Evaluation of cementless acetabular component migration

Roentgenograms of two human cadaveric pelves with three implanted acetabular components were taken in anatomic, tilted, and rotated positions to determine their effect on the measurement of cup migration. The best landmark for measuring migration along a vertical axis was the distance between the center of the cup and the teardrop line. The best measurement for cup migration along an horizontal axis was the distance between the center of the cup and the vertical line through the teardrop. When the teardrop is not visible, one should use the distance between the bottom of the cup and the obturator line, and the distance between the center of the cup and Kohler's line. Guidelines for roentgenographic comparability are as follows: at 10% magnification, the variation in distance between the obturator line and the teardrop line should be less than 5 mm, and the distance between the middle of the sacroiliac line and the vertical line through the pubis should be less than 0.5 cm.