The knee is the largest joint in the body. It was designed for bearing weight, stability and mobility. The knee is composed of four bones and three bone-to-bone joints. The most common injury of the knee is tendinitis. A tendon is the cord-like part of the muscle that attaches muscle to bone. There are several tendons that attach near and control the knee. Knee tendinitis refers to the irritation, and inflammation of the tendons around the knee. The common tendons injured are the patella tendon, hamstring tendons and the illiotibial band.