The efficacy of a “double-D-shaped” wire marker for radiographic measurement of acetabular cup orientation and wear

Abstract

Historically, wire markers were attached to cemented all-plastic acetabular cups to demarcate the periphery and to measure socket wear. The wire shape was either a semi-circle passing over the pole of the cup, or a circle around the cup equator. More recently, “double-D” shaped markers were introduced with a part-circular aspect passing over the pole and a semi-circular aspect parallel to the equatorial plane. This configuration enabled cup retroversion to be distinguished from anteversion. In this study, the accuracy of radiographic measurement of cup orientation and wear was assessed for cups with “double-D” and circular markers.Each cup was attached to a measurement jig which could vary the anteversion/retroversion and internal/ external rotation of the cup. A metal femoral head was fixed within the socket and radiographic images were created for all combinations of cup orientation settings. The images were measured using software with automatic edge detection, and cup orientation and zero-wear accuracies were determined for each setting.The median error for cup version measurements was similar for both types of wire marker (0.2° double-D marker, −0.24° circular marker), but measurements of the circular marker were more repeatable. The median inclination errors were 2.05° (double-D marker) and 0.23° (circular marker). The median overall “zero wear” errors were 0.19 mm (double-D marker) and 0.03 mm (circular marker). Measurements of the circular wire marker were much more repeatable.

Component Placement in Direct Lateral vs Minimally Invasive Anterior Approach in Total Hip Arthroplasty: Radiographic Outcomes From a Prospective Randomized Controlled Trial

“…A marathon x-ray marker wire indicates whether the calculated angle is anteverted or retroverted [69] (Figure 10).…”

Validation of a new 2-D technique for radiographic wear measurement of cemented, highly cross-linked polyethylene acetabular cups

“…The main limitation of the technique is that the all-PE cups need to have fully-circular wire markers. Accurate and consistent measurements are difficult to achieve if the cups have semi-circular or “double- D -shaped” wire markers [19] . A further limitation is that wear cannot be measured accurately if the radiographic version of the cup is very low (few degrees) because an ellipse cannot be fitted to the wire marker image due to merging of its opposite sides.…”