Study on the effects of arm abduction angle and cushion support during sonographic examination on the stiffness of supraspinatus muscle of sonographers using shear wave elastography.

OBJECTIVES: The incidence of work-related musculoskeletal disorder remains high in sonography. The aims of this study are to determine the changes in muscle stiffness with different arm abduction angles, and to investigate the effect of cushion support on reducing muscle load in the supraspinatus when sonographers scan with the arm abducted to different angles.

METHODS: This is a prospective crossover study. Twenty-three healthy female subjects aged between 20 and 23 years were included. Subjects were instructed to simulate performing standardized abdominal ultrasound scans. The changes in muscle stiffness of supraspinatus, measured as shear modulus, at rest and at 30°, 45°, and 60° arm abduction angles with and without cushion support were evaluated using shear-wave elastography. Styrofoam support was used for the cushion support.

RESULTS: Mean shear moduli of supraspinatus were 27.77 ± 5.84 kPa at rest and 41.63 ± 7.09 kPa, 63.88 ± 14.43 kPa, and 89.76 ± 16.55 kPa for 30°, 45°, and 60° arm abduction respectively, which corresponds to 53%, 116% increase in muscle stiffness when scanning arm abducted from 30° to 45° and 60° (p < .001). After applying cushion support, shear moduli dropped to 24.04 ± 5.60 kPa, 31.98 ± 6.06 kPa, 37.47 ± 5.61 kPa for arm abducted to 30°, 45°, and 60° respectively (p < .001). The muscle stiffnesses between 30° abduction without support and 60° abduction with support had no significant difference (p > .05).

CONCLUSIONS: Muscle stiffness of supraspinatus increased with increasing arm abduction angle during ultrasound scanning. Utilizing cushion support underneath the arm was effective in reducing muscle stiffness in supraspinatus. Our results provide scientific justification on postural modifications for sonographers.