Schematic showing the measurement of medial protrusion and cup coverage. Point O is the center of the cup component. AB is the diameter of the cup component. Point C is the intersection between the edge of the cup implant and the ilium. Point D and point E are the intersections between the medial edge of the acetabular component and Kohler’s line. The rate of cup coverage = [(180° − ∠AOC)/180°] × 100%. The rate of medial protrusion = (∠DOE/180°) × 100%