Fluid flow around model femoral components of differing surface finishes: in vitro investigations.

We studied fluid flow at the stem-cement interface of bonded and debonded, polished and rough model femoral components. In a first series of experiments, fluid flow along the interface between bone cement and well-fixed model femoral components, differing in surface finish, and in shape, was measured. Fluid migration along the bone-cement interface of rough stems (Ra 3 microm) was greater than that on polished stems (p < 0.001). This was true of cylindrical and conical tapered stems. On stems with the same surface finish, shape did not influence fluid migration. In a second series of experiments, fluid flow along the stem-cement interface of 5 highly polished and 10 rough-finished (5 of Ra approximately 1.5 microm and 5 of Ra approximately 3 microm), debonded, tapered circular stems was measured. None of the rough stems could prevent fluid flow along the stem-cement interface. Polished tapered stems sealed the interface and, after 48 hrs of continuous pressure, no fluid flow was observed. This difference in the ability to seal the stem-cement interface between rough and polished stems was significant (p < 0.001). The difference in fluid migration along the stem-cement interface of rough and polished stems which we observed offers a plausible explanation of the occurrence of osteolysis distal to the articulation of cemented THR in the presence of cement mantle defects. It may also explain why osteolysis is uncommon with polished double-tapered stems.