Diagnosis of acetabular retroversion: Three signs positive and increased retroversion index have higher specificity and higher diagnostic accuracy compared to isolated positive cross over sign

Objectives: The crossover-sign (COS) is a radiographic sign for diagnosis of acetabular-retroversion(AR) in patients with femoroacetabular-impingement (FAI) but overestimates AR. Three signs combined with retroversionindex (RI) could potentially improve diagnostic-accuracy.Aims:(1) To calculate central acetabular-version (AV, CT/MRI) in patients with isolated positive COS and in patients with three radiographic signs for AR on radiographs (AP).(2) To calculate diagnostic performance of positive COS and of three signs combined with retroversion-index (RI) > 30% on radiographs (AP) to detect global AR (AV < 10?degrees, CT/MRI). Methods: A retrospective, IRB-approved, controlled diagnostic study comparing radiographic signs for AR (AP radiographs) with MRI/CT-based measurement of central AV was performed. 462 symptomatic patients (538 hips) with FAI or hip-dysplasia were compared to control-group (48 hips). Three signs for AR(on radiographs) were analyzed: COS, posterior-wall-sign and ischial-spine-sign. RI (synonym cross-over-index) quantifies overlap of anterior and posterior wall in case of positive COS. Diagnostic performance for COS and for three signs combined with RI > 30% to detect central AV < 10 (global AR) was calculated.Results:(1) Central AV was significantly (p < 0.001) decreased (13 & PLUSMN; 6?degrees, CT/MRI) in patients with three signs for AR and RI > 30% on radiographs compared to patients with positive COS (18 & PLUSMN; 7 degrees).(2) Sensitivity and specificity of three signs combined with RI > 30% on radiographs was 85% and 63% (87% and 23% for COS). Negative-predictive-value (NPV) was 94% (93% for COS) to rule out global AR (AV < 10, CT/MRI). Diagnostic accuracy increased significantly (p < 0.001) from 31% (COS) to 68% using three signs.Conclusion: Improved specificity and diagnostic accuracy for diagnosis of global AR can help to avoid misdiagnosis. Global AR can be ruled out with a probability of 94% (NPV) in the absence of three radiographic signs combined with retroversion-index < 30% (e.g. isolated COS positive).