Communicating semimembranoso-gastrocnemial Bursa.

In a prospective study we examined lateral radiographs of the knee joint before and after flexion exercises, in 300 consecutive arthrograms. We use the following definitions: (a) a popliteal or Baker's cyst is a clinical diagnosis and implicates a palpable popliteal mass, mostly in adults; (b) a communicating bursa is the semimembranoso-gastrocnemial bursa (s.g. bursa) communicating with the knee joint which is visible in the lateral arthrogram of the knee. It appears that the communicating s.g. bursa is more often present with knee pathology. The bursa has no other clinical or therapeutic significance. Such a bursa is not more commonly seen with an effusion. A bursal or synovial rupture is not correlated with knee pathology. Arthrography does not cause synovial rupture and seldom causes a bursal rupture.