The relationship between lysis and loosening in failed anatomic medullary locking components.

Lysis does not cause loosening of extensively porous-coated, apparently well-fixed femoral components. We attribute this in large part to the fact that the area of strongest bone ingrowth is in the femoral diaphysis remote from the joint space. In contrast, for the acetabular component, osteolysis can be the sole or a contributing factor to loosening. We attribute this difference to the fact that the bone-implant interface of the acetabular component is much closer to the joint space and more readily accessible to osteolytic damage. In the future, with improved bearing surfaces, lysis may occur less frequently. Whether lysis is diminished as a result of these new designs, the authors contend that without adequate initial fixation, loosening will still occur. Because of our observations concerning osteolysis and loosening, we are more cautious in revising patients for osteolyis and do not revise when osteolysis first becomes apparent. Rather, we closely monitor osteolysis in these patients. For us, the question of when to operate for osteolysis remains unanswered.