Rotator Cuff Examination: Key Muscle Actions and Diagnostic Tests

What is the function of the rotator cuff?

The glenoid fossa is relatively shallow and the glenohumeral joint relatively unstable. Thus the purpose of the muscles of the rotator cuff is to stabilize the glenohumeral joint and to allow movement of the arm in certain directions.

Supraspinatus: Function and Empty Can Test

There are 4 muscles that comprise the rotator cuff. Supraspinatus, superior to the spine of the scapula, allows movement in the first 15 degrees of abduction. It is the most commonly injured rotator cuff muscle. It can be best isolated by the Empty Can test.

1) Abduct the straight arm to 90 degrees in the scapular plane, moving the arm forward approximately 30 degrees anterior to this plane.

2) The shoulder is then fully internally rotated by asking the patient to make a thumbs down sign.

3) The examiner than pushes down on the extended arm while the patient resists the effort.

If pain occurs with resistance, it is a positive sign and indicates inflammation of the Supraspinatus. If weakness occurs, it indicates a tear of the Supraspinatus.

Infraspinatus and Teres Minor Function and Testing

The Infraspinatus muscle resides below the scapular spinous process. It helps with external rotation of the arm.

The Teres Minor muscles also assists with external rotation of the arm. Both muscles can be tested by asking the patient to bend the elbow to 90 degrees and externally rotate the arm against examiner resistance. Pain indicates inflammation. Weakness indicates a tear.

Subscapularis Function and Testing

Subscapularis assists in internal rotation of the arm. It can be tested by apply resistance to internal rotation of the arm with elbow flexed at 90 degrees.

Mnemonic: SITS (Supraspinatus, Infraspinatus, Teres Minor, Subscapularis)