The usual popliteal cyst is the enlarged semimembranosus bursa. This constant bursa is located beneath the deep fascia of the popliteal space in the interval between the semimembranosus muscle and the medial head of the grastrocnemius muscle and is intimately attached to the posterior capsule of the knee joint and its bordering muscles. It may communicate with the knee joint by a small opening. Its anatomy has been well described by Wilson.1
Semimembranosus bursitis is not common. Wilson reported 21 cases from the Hospital for Special Surgery, and Meyerding and Van Demark2 15 cases from the Mayo Clinic.
Some, as Meyerding and Van Demark, state that enlargement of this bursa is not caused by trauma and is often associated with rheumatoid arthritis or osteoarthritis. Were arthritic association significant, it would be seen more often.
This report shows the clinical association by common trauma of the enlarged semimembranosus bursa
BURMAN M. SEMIMEMBRANOSUS BURSITISASSOCIATION WITH TEAR OF THE INTERNAL MENISCUS OF THE KNEE JOINT BY COMMON TRAUMA. JAMA. 1944;124(1):29–30. doi:10.1001/jama.1944.02850010031006
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