PRODUCTION OF CARTILAGE COLLAGENS DURING METAPHYSEAL BONE HEALING IN THE MOUSE

Small defects of unfractured bone are believed to heal without a carti laginous intermediate. We have determined the ex-tent of cartilage pro duction in an experimental model of metaphyseal bone repair involving defects in both cortical and cancellous bone, but no fracture. Norther n analyses revealed the presence of mRNAs for type X and II collagens in the repair tissue. Immunohistology confirmed subperiosteal depositi on of both collagen types adjacent to the defect. While the mRNAs for the two collagen types peaked by one week of defect healing, immunodet ectable type X collagen was not observed until the second week. The da ta suggest that reactivity of periosteum and activation of chondrogene sis and subsequent endochondral ossification programs are involved in murine bone repair regardless of defect type.