Sleeves for affixing artificial joints to bone

A sleeve for affixing a component of an artificial joint to bone, said joint having a joint motion surface, said sleeve comprising a body having a longitudinal axis which defines first and second ends, the first end being towards the joint motion surface and the second end being away from the joint motion surface when the sleeve is implanted in the bone, said body having an outer surface which includes a plurality of terraces, each terrace lying in a plane substantially perpendicular to the longitudinal axis, the perimeter of the outer edge of each terrace located in the region of the first end of the body comprising (a) a portion of a circle centered on the longitudinal axis and (b) a portion of an ellipse whose center is offset from the longitudinal axis, said portion of an ellipse, for each of the terraces, (a) being a portion of a common ellipse so that all of the elliptical portions have the same shape, and (b) including a vertex of the ellipse, the perimeters of the terraces located in said first end region having lengths such that for each pair of adjacent terraces, the perimeter of the outer edge of the terrace closer to the first end is longer than the perimeter of the outer edge of the terrace closer to the second end, at least some of said first end perimeters having an oblong form wherein the elliptical portion of the perimeter is half an ellipse and the perimeter includes two lines which are parallel to the ellipse's major axis, and tangent to the ellipse at the ends of its minor axis and spaced from one another by a distance which is less than the diameter of the circular portion of the perimeter.