Comparison of Monoblock and Modular Femoral Stem on Isolated Acetabular Revision with Use of Uncemented Cup

ABSTRACT

Purpose: The purpose of our study was to assess the clinical and radiological results of isolated acetabular revision and the differences in the results between monoblock and modular femoral stems. Materials and Methods: Between October 1991 and June 2002, 39 patients (39 hips) underwent isolated acetabular revisions with use of uncemented cups and bone grafts. The mean period of follow-up was 5 years 3 months (range, 2 years 1 month to 9 years 8 months). The mean age of the patients at the time of the surgery was 51 years old (range, 26 to 75 years old). The monoblock femoral stems were used in 19 hips and the modular femoral stems were used in 20 hips. The monoblock stems were retained without exchange provided that there was no gross scratch on the femoral head and the femoral stem was confirmed to be stable and fixed intraoperatively. In the modular stems, the femoral heads were always exchanged with new ones. Results: The mean Harris hip score improved from 57 to 87 points. Radiologically, all the stems retained at surgery remained well osseointegrated without osteolysis. Re-revisions of the acetabular components were performed in 5 hips using monoblock stems due to periacetabular osteolysis caused by excessive wear of polyethylene and subsequent loosening of the cups in 3 hips and mechanically unstable acetabular cups without osteolysis in 2 hips. The mean wear rate of polyethylene coupled with the monoblock stem was 0.27 mm/year which was greater than the 0.11 mm/year in the cases with modular stems. Conclusion: To prevent failure of acetabular cups that may occur later by excessive wear of polyethylene, we recommend revision of the well-fixed monoblock femoral stems even though there is no gross scratch on the femoral heads of the monoblock stems.