O’Brien’s test and the empty can test look superficially similar, with the arm raised and the examiner pushing down, but they are designed to diagnose entirely different shoulder problems. O’Brien’s test targets labral tears (particularly SLAP lesions) and acromioclavicular joint pain, while the empty can test (also called Jobe’s test) evaluates the supraspinatus tendon, the most commonly torn part of the rotator cuff. In practice, both tests have real limitations in accuracy, and the research on their underlying mechanics has challenged some of the original reasoning behind them.
How Each Test Is Performed
The empty can test is relatively straightforward. You sit or stand with your arm raised to about 90 degrees in the scapular plane (roughly halfway between straight ahead and straight to the side), with your elbow straight and your thumb pointing downward as though you are pouring out a can. The examiner then pushes your arm downward while you resist. If you feel pain or cannot hold the position, the test is considered positive for supraspinatus pathology. A closely related version, the full can test, uses the same arm position but with the thumb pointing upward instead.
O’Brien’s test, formally called the active compression test, involves two steps. You stand with your arm flexed forward to 90 degrees, elbow fully extended, then bring the arm slightly across your body (about 10 to 15 degrees of adduction) with the thumb pointing downward. The examiner pushes down against your resistance. Then the test is repeated with your palm fully turned upward (supinated). A positive result means pain during the first position that goes away in the second.1Ewha Medical Journal. Physical examinations for older adults with shoulder pain: a narrative review Where the pain is located determines what the test implicates: pain felt deep in the shoulder suggests a labral problem, while pain localized on top of the shoulder points to the acromioclavicular (AC) joint.
Different Structures, Different Questions
The two tests exist to answer fundamentally different clinical questions. When a clinician reaches for the empty can test, they are asking: is this person’s supraspinatus tendon torn or damaged? The supraspinatus sits on top of the shoulder blade and is the rotator cuff muscle most vulnerable to wear, impingement, and tearing. The empty can position was thought to isolate this muscle’s contribution, making weakness or pain during the test a clue that the tendon is compromised.
O’Brien’s test asks a different question entirely: is there a tear in the labrum, specifically the superior labrum where the biceps tendon anchors (a SLAP lesion), or is the AC joint irritated? The logic behind the two-step approach is that internal rotation with downward loading should stress the labrum and the AC joint, while external rotation should relieve that stress. Pain that appears and disappears with these positional changes was supposed to help the clinician pinpoint the source.2Techniques in Shoulder & Elbow Surgery. Examination of the Shoulder
Because these tests target different anatomical structures, they are not interchangeable. A clinician suspecting a rotator cuff tear would not use O’Brien’s test, and one suspecting a SLAP tear would not rely on the empty can. In a thorough shoulder exam, both might appear alongside several other maneuvers, each probing a different part of a complex joint.
How Accurate Is the Empty Can Test?
The empty can test’s reputation as a go-to screening tool for supraspinatus tears rests on reasonable numbers but not outstanding ones. In one large cohort study, Jobe’s test (the empty can) had a sensitivity of about 88% and a specificity of around 62% for supraspinatus tears, with a positive likelihood ratio of 2.30.3PubMed Central. The Diagnostic Accuracy of Special Tests for Rotator Cuff Tear: The ROW Cohort Study That means the test catches most true tears (high sensitivity) but generates a fair number of false positives (moderate specificity). The full can variant, where the thumb points up, showed a different tradeoff: lower sensitivity (about 70%) but higher specificity (about 81%).3PubMed Central. The Diagnostic Accuracy of Special Tests for Rotator Cuff Tear: The ROW Cohort Study
For subacromial impingement syndrome, the empty can test performs reasonably well as a confirmatory test, with a positive likelihood ratio of about 3.9 in one study evaluating several physical exam maneuvers.4PubMed Central. Reliability and diagnostic accuracy of 5 physical examination tests and combination of tests for subacromial impingement That is helpful but not definitive on its own. A systematic review and meta-analysis of shoulder physical exam tests found that the supraspinatus test (which is essentially the empty can) achieved the highest diagnostic odds ratio among tests for full-thickness rotator cuff tears, with a sensitivity of 0.74 and specificity of 0.77, but concluded that no single physical exam test showed superior clinical performance overall.5BMC Musculoskeletal Disorders. Physical examination tests of the shoulder: a systematic review and meta-analysis of diagnostic test performance
How Accurate Is O’Brien’s Test?
