In 21 cases of severe secondary protrusio acetabuli with extensive or total destruction of the acetabular cortical structures, the double anchorage of conventional polyethylene cups with nine Müller acetabular reinforcement rings and 12 Burch-Schneider anti-protrusio reinforcement cages was carried out. They were applied in combination with reconstructive surgery of cancellous bone in three primary total hip replacements and in 18 revision operations for loosened acetabular cups following total arthroplasties. Indication for and technique of the acetabular reinforcement are described. The radiological and clinical results in 21 patients followed up were satisfactory. They confirm the efficiency of these screw-fixed reinforcement implants for the solid fixation of the plastic cup in patients with extreme acetabular deficiencies.