MRI assessment of Suprapinatus atrophy and fatty replacement

THOMAZEAU's OCCUPATION RATIO (SUPRASPINATUS)
 Muscle atrophy of the supraspintatus is assessed by method suggested by Thomazeau et al, by which the 'occupation ratio' is calculated. Occupation ratio has been defined as the ratio between the cross section of the muscle belly and that of its fossa on the Y-view. The Y-view is the oblique sagittal (T1 WI) plane that crosses the scapula through the medial border of the coracoid process.




Stage I (Occupation Ratio between 1.00 and 0.60) = Normal or slightly atrophied.
Stage II(Occupation Ratio between 0.60 and 0.40) = Moderately atrophied.
Stage III(Occupation Ratio less than 0.40)               = Severely atrophied.

Two methods using line(original) and ellipse (modified Thomazeau's) are being used, and both have been found to be in good correlation and are equally useful.


GOUTALLIER's GRADING OF FATTY INFILTRATION (ROTATOR CUFF)
Grade 0 : Normal muscle with no fatty streaks.
Grade 1 : Mild fatty infiltration (few fatty streaks).
Grade 2 : Moderate fatty infiltration (equal amounts of fat and muscle).
Grade 3 : Severe fatty infiltration (more fat than muscle).


Ref: AJR, APRIL 2008 : Atrophy and fatty infiltration of the supraspinatus muscle: Sonography Vs MRI