O’Brien’s test has a more troubled diagnostic track record, especially for the SLAP lesions it was originally designed to detect. One study found that the O’Brien test was positive in 63% of patients being evaluated for labral pathology, but its positive predictive value was only 34%, its specificity just 31%, and its sensitivity 54%.6PubMed. The crank test, the O’Brien test, and routine magnetic resonance imaging scans in the diagnosis of labral tears Those numbers are barely better than a coin flip for ruling in a SLAP tear. Another study of recreationally active patients reported a sensitivity of 64% and overall accuracy of 54% for SLAP lesions.7PubMed Central. Clinical and arthroscopic findings in recreationally active patients
Interestingly, more recent research suggests the test may actually perform better for a different type of labral tear than the one it was intended for. A study that broke down O’Brien’s test results by tear location found the highest sensitivity (83%) and specificity (62%) for posteroinferior labral tears, not SLAP tears. The test’s diagnostic value, as measured by area under the curve, was classified as a failure for SLAP tears (0.55) and anteroinferior tears (0.22), and only poor for posteroinferior tears (0.69).8PubMed Central. The O’Brien test demonstrates a higher diagnostic value in identifying posteroinferior labral tears than superior labral anterior to posterior (SLAP) tears That is a striking finding: the test is more useful for a tear it was not specifically designed to detect.
When used to evaluate AC joint pain rather than labral tears, O’Brien’s test shows a different pattern. A systematic review found it had the highest reported specificity among AC joint tests but also the lowest reported sensitivity.9PubMed Central. A concise evidence-based physical examination for diagnosis of acromioclavicular joint pathology: a systematic review In plain terms, a negative O’Brien’s test does not reliably rule out AC joint problems, but a clearly positive test at the AC joint location may help confirm a diagnosis. Meanwhile, a study using diagnostic anesthetic injections into the AC joint found that none of the traditional AC joint tests, including O’Brien’s, could reliably discriminate between patients who did and did not have genuine AC joint pain.10PubMed Central. Shoulder pain in primary care: diagnostic accuracy of clinical examination tests for non-traumatic acromioclavicular joint pain
Why the Underlying Mechanics Are Shakier Than Expected
Both tests were designed with a specific biomechanical rationale, but research has poked significant holes in each one. The empty can test was supposed to selectively activate the supraspinatus muscle, so that weakness or pain during the test would point specifically to supraspinatus damage. EMG studies have undermined this assumption. One study recorded activity from 13 shoulder muscles during both the empty can and full can tests and found that nine and eight other shoulder muscles, respectively, were activated just as strongly as the supraspinatus.11PubMed. The ’empty can’ and ‘full can’ tests do not selectively activate supraspinatus The researchers concluded the tests do not primarily activate supraspinatus while minimizing other muscles, and therefore do not satisfy a basic requirement for being valid diagnostic tools for supraspinatus-specific pathology. A separate EMG study did find that supraspinatus and subscapularis were somewhat more active during the empty can test than during the full can test, but the difference was a matter of degree rather than isolation.12PubMed Central. Electromyographic study of rotator cuff muscle activity during full and empty can tests
O’Brien’s test faces a different but equally serious problem. The original idea was that the internally rotated, loaded position (thumb down) would tension the biceps-labral complex, stressing a torn labrum, while the externally rotated position (palm up) would relieve that tension. A study directly tested this by measuring both active biceps tension via EMG and passive tension in cadaver specimens. The result was the opposite of what was predicted: tension in the long head of the biceps was actually higher in the supposedly relieving “negative” position (palm up), directly refuting the proposed anatomic basis of the test.13PubMed. An evaluation of the anatomic basis of the O’Brien active compression test for superior labral anterior and posterior (SLAP) lesions
Cadaveric work has offered a different explanation for why the internally rotated position provokes symptoms. When shoulders were positioned to simulate O’Brien’s test, all of the internally rotated specimens showed direct contact between the lesser tuberosity and subscapularis tendon and the superior glenoid and labrum. In the externally rotated position, no such contact occurred.14PubMed. An anatomic evaluation of the active compression test So the test may provoke pain not by tensioning the biceps anchor, as originally claimed, but through a mechanical impingement effect. This matters because it means the test could easily be positive in people who have impingement or other internal contact problems but no labral tear at all, which helps explain its high false positive rate for SLAP lesions.
