MRI-based 3-dimensional volumetric assessment of fatty infiltration and muscle atrophy in rotator cuff tears

The 3-Dimensional Fatty Infiltration in the Overall Supraspinatus Can Be Predicted by Localized Sectional Accumulation Units

“…It is intriguing, although the reason is not entirely understood, that a few patients had somewhat greater FIs in certain parts of the muscle, typically both the proximal and distal parts. This nonuniform distribution was mainly found with small-to-medium tears (Cases 2, 5, and 7), which is partially consistent with previous studies showing such a nonuniform distribution in established animal models of either chronic neurologic impairment of the RC or RCTs and in patients with mild-to-moderate FI 12,32-34 . Higher FI tended to concentrate at the muscle-tendon junction and proximal dorsal side in the above circumstances 12,32-34 .…”

“…However, the available information does not allow us to further explain either the mechanism underlying the bipolar fat distribution seen in some cases or the reason that the fat distribution was typically more uniform, with no obvious signs of preferential infiltration in certain areas, in the large or massive tears in the present study. FI is typically greater, however, in tears of greater magnitude, as shown by our findings and numerous earlier studies 7,12 . In light of our results and prior findings, it is tempting to speculate that FI that is extensive and uniform and includes the muscle belly in particular may result when infiltration exceeds a physiological “tipping point” dependent on tear size, as Wallenberg et al first indicated 12 .…”

“…FI is typically greater, however, in tears of greater magnitude, as shown by our findings and numerous earlier studies 7,12 . In light of our results and prior findings, it is tempting to speculate that FI that is extensive and uniform and includes the muscle belly in particular may result when infiltration exceeds a physiological “tipping point” dependent on tear size, as Wallenberg et al first indicated 12 . This calls for further analysis in a broad spectrum of RCTs involving partial-thickness tears and small and medium full-thickness tears in a larger cohort.…”

“…However, even the cases without grossly nonuniform trends from proximal to distal exhibited these shorter-scale fluctuations, so the FI in an individual slice would be very unlikely to reflect the overall FI of the muscle, probably accounting for the substantial discrepancy between these 2 values in earlier investigations 7,8,12,14 . In contrast, we calculated the overall FI in SAUs composed of stacks of neighboring slices using the volume integration equation 7,12 , more closely reflecting the 3D FI in that localized spatial region of the muscle. A recent animal model depicted adipose tissue diffusely deposited between muscle fibers and showed that the mean and SD of the fat percentage in volumetric intensity histograms from microcomputed tomography images of an oblique cylinder within the muscle could effectively predict the overall FI in the supraspinatus (R 2 = 0.91) 15 .…”

“…The 3D approaches may represent a new gold standard for assessing FI 14 . These approaches involving manual or semiautomatic image segmentation in each slice and post-processing, however, are usually labor-intensive and time-consuming, which may not be appropriate for larger cohorts or daily clinical work 7,8,12,14,15 . A relatively rapid yet reliable quantification method is highly desirable for estimating the overall FI accurately.…”