Callus response to micromovement after elongation in the rabbit.

The purpose of this investigation was to determine whether induced micromovement could improve the consolidation of diaphyseal elongation by callus distraction. Two series of paired rabbit hindlimbs were studied. The surgical procedure, waiting period, and elongation period were identical. One hindlimb was then left under neutralization conditions, but the other limb was stimulated by axial micromovements. Reproducible tibial osteotomy and lengthening of the two tibiae were confirmed radiographically. The mineralized callus was quantified by dual-beam x-ray absorptiometry. The anteroposterior and lateral diameters of the callus were measured. A semiquantitative histologic study allowed the ratio between fibrous or cartilaginous callus or both and mineralized callus to be determined. Bones were axially compressed to failure. Callus volume, callus mineral content, callus mineral density, and mechanical forces required to failure were significantly superior on the stimulated side compared with the neutralized side, so micromovements applied after the end of elongation were beneficial for bone healing. Mechanical forces required to failure were significantly correlated to callus volume and callus mineral density.