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.
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