Pain Versus Weakness and Why It Matters
One practical issue that often gets overlooked in clinical settings is whether you interpret a positive test based on pain, weakness, or both. For the empty can test, this distinction turns out to be surprisingly consequential. One study compared pain provocation rates between the empty can and full can positions and found that the empty can provoked pain in about half of shoulders tested, while the full can provoked pain in about 43%, a difference that was not statistically significant.15PubMed. Which is more useful, the “full can test” or the “empty can test,” in detecting the torn supraspinatus tendon?
A more telling finding came from research comparing rotator cuff tears with cervical spondylotic amyotrophy, a condition where nerve compression in the neck causes shoulder muscle weakness that mimics a rotator cuff tear. Using weakness alone as the criterion for a positive empty can test yielded a specificity of 0%, meaning it could not distinguish a cuff tear from a neck problem at all. But when pain provocation was used as the criterion, specificity jumped to 96%.16PubMed Central. Muscle Weakness in the Empty and Full Can Tests Cannot Differentiate Rotator Cuff Tear from Cervical Spondylotic Amyotrophy: Pain Provocation is a Useful Finding The clinical takeaway is that an examiner who notes only that you were “weak” on the empty can test may be missing the most diagnostically useful information. Pain during the maneuver, not just an inability to hold position, is what points toward an actual rotator cuff tear rather than a problem originating in the neck.
Why Clinicians Use Test Batteries Instead of Single Tests
Given the modest accuracy of both O’Brien’s and the empty can test when used alone, experienced clinicians rarely base a diagnosis on any single maneuver. The pattern across shoulder research is consistent: combining multiple tests substantially increases sensitivity, though at the cost of specificity. In one study of recreationally active patients, using a combination of shoulder tests for SLAP lesion diagnosis raised sensitivity considerably compared with any individual test, while specificity dropped.7PubMed Central. Clinical and arthroscopic findings in recreationally active patients
For AC joint pathology, the picture is similar. The systematic review that examined AC joint tests found that no individual special test demonstrated both high sensitivity and high specificity.9PubMed Central. A concise evidence-based physical examination for diagnosis of acromioclavicular joint pathology: a systematic review The clinical reality is that a shoulder exam is a process of accumulating clues from multiple directions, not a single decisive move. A clinician might run the empty can test for the supraspinatus, Hawkins and Neer tests for impingement, O’Brien’s for the labrum and AC joint, and Speed’s test for the biceps tendon, then weigh the overall pattern against your history and the mechanism of injury.
Newer examination protocols have tried to formalize this approach. One system called the 3-Pack examination, which includes a modified active compression test alongside a throwing test and bicipital tunnel palpation, has shown better inter-rater reliability than traditional individual maneuvers for evaluating the biceps-labrum complex.17Arthroscopy Techniques. A Comprehensive Review of the Physical Examination for the Biceps-Labrum Complex of the Shoulder The idea is that bundling tests in a standardized sequence helps different examiners arrive at the same conclusion more consistently.
