Measurement of acetabular version on the axiolateral radiograph.

There are 3 definitions of acetabular version: true (anatomic) version, planar (radiographic) version, and operative version. Although planar version can be measured on standard radiographs, the measurement may be inaccurate when applied to metal-backed acetabular components. However, another version angle is depicted clearly on an angled, cross-table lateral radiograph of the hip--the axiolateral view, and this angle readily distinguishes anteversion from retroversion. If the angle of the xray beam is known or is standardized, version measured on the axiolateral view can be converted to the other version angles. Nomograms for these conversions are presented. In most cases, acetabular version measured on the axiolateral radiograph closely approximates planar version.