Why high frequency of distraction improved the bone formation in distraction osteogenesis?

Distraction osteogenesis, currently a standard method of bone lengthening, is based upon the "tension-stress principle", as proposed by G.A. Ilizarov. Mechanical stimulation by distraction induces biological responses of skeletal regeneration that is accomplished by a cascade of biologic processes including differentiation of pluripotential tissue, angiogenesis, mineralization, and remodeling. The exact mechanism by which strain stimulates bone formation remains unclear. Distraction rate and rhythm must have great influence on the quality of the newly formed bone generated by mechanical traction. The preliminary results demonstrated that for a given rate higher frequency of distraction improved the bone formation, but the mechanism remains unclear. In this article we present a hypothesis that the reason why higher frequency of distraction improved the bone formation for a given rate is that higher frequency of distraction provides smaller microtrauma to tissues within the gap and longer existence time of the microenvironment stimulating tissues within the gap than low frequency distraction. This hypothesis, if proven to be valid, will not only represent a breakthrough in research of mechanism of distraction osteogenesis, but also will open a new door to the bone regeneration.