Muscle atrophy and fatty degeneration.

Muscle atrophy and fatty degeneration

Atrophy of the supraspinatus muscle could be assessed by calculating the occupation ratio of the supraspinatus fossa. On the most lateral oblique sagittal image, atrophy of the supraspinatus muscle is diagnosed if the supraspinatus muscle occupies less than half the area of the fossa.

The tangent sign describes an additional straight line drawn from the top of the coracoid process to the top of the spine of the scapula on the same oblique sagittal image as above. Atrophy is diagnosed when the superior border of the muscle lies below the tangent line.

Supraspinatus muscle atrophy, tangent sign. Sagittal oblique T1-weighted image showing the upper border of supraspinatus muscle below the line extending between the scapular plate and spine.

Fatty degeneration of the supraspinatus muscles could be assessed on the T1-weighted oblique sagittal image in which the spine and body of the scapula appear. Fatty degeneration could be classified as either low (grade 0; no fat or grade 1; some fatty streaks) or moderate (grade 2; muscle > fat) or advanced (grade 3; muscle = fat and grade 4; muscle < fat).