Comparison of supraspinatus sonographic thickness in empty can, full can and hug up testing positions in healthy women

Background: Rotator cuff injuries are the most common causes of shoulder pain and supraspinatus muscle is usually involved. Clinical tests are available and inexpensive tools for assessment of shoulder dysfunctions. The empty can (EC) and full can (FC) tests are considered as shoulder gold standard tests. Recently, hug up (HU) test has been developed to assess the supraspinatus. So far, no ultrasonographic study has compared supraspinatus muscle thickness in these testing positions. The present study aimed to compare the supraspinatus muscle thickness in the hug up testing position with the full can and empty can testing positions in young and healthy women. Methods: Forty healthy women (mean age 21.62±2.4 years) participated in this cross-sectional-comparative study from April to June 2018 in the Biomechanic Laboratory of Rehabilitation School, Shahid Beheshti University of Medical Sciences in Tehran, Iran. The supraspinatus muscle thickness was scanned during rest and contracted states with a 0.5 Kg weight cuff. For contracted states, (A) EC testing position: the arm was at 90º abduction in the scaption plane with the thumb-down, (B) FC testing position: the arm was maintained at 90º abduction in the scaption plane with the thumb-up, (C) HU testing position: the palm of hand was placed on the opposite shoulder with the elbow flexed. Results: The Bonferroni test showed significant differences (P<0.001) between the muscle thickness in the rest and the testing positions. The muscle thickness in the empty can testing position was significantly less than the full can testing position (P=0.001), no significant difference was found between the muscle thickness in the hug up testing position compared to the full can and empty can testing positions. Conclusion: All of the empty can, full can and hug up testing positions demonstrated increased mean muscle thickness when compared to the rest position and the greatest muscle thickness was in the full can testing position. It seems that supraspinatus muscle thickness in hug up testing position is similar with empty can and full can testing positions.