The Modified Assessment Tool Based on Scapular Y-View for Global Fatty Infiltration in the Supraspinatus Muscle: Correlation, Predictive Performance, and Reliability Analyses

Abstract

Background: The accurate evaluation of rotator cuff (RC) fatty degeneration after tears is critical for appropriate surgical decision making and prognosis. However, there is currently no reliable and practical tool to reflect the global fatty infiltration (Global-FI) throughout the 3-dimensional (3D) volumetric RC muscles. Purpose: (1) To determine the correlations between 2 modified assessment tools and the Global-FI and their predictive performances and reliabilities for Global-FI prediction, and (2) to compare these predictive parameters with those of the conventional tool using a single scapular Y-view slice. Study Design: Cohort study (diagnosis); Level of evidence, 3. Methods: A total of 49 patients with full-thickness RC tears scheduled to undergo arthroscopic repairs were included, and their surgical shoulders underwent 6-point Dixon magnetic resonance imaging preoperatively. The Global-FI was measured by calculating the 3D-volumetric fat fraction (FF) of the whole supraspinatus muscle through all acquired oblique sagittal slices. As a commonly used radiological landmark, the scapular Y-view was used to evaluate single-plane fatty infiltration (Y-FI) by calculating the FF in 1 slice, defined as the conventional assessment tool. Two modified assessment tools expand the analytic imaging by integrating the FFs from the scapular Y-view slice and its neighboring slices, which were calculated by averaging the FFs of these 3 slices (meanY3-FI) and accumulating local 3D-volumetric FFs from 3 slices (volY3-FI), respectively. The correlations between 3 assessment tools and the Global-FI were analyzed, and the predictive performance for Global-FI prediction using these tools was determined by goodness of fit and agreement. Moreover, the inter- and intraobserver reliabilities of these assessment tools were evaluated. Similar analyses were performed in the small-medium, large, or massive tear subgroups. Results: The Y-FI was significantly higher than the Global-FI in all cases and tear size subgroups, while the 2 modified assessment tools (meanY3-FI and volY3-FI) did not significantly differ from the Global-FI. All assessment tools were significantly correlated with the Global-FI, but the meanY3-FI and volY3-FI showed stronger correlations than the Y-FI, which was also determined in different tear sizes. Moreover, the regression models of the meanY3-FI and volY3-FI showed superior goodness of fit to Y-FI in Global-FI prediction in all cases and subgroups, with larger coefficients of determination ( R2) and smaller root mean square errors. The predicted Global-FI using the regression model of volY3-FI had the best agreement with the measured Global-FI, followed by the meanY3-FI, both showing smaller biases and standard deviation of the percentage difference between predicted- and measured Global-FI than the conventional Y-FI. In addition, the 2 modified assessment tools achieved better interobserver and intraobserver reliabilities than the conventional tool in all cases and subgroups. Conclusion: Two modified assessment tools (meanY3-FI and volY3-FI) were comparable with the Global-FI of the whole supraspinatus muscle, showing stronger correlations with the Global-FI and better predictive performances and reliabilities than the conventional tool (Y-FI). Moreover, the volY3-FI was slightly superior to meanY3-FI in the predictive performance and reliability.

Longitudinal Changes in Overall 3D Supraspinatus Muscle Volume and Intramuscular Fatty Infiltration After Arthroscopic Rotator Cuff Repair

“…2-C) to calculate the 3D muscle and intramuscular fat volumes. The 3D FI was calculated as the percentage of intramuscular fat volume to total muscle volume 1,9,11,21,22 . This 3D measurement method has been reported to have good intra- and interobserver reliabilities 9 .…”

“…2-A), a semiautomatic segmentation program (www.itksnap.org), to stack and integrate all images for 3D reconstruction according to the reported methods in previous studies (Fig. 2-B) 9,21,22 . The 3D models of the supraspinatus muscle and fat were automatically reconstructed from all 2D binary images (Fig.…”

“…This considerable debate might be primarily attributed to the single-plane-based grading systems or quantitative methods, as the lateralization of the myotendinous unit caused by the repair immediately alters the specific magnetic resonance imaging (MRI) slice used for assessments 1,9,11,18,19 . Recent biopsy and clinical studies have determined the spatial variability in the fraction of fat within the supraspinatus and infraspinatus muscles 9,[20][21][22] . The lateralization and variability have probably confounded the assessment of the longitudinal changes in the muscle atrophy or FI, since the single 2D slice cannot represent the overall 3-dimensional (3D) volume 9,10,19 .…”

“…More importantly, intramuscular FI is still measured on the basis of single-plane protocols, which have not been demonstrated to have better than moderate intra- and interobserver reliabilities 4,6,11,14,15 . Recently, some authors have reported the advantages of 3D intramuscular FI evaluation compared with evaluation using a single plane: capture of morphologic information on all fat in the supraspinatus, with superior intra- and interobserver reliabilities 9,21,22 . However, as that method has rarely been used to analyze postoperative outcomes, quantitative 3D data revealing the longitudinal changes in supraspinatus muscle volume and intramuscular FI are scarce.…”

Natural History of Quantitative Fatty Infiltration and 3D Muscle Volume After Nonoperative Treatment of Symptomatic Rotator Cuff Tears

“…Single-slice measurements in 2-dimensional (2D) Y-views are appealing, especially in the clinical setting, but, as intramuscular fat distribution is inhomogeneous [33][34][35] , the measurements hardly correlate with the global 3D FF 28,33,[36][37][38] . For this reason, Xu et al proposed a modified assessment tool 39 consisting of the mean of 3 FF measurements on 6-point Dixon sagittal images: the scapular Y-view and 2 adjacent slices. They showed that this mean FF correlates strongly with the 3D volumetric global FF of the entire supraspinatus (SSP) muscle 39 .…”