O'Brien's Test (SLAP): how to assess the labrum and AC joint

O'Brien's test, also known as the Active Compression Test, is one of the most interesting shoulder tests because a single movement can give you clues about two different structures: the glenoid labrum (SLAP lesions) and the acromioclavicular joint. It's especially useful in throwing sports, weightlifting, and contact sports.

What does this test measure?

O'Brien's test aims to reproduce pain through compression and shear of:

• The superior labrum (SLAP lesions - Superior Labrum Anterior to Posterior), by comparing the position with the arm in internal rotation (pronation) vs. external rotation (supination)
• The acromioclavicular (AC) joint, if the pain is located specifically on top of the shoulder, near the distal clavicle

The key to the test is comparing where the pain occurs in each of the two forearm positions.

Equipment needed

• None

Step-by-step protocol

1. The person stands, with the arm to be tested raised to 90° of flexion and adducted about 10-15° toward the midline of the body
2. First position: the arm in full internal rotation (thumb pointing down, as if emptying a can)
3. Apply downward resistance to the arm, asking the person to resist ("push up against my hand")
4. Second position: repeat the same movement, but with the arm in full external rotation (palm up, supinated)
5. Apply the same downward resistance
6. Compare the pain between both positions and note its exact location (inside the shoulder vs. top/AC joint)

Common mistakes

• Not maintaining the 10-15° of adduction (the test is performed in the "O'Brien plane," not in pure abduction)
• Not specifically asking where the pain is in each position (this is the most important part of the test)
• Confusing generalized fatigue discomfort with the specific pain the test is looking for

How to interpret the result

Result	Interpretation
No pain in either position	Negative
Pain inside the shoulder in internal rotation, that improves or disappears in external rotation	Positive for the labrum (suggests SLAP lesion)
Pain located on top of the shoulder / AC joint, present in both positions (doesn't change with rotation)	Positive for AC joint pathology

The sensitivity and specificity of O'Brien's test for SLAP lesions vary across studies (moderate-to-high sensitivity, more limited specificity), so it's rarely used in isolation to confirm a labral lesion.

It's a screening test: it points you toward where to focus your suspicion, but confirming a SLAP lesion requires imaging (MRI, ideally with contrast) and, in many cases, arthroscopy.

Related tests

O'Brien's test works well alongside:

• Yergason's test — the long head of the biceps inserts into the superior labrum, so both tests can be related in SLAP lesions
• Apprehension test — if you also suspect anterior instability associated with the labral lesion

Why tracking it matters

Labral lesions and AC joint pathology call for very different training approaches: while an irritated AC joint can improve by avoiding certain horizontal ranges of motion, a SLAP lesion may require completely modifying throwing or pulling patterns. With Movalytics you can log O'Brien's test result specifying the location of the pain (labrum vs. AC) and the side, so that detail is available when you adjust programming.

Frequently asked questions

Is O'Brien's test very painful? It can cause localized discomfort or pain if there's pathology, but it shouldn't be intense or last long. If the pain is very sharp, stop the test. Why compare internal rotation with external rotation? Because in internal rotation the biceps tendon and superior labrum are more compressed/tensioned, while in external rotation that tension is reduced. If the pain disappears when rotating externally, it points more toward the labrum/biceps than another structure. Does a positive O'Brien's test for the AC joint mean there's arthritis? Not necessarily established arthritis, but it does suggest irritation or overload of the acromioclavicular joint, which can have various causes (overuse, prior trauma, degenerative changes).