| Summary: | Purpose To investigate the effect of patient positioning on tendinosis grade, visible range, and infraspinatus
tendon (IST) thickness, and to determine the feasibility of internal rotation (IR) position to
assess IST on ultrasound (US).
Materials and Methods This study included 52 shoulders of 48 subjects who were evaluated for IST
in three different positions: neutral position (N), IR, and position with the ipsilateral hand on the
contralateral shoulder (HC). Two radiologists retrospectively graded IST tendinosis from grade 0 to
grade 3 and the visible range from grade 1 to grade 4. The thickness of the IST was measured by
another radiologist with a short-axis view. A generalized estimating equation was used for statistical
analysis.
Results The tendinosis grades were higher in the HC position than in the IR position, with a cumulative
odds ratio of 2.087 (p = 0.004, 95% confidence interval [CI]: 1.268–3.433). The tendinosis grades in
the HC position (p = 0.370) and IR position (p = 0.146) were not significantly different from those in
the N position. The overall difference in IST thickness was significant (p < 0.001), but the visible range (p = 0.530) was not significantly different according to position.
Conclusion Patient positioning significantly affected the grade of tendinosis and thickness but not
the visible range of the IST. The IR position is a feasible position for assessing the IST on US.
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