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Shah K.1, Brennan M.1, Bucantis J.1, Kust E.1, Washatka J.1, McClure P.1
1Arcadia University, Physical Therapy, Glenside, United States
Background: Muscle atrophy has been reported in patients with rotator cuff pathology. Presumably, exercise yields positive changes in muscle structure which may be associated with improved strength and function, though this has not been well-studied. Ultrasound (US) imaging has been used extensively for examining shoulder pathology. However, reliability of shoulder muscle size measurement with US is not well established. A few studies have reported variable reliability, 0.45-0.88, of rotator cuff muscle size using US. Further, the relationship between muscle cross-sectional area (CSA) and torque measures is not known.
Purpose: The aim of this study was to establish the reliability of shoulder muscle size using US, examine side-to-side differences and to determine the relationship between size and torque.
Methods: Supraspinatus and infraspinatus muscle size of both shoulders was obtained using US. Multiple scans were performed a mean of 1.9 days apart. Supraspinatus images were captured in the transverse view at the suprascapular notch identified with the US with subject in a seated position and arm resting on a pillow. The infraspinatus muscle CSA was determined with subject in prone position. Using bony landmarks and a custom made template to standardize the measurement location, serial images of the muscle were obtained and spliced to calculate the CSA. Three scans were performed at each session and averaged. Size measurements (cm2) were then performed using ImageJ analysis. Abduction and external rotation torque (normalized to body weight) was calculated using force measures from a hand-held dynamometer and moment arm length.
Results: 19 asymptomatic, healthy adults (mean age 30.8 years (11.8); 12M/7F) were included in this study. The ICC, SEM and MDC values for the between-session reliability for muscle size measurements were as follows: supraspinatus ICC 0.97 (0.93-0.99, 95%CI) SEM 0.3, MDC95 0.8 and infraspinatus ICC 0.95 (0.86-0.98, 95% CI), SEM 1.3, MDC95 3.1. The mean CSA for supraspinatus and infraspinatus for the right arm (7.3 (1.7) and 16.5 (5.7)) were not different, p>0.05, from the left arm (6.9 (1.5) and 14.3 (5.5)). The abduction torque and external rotation torque were not strongly related to the muscle size measurements (range of r values = 0.18 to 0.37).
Conclusion(s): The results of this study show excellent reliability for supraspinatus and infraspinatus muscle CSA measurements. Since there was no difference between the muscle CSA between sides, the contralateral arm measures may be used as an index. Correlation between muscle size and torque was not strong. Future steps include examining the change in muscle size in response to an exercise program.
Implications: Understanding mechanisms associated with pathology and response to exercise is important to guide practice. Muscle size represents a key variable and US offers a feasible and reliable measurement method. Further examination of the relationship between muscle size changes, and functional changes is warranted.
Funding acknowledgements: None
Topic: Musculoskeletal: upper limb
Ethics approval: This study was approved by the Institutional Review Board (#15-11-28) at Arcadia University, Glenside, PA, USA.
All authors, affiliations and abstracts have been published as submitted.
