The American Academy of Orthopaedic Surgeons website reports that 19.4 million people visited physicians' offices in 2003 because of knee injuries. The knee is the most easily injured joint in the body, and the largest. It provides support for the body and allows the legs to bend and straighten. Exercise and overuse can cause damage to any one of the many parts of the knee.
Tendons
When tendons are stretched beyond their capability, they can tear, leading to inflammation. This is called tendonitis. Athletes are prone to inflammation in the patellar tendon. This tendon, a tough cord of tissue, connects the thigh muscle to the lower leg bone. Pain and swelling can occur in one or both knees and worsen when exercising. This type of injury requires rest for the tendon to fully heal. Exercising before it has repaired itself may lead to the tendon tearing again.
Ligaments
There are four major ligaments in the knee, all of which can be injured during exercise. Ligaments are tough bands of tissue that connect the thighbone to the lower leg bones. The anterior cruciate ligament, or ACL, and the posterior cruciate ligament, or PCL, are the two more common ligaments to suffer damage. Injury to the ACL occurs by a twisting motion, or sudden, rapid movement, while injury to the PCL is often from a blow to the knee. The medial collateral ligament, or MCL, can also suffer injury from a blow to the knee. A tear to one of these ligaments can cause immediate pain or popping sounds. The knee may give away since it can't bear the weight of the leg.
Cartilage
The meniscus is a C-shaped piece of tough, rubbery cartilage that is attached to the ligaments. The connective tissue acts as a shock absorber. Injury to the meniscus can occur in different places and cause pain and swelling. Cartilage tears can happen along with ligament tears. These types of tears are often seen with twisting or sudden, turning motions. Sometimes surgery is needed to pin or screw cartilage pieces into place. Occasionally a brace is worn to help the knee avoid further injury.
Arthritis
Years of exercise and overuse can lead to arthritis. The typical arthritis from wear and tear is osteoarthritis, the degeneration of the cartilage. It develops gradually over time and can cause varying degrees of pain. It may present with swelling and stiffness, and the knee may crack and pop. Medicines can help reduce the swelling and ease the pain. Continued exercise can help strengthen the knee and improve movement.
Osgood-Schlatter Disease
Osgood-Schlatter disease is typical among young athletes, mostly affecting teenagers and pre-teenagers. It is caused by running or jumping and creating stress on part of the growth area of the upper shinbone. The tendon may tear away from the bone. The pain is usually worse with exercise; there may be swelling and below the kneecap may be tender.
