ATROPHY OF THE SUPRASPINATUS BELLY - ASSESSMENT BY MRI IN 55 PATIENTSWITH ROTATOR CUFF PATHOLOGY

A study of 5 fresh cadaveric shoulders demonstrated that an oblique-sa gittal plane which crosses the scapula through the medial border of th e coracoid process offers a view of the supraspinatus fossa mostly lim ited by bone. This view could easily be reproduced by MRI and we calle d it the Y-shaped view. It allowed a reliable measurement of supraspin atus muscle atrophy by the calculation of the occupation ratio (R) whi ch 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 prospecti ve study based on 55 shoulders divided into 3 groups with different ro tator cuff status: group I, 15 controls; group II, 10 degenerative cuf fs, without tears; group III, 30 operated tears. There was no differen ce 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 exte nt of the tear in both the sagittal and coronal planes aggravated the muscle atrophy. We propose a three-stage classification to improve ind ications for rotator cuff tear treatment.