Temporal variation of applied inter fragmentary displacement at a bone fracture in harmony with maturation of the fracture callus

The amplitude of inter fragmentary displacement in long bone fractures greatly influences the pattern and speed of healing. Unfortunately, the amplitude of natural cyclical displacement arising from patient activity is random because of the inherent flexibility of fixation devices under natural loading. Although fixators may be designed to control the amplitude of this displacement, the amplitudes most beneficial to healing have not been determined. Furthermore, the appropriate amplitude must vary during healing as the reparative tissue (callus) progresses histologically and stiffens during maturation. In this study on an experimental fracture, the amplitude of applied cyclical displacement is varied during healing to correspond with the inverse of the callus stiffness versus time curve. In vivo mechanical stiffness tests on the callus indicate that the end point of the fixation period is achieved more rapidly than with a constant level of applied displacement.