Fatty atrophy of supraspinatus and infraspinatus muscles: accuracy of US.
OBJECTIVE
To prospectively evaluate the accuracy of ultrasonography (US) in depicting fatty atrophy of the supraspinatus (SSP) and infraspinatus (ISP) muscles, with magnetic resonance (MR) imaging as the reference standard.


METHODS
Institutional review board approval and informed consent were obtained. SSP and ISP muscles of 65 consecutive patients (27 women, 38 men; mean age, 53.1 years; range, 28-83 years) with possible rotator cuff tears were evaluated with US in two planes. Visibility of muscle contour, pennate pattern, the central tendon, and muscle echogenicity was assessed by two radiologists. On the basis of these findings, diagnosis of substantial fatty atrophy was made at US. Accuracy, sensitivity, specificity, proportion of over- and underestimations, and interobserver agreement in diagnosis of substantial (grade 2 or greater) muscle atrophy were determined. Fatty atrophy was graded at MR imaging as follows: score of 0 = no intramuscular fat, score of 1 = some fatty streaks, score of 2 = fat evident but less extensive than muscle, score of 3 = fat equal to muscle, and score of 4 = fat more extensive than muscle.


RESULTS
For readers 1 and 2, the accuracy of US in depicting fatty atrophy of SSP muscle was 75% (49 of 65) and 72% (47 of 65), sensitivity was 89% (eight of nine) and 100% (nine of nine), and specificity was 73% (41 of 56) and 68% (38 of 56), respectively. For readers 1 and 2, the accuracy of US in depicting fatty atrophy of ISP muscle was 85% (55 of 65) and 80% (52 of 65), sensitivity was 58% (11 of 19) and 63% (12 of 19), and specificity was 96% (44 of 46) and 87% (40 of 46), respectively. Overestimation of SSP muscle atrophy was more common (23% [15 of 65] for reader 1 and 28% [18 of 65] for reader 2) than underestimation (2% [one of 65] for reader 1 and 0% [0 of 65] for reader 2). For readers 1 and 2, overestimation of ISP muscle atrophy was 3% (two of 65) and 9% (six of 65) and underestimation was 12% (eight of 65) and 9% (seven of 65), respectively. Interobserver agreement was moderate for SSP (kappa = 0.55) and substantial for ISP (kappa = 0.71) muscles.


CONCLUSIONS
US is moderately accurate in the diagnosis of substantial fatty atrophy of the SSP or ISP muscle.
Strobel
Klaus
K
Department of Radiology, Orthopedic University Hospital, Balgrist, Zurich, Switzerland. klaus.strobel@urz.ch
Hodler
Juerg
J
Meyer
Dominik C
DC
Pfirrmann
Christian W A
CW
Pirkl
Christoph
C
Zanetti
Marco
M
D000273:Adipose Tissue / Q000000981:diagnostic imaging* / Q000473:pathology; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003287:Contrast Media; D005260:Female; D019786:Gadolinium DTPA; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009133:Muscular Atrophy / Q000000981:diagnostic imaging* / Q000473:pathology; D011446:Prospective Studies; D017006:Rotator Cuff / Q000000981:diagnostic imaging*; D000070636:Rotator Cuff Injuries; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric; D014463:Ultrasonography
D003287:Contrast Media; D019786:Gadolinium DTPA