Key result
AP radiographs show low agreement with CT for cross-over and posterior wall signs, confounded by pelvic tilt.
Why the study?
Do AP radiographs provide reliable diagnostic measures for acetabular retroversion compared to CT scans in patients with FAI?
Cross-Sectional (n=50)
Do AP radiographs provide reliable diagnostic measures for acetabular retroversion compared to CT scans in patients with FAI?
AP radiographs are considerably limited by pelvic tilt and should not be used as the sole basis for surgical decision-making in acetabular retroversion.
COS/PWS accuracy vs CT in FAI remains uncertain; leaves open standardized use before changing diagnostic pathways.
Diagnosis of acetabular retroversion is essential in femoroacetabular impingement (FAI), but its assessment from radiographs is complicated by pelvic tilt and the two-dimensional nature of plain films. We performed a study to validate the diagnostic accuracy of the cross-over sign (COS) and the posterior wall sign (PWS) in identifying acetabular retroversion. COS and PWS were evaluated from radiographs and computed tomography (CT) scans as the standard of reference in 50 hips of subjects with symptoms of FAI. A CT-based method using three-dimensional (3D) models was developed to measure the COS, PWS, true acetabular version, and pelvic tilt relative to the anterior pelvic plane. The new CT-based method aimed to eliminate errors resulting from variations in the position and orientation of the pelvis during imaging. A low level of agreement for COS and PWS was found between radiographs and CT scans. A positive COS strongly correlated with pelvic tilt. These results suggest that COS and PWS determined from anteroposterior radiographs are considerably limited by pelvic tilt and inherent limitations of radiographs. Their use as the sole basis for deciding whether or not surgical intervention is indicated seems questionable.
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Wassilew et al. (2012) conducted a cross-sectional in Femoroacetabular impingement (FAI) (n=50). Anteroposterior radiographs (cross-over sign and posterior wall sign) vs. Computed tomography (CT) scans was evaluated on Agreement of cross-over sign (COS) and posterior wall sign (PWS) between radiographs and CT scans. Anteroposterior radiographs demonstrated a low level of agreement with CT scans for evaluating the cross-over and posterior wall signs, which were strongly confounded by pelvic tilt.
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