Knee pain is a common condition that can affect people of all ages. It can be caused by a variety of factors, including injury, overuse, arthritis, and other medical conditions.

Some of the most common causes of knee pain include:

• Knee injuries, such as ligament sprains, meniscus tears, or fractures
• Overuse injuries, such as runner's knee or tendonitis
• Osteoarthritis or rheumatoid arthritis
• Patellofemoral pain syndrome, which is caused by a misalignment of the kneecap and can cause pain during activities that involve bending the knee, such as climbing stairs or squatting
• Bursitis or tendinitis, which are caused by inflammation of the bursae or tendons in the knee
• Gout, a type of arthritis caused by the buildup of uric acid crystals in the joints

Treatment for knee pain depends on the underlying cause of the pain. It may include rest, ice, compression, and elevation (RICE) to reduce inflammation and pain. Nonsteroidal anti-inflammatory drugs (NSAIDs) may also be recommended to help with pain and swelling. In some cases, physical therapy may be recommended to help with range of motion and strengthening exercises. For more severe cases, surgery may be necessary to repair or replace damaged joint structures.

Prevention of knee pain can be achieved by maintaining a healthy weight, wearing proper footwear during exercise, using proper form during exercise, and incorporating low-impact exercises such as swimming or cycling into your routine.

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 a tear 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, soccer or other sports that require sudden changes in direction.
• Fractures. The bones of the knee, including the kneecap (patella), can be broken during falls or auto accidents. Also, people whose bones have been weakened by osteoporosis can sometimes sustain a knee fracture simply by stepping wrong.
• Torn meniscus. The meniscus is the tough, rubbery cartilage that 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 causes irritation and inflammation of one or more tendons — the thick, fibrous tissues that attach muscles to bones. This inflammation can happen when there's an injury to the patellar tendon, which runs from the kneecap (patella) to the shinbone and allows you to kick, run and jump. Runners, skiers, cyclists, and those involved in jumping sports and activities may develop patellar tendinitis.

Mechanical problems

Some examples of mechanical problems that can cause knee pain include:

• 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, in which case the effect is something like a pencil caught in a door hinge.
• Iliotibial band syndrome. This occurs when the tough band of tissue that extends from the outside of your hip to the outside of your knee (iliotibial band) becomes so tight that it rubs against the outer portion of your thighbone. Distance runners and cyclists are especially susceptible to iliotibial band syndrome.
• Dislocated kneecap. This occurs when the triangular bone that covers the front of your knee (patella) slips out of place, usually to the outside of your knee. In some cases, the kneecap may stay displaced and you'll be able to see the dislocation.
• Hip or foot pain. If you have hip or foot pain, you may change the way you walk to spare your painful joint. But this altered gait can place more stress on your knee joint and cause knee pain.

Types of arthritis

More than 100 different types of arthritis exist. The varieties most likely to affect the knee include:

• 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-containing 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. Septic arthritis often occurs with a fever, and there's usually no trauma before the onset of pain. Septic arthritis can quickly cause extensive damage to the knee cartilage. If you have knee pain with any of the symptoms of septic arthritis, see your doctor right away.

Other problems

Patellofemoral pain syndrome is a general term that refers to pain arising between the kneecap and the underlying thighbone. It's common in athletes; in young adults, especially those whose kneecap doesn't track properly in its groove; and in older adults, who usually develop the condition as a result of arthritis of the kneecap.

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

• Keep extra pounds off. Maintain a healthy weight; it's one of the best things you can do for your knees. Every extra pound puts additional strain on your joints, increasing the risk of injuries and osteoarthritis.
• Be in shape to play your sport. To prepare your muscles for the demands of sports participation, take time for conditioning.
• Practice perfectly. Make sure the technique and movement patterns you use in your sports or activity are the best they can be. Lessons from a professional can be very helpful.
• Get strong, stay flexible. Weak muscles are a leading cause of knee injuries. You'll benefit from building up your quadriceps and hamstrings, the muscles on the front and back of your thighs that help support your knees. Balance and stability training helps the muscles around your knees work together more effectively.
• And because tight muscles also can contribute 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.

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 the conditions causing your knee pain, such as rheumatoid arthritis or gout.

Therapy

Strengthening the muscles around your knee will make it more stable. Your doctor may recommend physical therapy or different types of strengthening exercises based on the specific condition that is causing your pain.

If you are physically active or practice a sport, you may need exercises to correct movement patterns that may be affecting your knees and to establish good technique during your sport or activity. Exercises to improve your flexibility and balance also are important.

Arch supports, sometimes with wedges on one side of the heel, can help shift pressure away from the side of the knee most affected by osteoarthritis. In certain conditions, different types of braces may be used to help protect and support the knee joint.

Injections

In some cases, your doctor may suggest injecting medications or other substances directly into your joint. Examples include:

• Corticosteroids. Injections of a corticosteroid drug into your knee joint may help reduce the symptoms of an arthritis flare and provide pain relief that may last a few months. These injections aren't effective in all cases.
• Hyaluronic acid. A thick fluid, similar to the fluid that naturally lubricates joints, hyaluronic acid can be injected into your knee to improve mobility and ease pain. Although study results have been mixed about the effectiveness of this treatment, relief from one or a series of shots may last as long as six months.
• Platelet-rich plasma (PRP). PRP contains a concentration of many different growth factors that appear to reduce inflammation and promote healing. Some studies have found that PRP may benefit certain people with osteoarthritis, but more studies are needed.

Surgery

If you have an injury that may require surgery, it's usually not necessary to have the operation immediately. Before making a 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 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, remove or repair damaged cartilage (especially if it is causing your knee to lock), and reconstruct torn ligaments.
• Partial knee replacement surgery. In this procedure, your surgeon replaces only the most damaged portion of your knee with parts made of metal and plastic. The surgery can usually be performed through small incisions, so you're 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.
• Osteotomy. This procedure involves removing bone from the thighbone or shinbone to better align the knee and relieve arthritis pain. This surgery may help you delay or avoid total knee replacement surgery.