Subacromial Content to Subacromial Space Ratio in Neutral Position of the Arm as Diagnostic Criteria of Subacromial Impingement Syndrome

Background: Shoulder impingement syndrome is one of the main causes of shoulder disability of working-class individuals. Currently, dynamic sonography of the shoulder is the modality of choice for the evaluation of shoulder impingement syndrome. The ratio of subacromial contents (SAC) and subacromial space (SAS) in neutral arm position could be used as a diagnostic parameter for the subacromial impingement syndrome (SIS), especially in patients who have difficulties in the elevation of their shoulders due to pain. To use the SAC to SAS ratio as a sonographic criterion for the diagnosis of SIS. Methods: SAC and SAS of 772 shoulders were vertically measured in coronal view with linear transducer 7-14MHz of Toshiba Xario Prime ultrasound unit, while the patient arm was kept in the neutral position. The ratio of both the measurements was calculated, to be used as a diagnostic parameter of the SIS. Results: The mean SAS was 10.79 +/- 1.94 mm and SAC was 7.65 +/- 1.43 mm. SAC-to-SAS ratio for normal shoulders was a focused value with narrow standard deviation (0.66 +/- 0.03). However, shoulder impingement is confirmed by any value falls out of the range of ratio for normal shoulders. Area under the curve at 95% confidence interval was 96%, while the sensitivity at 95% confidence interval was 99.25% (97.83%-99.85%), and specificity was 80.86% (76.48%-84.74%). Conclusion: SAC-to-SAS ratio in neutral arm position is a relatively more accurate sonographic technique for the diagnosis of SIS.