HISTOLOGICAL ANALYSIS OF A PROXIMALLY POROUS-COATED FEMORAL HIP STEM IMPLANTED FOR 2 YEARS

A straight stem femoral component with a proximal porous coating (6 cm ) of sintered-bead Co-Cr-Mo was surgically retrieved after 2 years of successful clinical use. The coating had a mean pore-size of 300 mum a nd a mean porosity of 30%. The implant was removed following a traumat ic sub-stem femoral fracture. A combination of hard and soft tissue in growth was demonstrated on the majority of the coated surface and unde r the collar of the femoral stem. Direct cortical bone integration int o the porous coated surface of the implant was observed below the coll ar, but was not observed in the porous coating at the approximate midp ortion of the medial coating. Proximal porous coating of the femoral s tem, as seen in this retrieval specimen, appeared to stabilize the pro sthesis successfully. Adaptive bone remodelling occurred in the medial section of the prosthesis adjacent to the porous coating. Lack of ing rowth and bone resorption in the cortical bone of the medial mid-porou s region may represent a stress shielding phenomenon. Further prosthet ic refinement and porous coating design alterations may reduce this re sorptive response.