Knee Pain Health Article

Definition

Knee pain refers to any aching or burning pain in the knee joint. Knee pain can be a symptom of numerous conditions and diseases, including knee stress, osteoarthritis, injury, gout, infection, and bursitis.

Description

Knee pain is very common. Each year, millions of Americans visit the doctor for knee pain. It is the most frequent reason for visits to an orthopedist (bone and joint surgeon).

To understand the various causes of knee pain, it is important to know how the knee functions. The knee refers to the joint where the femur (thigh bone) meets the tibia (largest lower leg bone). In front of this joint lies the patella (knee cap). The joint is lined by a membrane called a synovial sac. The synovial sac produces synovial fluid which acts as a lubricant much in the way that oil lubricates the moving parts of machinery. Other tissues that make up the knee joint include cartilage, muscles, tendons, and ligaments. The upper end of the tibia has cartilaginous shock absorbers called menisci (singular meniscus). Other protective structures are the bursae, which cushion areas of friction in the joint. Most of the muscles involved with joint mobility originate in the thigh, cross the knee joint, and attach to the tibia.

The knee supports two to three times a person's body weight. It is a complex joint that allows for a considerable range in mobility. In addition to simple flexion (bending) and extension (straightening) movements, the knee joint is designed to allow for rotation, gliding, and rolling movements. To allow for complex mobility and joint stability, joint strength is sacrificed, making the knee vulnerable to injury.

Causes & symptoms

Knee pain is a symptom of many different diseases and conditions. Short-term knee pain may be the result of excess stress on the knee. Possible causes of knee pain include:

• Arthritis. Osteoarthritis (joint degeneration), rheumatoid arthritis (joint inflammation), and septic arthritis (joint infection) can cause knee pain.
• Bursitis. Inflammation of the bursae of the knee can cause knee pain. Bursitis, sometimes called house-maid's knee, can be caused by infection, gout, rheumatoid arthritis, injury, illness, or chronic irritation (crawling or kneeling).
• Cysts. A cyst is a fluid-filled sac. Cysts associated with the knee can cause swelling and knee pain or discomfort.
• Fracture. Breakage or crack in any of the bones associated with the knee joint can cause knee pain.
• Gout. A faulty chemical process leads to high levels of uric acid in the blood which causes inflammatory arthritis, crystal deposits in joints, joint destruction, and joint pain.
• Ligament injury or instability. The ligaments supporting the knee may be injured or strained by persons who participate in sports, particularly football, rugby, lacrosse, basketball, skiing, soccer, and volleyball. Other accidents can also cause ligament damage.
• Loose bodies. This condition refers to any loose objects that float around the knee and cause problems. They also are called "joint mice" because of their elusive nature.
• Meniscus conditions. Damage, usually in the form of a tear, to the menisci can result from degenerative changes associated with advancing age or sports-related injury. Sports that commonly cause menisci damage include football, basketball, soccer, tennis, lacrosse, and skiing.
• Osteonecrosis. Degeneration of the bones associated with the knee cause pain and deformity.
• Patellofemoral pain. Also known as anterior knee pain syndrome, this condition is characterized by pain around the knee cap. The exact cause of patellofemoral pain is unknown but is probably related to muscle inadequacy, lack of flexibility, rapid growth, or bone positioning.