Copyright 2009
Definition
Bursitis of the knee joint is an inflammatory process involving one of the several bursa of the knee which can become irritated and even infected.
The bursae of the knee are sac-like structures that provide padding and facilitate gliding in areas where tendons move. There are a total of 11 bursa of the knee but only 4 major ones that clinically will result in pain with bursitis. The four bursa are the prepatellar bursa that overlies the patella, the infrapatellar bursa which overlies the patellar tendon, the deep patellar burs which is deep to the patellar tendon, and the pes anserine bursa which overlies the hamstring tendons which attach at the proximal media tibia at the pes anserine.
Their unique structure consists of a thin sac-like structure that has a small amount of synovial fluid within and represents a potential empty space that can become enlarged, inflamed, and infected.
The function of the bursa is to provide smooth gliding of tendons.
The most common site of an inflamed bursa is the prepatellar bursa which is termed “housemaid” knee since it can be seen in those that are on there knees. This bursa can become inflamed and even infected necesitating incision and drainage. Pes bursitis is inflammation of the pes anserine bursa and can be seen in runners and soccer players. Point tenderness will exist around the pes bursa which is just distal to the joint line and on the medial aspect of the knee. Infrapatellar bursitis occurs over the patellar tendon. Prepatellar burisitis on children can become very enlarged and mistaken for a septic knee. Many of these knees grow out MRSA on culture.
Diagnosis is usually made with clinical examination and MRI is rarely used for confirmation, or to rule out other concommitant diseases. If a septic joint is in question, aspiration of the joint becomes necessary to rule out intra-articular bacteria. Typical prepatellar bursitis has a fluctuant mass on physical exam that lies directly over the patella and is red and inflamed.
Treatment includes physical therapy and NSAIDs when there is just inflammation without infection. Occasionally injection is used when NSAIDs and physical therapy fail. When the prepatellar bursa is involved and infected, if there is obvious pus as determined by a fluctuant mass, incision and drainage to clear the bacterium from the bursa becomes necessary. Typicall, the prepatellar bursa is the only bursa that becomes infected enough to warrant surgical incision and drainage.
References
http://www.mayoclinic.com/health/knee-bursitis
http://www.wheelessonline.com/ortho/bursae_and_bursitis_of_the_knee
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