The knee has the most bursae of any joint in the body and can be divided into three groups: anterior, posterior lateral, and posterior medial. The more clinically important ones are the prepatellar bursa, the goose foot bursa, and the intra-N fossa bursa. 1, prepatellar bursitis The prepatellar bursa is located in the front of the patella and becomes inflamed with increased synovial fluid and bursal enlargement. Trauma or infection often causes acute inflammation of the bursa. It is characterized by pain and swelling of the prepatellar bursa, inability to walk with knee flexion, localized pressure pain and fluctuation, and blood or bloody fluid on puncture. In the case of acute septic bursitis, there is not only local redness, swelling, heat, pain, and obvious pressure pain, but also often systemic symptoms, mostly in children, whose performance is very similar to septic knee osteoarthritis, which is easily misdiagnosed, and thus the infection can be brought into the knee cavity during puncture. It is easy to misdiagnose the problem, so the infection can be brought into the knee cavity during puncture. It can also be mistakenly introduced into the knee joint during incision and drainage, resulting in septic arthritis, which can lead to serious consequences. Chronic bursitis occurs in miners and people who often work on their knees, and can also develop as a result of improper treatment of acute bursitis. It is characterized by a limited hemispherical bulge in front of the patella with mild pain, and on examination a fluctuating soft tissue mass with mild pressure pain that does not affect knee motion. In the acute phase of traumatic bursitis, rest, hot compresses, and puncture and fluid injection of hydrocortisone acetate or confirmatory suxamethasone A, followed by compression bandaging, are usually curable. Chronic bursitis, with fluid extraction and intracapsular injection of corticosteroids, has good efficacy. Bursal resection is performed for non-surgical treatment without significant success. For septic bursitis should be punctured and injected with effective antibiotic treatment after pus extraction, and when ineffective, should be incised and drained, and then perform bursal resection after the inflammation subsides. 2, goose foot bursitis Goose foot bursa is located in the suture muscle, thin femoral muscle, semitendinosus tendon deep surface and tibial collateral ligament between the bursa, because these three tendons composed of the joint tendon, shaped like a goose foot and named. Direct blows, frequent local recurrent small traumas, such as horseback riding, or excessive knee extension and flexion twisting are often the cause of this disease. It presents as a medial knee swelling of variable size and fluctuating sensation, and is painful when the patient flexes the knee with force and extends and rotates it. The diagnosis should be differentiated from chronic knee osteoarthritis, medial meniscal cysts, and tendon sheath cysts. The treatment is the same as before and is usually curable with non-surgical treatment. In case of failure, bursal resection is performed. N fossa cysts, also known as Baker cysts, are bursitis in the N fossa, and there are many bursae in the N fossa. more than half of the N fossa cysts are located between the semimembranosus muscle and the medial head of the gastrocnemius muscle, and about half have a hole that connects to the joint cavity. There are two types of N fossa cysts: primary and secondary. Primary N-fossa cysts are most often seen in children and are bilateral, but not necessarily concurrent, with the cyst originating in the joint cavity and no lesion in the joint itself. The true pathogenesis is unclear. Secondary N-fossa cysts are seen in adults and are often secondary to osteoarthritis, meniscal lesions, and rheumatoid arthritis. The onset is associated with increased intra-articular pressure and the spillage of intra-articular fluid through the orifice between the joint and the bursa, resulting in the formation of cysts. The initial symptoms of N fossa cyst are not obvious, only discomfort or swelling in the N fossa. When the cyst increases in size, then a mass appears at the back of the knee joint, making it difficult to flex the knee. The mass is round or oval in shape, with a smooth, elastic surface and no or only light pressure pain, and it becomes obvious and hard when the knee is extended and less obvious and softer when the knee is flexed. x-ray is helpful in ruling out bony lesions of the knee, but is not very helpful in diagnosing the N-fossa cyst itself. Larger N-fossa cysts should be surgically removed and the defect in the joint capsule does not have to be repaired. In a few cases of postoperative recurrence, the cyst may be surgically removed again. N-fossa cysts in young children can be followed up and observed, and those that do not disappear after the age of 5 years can be surgically removed. Smaller N-fossa cysts can be aspirated and injected with corticosteroid drugs, which have some effect. If the cyst is caused by intra-articular lesions, the intra-articular lesions should be treated first, and if the cyst does not disappear after the intra-articular lesions are cured, the cyst should be removed again.