Don't throw away the ring: indications and use

Protective rings are a valuable adjunct in revision acetabular surgery. Two types of rings are used. The roof ring, which is the smaller of the 2 rings, provides support from the ilium to the inferomedial part of the acetabulum. The reconstructive ring or cage provides support from the ilium to the ischium. Both devices can be used to protect morcellized or structural bone-graft. The roof ring can be used with morcellized graft if the ring can make contact with host-bone at the superior and inferomedial aspect of the acetabulum. If the defect is more global but still contained so that the entire acetabulum is filled with morcellized bone, the larger reconstructive ring should be used. Small structural grafts that support <50% of the cup may be protected by a roof ring. Larger structural grafts that support >50% of the cup should be protected by a reconstructive ring.