Bursae

Extended Definition

Bursae are small, slippery sacs located throughout the body wherever tissues might rub against each other—particularly around joints. There are over 150 bursae in the human body, with the largest ones found near large joints like the shoulders, hips, and knees. These sacs are filled with a small amount of lubricating fluid similar to synovial fluid and serve as cushions that reduce friction between moving structures.

In a healthy state, bursae are thin and barely noticeable. However, when irritated or injured, they can become inflamed, swollen, and painful—a condition called bursitis. The bursa fills with excess fluid, becoming thickened and tender. Common causes include repetitive movements, prolonged pressure, injury, infection, or underlying conditions like osteoarthritis or rheumatoid arthritis.

In the knee, several important bursae can become problematic. The prepatellar bursa sits in front of the kneecap and can become inflamed from frequent kneeling (“housemaid’s knee”). The pes anserine bursa on the inner side of the knee below the joint line often becomes irritated in people with knee osteoarthritis. The suprapatellar bursa actually connects with the main knee joint space. Bursitis symptoms include localized swelling, warmth, tenderness, and pain with movement or pressure. Treatment typically involves rest, ice, anti-inflammatory medications, physical therapy, and sometimes corticosteroid injections directly into the bursa. It’s important to distinguish bursitis from joint problems, as they require different treatment approaches, though they can occur together in people with arthritis.