Atrophy and fatty infiltration of the supraspinatus muscle: sonography versus MRI.

Objective: The objective of our study was to compare sonography with MRI for the evaluation of supraspinatus muscle atrophy and fatty infiltration.

Subjects And Methods: Forty-five shoulders in 39 patients who had undergone shoulder MRI for the assessment of rotator cuff disease were evaluated blindly with sonography. Supraspinatus muscle atrophy was quantitatively assessed by calculating the occupation ratio (cross-sectional surface area of the supraspinatus muscle belly divided by that of its fossa). This was done by reproducing on sonography the equivalent of the "Y" view on MRI. Fatty infiltration was assessed by evaluating supraspinatus muscle echogenicity compared with that of the trapezius muscle and pennate pattern. The occupation ratio and fatty infiltration of the supraspinatus muscle on sonography were compared with these findings on MRI.

Results: Occupation ratios calculated on sonography images ranged from 0.07 (severe atrophy) to 0.81 (normal) and correlated with the ratios calculated on MRI (R = 0.90; 95% CI, 0.83-0.95). All 20 shoulders with no fatty infiltration on MRI had normal echogenicity and a pennate pattern on sonography. Eight of the 10 shoulders with mild fatty infiltration on MRI had an effaced pennate pattern and mild hyperechogenicity on sonography. In 13 of the 15 shoulders with moderate to severe fatty infiltration on MRI, the pennate pattern was absent and marked hyperechogenicity was present on sonography.

Conclusion: Our study suggests that there is a good correlation between sonography and MRI for the assessment of supraspinatus muscle atrophy and fatty infiltration.