What is bursitis?
A bursa is a closed fluid-filled sac that functions as a gliding surface to reduce friction between tissues of the body. Bursae is plural for bursa. The major bursae are located adjacent to the tendons near the large joints, such as the shoulders, elbows, hips, and knees. When a bursa becomes inflamed, the condition is known as bursitis. Most commonly, bursitis is caused by local soft tissue trauma or strain injury, and there is no infection (aseptic bursitis). On rare occasions, the bursa can become infected with bacteria. This condition is called septic bursitis.
What is knee bursitis?
The knee joint is surrounded by three major bursae. At the tip of the knee, over the kneecap bone, is the prepatellar bursa. This bursa can become inflamed (prepatellar bursitis) from direct trauma to the front of the knee. This commonly occurs when maintaining a prolonged kneeling position. It has been referred to as "housemaid's knee," "roofer's knee," and "carpet layer's knee," based on the patient's associated occupational histories. It can lead to varying degrees of swelling, warmth, tenderness, and redness in the overlying area of the knee. As compared with knee joint inflammation (arthritis), it is usually only mildly painful. It is usually associated with significant pain when kneeling and can cause stiffness and pain with walking. Also, in contrast to problems within the knee joint, the range of motion of the knee is frequently preserved.
Prepatellar bursitis can occur when the bursa fills with blood from injury. It can also be seen in rheumatoid arthritis and can occur from deposits of crystals, as seen in patients with gouty arthritis and pseudogout. The prepatellar bursa can also become infected with bacteria (septic bursitis). When this happens, fever may be present. This type of infection usually occurs from breaks in the overlying skin or puncture wounds. The bacteria involved in septic bursitis of the knee are usually those that normally cover the skin, called staphylococcus. Rarely, a chronically inflamed bursa can become infected by bacteria traveling through the blood.
