Knees obtained after amputation were fixed with formalin after the joint
space was distended with air. The joints were then either dissected or
frozen and sectioned vertically with a band saw in planes comparable to
those visualized during arthrography. By comparing these anatomical
specimens and arthrograms, the anatomical explanations for some normal
variations visible or arthrograms could be identified. These variations
included the appearance of the popliteus tendon and the posterior part of
the lateral meniscus, the air-filled cul-de-sac posterior to the medial
meniscus, and the interconnections of the joint space and the gastrocnemius
and semimembranosus bursae.