Experimental study of the effect of weight bearing on fracture healing in the canine tibia.

The authors compared the effects of decreased loading, increased loading, and baseline loading on the early (six weeks) and intermediate (12 weeks) healing of tibial fractures treated with an external fixator in adult dogs. The different loading conditions were verified by gait studies. Periosteal bone in the increased-loading fracture site was significantly increased compared with the decreased-loading site at both time intervals, and with the baseline-loading site at six weeks. The mechanical variables of energy absorption and angle of rotation at six weeks were significantly increased in the increased-loading fracture site compared with the decreased-loading site and baseline-loading site. Blood flow to the increased-loading fracture site was significantly higher than that to the decreased-loading fracture site at six weeks. Five dogs were studied at 12 weeks to compare the effects of decreased loading to increased loading. The increased-loading fracture showed significantly increased rotation, torque, and energy absorption to failure. Blood flow was not measured in the 12-week animals.