The O’Brien’s Test, also commonly known as the Active Compression Test, is a standardized physical examination maneuver employed by healthcare professionals to help determine the source of shoulder pain. This diagnostic tool is categorized as a provocative test, meaning it is designed to place specific stress on structures within the shoulder joint to reproduce the patient’s symptoms. The test itself involves a distinct two-part procedure that allows the examiner to compare the patient’s response under different rotational loads on the shoulder. This comparison ultimately helps differentiate between two of the most common pathologies affecting the shoulder joint.
How the Test is Performed
The O’Brien’s Test is performed with the patient standing or seated, and it requires the use of two specific arm positions against a resistance applied by the examiner. In the first phase, the patient raises the affected arm forward to 90 degrees of flexion, positioning it approximately 10 to 15 degrees inward across the body, known as horizontal adduction. The patient then fully internally rotates their arm, turning the palm downward so the thumb points toward the floor. In this position, the clinician applies a downward force to the patient’s arm, and the patient is instructed to resist this pressure.
The second phase of the test involves the patient rotating the arm into full external rotation, which turns the palm upward so the thumb points away from the body. The patient maintains the same 90-degree flexed and slightly adducted position throughout this change in rotation. Again, the clinician applies the exact same downward force to the arm, and the patient resists. A positive result for a specific pathology is recorded if the pain or other symptoms experienced during the first phase (thumb down) are significantly reduced during the second phase (thumb up).
Primary Finding: Superior Labral Tears
The primary pathology the O’Brien’s Test is designed to detect is a Superior Labrum Anterior to Posterior (SLAP) lesion, a tear in the labrum, the cartilage ring surrounding the shoulder socket. These lesions frequently involve the attachment point of the long head of the biceps tendon, which anchors directly into the superior aspect of the labrum. The unique mechanics of the test are intended to stress this specific attachment site.
During the first phase of the test, when the arm is internally rotated and slightly adducted, the biceps tendon creates a “peel-back” force on the already torn superior labrum. This action is thought to mechanically destabilize the labral fragment, which then provokes the patient’s pain, often described as a deep, internal ache or clicking sensation within the glenohumeral joint. This internal rotation and adduction position specifically increases shear and compressive forces on the superior labrum.
When the arm is moved into external rotation for the second phase, the tension and peel-back force on the biceps-labral complex are relieved. This reduction in mechanical stress on the torn tissue explains why a patient with a true SLAP lesion will experience a marked reduction of their deep shoulder pain in this second position. This pain relief is the characteristic indicator that the patient’s symptoms are originating from the labrum rather than another structure. The original description of the test suggested high diagnostic accuracy, though later studies have shown that the sensitivity, or the ability to correctly identify a SLAP tear, varies widely across different patient populations.
Secondary Finding: Acromioclavicular Joint Issues
While the test is most recognized for its association with SLAP lesions, it is also a valuable tool for identifying pathology in the Acromioclavicular (AC) joint, where the collarbone meets the highest point of the shoulder blade. The specific arm position used in the O’Brien’s Test, particularly the combination of 90 degrees of flexion and horizontal adduction, is known to maximally compress and load the AC joint. This compression can reproduce pain if the joint is arthritic, inflamed, or sprained.
Differentiating between a SLAP tear and an AC joint problem using this test relies heavily on the patient’s description of the pain location. A patient with an AC joint issue will report pain that is localized and superficial, directly over the top of the shoulder. Crucially, the pain caused by AC joint compression is often not relieved, or is only slightly relieved, when the arm is externally rotated in the second phase of the test. The compression applied to the joint remains high regardless of the rotational change, meaning the painful stimulus persists.
Diagnostic Value and Alternatives
The O’Brien’s Test is considered a screening tool within a broader physical examination and is rarely definitive on its own for a diagnosis. The diagnostic accuracy of any single physical maneuver is limited and must be interpreted within the context of a patient’s complete medical history and other symptoms. For instance, the sensitivity and specificity values reported in the scientific literature for detecting a SLAP tear show a large range, suggesting that the test can sometimes produce false positive or false negative results.
Because of these inherent limitations, clinicians will often perform a battery of tests rather than relying on a single maneuver. Other procedures, such as the Speed’s Test or the Biceps Load II Test, are frequently used alongside the O’Brien’s Test to help confirm or refute a suspected diagnosis. If the physical examination suggests a labral or AC joint injury, the physician will order a Magnetic Resonance Imaging (MRI) scan to confirm the precise location and extent of the injury before determining a final treatment plan.