Anatomy and function of the communication between knee joint and popliteal bursae.

The anatomy and function of the opening between the knee joint cavity and gastrocnemio-semimembranosus bursa was studied in 120 necropsy specimens of knee joints both by conventional knife dissection and by a newly modified technique of serial cryosectioning of undecalcified joints frozen at various angles of flexion. The communication invariably took the shape of a transverse slit separating the capsule from the undersurface of the gastrocnemius tendon. On flexion it opened as the pull from the semimembranosus tendon and the medial meniscus widened the gap. On extension the communication was closed by compression by the overlying tendons. A functional closing action was invariably demonstrated, whereas no unidirectional valve mechanism was found.