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 Row along the interface between bon e cement and well-fixed model femoral components, differing in surface fini sh, and in shape, was measured. Fluid migration along the bone-cement inter face of rough stems (Ra 3 mu m) was greater than that on polished stems (p < 0.007). 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 interfa ce of 5 highly polished and 10 rough-finished (5 of Pa similar to 1.5 mu m and 5 of Ra similar to 3 mu m), debonded, tapered circular stems was measur ed. 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 ab ility to seal the stem-cement interface between rough and polished stems wa s 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 un common with polished double-tapered stems.