Osteonal remodeling in response to screw implantation in canine femora

We examined the patterns of osteonal remodeling associated with the implantation of a screw in the femoral diaphysis of four mongrel dogs. The dogs were killed at intervals ranging from 11 to 93 days after implantation, and resorption spaces and tetracycline-labeled osteons were counted as functions of postimplant time and distance from the screw. The contralateral femur was used as a control. We found that implantation of the screw initiated a sequence of remodeling activity at the screw site; numerous resorption spaces were observed after 3 weeks, followed by numerous refilling osteons at 7 weeks. When sequential sections along the shaft adjacent to the screw were examined, it appeared that the increased resorption and refilling activity subsequently migrated away from the screw site, both proximally and distally. Also, both the implanted and control femurs exhibited occasional zones along the shaft within which the numbers of labeled osteons were sharply reduced. These "extinction zones" were found to be associated with local maxima in resorption space density. We further noted that the ratio of singly to doubly labeled osteons in the experimental control femurs was high as compared with that in humans, but similar to that previously observed in the canine iliac crest.