[Exchange of acetabular cups with severe bone defects using antiprotrusion cages]

Abstract

Objective: Replacement of a loosened acetabular cup attended by massive bone defects involving both columns. Acetabular restoration and proof fixation of a new acetabular cup to restore a pain-free joint function.

Indications: Segmental acetabular bone defects involving both columns (Paprosky type 3A, 3B) with loosened acetabular cup or a Girdlestone situation. In case of pelvic discontinuity (Paprosky type 4) combination with reconstructive osteosynthesis plates (for example, Synthes company, Bochum, Germany).

Contraindications: In cases of complete absence of the posterior and especially cranioposterior column combination with structural allograft reconstruction necessary. Relative: acetabular defects, that can be reconstructed by other, smaller implants, for example, press-fit acetabular cups.

Surgical technique: Exposure of the acetabulum by a conventional approach. Removal of the loosened acetabular cup. Cleaning of the acetabulum with a sharp spoon. Rebuilding of the hip center with a reamer. Choice of the size of the antiprotrusion ring using trial implants. Access chiseling for the inferior implant flange into the ischium. If necessary, adaptation of the superior and inferior flange alignment to the individual anatomy by bending. Filling of bone defects with allogenic bone chips. Knocking in of the inferior flange into the ischium. Simultaneous knocking in of both the ring in the acetabulum and the superior flange at the ischium. Screwing in of bolts from the interior of the ring into the iliac bone in the direction of hip forces. Additional positioning of screws due to the superior flange into the iliac bone. Cementing in of a polyethylene cup in the antiprotrusion ring.

Postoperative management: Antithrombotic prophylaxis, physical therapy, gait training under full weight bearing of the limb.

Results: 30 acetabular cup revisions with a new Burch-Schneider ring underwent prospective clinical and radiologic examination and were analyzed for an average follow-up of 20.6+/-7.8 months (3-36 months). The Harris Hip Score increased from preoperative 46.6 to postoperative 75.9 points. A loosening of the cage was not recorded.