Digital fluoroscopic assessment of the scapulohumeral rhythm

Previous studies have shown that abnormal rotation of the scapula is associated with shoulder pathology. Among the methods which have been proposed, planar x-ray measurements are probably the only methods, which enable clinicians to assess accurately and objectively the scapulohumeral function in vivo. The aim of this study was to develop a method for the assessment of scapulohumeral kinematics using digital fluoroscopy. Anteroposterior images of the right glenohumeral joint were taken, in thirty-four healthy males, with the arm at rest, 30 degrees, 60 degrees, 90 degrees, 120 degrees, 150 degrees and maximum abduction, in the scapular plane. High inter- and intra-examiner reliability was observed regarding the arm and scapular angle measurements (ICC = 0.92-0.99). The positioning of the arm at the proposed angles was also highly accurate (< 2.3 degrees misplacement) and reproducible (CV% < 5.3%). The mean radiation dose was 0.075 mSv (+/- 0.027 mSv). At the resting position the scapula was in slight downward rotation (-2.4 degrees +/- 4.3 degrees) and the arm in slight abduction (1.5 degrees +/- 6.6 degrees). The mean maximum scapular rotation and the mean maximum arm abduction was 61.4 degrees (+/- 5.2 degrees) and 162.4 degrees (+/- 6.6 degrees) respectively. A curvilinear relationship was found between the arm angle (AA) and the scapular angle (SA) (p < 0.0001). The AA:SA ratio for the entire range of abduction was 2.5:1. The greatest contribution of the scapula (1.7:1) achieved at 30 degrees-60 degrees of arm. The high accuracy and reliability of our method and the low radiation recordings suggests that digital fluoroscopy may be considered for further investigation of the scapulohumeral kinematics in both healthy and pathological shoulders.