LOCALIZATION OF BONE-FORMING CELLS DURING FRACTURE-HEALING BY OSTEOCALCIN IMMUNOCYTOCHEMISTRY - AN EXPERIMENTAL-STUDY OF THE RABBIT TIBIA

An immunocytochemical method was used to localise osteocalcin-producin g cells during fracture healing in a rabbit model. In preliminary stud ies, tibial growth plates from young rabbits were used as a source of new bone formation, in order to determine the optimal tissue preparato ry techniques. In the present study, a tibial shaft fracture was creat ed in adult rabbits to study closed fracture healing. An indirect pero xidase method was used to stain paraffin-embedded tissue sections for osteocalcin. Osteocalcin-producing cells were positively identified at the periosteal and endosteal surfaces near the fracture site. Osteoca lcin staining was not demonstrated in the surrounding soft tissues. At the interface between newly formed bone trabeculae and the cartilage layer within the callus, chondrocytic cells consistently showed locali sation of osteocalcin. Within cartilaginous areas of the callus, some chondrocytes showed positive staining for osteocalcin. These cells wer e often seen in the proximity of blood vessels. The findings suggest t hat during fracture healing, under certain conditions, chondrocytes ar e capable of producing osteocalcin and thus could be considered capabl e of possible transformation into osteoblasts.