Drop Arm Test: Diagnostic Significance
A positive drop arm test is most suggestive of a supraspinatus tear, as this test specifically evaluates the integrity and function of the supraspinatus tendon by assessing the patient's ability to eccentrically control shoulder abduction.
Understanding the Drop Arm Test
The drop arm test involves passively abducting the patient's arm to 90 degrees, then releasing it and asking the patient to slowly lower the arm back to neutral position. When this maneuver elicits significant pain or the patient cannot control the descent (the arm "drops"), it indicates supraspinatus pathology 1, 2.
Diagnostic Performance
Specificity for Supraspinatus Tears
The drop arm test demonstrates exceptionally high specificity for detecting supraspinatus tears:
- Specificity ranges from 0.93 to 0.99 across multiple studies, making it one of the most specific tests for rotator cuff pathology 1, 2
- The test has a positive predictive value of 0.97, meaning when positive, there is a 97% probability that a supraspinatus tear is present 2
- The diagnostic odds ratio is particularly strong when combined with other tests like the Neer sign 1
Distinguishing Full-Thickness from Partial Tears
The drop arm test shows equal specificity (0.98) for both partial and full-thickness tears, making it reliable across the spectrum of rotator cuff pathology 2. The combination of the painful arc sign, drop arm sign, and infraspinatus muscle test produces the best post-test probability (91%) for full-thickness rotator cuff tears 3.
Why Not the Other Options?
Subacromial Impingement
While subacromial impingement can cause pain with shoulder movement, the Neer and Hawkins tests are more specific for impingement syndrome rather than the drop arm test 3. The drop arm test specifically assesses tendon integrity, not just impingement 1.
Osteoarthritis of Glenohumeral Joint
Glenohumeral osteoarthritis typically presents with global loss of range of motion and pain at end-range, not the specific inability to control eccentric abduction that characterizes a positive drop arm test 4.
Acromioclavicular Ligament Tear
AC joint pathology is better assessed with the cross-body adduction test, which stresses the AC joint specifically 3. The drop arm test does not isolate AC joint structures.
Distal Clavicular Fracture
Fractures would be evident on plain radiographs and would present with localized tenderness, deformity, and crepitus rather than the specific functional deficit seen with the drop arm test 4, 5.
Clinical Interpretation Considerations
Sensitivity Limitations
The drop arm test has relatively low sensitivity (0.19-0.73), meaning a negative test does not rule out a supraspinatus tear 1, 2, 6. The test is most useful when positive, not when negative.
Optimal Positivity Criteria
The test should be considered positive when there is pain associated with weakness or inability to control the descent, as this combination shows the highest diagnostic precision 1, 7.
Next Steps After Positive Test
When the drop arm test is positive, MRI without contrast or ultrasound (if local expertise available) should be obtained to confirm the diagnosis and assess tear characteristics including size, retraction, muscle atrophy, and fatty infiltration 4, 8. These imaging findings are critical for determining whether conservative management or surgical intervention is appropriate 8.
The American College of Radiology rates both MRI without contrast and ultrasound as 9/9 for appropriateness in evaluating suspected rotator cuff pathology 4, 8.