An acetabular cup system includes an acetabular cup having a wall with an inner surface and an outer surface. The acetabular cup includes a fixation opening through the wall, the fixation opening including a first wall portion adjacent to the inner surface and a second wall portion adjacent to the outer surface. The acetabular cup system also includes a fixation fastener including a head and a shaft with a bone-anchoring portion. The fastener can be inserted though the fixation opening. The head includes a first head portion engageable with the first wall portion and a second head portion engageable with the second wall portion.