Observations on the Lymphatic Drainage of Joint Cavities.

The physiology of joints depends at least in part upon the mechanism for fluid exchange in these structures. Considerable attention has been given in the past to the factors which determine the formation and characteristics of intra-articular effusions, but the ways in which they can be removed are imperfectly known. From a consideration of the factors involved in the equilibrium between the capillaries beneath the synovial membrane and a joint effusion containing protein, one may conclude that absorption by way of the capillaries will cease when the filtration and osmotic pressure relations within the capillaries and within the joint space are in equilibrium. Furthermore, such equilibrium relations can become established with fairly large amounts of effusion fluid remaining within the joint. It may be pointed out also that absorption by way of the blood capillaries would be slow even under ideal conditions.

It is the purpose of this communication to direct attention to the lymphatic system as the most important factor concerned in the drainage of joints under both normal and pathological conditions. This is not a new or original concept but it has not received the emphasis in the past which it demands. It is known that the synovial membrane is abundantly supplied with lymphatic capillaries, but we have been unable to find any specific statement about the lymphatic trunks which drain these capillaries.

Utilizing the knee joints of cats we have determined by injections of solutions containing methylene blue that the lymphatic capillaries of the synovial membrane unite in the popliteal space, with a lymphatic trunk coming from the foot and running up Hunter's canal and then into the pelvis, where it ends in a deep subinguinal lymph node situated at the brim of the pelvis just lateral to the mid line.