An anchor for securing an implant within bone. In one embodiment, the anchor is used to aid in securing an acetabular cup within an acetabulum. The anchor may be implanted within an ischial defect of the pelvis, and is attached to an outer surface of the acetabular cup shell. The anchor is made at least in part of, and may be made entirely of, a porous metal material to facilitate the ingrowth of surrounding bone into the anchor for osseointegrating the anchor into the surrounding bone. The anchor may be secured to the acetabular shell by a screw fastener or by cement, for example. The anchor may be secured to the acetabular shell before the anchor and the acetabular shell are together implanted into the acetabulum, or the anchor may be implanted into the ischial defect, followed by seating the acetabular shell in the acetabulum and then securing the acetabular shell to the anchor.