Assistant
Definition
By Gregory R. Waryasz, MD
The semimembranosus bursa of the musculoskeletal system is characterized by its location.
It is part of the knee joint. It consists of a synovial fluid surrounded by a synovial membrane.
Its unique structural feature is that it is located between the semimembranosus tendon and the medial head of the gastrocnemius.
The semimembranosus bursa as well as all other bones, muscles, and ligaments of the body are derived of mesodermal origin in the embryo.
The function of the bursa is to provide a cushion between bones, tendons, and muscles. This helps to reduce friction and allow free movement of structures.
Common diseases include bursitis and Baker’s cysts. Bursitis is inflammation of the bursa. A Baker’s cyst is an abnormal fluid-filled sace of synovial membrane in the popliteal fossa. It can be due to herniation of the gastrocnemius or semimembranosus bursa into the popliteal fossa.
Commonly used diagnostic procedures include clinical history, physical exam, and MRI.
It is usually treated with physical therapy and NSAIDs.
References
Elstrom J, Virkus W, Pankovich (eds), Handbook of Fractures (3rd edition), McGraw Hill, New York, NY, 2006.
Koval K, Zuckerman J (eds), Handbook of Fractures (3rd edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.
Lieberman J (ed), AAOS Comprehensive Orthopaedic Review, American Academy of Orthopaedic Surgeons, 2008.
Moore K, Dalley A (eds), Clinically Oriented Anatomy (5th edition), Lippincott Williams & Wilkins, Philadelphia, PA, 2006.