Prospective, Randomized, Surgeon-Blinded Comparison of Standard Magnification Assumption vs Magnification Marker...

We undertook this prospective, randomized, surgeon-blinded study to compare the accuracy of using of a magnification marker on preoperative radiographs for templating vs using a standard 21% magnification.

One hundred consecutive total hip arthroplasties were randomized to preoperative templating using a 25-mm magnification marker (50 patients) or a standard 21% magnification (50 patients). Intraoperative data were collected regarding the actual and predicted size of the femoral and acetabular components.

The 2 groups were found to be comparable with respect to body mass index (28.9 vs 27.9, P = .26) and gender (P = .69). In the magnification marker group, we predicted the femoral size within 1 size in 80% of the cases and the acetabular component in 94%. In the group of a standard 21% magnification, we predicted the femoral size within 1 size in 90% of the cases and the acetabular component in 96%. These proportions did not statistically differ (femur: χ²P = .16, odds ratio = 2.3, 95% confidence interval = 0.7-7.1; acetabulum: χ²P = .65, odds ratio = 1.5, 95% confidence interval = 0.3-9.6).

We did not detect a statistically significant difference in accuracy by using one method over the other when comparing the accuracy of component size selection. As the use of the magnification marker adds to the time and expense of preoperative radiographic acquisition, we feel using a standard 21% magnification is an equally accurate technique.