MicroStructured[feb9] Omnifit[feb9] Acetabular Components: Concerns with Locking System Complications and Excessive Polyethylene Wear

　　　　　Background. We began to use cementless MicroStructuredh Omnifith acetabular components in November 1988. Liner dislodging and excessive polyethylene wear later occurred in some of our patients. This finding prompted us to review our experience with the use of such modular acetabular components. Methods. A total of 887 hips in 672 patients, which had been fitted with cementless MicroStructuredh Omnifith acetabular components, were evaluated for locking system complications using radiographic examinations. Of the cases, 240 hips which had received a 26-mm femoral head (group 1) and 110 hips which had received a 32- mm femoral head (group 2) were compared using a digitiser to determine the influence of femoral head size on polyethylene wear. Results. There were two types of radiographic signs of locking system complications in 7 hips, at a mean time of 2.9 years after implantation. The incidence of liner locking system complications using this modular acetabular component was 0.8%. The mean liner wear rate per year was 0.15 mm in group 1 and 0.20 mm in group 2 (p<0.005). The initial polyethylene thickness ranged from 5.9 to 13.6 mm in group 1, compared with 3.9 to 10.6 mm in group 2 (p<0.005). Conclusion. A patient who has received a total hip arthroplasty that includes a MicroStructuredh Omnifith acetabular component should be monitored frequently for radiographic signs of locking system complications. In this study, the mean liner wear rate was significantly higher in group 2. Inadequate polyethylene thickness in this group was implicated as the major cause of excessive polyethylene wear.