Effect of amplitude of micromotion on bone ingrowth into titanium chambers implanted in the rabbit tibia

The micromotion chamber for implantation in the rabbit tibia consists of two titanium components that have a 1 mm contiguous pore for bone ingrowth. The fixed, outer cylinder of the chamber contains a movable inner core that can be manually rotated. The model is unique because specific, discrete, daily periods of motion of a predetermined amplitude and frequency can be delivered to the ingrowing tissue. In the present study, we compared the histological and scintigraphic results of bone ingrowth into chambers having a congruently shaped interface that was moved 20 cycles/d with an amplitude of either 0.5 or 0.75 mm. Histological sections from both amplitude groups contained extensive new woven and trabecular bone, embedded in a fibrovascular network. However, the chambers with a larger amplitude of motion yielded less bone ingrowth than those with a smaller amplitude. These studies suggest that short, discrete periods of motion can stimulate the formation of fibrous tissue rather than bone using the parameters chosen in this model.