the ligament that extends from the outside of your pelvic bone to the outside of your tibia (iliotibial band) becomes so tight that it rubs against the outer portion of your femur. Distance runners are especially susceptible to iliotibial band syndrome.
• Chondromalacia patellae (patellofemoral pain syndrome). This is a general term that refers to pain arising between your patella and the underlying thighbone (femur). It's common in young adults, especially those who have a slight misalignment of the kneecap; in athletes; and in older adults, who usually develop the condition as a result of arthritis of the kneecap.
• Osgood-Schlatter disease. This condition affects the softer area of bone near the top of the shinbone, where bone growth occurs. It's most common in boys who play games or sports that involve running or jumping. The discomfort can last a few months and may continue to recur until the child's bones stop growing.
• Osteochondritis dissecans. Caused by reduced blood flow to the end of a bone, osteochondritis dissecans is a joint condition in which a piece of cartilage, along with a thin layer of the bone beneath it, comes loose from the end of a bone. It occurs most often in young men, particularly after an injury to the knee.

Risk factors

A number of factors can increase your risk of having knee problems, including:

• Age. Certain types of knee problems are more common in young people — Osgood-Schlatter disease and patellar tendinitis, for example. Others, such as osteoarthritis, gout and pseudogout, tend to affect older adults.
• Sex. Teenage girls are more likely than are boys to experience an ACL tear or a dislocated kneecap. Boys, on the other hand, are at greater risk of Osgood-Schlatter disease and patellar tendinitis than girls are.
• Excess weight. Being overweight or obese increases stress on your knee joints, even during ordinary activities such as walking or going up and down stairs. It also puts you at increased risk of osteoarthritis by accelerating the breakdown of joint cartilage.
• Mechanical problems. Certain structural abnormalities, such as having one leg shorter than the other, misaligned knees and even flat feet, can make you more prone to knee problems.
• Lack of muscle flexibility or strength. A lack of strength and flexibility are among the leading causes of knee injuries. Tight or weak muscles offer less support for your knee because they don't absorb enough of the stress exerted on the joint.
• Certain sports. Some sports put greater stress on your knees than do others. Alpine skiing with its sharp twists and turns and potential for falls, basketball's jumps and pivots, and the repeated pounding your knees take when you run or jog all increase your risk of knee injury.
• Previous injury. Having a previous knee injury makes it more likely that you'll injure your knee again.

Complications

Not all knee pain is serious. But some knee injuries and medical conditions, such as osteoarthritis, can lead to increasing pain, joint damage and even disability if left untreated. And having a knee injury — even a minor one — makes it more likely that you'll have similar injuries in the future.

Preparing for your appointment

You're likely to start by seeing your family doctor. Depending upon the cause of your problem, he or she may refer you to a doctor specializing in joint diseases (rheumatologist), joint surgery (orthopedic surgeon) or sports medicine.

What you can do
Prior to the appointment, you may want to write a list that answers the following questions:

• When did you begin experiencing symptoms?
• Have your symptoms been continuous or occasional?
• How severe are your symptoms?
• What, if anything, seems to improve your symptoms?
• What, if anything, appears to worsen your symptoms?
• Do you exercise or play sports?
• Do you experience any swelling, instability or locking of the knee?
• Are you experiencing symptoms in other areas, or just in your knee?
• Have you ever had knee pain before? If so, do you know what the cause was?

What to expect from your doctor
During the physical exam, your doctor is likely to:

• Inspect your knee for swelling, pain, tenderness, warmth and visible bruising
• Check to see how far you can move your lower leg in different directions
• Push on or pull the joint to evaluate the integrity of the structures in your knee

Tests and diagnosis

Imaging tests

• X-ray. Your doctor may first recommend having an X-ray, which can help detect bone fractures and degenerative joint disease.
• Computerized tomography (CT) scan. CT scanners combine X-rays taken from many different angles, to create cross-sectional images of the inside of your body. CT scans can help diagnose bone problems and detect loose bodies.
• Ultrasound. This technology uses sound waves to produce real-time images of the structures within and around your knee, and how they are working. Your doctor may want to maneuver your knee into different positions during the ultrasound, to check for specific problems.
• Magnetic resonance imaging. MRI uses radio waves and a powerful magnet to create 3-D images of the inside of your knee. This test is particularly useful in revealing injuries to soft tissues such as ligaments, tendons, cartilage and muscles.

Lab tests
If your doctor suspects an infection, gout or pseudogout, you're likely to have blood tests and sometimes arthrocentesis, a procedure in which a small amount of fluid is removed from within your knee joint with a needle and sent to a laboratory for analysis.

Treatment and drugs

Treatments will vary, depending upon what exactly is causing your knee pain.

