Bursa are small, fluid-filled sacs that protect muscles, tendons, and other soft tissues around joints from external factors and bones. Their primary role is to protect bone tissues from trauma and friction. They are most commonly found in mobile areas of the body such as the knee, shoulder, and hip joints.

When bursa are subjected to sudden trauma or repeated light but prolonged pressure, they can become inflamed and swell with fluid. This condition is called bursitis, meaning inflammation of the bursa sac. Cases where symptoms last less than three weeks and respond well to treatment are defined as acute bursitis. Bursitis that does not heal despite treatment or recurs frequently is referred to as chronic bursitis.

While numerous bursae are found in many joints throughout the body, one of the most common types of bursitis is prepatellar bursitis. The prepatellar bursa is located directly in front of the kneecap (patella), between the patella and the skin tissue. Its function is to provide protection by reducing pressure and friction on the kneecap when the knee makes contact with the ground. Inflammation, fluid accumulation, and swelling of this bursa is called prepatellar bursitis.