A patella, or the fragment of another bone, imbedded fresh in the muscle of the animal from which it was removed, has a tendency to disappear, but does not disappear, at least for a long time. In none of our cases had it disappeared completely. Its structure becomes less dense.
The bone tissue itself may be replaced by fibrous tissue, especially at or near the circumference, or it may be absorbed. Absorption is the rule in the interior. Occasionally typical rarefying osteitis by osteoclasts is seen. More frequently the process seems to be one of simple absorption-'halisteresis.' The method of absorption is often difficult to determine, for about many of the trabeculae there are no giant cells, no leucocytic infiltration, and no increased vascularity of the marrow.
Many of the cells disappear early from the bone. Others stain well after the expiration of a long time. Death of bone is the rule.
A patella, with a complete investment of bone and cartilage, does not resist absorption better than a bone fragment whose marrow is exposed to the surrounding tissue.
A blood supply is established in the marrow of the buried bone.
The marrow has a tendency to become fatty and fibrous, though patches of lymphoid may persist. It is engorged in animals who have died with an acute infectious disease, as is the marrow of normal bone in such circumstances. In other words, it is functionating as marrow.
Cartilage becomes eroded at its surface, and is replaced by fibrous tissue. Sometimes it disappears completely in areas. Its cells often stain well after a long time. Sometimes they die after a shorter time. The buttress underneath the cartilage almost always disappears early.
Judging from appearances, the buried bone becomes smaller in size.
Roughly, the changes in bone and cartilage are the same as those seen in arthritis of Type I-atrophic, or proliferative arthritis.
(C) 1919 All Rights Reserved.The Journal of Bone and Joint Surgery, Inc.