An autoradiographic study of femoral-fracture repair using tritiated thymidine was made on forty-two female mice, five weeks of age.
Assessment of the periosteal labeling index was obtained from one hour to fourteen days after fracture.
Results showed that the initial proliferative response is seen in the periosteum and adjacent soft tissues sixteen hours after fracture. No increase in proliferation was observed at eight hours. The reaction was not limited to the fracture site but extended along the entire femoral diaphysis. The maximum increase of the labeled periosteal population (25.4 per cent) was observed at thirty-two hours after fracture.
After thirty-two hours, the size of the labeled population decreased with increasing time. The decrease was more apparent away from the fracture site, so that within five days of fracture the proliferative potential was similar to that of the non-fractured control femur. Fourteen days after fracture, the labeled population of periosteal cells at the fracture site was still above the value of the controls. The course of fracture repair was followed autoradiographically.