Atrophy of the supraspinatus belly. Assessment by MRI in 55 patients with rotator cuff pathology.

A study of 5 fresh cadaveric shoulders demonstrated that an oblique-sagittal plane which crosses the scapula through the medial border of the coracoid process offers a view of the supraspinatus fossa mostly limited by bone. This view could easily be reproduced by MRI and we called it the Y-shaped view. It allowed a reliable measurement of supraspinatus muscle atrophy by the calculation of the occupation ratio (R) which is the ratio between the surface of the cross-section of the muscle belly and that of the fossa. This ratio was calculated in a prospective study based on 55 shoulders divided into 3 groups with different rotator cuff status: group I, 15 controls; group II, 10 degenerative cuffs, without tears; group III, 30 operated tears. There was no difference between groups I (mean ratio 0.7) and II (mean ratio 0.62), but the ratio was decreased in group III (mean ratio 0.44), in which the extent of the tear in both the sagittal and coronal planes aggravated the muscle atrophy. We propose a three-stage classification to improve indications for rotator cuff tear treatment.