Plain Radiographic Signs of Acetabular Retroversion Can Accurately Detect Global Retroversion With High Sensitivity...

To examine the relationship between radiographic signs of acetabular retroversion (AR) in symptomatic femoroacetabular impingement syndrome (FAIS) patients and global AR (GAR) measured on 3-dimensional imaging.

A retrospective cohort study was conducted to identify patients between 2017 and 2024, with radiographic and clinical FAIS. Standardized pelvic radiographs were analyzed for crossover sign (COS; including crossover percentage), ischial spine sign (ISS), and posterior wall sign (PWS). Alpha angle, femoral torsion, lateral center-edge angle (LCEA), and acetabular version at 1, 2, and 3 o'clock were collected from computed tomography (CT) scans. Patients with AR, defined as >/=5° of retroversion relative to normal values at the 1, 2, and 3 o'clock positions were identified. The sensitivity and specificity of each sign were calculated using CT scans to establish groups of focal and GAR. Continuous variables were compared using one-way analysis of variance and linear regression analyses.

Of the 273 cases, 209 were included. Patients were categorized into the following groups: globally retroverted (n = 56), focally retroverted (n = 74), and normal version (n = 79). The GAR minimal clinically important difference (MCID) is .086°, focal AR MCID is .062°, and normal range acetabular version is .063°. COS and PWS were most sensitive at detecting CT-confirmed AR at 91.6%. Combined crossover percentage greater than 30%, with all positive plain X-ray signs of AR, was most specific at 94.6%. A significant association between crossover percentage and extent of AR at the 3 o'clock position was observed (R² = .1008, P = .0003). Gender-based sensitivity and specific analyses show COS and PWS are most sensitive, and an isolated COS% greater than 30% is most specific at detecting GAR in male patients. A positive ISS was more prevalent among females, whereas a positive PWS was more prevalent among males.

This retrospective review of patients with symptomatic FAIS and radiographic signs of FAI accurately detects GAR with high sensitivity and specificity without a CT scan. Crossover percentage was associated with the extent of AR and may be valuable as a predictive tool. This may help identify patients with more complex deformities that may benefit from CT imaging.

Level III, retrospective diagnostic case series.