What position should the humerus be in during the Empty Can Test?

The Empty Can Test is designed to assess the integrity of the supraspinatus muscle, which is one of the four rotator cuff muscles responsible for shoulder stabilization and movement. The correct position for the humerus during this test is abducted to 90 degrees in the scapular plane. This positioning helps to isolate the supraspinatus by ensuring that the arm's alignment is optimal for eliciting a response from this particular muscle.

The scapular plane is about 30 degrees forward from the frontal plane and is critical for effectively placing the supraspinatus in a position where it is most active. Abducting to 90 degrees allows for proper mechanics and minimizes the involvement of other muscles, providing a clearer assessment of the supraspinatus.

In contrast, other positions such as abduction directly to the frontal plane or adduction with the arm at the side do not effectively target the supraspinatus muscle in the same manner, which could lead to misleading test results. Similarly, extending the arm above the head would likely recruit other muscle groups, thus compromising the specificity of the test for supraspinatus involvement.