Histology of porous-coated acetabular components. 25 cementless cups retrieved after arthroplasty.

25 hemispherical acetabular components retrieved from patients who had a total hip arthroplasty (THA) were studied histologically. All of the components had titanium fiber metal porous coatings and were implanted with adjuvant screw fixation, 18 in primary THA and 7 in revision THA. None of the cups had been removed because of infection or failure of fixation. The components had been in place an average of 30 (1-140) weeks. 18 cups had bone ingrowth into the porous coating. Up to one third of the available void space within the porous coating was occupied by bone, while the maximal proportion of the area of the bone-implant interface with bone ingrowth was over 80 percent. Bone ingrowth was more often observed at the dome and in the vicinity of sites of screw fixation than elsewhere. Peripherally, bone ingrowth was less consistent, and in isolated areas fibrocartilage and mineralized fibrocartilage were occasionally observed. The longer-term cases had more bone ingrowth than the shorter-term cases. Apparent metallic debris was observed within histiocytes adjacent to screw holes, and the amount of this material increased with duration of implantation.