Comparative Evaluation of Cross-table and Ducroquet Incidences for Measurement of the Hip Alpha Angle.

The purpose of the present paper is to compare the equivalence of the measurement of the alpha angle using the Ducroquet and cross-table lateral views.  We have recruited 90 patients, resulting in 95 hips. We have standardized the realization of the radiographic views. The incidence of the lateral cross-table views were taken with 15° of internal rotation with the patient in the supine position, and the incidence of the Ducroquet views was standardized with the patient in the supine position, with 90° of flexion and 45° of abduction of the hip. The alpha angle was measured in both lateral views, by two musculoskeletal radiologists. The measurements were performed in 2 different times: an initial evaluation and another 4 weeks afterwards. The t Student test was used and calculated the intraclass correlation coefficient (ICC).  We have found a good intraobserver correlation for both views in different times; there was no statistically significant difference between the measurements performed by the two views. However, the interobserver correlation was low.  In conclusion, the Ducroquet profile view is a good choice for the α angle measurement and can be used instead of the cross-table view.