The knee is a complicated joint, allowing us to run, jump, squat and move about our world. Because of the many important elements of the joint, knee pain can be a real concern. Pain in the knee is caused by a variety of factors.
Meniscus Tear
The knee joint contains two structures responsible for the absorption and distribution of weight-bearing forces across the joint surface, as well as stabilizing the knee to a large degree. The clinical term for each of these structures is "meniscus"; the name also describes its shape within the knee. Made of cartilage, the meniscus accommodates the knobs of the knee called the femoral condyles.
There are several injuries that can occur to the knee joint that also can damage the meniscus. When this occurs, the meniscal cartilage will tear. A torn meniscus can cause severe pain and mobility difficulties in the knee. The torn portions can scuff adjacent smooth joint surfaces, causing swelling and inflammation. Because there is a very limited blood supply to the menisci, most tears require surgical repair or partial or total removal.
Infection
Infections in the knee joint can be caused by a wide variety of factors, such as direct penetrating wounds into the knee joint itself, seeding of microorganisms to the knee from other remote sources such as skin abrasions elsewhere on the body or bacteria already present in the bloodstream, called septicemia.
Arthritis
Arthritis, the catch-all term given for any disruption of the normal smoothness of the knee joint, can be the source of considerable knee pain. Arthritis can exist in various forms of severity, ranging from mild inflammation and swelling to severe joint destruction with excessive fluid buildup, bone spur formation and mobility deficits. Regardless of the specific cause, the main components of arthritis can include joint lining inflammation, called synovitis; varying degrees of damage to the joint cartilage; reduced, or compromised, joint mobility; pain with weight-bearing; increased warmth to the area; and various degrees of joint instability.
Overuse Injuries
Overuse injuries are common among athletes as well as in people with occupations that require repetitive performance of activities involving the knee joint, such as squatting, climbing and prolonged standing. These injuries or conditions typically arise in the form of tendinitis, or ligament strains. They also can become evident with activities that require the knee to remain in a fixed position for extended periods of time, such as sitting and kneeling.
Sprains / Strains
Ligament injuries--otherwise known as sprains, although not necessarily located deep within the joint--are frequently the cause of knee pain. These are seen especially in various contact sporting events such as football and ice hockey. They can occur in different grades of severity, and knee pain tends to correspond to the severity if the ligament sprain.
