Femoral fractures were created in rats to determine whether there were
differences in healing under conditions of immobilization and under
conditions of immediate weight-bearing. Histological and roentgenographic
differences were present by the second week after fracture and differences
in mechanical properties were also present. These differences became
progressively greater during the next three weeks. Functional
weight-bearing was found to accelerate the rate of fracture healing and to
improve significantly the strength of the healing bone.