ANTEROPOSTERIOR PELVIC RADIOGRAPHS TO ASSESS ACETABULAR RETROVERSION: HIGH VALIDITY OF THE “CROSS-OVER-SIGN”

Abstract

Background: Acetabular retroversion has been proposed to contribute to the development of osteoarthritis of the hip. For the diagnosis of this condition, conventional AP pelvic radiographs may represent a reliable, easily available diagnostic modality as they can be obtained with a reproducible technique allowing the anterior and posterior acetabular rims to be visible for assessment. This study was designed to

1. establish a method to directly quantify anatomic acetabular version on AP pelvic radiographs and to

2. determine the validity of the radiographic “cross-over-sign” to detect acetabular retroversion.

Methods: Using 43 desiccated pelves (86 acetabuli) the anatomic acetabular versions were measured at three different transverse planes (cranially, centrally and caudally). From these pelves, standardized AP pelvic radiographs were obtained. To directly measure central acetabular version (AV), a modified radiographic method is introduced for the use of AP pelvic radiographs. Moreover, the validity of the radiographic “cross-over-sign” to detect cranial acetabular retroversion was determined.

Results: The mean central and caudal anatomic AV were approximately 20°, the mean cranial AV was 8°. Cranial retroversion (AV < 0°) was present in 19 of 86 hips (22%). A linear correlation was found between the central and cranial AV. Below 10° of central AV, all acetabuli were cranially retroverted. Between 10° and 20°, 30% of the acetabuli were cranially retroverted and above 20°, only one of 45 acetabuli was cranially retroverted. The radiographic measurement of the central AV (20.3° ± 6.5) correlated strongly with the anatomic AV (20.1° ± 6.4). The sensitivity of the ‘cross-over-sign’ to detect an cranial acetabular anteversion of less than 4° was 96%, its specificity 95%, and the positive predictive and negative predictive values 90% and 98%, respectively.

Conclusions: The cranial AV is on average 12° lower than the central AV, with the latter directly measurable from AP pelvic radiographs. A central AV of less than 10° was associated with cranial retroversion. The presence of a positive ‘cross-over-sign’ is a highly reliable indicator of cranial AV of < 4°.