The knee is a complex structure, engineered to allow mobility, and speed, while supporting the body's weight. This sturdy hinge is the largest joint in the body, but it is not invulnerable to damage. Its intricate construction involves four bones, four ligaments, two types of cartilage, and tendons that attach two major muscle groups--the hamstrings and the quadriceps. Any of these structures can be damaged by an injury, and pain and swelling are a common result.
Ligament Injuries
The stretching or rupture of a knee ligament is a common occupational hazard of professional athletes. Ligaments connect bone to bone, and provide stability in the knee. Four ligaments support the knee: the medial collateral, lateral collateral, anterior cruciate and posterior cruciate. According to the British healthcare organization Bupa, a ligament tear may be first detected by a popping sound or sensation, followed by the inability to put weight on the joint. Damage to any of the four knee ligaments can result in pain, swelling and instability.
Tendonitis
Knee pain that worsens upon jumping, running, or climbing stairs could be the result of tendonitis, according to the Mayo Clinic. Tendons are thick fibrous bands of connective tissue that attach muscle to bone. Inflammation in a tendon is known as tendonitis. The patellar tendon, which attaches the quadriceps muscle to the tibia, or shin bone, is particularly vulnerable to inflammation in athletes such as skiers and runners. Swelling on the kneecap, or just below it, can indicate tendonitis.
Osgood-Schlatter Disease
Osgood-Schlatter disease occurs in teens and adolescents who are active in athletics. It is due to overuse of the knee joint, and is characterized by pain and tenderness that worsens when active, as well as swelling. This condition usually ends once the individual has finished growing.
Cartilage Damage
The meniscus, a disc made of cartilage that enables smooth movement between the femur and tibia, is prone to tearing. Meniscal tearing is characterized by a delayed post-injury swelling that gradually increases, plus pain, and the sensation that the knee is "locked."
Dislocated Patella
The patella, or kneecap, can slide out of position, resulting in intense pain, swelling and difficulty extending the knee. A dislocated kneecap is noticeably visible through the skin.
Arthritis
Rheumatoid, septic and osteoarthritis can cause knee pain and swelling. Each of these types of arthritis has a different origin. Rheumatoid arthritis is an autoimmune disorder wherein the body attacks its own tissues, resulting in erosion of the lining of the joints. Osteoarthritis is due to wear and tear, and is common in aging athletes who have endured repeated joint injuries. Septic arthritis is caused by an infection of the joint, and can be accompanied by fever.
Bursitis
Bursitis is an inflammation of the small, fluid-filled pouches that protect the knee. If the knee feels warm, and is swollen, red and painful, then bursitis could be the cause.
