American Board of Internal Medicine (ABIM) Certification Practice Exam

A positive external rotation lag test suggests which of the following?

1. Injury to the trapezius muscle

2. Tear of supraspinatus and infraspinatus muscles

3. Rotator cuff tendinitis

4. Fracture of the humeral head

The correct answer is: Tear of supraspinatus and infraspinatus muscles

A positive external rotation lag test is indicative of a tear of the supraspinatus and infraspinatus muscles. This test evaluates the integrity of the rotator cuff, specifically the external rotators of the shoulder. During the test, the patient attempts to maintain an externally rotated position of the arm while the examiner eases the arm into this position. If the patient is unable to hold the arm in this position and the arm falls back into internal rotation, it suggests a significant weakness or dysfunction in the external rotators, which are primarily the infraspinatus and, to some extent, the supraspinatus muscles. In cases of rotator cuff tears, particularly involving the supraspinatus and infraspinatus, there is a loss of the stabilizing and mobilizing function of the muscles, which is clearly demonstrated during this lag test. The inability to maintain the external rotation highlights the compromised muscle integrity and strength in these specific muscles. Other options, such as injury to the trapezius muscle or conditions like rotator cuff tendinitis, do not typically result in a positive external rotation lag test. The trapezius muscle primarily contributes to shoulder elevation and stabilization rather than external rotation, while tendinitis often presents differently, with