What does a positive empty can test indicate?

Empty Can Test: Diagnostic Indicator for Supraspinatus Tendon Pathology

A positive empty can test indicates a supraspinatus tendon tear when interpreted by the presence of muscle weakness during the maneuver, not pain alone. 1, 2

What the Test Indicates

The empty can test is a clinical examination maneuver used to assess the integrity of the supraspinatus tendon, one of the four rotator cuff muscles. When positive, it suggests:

• Supraspinatus tendon tear (either full-thickness or partial-thickness) 1, 3
• Rotator cuff pathology requiring further diagnostic workup 2

Critical Interpretation: Weakness vs. Pain

Muscle weakness is the gold standard criterion for interpreting a positive test result, not pain provocation. 1, 2 The evidence clearly demonstrates:

• Weakness interpretation: 70-75% accuracy for detecting supraspinatus tears 1, 2
• Pain interpretation: Significantly lower diagnostic precision and should not be used as the primary positive indicator 1
• Pain or weakness combined: Lower specificity and accuracy compared to weakness alone 2

Important Caveat: Pain as a Differentiating Feature

While weakness alone is the best diagnostic criterion, pain provocation during the empty can test is highly useful for distinguishing rotator cuff tears from cervical spondylotic amyotrophy (CSA), which can mimic shoulder pathology. 4 Pain during the test has 88.9% sensitivity and 96.0% specificity for differentiating rotator cuff tears from CSA, whereas weakness cannot differentiate between these conditions (0-4% specificity). 4

Diagnostic Limitations

The empty can test has several important limitations:

• Cannot distinguish between partial- and full-thickness tears - both produce positive results with similar frequency 1, 3
• Severity-dependent sensitivity - tears larger than 1 cm show better diagnostic precision 1
• Higher pain provocation compared to the full can test (50% vs. 43%), which may cause patient discomfort without improving diagnostic accuracy 2

Optimal Testing Strategy

Combining multiple tests significantly improves diagnostic accuracy. 1 The recommended approach:

• Use at least 3 tests together: empty can + full can + zero-degree abduction test achieves the best diagnostic performance (AUC 0.795) 1
• Interpret weakness as the positive finding in all three tests 1, 2
• Consider the full can test as equivalent or superior - it has comparable accuracy (75% vs. 70%) with less pain provocation 2

Clinical Algorithm

When performing the empty can test:

1. Position: Arm elevated to 90° in the scapular plane (30-45° anterior to coronal plane), internally rotated with thumb pointing down
2. Maneuver: Apply downward resistance while patient attempts to maintain position
3. Positive result: Inability to resist downward pressure (weakness) 1, 2
4. Document pain separately: Note if pain occurs, as this helps differentiate from cervical pathology 4
5. Confirm with additional tests: Perform full can and zero-degree abduction tests 1
6. Next step: Positive findings warrant imaging (MRI) for definitive diagnosis 2, 3

Common Pitfall

Do not interpret pain alone as a positive test result. 1, 2 Pain during the empty can test occurs in approximately 50% of patients but has poor diagnostic accuracy when used as the sole criterion. 2 This leads to false-positive results and unnecessary imaging or interventions.