Accuracy and precision of version angle measurements of the acetabular component after total hip arthroplasty.

The orientation of the acetabular component after total hip arthroplasty is expressed with inclination angle and anteversion angle (VA). We studied the differences in accuracy and precision between VA measured on AP radiographs of the pelvis and those measured on cross-table lateral radiographs when compared to the gold standard measurements on CT using a supine functional pelvic plane as reference. VA was measured for 66 hips at one week after surgery on an AP radiograph of the pelvis (VAP), a cross-table lateral radiograph of the hip (VCL), and CT of the pelvis. Mean (± SD) of error was 2.8° ± 4.1° for VCL, and -0.57° ± 3.1° for VAP. VAP showed a higher accuracy and precision than VCL. For measurements of VA, we recommend that they be made on an AP radiograph of the pelvis rather than a cross-table lateral radiograph of the hip.