The preferable shoulder position can isolate supraspinatus activity superior to the classic empty can test: an electromyographic study

Review written by Dr Angela Cadogan info

Key Points

  1. Shoulder positions with lower degrees of abduction and horizontal flexion are more specific to supraspinatus (SSP) function than to deltoid function.
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BACKGROUND & OBJECTIVE

Rotator cuff tears, particularly involving the supraspinatus (SSP) tendon, are a common cause of chronic shoulder disability. Some tears, such as traumatic rotator cuff tears, may require early surgical repair where early identification is important to avoid delays in accessing appropriate treatment.

The clinical evaluation of suspected SSP tears relies on muscle strength tests and there are also several ‘special’ tests including the "empty can" (EC) and "full can" (FC) tests that are commonly used in the diagnosis of rotator cuff tears. However, the diagnostic accuracy of these tests remains variable at best (1). One of the reasons for this may be the inability to isolate the SSP from deltoid during the test which may ‘mask’ pain or weakness of the SSP.

This study aimed to determine the shoulder position that best isolates SSP activity from deltoid activity and evaluate the electromyographic (EMG) activity of shoulder muscles during resisted abduction in different positions.

The diagnostic accuracy of ‘special’ tests including the empty can and full can test remains variable at best in the diagnosis of rotator cuff tears.
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The addition of horizontal flexion and external rotation to during the manual muscle test for supraspinatus may further increase supraspinatus activation compared with deltoid.

METHODS

  • A controlled laboratory EMG study was conducted on the dominant arm of 21 healthy male participants (18-40 yrs, average age 29 yrs).
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