The knee is the largest joint in the body. It was designed for stability, mobility and for bearing weight. The knee is made up of four bones and three different bone-to-bone joints. These is the patella-femoral joint, tibio-femoral joint, and the tibio-fibular joint. The knee joint itself is surrounded by eleven separate bursae. A bursa is a fluid filled sack that is used to help reduce friction between tendons, and also between tendons and bones. The following are the four major bursae in the knee: Suprapatella bursa is found between the distal femur and the quadriceps tendon. It allows the quadriceps tendon to move freely over the distal femur. It allows for full flexion and extension in the knee and can be aggravated by a direct impact or from repetitive stressful and strenuos motions. Prepatella bursa is found at the top of the knee covering the kneecap. Bursitis of the prepatella bursa is also known as “carpet layer’s knee,” “housemaid’s knee” or “roofer’s knee.” It can be caused by an acute blow to the knee or from being in a prolonged kneeling position. Infrapatella Bursa is located underneath the kneecap, under the large patella tendon. It is commonly associated with patella tendonitis or from a jumping injury called “jumper’s knee,” which involves repetitive impacts on the knee. Anserine Bursa is located on the inside of the knee. It is found in the area where the hamstring muscle inserts into the lower leg connecting the two. When this bursa becomes inflamed it can produce pain in the inside of the knee, especially when descending stairs.