Examiner Reliability and What It Means for You
An underappreciated problem with shoulder physical exam tests is that two different clinicians performing the same test on the same patient may not agree on whether it is positive. In a study evaluating traditional examination maneuvers including the empty can and full can tests for biceps-labrum complex disease, inter-rater reliability was weak to moderate, with kappa coefficients ranging from about 25 to 56.17Arthroscopy Techniques. A Comprehensive Review of the Physical Examination for the Biceps-Labrum Complex of the Shoulder A kappa below 40 is generally considered poor agreement, meaning that for some of these tests, examiners frequently disagreed. The active compression test (O’Brien’s) fared better in the 3-Pack protocol, with a kappa of about 71, indicating substantially better agreement.
This reliability issue has real implications if you are being evaluated for shoulder problems. The same shoulder, examined by two different physical therapists or orthopedists, might yield different test findings depending on subtle differences in arm positioning, how much force the examiner applies, and how they interpret your pain response. This is one reason why imaging (MRI, sometimes with contrast injected into the joint) remains the gold standard for confirming labral tears and rotator cuff pathology. Physical exam tests function as a triage and screening tool, helping clinicians decide whether imaging is warranted and which structures to look at most carefully, rather than as a definitive diagnosis.
When One Test Might Be Chosen Over the Other
If your injury story involves overhead throwing, a fall onto an outstretched hand, or a sensation of catching or clicking deep in the shoulder, a clinician is more likely to reach for O’Brien’s test (along with other labral tests) because the clinical suspicion leans toward a labral problem. If the story involves gradual onset of pain with overhead activities, difficulty sleeping on that side, or weakness lifting objects away from the body, the empty can test and other rotator cuff maneuvers take priority because the suspicion is a cuff tear or tendinopathy.
Age plays a role in this decision too. Rotator cuff tears become dramatically more common with age, and the empty can test’s high sensitivity for supraspinatus tears makes it a natural choice in someone over 50 with insidious shoulder pain. SLAP lesions, by contrast, are more often seen in younger, active populations (particularly overhead athletes), which is where O’Brien’s test gets the most use. The two tests are not really competing against each other in most clinical scenarios; they occupy different lanes in the diagnostic workup.
That said, the overlap in arm position between the two tests (both involve the arm raised with the thumb down at some point) occasionally leads to confusion for patients who have had both performed in the same visit. The key distinction is the direction of arm movement and where you report pain. O’Brien’s test adds the cross-body adduction component and the two-position comparison, while the empty can test positions the arm more toward the side and focuses on resisted abduction strength and pain.
The AC Joint Complication
O’Brien’s test has an additional wrinkle that does not apply to the empty can test: it can be positive for two completely different reasons. Deep shoulder pain during the test suggests a labral issue, while pain felt at the top of the shoulder, right where the collarbone meets the acromion, suggests AC joint irritation. In theory, the examiner localizes the pain and interprets the result accordingly. In practice, patients often have trouble pinpointing exactly where their pain originates during a provocative test, and more than one structure can be painful simultaneously.
This dual-purpose nature is both a strength and a weakness. It makes O’Brien’s test a versatile screening maneuver but also increases ambiguity. A positive O’Brien’s test in a patient with both some AC joint arthritis and a possible labral tear can be difficult to parse without imaging or a diagnostic injection to isolate the pain source. The primary care study using anesthetic injections to verify AC joint pain confirmed this challenge, finding that the traditional tests could not reliably discriminate AC joint problems from other sources of shoulder pain.10PubMed Central. Shoulder pain in primary care: diagnostic accuracy of clinical examination tests for non-traumatic acromioclavicular joint pain
For the empty can test, this kind of diagnostic ambiguity is less of an issue because the test is interpreted more straightforwardly: pain or weakness during resisted elevation in the supraspinatus line implicates the supraspinatus. The trade-off is that, as the EMG research showed, the muscle activation is not nearly as specific to the supraspinatus as once believed. Still, the clinical utility of the empty can test remains broadly accepted for screening purposes, even if the theory behind why it works has shifted somewhat from the original description.