A more reliable method to assess acetabular component position.

Background: Acetabular component position is associated with joint function and bearing wear. Current techniques for determining acetabular component version on standard radiographs lack reliability. Other, more consistent techniques are time-consuming and require additional equipment or software.

Questions/purposes: We compared three methods of acetabular component position assessment: (1) Einzel-Bild-Roentgen-Analyse (EBRA), (2) Woo and Morrey, and (3) the new ischiolateral method.

Patients And Methods: We assessed axial component position for 52 hips, with at least three radiographic series, using EBRA, and on true lateral radiographs using the Woo and Morrey method and a new method that uses the ischium as a skeletal landmark, the ischiolateral method.

Results: The mean SDs of the ischiolateral (2.15°) and EBRA (2.06°) methods were lower than that of the Woo and Morrey method (3.65°) but were not different from one another. We observed a SD of greater than 4° in 19 (36.5%) hip series using the Woo and Morrey method, compared to six series (11.5%) for both the ischiolateral and EBRA methods. Twenty-four (12.6%) Woo and Morrey measurements were greater than 4° from the mean for the hip series, compared to seven (3.8%) for ischiolateral and nine (4.7%) for EBRA. The intraclass correlation coefficients for intra- and interobserver reliability for the ischiolateral method and EBRA were the same (0.9).

Conclusions: Referencing the ischium standardizes pelvic position on each lateral radiograph and provides a simple and reliable means to assess axial component position, which is a surrogate for the planar anteversion measured by EBRA.