What does a positive empty can and drop arm test in a shoulder exam indicate?

Positive Empty Can and Drop Arm Tests in Shoulder Examination

Positive empty can and drop arm tests in a shoulder examination strongly indicate rotator cuff pathology, specifically a tear of the supraspinatus tendon. These clinical tests are valuable components of the shoulder examination for identifying rotator cuff tears, though they should be interpreted in the context of other clinical findings.

Understanding the Tests

Empty Can Test

• The empty can test is performed with the shoulder at 90° abduction, full internal rotation, and 30° forward flexion, maintained against resistance 1
• A positive test is indicated by:
  • Weakness during resistance (though this has low specificity) 2
  • Pain provocation (which has high specificity for rotator cuff tears) 2

Drop Arm Test

• The drop arm test evaluates the patient's ability to maintain the arm in abduction and then slowly lower it
• A positive test occurs when the patient cannot control the descent of the arm or experiences significant pain 3
• This test specifically suggests a full-thickness rotator cuff tear 3

Diagnostic Accuracy

• Pain provocation during the empty can test has high specificity (96.0%) and positive predictive value (96.0%) for rotator cuff tears 2
• Muscle weakness alone during these tests is not sufficient to differentiate rotator cuff tears from other conditions like cervical spondylotic amyotrophy 2
• The specificity of these tests improves after subacromial injection, making them more valuable in clinical diagnosis 3

Important Considerations

Muscle Activation Patterns

• Contrary to previous beliefs, the empty can test does not selectively activate the supraspinatus muscle 1
• During the empty can test, EMG activity is seen in the supraspinatus, infraspinatus, and middle deltoid 1
• Recent research shows that nine other shoulder muscles are highly activated alongside supraspinatus during the empty can test 4

Clinical Implications

• These tests should be used as part of a comprehensive shoulder examination, not as standalone diagnostic tools 2, 3
• MRI without contrast is considered the gold standard imaging modality (rated 9/9 for appropriateness) for confirming rotator cuff pathology when these tests are positive 5
• Ultrasound is equally appropriate (also rated 9/9) for evaluating rotator cuff integrity when performed by experienced operators 5

Improving Diagnostic Accuracy

• Combining the empty can and drop arm tests increases both sensitivity and specificity for rotator cuff tears 3
• Pain provocation is more diagnostically valuable than weakness alone 2
• Recent research suggests that a modified position (30° shoulder abduction, 30° horizontal flexion, and external humeral rotation) may better isolate supraspinatus function than the classic empty can test 6

Management Implications

• Positive tests warrant further investigation with imaging to confirm diagnosis and determine the extent of the tear 5
• MRI can provide additional important information about tendon retraction, muscle atrophy, and fatty infiltration that guides treatment decisions 5
• These findings help determine whether conservative management or surgical intervention is appropriate 5

Remember that while these tests are valuable clinical tools, they are most useful when interpreted alongside other clinical findings and appropriate imaging studies to confirm the diagnosis and guide treatment planning.