Knee joint bursa

by Nathan Wei, MD, FACP, FACR

Nathan Wei is a nationally known board-certified rheumatologist and author of the Second Opinion Arthritis Treatment Kit. It's available exclusively at this website... not available in stores.

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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 the 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.

The anserine bursa is located inferior and medial to the knee joint. This bursa most commonly becomes inflamed in middle-aged women. This condition is referred to as anserine bursitis. Anserine bursitis is particularly common in those who are overweight. These patients notice pain in the inner knee while climbing or descending stairs. When patients develop inflammation of this bursa, in addition to the pain they will have swelling and tenderness. Anserine bursitis is generally treated with ice, rest, and oral anti-inflammatory and/or pain medicines, although cortisone injections are also given.

The semi membranosus/medial head of the gastroc bursa is located in the back of the knee. Patients with effusions (fluid in the joint) will often get what is called a Baker’s cyst when the fluid in the knee joint pushed in to the semi membranous bursa. This causes swelling and pain in the back of the knee. This is because fluid can enter the bursa through a one-way valve system that does not allow the fluid to return. Over time the fluid accumulates in the back of the knee. If this bursa ruptures, the fluid may dissect down into the calf. Treatment involves recognition, ensuring that the patient does not have thrombophlebitis (blood clot) in the leg. If the diagnosis of ruptured Baker’s cyst is made, then treatment involves aspiration of fluid from the knee joint done with ultrasound guidance, injection with glucocorticoid, elevation of the leg, and ice.

The prepatellar bursa is located in front of the knee cap. This bursa can become inflamed (prepatellar bursitis) from direct trauma to the front of the knee. It has been referred to as "housemaid's knee," "roofer's knee," and "carpetlayer's knee," based on the patient's occupational history. It can lead to varying degrees of swelling, warmth, tenderness, and redness in the overlying area of the knee. 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 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 staphylococcus.

The treatment of any bursitis depends on whether or not it involves infection. Aseptic prepatellar bursitis can be treated with ice compresses, rest, and anti-inflammatory and pain medications. Occasionally, it requires aspiration of the bursa fluid. This procedure involves removal of the fluid with a needle and syringe under sterile conditions using ultrasound guidance. Noninfectious knee bursitis can also be treated with an injection of cortisone medication into the swollen bursa. This is sometimes done at the same time as the aspiration procedure.

Septic bursitis requires further evaluation and treatment. The bursal fluid can be examined in the laboratory for the microbes causing the infection. It requires antibiotic therapy, often intravenously. Repeated aspiration of the inflamed fluid may be required. Surgical drainage and removal of the infected bursa sac (bursectomy) may also be necessary.

The infra patellar bursa is located just below the knee cap beneath the large tendon that attaches the muscles in front of the thigh and the kneecap to the prominent bone in front of the lower leg. When the bursa is inflamed inflamed, the condition is called infrapatellar bursitis. It is commonly seen with inflammation of the adjacent tendon as a result of a jumping injury, hence the name "jumper's knee." This condition is generally treated with ice, rest, and oral anti-inflammatory and/or pain medicines.

Treatment involves aspiration of the fluid and injection (ultrasound-guided)with glucocorticoid solution.

The suprapatellar bursa is located above the patella. Bursitis here is relatively uncommon. Treatment is similar to that for the other types of bursitis.

Smaller bursae are located near the collateral ligaments along the sides of the knee. These may become inflamed if the adjacent ligament is stressed or injured. Rest, anti-inflammatory drugs, ice, and physical therapy are usually effective. Corticosteroid injection is sometimes used but this area probably is best not injected because of the possibility of weakening of the ligament leading to subsequent rupture.

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