Spatial orientation of the microscopic elements of cortical repair bone

This study was designed to assess whether the original orientation of the elements of cortical diaphyseal bone is reestablished during 18 months of repair. Full thickness 3-mm drill holes were created surgically through the tibial and femoral cortices of adult rabbits and studied by light and polarizing microscopic analysis at 1, 4, 8, and 16 weeks and 6, 12, and 18 months after the defects were created. From 16 weeks to 12 months the defects were repaired fully with lamellar bone, while the longitudinal spatial orientation of the repair lamellae was at a distinct angle to that of the original bone. At 18 months, the internal organization of the major individual microscopic elements (osteons) were reconstituted in a manner similar to that of the original bone; however, the three-dimensional spatial orientation of the osteons in the repair bone relative to the long axis of the osteons of the adjacent original bone and of the bone removed to create the defect was not reestablished completely. The imperfect spatial disposition of the microscopic elements of bone tissue may contribute significantly to refracture of a long bone after removal of screws from plated or unplated long bone fractures.