Effect of early axial dynamization on tibial bone healing - A study in dogs

Early axial dynamization and its effect on experimental tibial bone healing was compared with healing under rigid fixation in a time-sequenced manner using dogs, An external fixator that could be rigidly locked or set to allo w free axial movement while preventing bending and shear was used. Both tib ias were osteotomized and externally fixed, leaving a gap between bone ends of 2 mm, At 1 week, one side was dynamized, whereas the other side was kep t rigidly locked as a control. Dogs were euthanized at 1 day and 1, 3, 5, 8 , and 11 weeks after dynamization, The outcome measures were static and dyn amic load-bearing, periosteal callus development, new bone formation, callu s tissue composition, and mechanical strength. Load bearing was higher on t he dynamized limbs during standing for the first 5 weeks and during gait fo r the first 3 weeks after dynamization compared with the controls. Maximum periosteal callus size was reached faster and was distributed more symmetri cally on the dynamized side, The periosteal callus area decreased at 12 wee ks on the dynamized sides, but there was no significant change in the area on the control sides, Endosteal new bone formation and bone density decreas ed between 9 and 12,weeks only on the dynamized sides. The dynamized side s howed a significantly higher torsional stiffness at 6 weeks than did the co ntrols. There were no significant differences between dynamized and control tibias at other times, Maximum torque also tended to be higher on the dyna mized sides at the same time. Early axial dynamization appeared to accelera te callus formation and remodeling and to provide higher mechanical stiffne ss during early stages of bone healing.