Appositional bone bridging of primary gaps in the dome area of uncemented, porous acetabular components

Reported here are two cases of primary hybrid arthroplasties using a cemented stem and an uncemented, porous acetabular component. Because of the configuration of the acetabula, a residual central gap remained after implantation of the socket. Unimpacted grafts were used to fill the spaces. The gaps, amounting to 4 to 5 mm on the postoperative radiographs, had disappeared at the 30-40-month follow-up examination, with no radiolucent lines at the bone-implant interface. Both sockets were evaluated by roentgen stereophotogrammetric analysis for 2 years, and by using this technique for detecting micromovements, central migration as a reason for the disappearance of the gaps was precluded. Bony apposition of primary gaps of up to 5 mm in the central area of well-fixed porous acetabular components seems possible.