Development of bone canaliculi during bone repair

We recently found that silver impregnation staining with protargol (silver protein), that is, a modified Bodian method, is useful for histologically i dentifying the details of bone canaliculi structure, using thin sections of decalcified bone tissues. With this staining method, we conducted the pres ent study to assess the development of bone canaliculi during the process o f intramembranous ossification using a fracture-like stimulation model of t he rat femur. After making a drill-hole in the cortex of the rat femur, dec alcified thin sections were obtained after 3, 5, 7, and 14 days by the stan dard paraffin-embedding procedure. Silver staining for bone canaliculi was performed using our previously reported technique. The results showed that woven bone covered the fracture surface of the cortex after 5 days, then im mature lamellar bone attached to the woven bone after 7 days, and finally t he lamellar bone matured and became thick with appositional growth after 14 days. The osteocytes in the woven bone appeared at an early stage of bone repair and developed a few canaliculi that were short and irregularly distr ibuted in the osteoid matrix, while the osteocytes in the lamellar bone at a late stage formed many bone canaliculi that were long and regularly distr ibuted in mature bone matrix. Therefore, we concluded that woven bone osteo cytes may be necessary for induction of the lamellar bone osteocytes follow ed by active appositional growth of the lamellar bone at the early stage of hone repair, and also that both bone tissues could be clearly distinguishe d from one another based on the pattern of development of bone canaliculi b y the osteocytes, as seen with the use of our sensitive staining method. (C ) 2000 by Elsevier Science Inc. All rights reserved.