What signifies a positive result in O'Brien's test?

O'Brien's test is a clinical assessment used to identify a labral tear, particularly in the shoulder. A positive result in this test is characterized by the presence of pain when the shoulder is in an internally rotated position with the arm elevated in front, typically at around 90 degrees of flexion.

The rationality behind this test is based on the mechanics of shoulder motion and the common injuries associated with the shoulder joint, particularly the labrum. In a positive O'Brien's test, the internal rotation causes a mechanical impingement or stress in the area of the labrum, eliciting pain. When the shoulder is positioned in this way and pain is reproduced, it strongly suggests the presence of a labral injury.

Additionally, if the pain is alleviated when moving the arm into an externall rotated position, that further substantiates the test's effectiveness, as it reduces the impinging forces on the labrum.

In summary, pain during the internally rotated position while the arm is elevated is indicative of a labral lesion, making it a key sign in the context of O'Brien's test.