Dynamic interfragmentary motion in fractures during routine patient activity.

Natural interfragmentary motion was measured in tibial fractures during normal patient activity, and the results were interpreted using correlations from the literature to examine the influence of natural motion on healing. Ten patients were selected with reduced, diaphyseal tibial fractures stabilized with Orthofix external fixators. Three-dimensional motion was monitored with an instrumented spatial linkage during walking, standing, and muscle activities at 2 and 4 weeks postfixation. Fracture motion arising from dorsal to plantar flexion while supine produced peak cyclic displacements of the same order of magnitude as that seen during weightbearing activity. Thus, therapeutic exercise may be used to provide a stimulus to osteogenic repair processes in patients who are unable to bear weight. In 3 patients, maximum amplitudes of axial motion during walking were 1 mm or greater. This implied regular gap closure and high tissue strains within the 1 mm +/- 0.5 mm gaps. In 3 patients, axial motion was less than 0.25 mm. These 2 extremes may indicate a range of displacement relative to gap size that embraces inhibitive and stimulative influences on healing. Transverse shear displacements also varied greatly from between 0.6 and 0.75 mm in 3 patients to less than 0.2 mm in 5 patients.