What does the empty cans test evaluate for?

The Empty Can Test Evaluates for Supraspinatus Tendon Pathology

The empty can test primarily evaluates for supraspinatus tendon tears or dysfunction, though it lacks selectivity for isolating supraspinatus activity from other shoulder muscles. This test is commonly used in clinical practice as part of the shoulder examination to assess rotator cuff pathology.

Test Technique and Positioning

• The test is performed with the patient's arm positioned at:
  • 90 degrees of abduction
  • Full internal rotation (thumb pointing downward - "emptying a can")
  • 30 degrees of forward flexion
• The examiner applies resistance while the patient attempts to maintain this position

Diagnostic Value and Limitations

Sensitivity and Specificity

• The empty can test shows good sensitivity (88.6%) but limited specificity (58.8%) for supraspinatus tendon tears 1
• It has a higher risk of false positives compared to some other tests
• The test cannot reliably distinguish between partial-thickness and full-thickness tears 2

Muscle Activation Patterns

• Despite its widespread use, the empty can test does not selectively activate the supraspinatus muscle as once believed
• EMG studies demonstrate that during the test:
  • At least 8-9 other shoulder muscles show similar activation levels as the supraspinatus 3
  • The infraspinatus and middle deltoid are significantly activated during this maneuver 4
  • The test fails to isolate supraspinatus activity from other rotator cuff muscles 4

Interpretation of Results

• A positive test is indicated by:
  • Weakness (considered the most diagnostically accurate interpretation) 2
  • Pain (less specific indicator)
  • Both pain and weakness together
• Weakness shows better diagnostic precision than pain or using both criteria together 2

Improving Diagnostic Accuracy

• Combining multiple tests improves diagnostic value:
  • The combination of empty can, full can, and zero-degree abduction tests shows the best diagnostic accuracy (AUC 0.795) 2
  • Using at least 3 tests together significantly improves diagnostic value compared to any single test

Alternative Testing Positions

• Recent research suggests better isolation of supraspinatus activity in the position of:
  • 30° shoulder abduction
  • 30° horizontal flexion
  • External humeral rotation 5
• This alternative position demonstrates a higher supraspinatus-to-deltoid ratio (3.4) compared to the classic empty can position (0.8) 5

Clinical Implications

• While widely used, clinicians should be aware that the empty can test is not specific to supraspinatus pathology
• Test results should be interpreted in conjunction with other clinical findings and imaging studies
• The test is more accurate for detecting larger supraspinatus tears (>1 cm) than smaller ones 2
• Consider using multiple shoulder tests rather than relying on the empty can test alone

The empty can test remains a valuable component of the shoulder examination despite its limitations in isolating supraspinatus activity, particularly when combined with other clinical tests and appropriate imaging studies.