Are acetabular component alignment guides for total hip arthroplasty accurate?

The acetabular component orientation of total hip arthroplasty is of critical importance to the clinical results. Although navigation systems have recently been introduced, acetabular component alignment guides are still used in most of ordinary hospitals. However, the accuracy of alignment guides themselves has not been evaluated. Fifteen types of alignment guide were examined. In all the alignment guides, the angles actually indicated and those stated by manufacturers were different. Our results showed that usage of modern alignment guides inherently misleads anteversion into decrease by a mean of 6° (maximum, 12°) and inclination into increase by a mean of 2° (maximum: 4°). Such setting of alignment guides could be one of the factors of error in acetabular component orientation.