A Simple Device and Biplanar Technique to Improve Precision When Templating for Total Joint Arthroplasty

Accurate templating for arthroplasty procedures depends on reliably estimating image magnification. The authors designed a simple device and technique to accomplish this. It is a wedge with four 25-mm balls staggered at different heights, each representing a potential marker. The proper ball to use as the scaling marker is identified on an orthogonal view on the basis of its relationship with the anatomic feature of interest. Reviewing x-rays with known acetabular component diameters, the authors found that the staggered balls technique had a scaling error of 1.48 +/- 0.89%. Assuming a constant 20% magnification for all x-rays resulted in an error of 1.65 +/- 1.59%. Although similarly accurate, the difference in precision was found to be significant (P=0.012). The constant magnification method resulted in 2 outliers with >4% error, whereas there were no outliers with the novel technique. Staggered marker balls combined with orthogonal imaging is accurate and improves the precision of estimating radiograph magnification.

Automated summary

Accurate templating for arthroplasty procedures relies on reliably estimating image magnification. The authors' simple device using staggered marker balls in orthogonal imaging proved to be more precise compared to assuming a constant 20% magnification for all x-rays, with the novel technique having no outliers exceeding 4% error.