In human anatomy, a bursa is a small pouch filled with synovial fluid. Its purpose is to reduce friction between adjacent structures. The<unk>  bursa is one of several bursae of the knee joint, and is located between the patella and the skin.<unk>  is an inflammation of this bursa. Bursae are readily inflamed when irritated, as their walls are very thin. Along with the pes anserine bursa, the<unk>  bursa is one of the most common bursae to cause knee pain when inflamed.<unk>  is caused by either a single instance of acute trauma to the knee, or repeated minor trauma to the knee. The trauma can cause extravasation of nearby fluids into the bursa, which stimulates an inflammatory response. This response occurs in two phases: The vascular phase, in which the blood flow to the surrounding area increases, and the cellular phase, in which leukocytes migrate from the blood to the affected area. Other possible causes include gout, sarcoidosis, CREST syndrome, diabetes mellitus, alcohol use disorder, uremia, and chronic obstructive pulmonary disease. Some cases are idiopathic, though these may be caused by trauma that the patient does not remember. The<unk>  bursa and the olecranon bursa are the two bursae that are most likely to become infected, or septic. Septic bursitis typically occurs when the trauma to the knee causes an abrasion, though it is also possible for the infection to be caused by bacteria traveling through the blood from a pre-existing infection site. In approximately 80% of septic cases, the infection is caused by Staphylococcus aureus; other common infections are Streptococcus, Mycobacterium, and Brucella. It is highly unusual for septic bursitis to be caused by anaerobes, fungi, or Gram-negative bacteria. In very rare cases, the infection can be caused by tuberculosis.
Prepatellar bursitis
Infrapatellar bursitis
Ischial bursitis
Pes anserine bursitis
Retrocalcaneal bursitis
Patellar tendinitis
Olecranon bursitis
Plantar calcaneal bursitis