Joint surface incongruity and its maintenance: an experimental study.

The paper reports an experimental investigation into the mechanisms whereby the joints of living animals maintain their precise contours. The normal patter of joint incongruity in the rabbit's hip having first been established, three groups of experimental animals underwent operative procedures designed to reduce the joint pressure to a level unrealistic in normal life. In one group the hip was dislocated by manipulation; in a second group the muscles around the hip joint were divided; and in a third group the hind limb was disarticulated through the knee. When the animals were killed at intervals of a few weeks after the operations the experimental hip joint showed increased congruity in all cases. It is concluded that in immature animals there is a mechanism in joints to control the modelling of their shapes towards an ideal incongruity, and that that mechanisms is pressure sensitive.