Fig 1.
Flow chart of subject inclusion.
RCT = rotator cuff tear, CPPD = Calcium pyrophosphate dihydrate deposition disease, RCM = rotator cuff muscles.
Fig 2.
Anatomy of shoulder girdle and measurement example for “y-position”.
Left panel shows a sagittal T1-weighted MR-arthrography image of the right shoulder of a thirty-five-year-old male, and depicts the anatomy of the shoulder girdle muscles on the level of the glenoid cavity: supraspinatus (A), infraspinatus (B), teres minor (C), subscapularis (D), deltoid (E), trapezius (F), triceps brachii (G) and teres major (H). Right panel illustrates one of the two positions where the cross-sectional area (CSA) of the rotator cuff muscles was measured: the most lateral slice, where the corpus scapulae and the spina scapulae had a Y-shaped appearance. CSA in this patient measured supraspinatus (793 mm2, A), infraspinatus (969 mm2, B), teres minor (515 mm2, C) and subscapularis (1761 mm2, D).
Fig 3.
Measurement example for “set position”.
According to Yanagisawa et al. [19] the cross-sectional area (CSA) measurement of the rotator cuff muscles was also performed at more medial slices. Left panel shows a sagittal T1-weighted MR-arthrography image of the same patient (see Figs 2 and 4) and highlights the CSA measurement of the supraspinatus (955 mm2, A) and subscapularis (2306 mm2, D) 31 mm medial to the center of the glenoid cavity. The right panel, which shows an axial PD-weighted image, indicates the suggested measurement levels for males as the medial distance from the glenoid cavity base: 6 mm for the CSA measurement of the teres minor, 31 mm for supraspinatus and subscapularis (see reference line) and 55 mm for infraspinatus.
Fig 4.
For the cross-sectional area (CSA) measurement of the deltoid muscle no reference in the literature existed. Thus, three measurement levels have been defined on axial three-dimensional gradient echo MR-arthrography sequences: CSA was measured at the upper- (2816 mm2, top panel) and lower edge (4633 mm2, bottom panel) and the middle of the glenoid (4002 mm2, middle panel). Measurements were performed on the images of the same patient (see Figs 2 and 3).
Fig 5.
Distribution of cross-sectional area measurements.
The scatterplot displays the distribution of the measured cross-sectional area (CSA) for each muscle and the respective standard deviation indicated by the margins of the bar. The y-axis describes the measured CSA in the unit mm2, whereas the x-axis describes the various measured muscles.
Table 1.
Comparison between CSA measurements in the literature.
Table shows our results for the cross-sectional area (CSA) measurements at the set position in comparison to the measurements for rotator cuff muscles by Yanagisawa et al. [19], who suggested the set position to be most appropriate for maximal CSA assessment. Yanagisawa et al. divided the results into the groups males (♂) and females (♀). Additionally, the CSA measurements of the deltoid by Meyer et al. [20] were listed. All values are mean values with the unit mm2; “±” represents the standard deviation.
Table 2.
Correlation of muscle CSA measurements for transverse force couple.
Table summarizes the results of the correlation of the cross-sectional area (CSA) measurements between the transverse force couple (Inf. = M. infraspinatus, Ter. = M. teres minor; Sub. = M. subscapularis). CSA measurements of the rotator cuff muscles were performed at two different positions: the “y-position” and the “set position”.
Table 3.
Correlation of muscle CSA measurements for craniocaudal force couple.
Table summarizes the results of the correlation of the cross-sectional area (CSA) measurements between the craniocaudal force couple (Sup. = M. supraspinatus and the deltoid (Delt. sup. = M. deltoideus, at the upper edge of glenoid; Delt. mid. = M. deltoideus, at the middle of the glenoid; Delt. inf. = M. deltoideus, at the lower edge of glenoid). CSA measurements of the rotator cuff muscles were performed at two different positions: the “y-position” and the “set position”.