A positive O’Brien’s Test, also known as the Active Compression Test, suggests specific internal pathology within the shoulder joint. This maneuver helps pinpoint the source of a patient’s shoulder pain. It is a strong clinical indicator pointing toward damage involving the superior labrum or the acromioclavicular (AC) joint. A positive result must be interpreted alongside a patient’s symptoms and history to guide further diagnostic steps.
The Primary Indication: Superior Labrum Tears
The primary meaning of a positive O’Brien’s test is a Superior Labrum Anterior-Posterior (SLAP) tear. The labrum is a ring of specialized cartilage that lines the rim of the shoulder socket, serving to deepen the socket and stabilize the joint. SLAP tears occur in the top portion of this ring, spanning from the front (anterior) to the back (posterior) of the socket.
This area is susceptible to injury because the long head of the biceps tendon anchors directly into the superior labrum. When the test is performed, mechanical stress transmitted through the arm pulls on this biceps-labral complex. In a damaged shoulder, this tension causes the torn labrum flap to peel back or become compressed, generating pain.
The pain from a SLAP tear is typically described as deep within the shoulder joint and difficult for the patient to localize. Injuries result from a traumatic event, such as a fall onto an outstretched arm, or from repetitive overhead motions common in athletes. The O’Brien’s test is designed to provoke this mechanical irritation, helping identify this specific type of labral damage.
Understanding the Procedure and Pain Generation
The O’Brien’s test is a two-part maneuver comparing the patient’s pain response in two distinct arm positions.
The first phase involves the patient extending the arm forward to 90 degrees, bringing it slightly across the body (adduction), and maximally rotating the arm inward so the thumb points down. The clinician applies a downward force against the patient’s resistance in this internally rotated position. This combination of flexion, adduction, and internal rotation places maximum shear and compression forces on the superior labrum. If the patient experiences pain or a painful clicking sensation, it suggests a problem is being stressed.
In the second phase, the arm is held in the same flexed and adducted position, but fully rotated outward so the palm faces up. The clinician again applies a downward force against resistance. A positive test requires that the pain felt in the “thumb-down” position is significantly reduced or eliminated in this “palm-up” position. This reduction occurs because external rotation relieves the mechanical stress on the labrum, confirming the initial pain was provoked by internal rotation.
Alternative Finding: Acromioclavicular Joint Pathology
While strongly associated with labral tears, a positive O’Brien’s test can also indicate pathology within the Acromioclavicular (AC) joint. The AC joint is located on the very top of the shoulder, where the collarbone (clavicle) meets the acromion. The test is designed to maximally load and compress both the superior labrum and the AC joint.
Distinguishing between these two sources of pain relies on the patient’s description of the pain location. If the pain is reported as superficial and localized directly on top of the shoulder, it indicates an AC joint issue, such as arthritis or inflammation. Conversely, deep-seated pain that is hard to pinpoint within the shoulder joint suggests a labral injury. This distinction guides the clinician toward the correct source of discomfort.
Next Steps Following a Positive Result
A positive O’Brien’s test is a clinical indicator, not a definitive diagnosis, meaning further steps are necessary to confirm the specific pathology. The finding increases suspicion of a SLAP tear or AC joint problem, prompting advanced imaging.
The most common follow-up is a Magnetic Resonance Imaging (MRI) scan, often performed with a contrast dye injection, known as an MR Arthrogram. The contrast dye helps outline the labrum and cartilage, making tears or defects more visible than with a standard MRI.
Once the injury is confirmed and its severity assessed, initial management focuses on non-operative treatments. This includes rest, non-steroidal anti-inflammatory drugs (NSAIDs), and physical therapy to restore strength and range of motion. Surgical consultation may be required if the pathology is severe, such as a large or unstable labral tear, or if non-operative measures fail to relieve symptoms. The course of treatment depends entirely on the specific diagnosis confirmed by imaging and the patient’s level of pain and functional impairment.