Popliteal cysts: variations on a theme of Baker.

Adams in 1840 was the first to describe popliteal cysts, "the enlarged bursa is normally situated beneath the inner head of the gastrocnemius and communicates with the joint by a species of valvular opening." Baker whose name has been given to the cysts suggested in 1877 that the cyst may be a distended bursa related to the semimembranosus tendon. He also suggested that the cyst was connected with the knee synovium and pointed out that the fluid could not return to the joint. He considered that rupture could occur with the formation of calf cysts and that the leak could come from the popliteus bursa. He also commented (Case 1) on difficulty in distinguishing this syndrome from venous thrombosis. He quotes Foucher (1856) who described a typical history of a recurrent cyst with rupture. "An officer first noticed a small swelling in the inner side of the popliteal space, three days after a forced march on a rough road. The tumour only very gradually increased. About eighteen months after its first appearance a sudden effort at extending the leg caused a rupture of the wall of the cyst, the tumour disappearing at the same time that the calf of the leg began to swell. A bandage was applied, but the patient was not laid up. Two years afterwards the cyst was larger than ever; and for a short time the patient was obliged to lie up, as part of the fluid contents of the cyst, after a tight bandaging, had extended on both sides of the knee. Ultimately the disease disappeared." Foucher described 6 cases, but did not observe the communication of the cyst with the knee. Thus, though much of what we know today has been known for over a century, medical text books give scant attention to the subject. The varied clinical patterns derived from popliteal cysts still lead to misdiagnosis with undesirable if not disastrous consequences. Current knowledge of this subject is brought together in this review.