Topic Overview
Everyone has had a minor knee problem at one time or another. Most of the time our body movements do not cause problems, but it's not surprising that symptoms develop from everyday wear and tear, overuse, or injury. Knee problems and injuries most commonly occur during sports or recreational activities, work-related tasks, or projects around the home.

The knee is a joint, separated by two discs (menisci). It connects the upper leg bone (femur) to the lower leg bones (tibia and fibula) by ligaments and muscles. The quadriceps tendon connects the kneecap (patella) to upper leg muscles (quadriceps). The patellar tendon connects the kneecap to the lower leg bone (tibia). Articular cartilage covers the ends of the bones. See an illustration of the structures of the knee.

Knee pain may be caused by an injury to one or more of these structures, or it may have nothing to do with an injury. Common knee symptoms include:

Pain, soreness, or tenderness.
Swelling or bruising.
Loose or unstable joint.
Stiffness, decreased movement, or locking of the knee.
Snap, pop, or grinding with movement.

Sudden (acute) injuries
Injuries are the most common cause of knee problems. Sudden (acute) injuries may occur from a direct blow to the knee or from abnormal twisting, bending the knee, or falling on the knee. Pain, bruising, or swelling may be severe and develop within minutes of the injury. Nerves or blood vessels may be pinched or damaged during the injury. The knee or lower leg may feel numb, weak, or cold; tingle; or look pale or blue. Acute injuries include:

Sprain.
Strain.
Torn meniscus (see an illustration of the menisci).
Torn ligaments. The medial collateral ligament (MCL) is the most commonly injured ligament of the knee.
Fracture or dislocation of the knee. See an illustration of an X-ray of a broken knee cap.
Kneecap dislocation. This type of dislocation occurs more frequently in 13- to 18-year-old girls. Pieces of bone or tissue (loose bodies) from a fracture or dislocation may get caught in the joint and interfere with movement.

Overuse injuries
Overuse injuries occur with repetitive activities or repeated or prolonged pressure on the knee. Activities such as stair climbing, bicycle riding, jogging, or jumping stress joints and other tissues and can lead to irritation and inflammation. Overuse injuries include:

Bursitis.
Tendinitis.
Plica syndrome, which is a thickening or folding of the knee ligaments that can interfere with joint function.
Patellofemoral pain syndrome.
Iliotibial band syndrome.

Conditions that may cause knee problems
Problems not directly related to an injury or overuse may occur in or around the knee.
Osteoarthritis (degenerative joint disease) may cause knee pain that is worse in the morning and improves during the day. It often develops at the site of a previous injury. Other types of arthritis, such as rheumatoid arthritis, gout, and lupus, also can affect the knee.
Osgood-Schlatter disease causes pain, swelling, and tenderness in the front of the knee below the kneecap. It is especially common in boys ages 11 to 15.

A popliteal (or Baker's) cyst causes swelling in the back of the knee.
Osteochondritis dissecans causes pain and decreased movement because a piece of bone or cartilage or both inside the knee joint loses blood supply and dies.
nfection in the skin (cellulitis), joint (infectious arthritis), bone (osteomyelitis), or bursa (septic bursitis) can cause pain and decreased knee movement.

A problem elsewhere in the body, such as a pinched nerve or a problem in the hip, can occasionally cause referred pain in the knee.

Treatment for a knee problem or injury may include first aid measures, a knee brace, crutches, physical therapy, medication, and in some cases, surgery. Treatment depends on:

The location, type, and severity of the injury.
Your age, health condition, and activities (such as work, sports, or hobbies).

Review the Emergencies and Check Your Symptoms sections to determine if and when you need to see a health professional.