Demonstration of blood-vessellike structures in cartilaginous callus by antilaminin and antiheparin sulfate proteoglycan antibodies.

The vascularization of the callus of experimental nonfixated tibia fractures in rat was investigated with antibodies against two basement-membrane macromolecules, i.e., laminin and the heparin sulfate, low-buoyant-density proteoglycan. The purpose of the investigation was to study the relationship between the appearance of blood vessels and the development of cartilaginous callus. The ages of the callus were three, five, eight, and 11 days after the fracture, that is, from before the cartilage was demonstrable on Day 5 until the enchondral bone formation started on Day 11. The abundant blood vessels in the differentiating granulation tissue, in the periosteal callus, and in the cortical bone itself were stained, as were the endomysia of the surrounding myofibrils. During the whole course, the cartilaginous callus also contained vessellike structures stained by the antibodies. These structures are apparently nonfunctioning vessels. Also, some of the chondrocytes were stained by antilaminin. This study implies that cartilage is not formed as a result of insufficient blood supply, but rather as a natural link in a predetermined course of the migrating mesenchymal cells.