抄録
Introduction: The supraspinatus tendon attaches to the superior facet and the superior half of the middle facet, whereas the infraspinatus tendon attaches to the entire middle facet, making an overlap between these tendons. Therefore, it seems possible to identify the tendons involved in a tear judging from these facets. The purpose of this study was to differentiate the superior and middle facets on MRI. Materials and methods: Forty-two symptomatic shoulders of 40 patients without a bony spur or defect of the greater tuberosity on plane roentgenograms were enrolled in this study. T1 weighted images in the coronal oblique were obtained using a 0.5-T imager(Yokokawa Medical System RESONA: FOV 17cm, matrix 224×256,5.0 mm thickness/1.0 mm slice gap). The angle between the long axis of the humerus and the superior margin of the greater tuberosity (H-GT angle) were measured and the effect of the rotation of the humerus on H-GT angle was studied using cadaver shoulders.
Results and discussion: The greater tuberosity was visible in 5.1±0.9 slices (avg±SD), H-GT angle of the superior facet was 82.4±8.1°in the anterior 2.1±0.8 slices, and H-GT angle of the middle facet was 58.0±12.0°. H-GT angles of the superior facet and middle facet became closer in external rotation (74.9±9.9°,79.7±3.8°, respectively), and became apart in neutral (83.0±7.5°,58.0±12.0°), and internal rotations (82.5±9.0°,52.2±9.3°). Therefore, neutral and internal rotations seem to be desirable in identifying these facets on MRI.
Conclusion: The superior and middle facets, useful landmarks in localizing rotator cuff tears, can be identified on MRI, especially with the arm in neutral and internal rotations.
