Supraspinatus muscle elasticity measured with real time shear wave ultrasound elastography correlates with MRI spectroscopic measured amount of fatty degeneration

Institutional review board approval was acquired prior to the inception of this study, and informed consent was obtained from each patient.

Forty-two patients with history of rotator cuff tear were included in this study. Mean age of the patients was 58.8 ± 7,65 years (range from 40 to 76). Thirteen were female and 29 were male patients. Twenty-eight underwent rotator cuff repair, the time after surgery was 2.3 years (± 0.7). The other patients had a history of rotator cuff tear but were treated conservatively. Patients’ clinical features are shown in Table 1. The maximum diameter of the supraspinatus muscle was detected using conventional ultrasound (b-mode) and this area was marked using a gel capsule (Fig. 3). After detection of this area a shear wave ultra-sound measurement (SWE) of the supraspinatus muscle was performed with a Siemens Acuson S3000 ultrasound system (Siemens AG, Munich, Germany) using a linear transducer (10mHz) the SWV was assessed with the software of the ultrasound device (virtual touch tissue imaging quantification [VTIQ], Siemens Medical Solutions, Siemens AG, Munich, Germany). Tissue elasticity was measured by aligning the transducer parallel to the muscle fibers at the largest diameter of the supraspinatus muscle (Fig. 1). As the process of manually selecting data via the ultrasound system’s console has the potential to significantly introduce bias SWE was performed by one blinded radiologist (DK). The shear wave velocity (m/s) was measured at 10–15 points in the manually placed region of interest in 5 pictures trying to fully cover the muscles cross section. The forearm of the patients was placed on an armrest to avoid muscle contraction during the examination .

On the same day a standard MRI scan of the shoulder was obtained. The MR-spectroscopy (SPLASH-technique (spectroscopic fast low angle shot)) and the postprocessing for quantification of the fat/water ratio was performed using a previously described technique by our workgroup [11, 17] (Fig. 4) Measuring the same area as in the ultrasound elastography was ensured with a gel capsule fixed to the patient’s skin.

All MRIs were rated according the MRI-based Goutallier Classification (oblique-sagittal t1-weighted images) by 5 raters. According to the scaling by Fuchs et al. Grade 0 was defined as no fatty infiltration, grade 1 as some fatty streaking of the supraspinatus, grade 2 as less fat than muscle, grade 3 as equal amounts of fat and muscle, and grade 4 as more fat than muscle [9]. All raters were orthopedic surgeons with clinical focus in shoulder surgery.

The thickness of the overlying tissue was directly measured in oblique-sagittal t1-weighted images using the clinical PACS System.

The correlation between the methods was calculated using Pearson’s rank correlation test (ρ). Degrees of reliability were set to the scale determined by Landis and Koch [19]. A statistical power analysis was performed using G*Power 3.1 [7]. Power analysis revealed a minimum number of Patients of n = 32 to obtain a power of 80% for finding a significant difference between a Pearson’s ρ of 0.65 an 0.85 (β > 0.8).