Medications
Your doctor may prescribe medications to help relieve pain and to treat underlying conditions, such as rheumatoid arthritis or gout.

Therapy

• Physical therapy. Strengthening the muscles around your knee will make it more stable. Training is likely to focus on the muscles on the front of your thigh (quadriceps) and the muscles in the back of your thigh (hamstrings). Exercises to improve your balance are also important.
• Orthotics and bracing. Arch supports, sometimes with wedges on the inner or outer aspect of the heel, can help to shift pressure away from the side of the knee most affected by osteoarthritis. Different types of braces may help protect and support the knee joint.

Injections

• Corticosteroids. Injections of a corticosteroid drug into your knee joint may help reduce the symptoms of an arthritis flare and provide pain relief that lasts a few months. The injections aren't effective in all cases. There is a small risk of infection.
• Hyaluronic acid. This thick fluid is normally found in healthy joints, and injecting it into damaged ones may ease pain and provide lubrication. Experts aren't quite sure how hyaluronic acid works, but it may reduce inflammation. Relief from a series of shots may last as long as six months to a year.

Surgery
If you have an injury that may require surgery, it's usually not necessary to have the operation immediately. Before making any decision, consider the pros and cons of both nonsurgical rehabilitation and surgical reconstruction in relation to what's most important to you. If you choose to have surgery, your options may include:

• Arthroscopic surgery. Depending on the nature of your injury, your doctor may be able to examine and repair your joint damage using a fiber-optic camera and long, narrow tools inserted through just a few small incisions around your knee. Arthroscopy may be used to remove loose bodies from your knee joint, repair torn or damaged cartilage and reconstruct torn ligaments.
• Partial knee replacement surgery. In this procedure (unicompartmental arthroplasty), your surgeon replaces only the most damaged portion of your knee with parts made of metal and plastic. The surgery can usually be performed with a small incision, and your hospital stay is typically just one night. You're also likely to heal more quickly than you are with surgery to replace your entire knee.
• Total knee replacement. In this procedure, your surgeon cuts away damaged bone and cartilage from your thighbone, shinbone and kneecap, and replaces it with an artificial joint made of metal alloys, high-grade plastics and polymers.

Lifestyle and home remedies

Over-the-counter medications — such as acetaminophen (Tylenol, others), ibuprofen (Advil, Motrin, others) and naproxen (Aleve, others) — may help ease knee pain. Some people find relief by rubbing their knees with creams containing such ingredients as lidocaine, a numbing agent; or capsaicin — the substance that makes chili peppers hot.

Self-care measures for an injured knee include:

• Rest. Taking a break from your normal activities reduces repetitive strain on your knee, gives the injury time to heal and helps prevent further damage. A day or two of rest may be all that's needed for minor injuries. More severe damage is likely to need a longer recovery time.
• Ice. A staple for most acute injuries, ice reduces both pain and inflammation. A bag of frozen peas works well because it covers your whole knee. You can also use an ice pack wrapped in a thin towel to protect your skin. Although ice therapy is generally safe and effective, don't use ice for longer than 20 minutes at a time because of the risk of damage to your nerves and skin.
• Compression. This helps prevent fluid buildup in damaged tissues and maintains knee alignment and stability. Look for a compression bandage that's lightweight, breathable and self-adhesive. It should be tight enough to support your knee without interfering with circulation.
• Elevation. Because gravity drains away fluids that might otherwise accumulate after an injury, elevating your knee can help reduce swelling. Try propping your injured leg on pillows or sitting in a recliner

Alternative medicine

• Glucosamine and chondroitin. Study results have been mixed about the effectiveness of these supplements for relieving osteoarthritis pain. People who have moderate to severe arthritis pain appear to be helped more often than those who have minor arthritis pain.
• Acupuncture. Research suggests that acupuncture may help relieve knee pain caused by osteoarthritis. Acupuncture involves the placement of hair-thin needles into your skin at specific places on your body.

Prevention

Although it's not always possible to prevent knee pain, the following suggestions may help forestall injuries and joint deterioration:

• Keep extra pounds off.Maintaining a healthy weight is one of the best things you can do for your knees — every extra pound puts additional strain on your joints, increasing the risk of ligament and tendon injuries and even osteoarthritis.
• Get strong, stay limber. Because weak muscles are a leading cause of knee injuries, you'll benefit from building up your quadriceps and hamstrings, which support your knees. Balance and stability training helps the muscles around your knees work together more effectively. And because tight muscles also can lead to injury, stretching is important. Try to include flexibility exercises in your workouts.
• Be smart about exercise. If you have osteoarthritis, chronic knee pain or recurring injuries, you may need to change the way you exercise. Consider switching to swimming, water aerobics or other low-impact activities — at least for a few days a week. Sometimes simply limiting high-impact activities will provide relief.