An attempt has been made to define the conditions with respect to movement under which porous metal will bond to bone. It has already been shown that bone will grow into the pore of porous Vitallium under static conditions and under conditions of micromovement, as when stressed by the pull of a tendon. An experiment is described in which porous Vitallium staples were inserted across an unstable osteotomy site. No bonding occurred indicating that bone ingrowth will not occur in the presence of movement of this order of magnitude.
The implication of this observation in the design of porous coated endoprostheses is that some form of initial mechanical fixation is required, and this fixation must remain rigid for four months to allow bone ingrowth.