Background. Understanding the functional role of the supraspinatus (SSP) and deltoid muscles during shoulder motion is a basis for understanding rotator cuff pathology and for the development of appropriate rehabilitation protocols. The purpose of this study was to elucidate the coordination, focusing on activation timing, of the sub-regions of the SSP muscle and of the middle region of deltoid muscle during scapular plane abduction (scaption) using shear wave elastography (SWE). Methods. Twelve healthy male volunteers without any restrictions in their shoulder joints, altered posture or scapulothoracic dyskinesis were recruited to this study. Participants were instructed to sit on a chair with their back against the back-rest. Measurements of the non-dominant arm were obtained at rest and during isometric contraction at a neutral position and every 15° interval from 30° to 150° during scaption. Muscle activity was defined as the difference in SWE-measured stiffness between resting outcomes and those measured during muscle contraction (∆E = stiffness during contraction -stiffness at rest). Results. The anterior-middle sub-region of the SSP muscle and the middle region of the deltoid muscle presented a mountain-shape type curve with peaks at 60° (146.2 ± 26.6 kPa) and at 90° (142.0 ± 25.9 kPa), respectively. The anterior-superficial sub-region of SSP muscle peaked at 30° (102.1 ± 27.4 kPa), linearly decreasing thereafter. Conclusions. The anterior-superficial sub-region of the SSP muscle showed activity during initial range of motion, while the anterior-middle sub-region showed activity at early mid-range. On the contrary, the middle region of the deltoid muscle showed increased SWE-measured activity at late mid-range. A more refined approach focusing on the muscles sub-regions may lead to improved rehabilitation protocols.

Purpose The purpose of this study was to investigate if the three partitions (superior, middle, and inferior partitions) of the infraspinatus muscle previously described in anatomical studies will present different behavior during scapular plane abduction (scaption) as described using shear-wave elastography, especially during initial range of motion. Methods Eight volunteers held their arm against gravity 15° intervals from 30° to 150° in scaption. Shear-wave elastography was implemented at each position to measure shear modulus at rest and during muscle contraction, as a surrogate for muscle stiffness, of each partition. Muscle activity was defined as the difference in stiffness values between the resting positions and those during muscle contraction (ΔE = stiffness at contraction—stiffness at rest). Results The activity value for the middle partition was 25.1 ± 10.8 kPa at 30° and increased up to 105° (52.2 ± 10.8 kPa), with a subsequent decrease at larger angle positions (p < .001). The superior partition showed a flatter and constant behavior with smaller activity values except at higher angles (p < .001). Peak activity values for the superior partition were observed at 135° (23.0 ± 12.0 kPa). Increase activity for inferior partition began at 60° and showed a peak at 135° (p < .001; 32.9 ± 13.8 kPa). Conclusion Stiffness measured using shear-wave elastography in each partition of the infraspinatus muscle demonstrated different behavior between these partitions during scaption. The middle partition generated force throughout scaption, while the superior and inferior partitions exerted force at end range.

Background The purpose of this study was to evaluate the effect of fat infiltration, tear size, and post-operative tendon integrity, on post-operative contractility. Methods Thirty-five patients who underwent rotator cuff repair were included. The fat infiltration, tear size, and post-operative tendon integrity were evaluated by Goutallier stage, Cofield classification, and Sugaya classification, respectively. The muscle elasticity at rest and at contraction was assessed by real-time tissue elastography pre- and one-year post-operatively. We defined the difference in elasticity between at rest and at contraction as the activity value which reflects muscle contractility. Results The activity value in patients with Sugaya Type I tended to increase regardless of Cofield classification, whereas those with Sugaya Type III and IV tended to decrease. While the activity value in the patients classified as stage 1 and Type I tended to increase, patients classified as stage 2 showed decreased or constant in contractility even in those subjects classified as Type I. Stepwise multiple regression analysis showed both pre- (p = 0.004, r = -0.47) and post-operative activity values (p = 0.022, r = -0.39) to be significantly correlated only with the Goutallier stage. Conclusion Multiple regression analysis indicated only the Goutallier stage was a significant independent factor for contractility of the supraspinatus muscle. Supraspinatus muscle contractility in patients classified as Types III and IV based on the Sugaya classification tended to decrease post-operatively, while patients whose contractility increased post-operatively were characterized by having a Type I tendon integrity.

Ultrasound elastography has been used to evaluate the skeletal muscle stiffness as a biomarker for sarcopenia assessment. However, there is no consensus with respect to the size and location of the region of interest in assessing such fat infiltrated muscle. The objective of this study was to determine which cross-sectional area should be measured in torn disuse muscle with fat infiltration to accurately measure muscle activity using real-time tissue elastography (RTE). Methods: Twenty-seven patients, whose rotator cuff muscle with torn tendon was successfully repaired, were followed by programmed rehabilitation. RTE measurements of the supraspinatus muscle were obtained during muscle contraction before and one-year after surgery so that the activity value was defined as the difference between elastography measurements at rest and elastography measurements during contraction. Given that the patients with successfully repaired and completed rehabilitation showed an increased activity value, the sensitivity for three regions of interest; posterior portion of the anterior-middle subregion (AM-p), anterior region (AR), and whole cross-sectional area of the supraspinatus (whole) were compared with the number of patients showing an increase in activity values as sensitivity analysis. Results: The sensitivity showing an increase in activity values was 74.1% for the AM-p area, 70.4% for the AR area, and 81.5% for the whole area. Intraclass correlation coefficient 1,3 was 0.87-0.97 for the AM-p area, 0.88-0.98 for the AR area and 0.92-0.99 for the whole area. Conclusion:The whole cross-sectional area is suitable to measure muscle activity in muscle with fat infiltration. The results in this study will provide some beneficial information when ultrasound elastography is used for the assessment of sarcopenia muscle with fat infiltration.

No abstract