Acetabular component revision with a modular anti-protrusio cage

Current anti-protrusio cage designs are non-porous coated, one-piece and require cementation of a polyethylene liner into the cage. These factors limit the ability to gain permanent fixation by bone ingrowth, perform a trial reduction, and use different liner types to enhance hip stability. Results of a completely modular porous coated anti-protrusio cage (MAPC) designed to improve fixation and simplify intra-operative insertion were reviewed. Seventy-one acetabular component revisions with a MAPC were performed from 1998–2001 by two surgeons. Average follow-up was 29 months (range 24–50). The 46 females and 25 males had an average age 65. 36/71 operations were acetabular revisions only. Preoperatively 61/71 acetabulii had AAOS Type III, 9/71 Type IV, and 1/71 Type V bone loss. Five hips required bulk structural allograft (3 distal femur and 2 femoral head), the remainder required cancellous grafts only. Sixty-four of the 71 (90 percent) MAPC remain in place. Seven components were removed, 4 for infection, and 3 for loosening. Ten hips dislocated requiring four reoperations. One MAPC is definitely radiographically loose and four others have migration over 5mm, but patients remain asymptomatic. No MAPC has visible osteolysis. The Harris Hip Score improved from 33 to 77. At short-term follow-up, the MAPC is comparable to conventional one-piece anti-protrusio cages in terms of fixation and complications. Advantages include bone-ingrowth and long-term fixation, surgical technique similar to placement of a large hemispherical acetabular component, the ability to use trial components, and complete bearing surface modularity.