Protrusio acetabuli prosthetica.

Protrusio acetabuli prosthetica is a form of hip replacement failure in which intrapelvic component migration occurs. Three degrees of the entity are defined as determined by (1) prosthetic migration medial to the ilioischial line and (2) integrity of the medial acetabular wall. Entities predisposing to protrusio acetabuli prosthetica include overreaming, multiple pelvic perforations, osteopenic bone states, infection, trauma, heredity or acquired bone deficiency states, overactivity, and hypertrophic membrane formation. Treatment of the condition is contingent upon (1) reestablishment of the radiographically determined anatomic position of the acetabulum and (2) construction of a medial prosthetic or biologic buttress. Recent techniques of biologic medial-wall formation utilize either allograft or autograft bone in one of three configurations--bulk, chipped or pulverized. In cases of severe intrapelvic hip protrusion, resection arthroplasty may be the only alternative.