Can a shoulder X-ray classify acromion shape more accurately than CT or MRI?

Details

The study aimed to compare the diagnostic accuracy of supraspinatus muscle outlet X-ray films, oblique sagittal multislice helical CT (MSCT), and oblique sagittal MRI for subacromial impingement syndrome (SIS).

Researchers retrospectively analyzed imaging data from 106 patients diagnosed with SIS between January 2023 and December 2024. There were 32 males and 74 females, aged 43–70 years, with a mean age of 60.19 years. All patients underwent supraspinatus muscle outlet X-ray, MSCT, and MRI scans; the MSCT data also underwent three-dimensional reconstruction.

Two experienced radiologists independently assessed acromion morphology on each imaging modality using the Bigliani classification system. Inter-observer reliability was assessed using Kappa statistics. CT three-dimensional reconstructions served as the “gold standard.” Researchers calculated overall agreement, Kappa values, sensitivity, and specificity for the three modalities. They also plotted receiver operating characteristic (ROC) curves and calculated the area under the curve (AUC).

Inter-observer reliability was described as moderate for supraspinatus muscle outlet X-ray, oblique sagittal MSCT, and oblique sagittal MRI, with Kappa values of 0.62, 0.63, and 0.55, respectively. Against the CT three-dimensional reconstruction reference, overall agreement was 88.7% (94/106) for X-ray, 62.3% (66/106) for oblique sagittal MSCT, and 58.5% (62/106) for oblique sagittal MRI. Agreement with the reference was described as excellent for X-ray (Kappa=0.77), but lower for MSCT (Kappa=0.34) and MRI (Kappa=0.29).

The supraspinatus muscle outlet X-ray outperformed oblique sagittal MSCT and oblique sagittal MRI in sensitivity and specificity for distinguishing acromion types. Its AUC was consistently higher than those of the other two modalities, with its highest diagnostic performance for type III hooked acromion (AUC=0.939).

The authors concluded that supraspinatus muscle outlet X-ray provides the highest diagnostic accuracy for acromion classification in patients with SIS, particularly for identifying type III hooked acromion, which is strongly associated with SIS. Based on its superior sensitivity and agreement, they recommended considering it the primary screening tool. They described MSCT and MRI as valuable supplementary modalities for complex cases and preoperative evaluation.