Comparison of the effects of compression plates and external fixators on early bone-healing

We used two mechanically dissimilar devices, compression bone-plates and unilateral-frame external fixators, in a standard canine osteotomy model; both methods were highly successful in achieving mature bone union. Bone union was studied by histological, physiological, and biomechanical means. At 120 days after injury, union was biomechanically less mature on the external fixator side. These tibiae had less intracortical new-bone formation (p < 0.01), more bone resorption (p < 0.045), and more bone porosity (p < 0.04) when compared with paired tibiae that had been treated with compression plates. This higher level of bone turnover on the external fixator side was accompanied by an increase in blood flow (measured by clearance of ⁸⁵Sr) (p < 0.04). At the osteotomy site, pre-experimental or unlabeled bone and porosity were greater on the external fixator side and endosteal new-bone formation was greater on the plated side. Since the in vitro stiffness of the external fixator was less in all modes tested (compression, distraction, torsion, and anteroposterior bending) except lateral bending, it may be that the rigidity of the fixation is an important factor in early bone-remodeling of a healing osteotomy. Clinical Relevance: the optimum mechanical conditions for the healing of diaphyseal bone are not known. In this study, during the first 120 days of healing of standard osteotomies there was increased bone resorption and decreased bone formation in tibiae that were fixed with a unilateral-frame external fixator. Knowledge of the response during the early phase of bone-healing should be of benefit in the design and use of stabilizing devices.