Reamed surface topography and component seating in press-fit cementless acetabular fixation.

Thirty-eight paired, size-matched, fresh-frozen cadaver acetabulae were used to study reamed surface topography and the seating of on-line versus oversized noncemented components. Four commonly used constructs were considered: on-line reamed and 2-mm oversized hemispherical cups, and on-line reamed and 1-mm oversized dual-radius cups. Reamed surface topography was indexed by three-dimensional surfaces mathematically fitted to digitized castings. Component seating was indexed by the distribution of bone-cup contact and the thickness of the gap between the component backing and the bone. The reamed surfaces were better approximated by slightly blunt ellipsoids than by spheres, especially for the smaller acetabulae. Seating of the on-line hemispherical cups was best near the pole and poorest near the equator, whereas the converse was true for the 1-mm oversized dual-radius cups. The on-line dual-radius cups offered better overall compromise between polar and equatorial contact than did the 2-mm oversized hemispherical components.