What is the significance of a positive drop arm test and how is it managed?

Drop Arm Test: Clinical Significance and Management

What the Drop Arm Test Indicates

A positive drop arm test strongly suggests a full-thickness rotator cuff tear, particularly involving the supraspinatus tendon, and warrants immediate orthopedic evaluation and imaging. 1

Diagnostic Accuracy

• The drop arm test has a positive likelihood ratio of 3.3 for detecting rotator cuff disease, meaning a positive test moderately increases the probability of disease 1
• For full-thickness tears specifically, the test demonstrates 87% sensitivity and 88% specificity 2
• However, the test has poor sensitivity (38%) when pooled across multiple studies, meaning a negative test does NOT rule out rotator cuff pathology 3
• The test is performed by passively abducting the patient's arm to 90 degrees and asking them to slowly lower it; inability to control the descent or sudden dropping of the arm constitutes a positive test 4

Clinical Context and Interpretation

No single clinical test is sufficient to diagnose rotator cuff tears—you must use combinations of tests and patient factors. 3

The most accurate diagnostic approach combines:

• Patient age (older patients have higher pretest probability) 5
• Painful arc test (positive LR 3.7 for rotator cuff disease) 1
• External rotation lag sign >40° (100% sensitivity and 92% specificity for teres minor involvement) 2
• Infraspinatus muscle strength testing 4

The combination of painful arc sign, drop arm sign, and infraspinatus muscle test yields 91% post-test probability for full-thickness rotator cuff tears 4

Management Algorithm

Immediate Assessment (Positive Drop Arm Test)

1. Perform additional rotator cuff tests immediately:

   • External rotation lag sign (if >40°, highly specific for teres minor tear) 2
   • Internal rotation lag sign (positive LR 5.6 for full-thickness tears; negative LR 0.04 effectively rules out full-thickness tears) 1
   • Painful arc test (most accurate pain provocation test with negative LR 0.36) 1
   • Infraspinatus strength testing 4

2. Obtain MRI or MR arthrography to confirm diagnosis and characterize tear size, as clinical examination alone has insufficient diagnostic accuracy (AUC 0.73) 5

3. Refer to orthopedic surgery for evaluation of surgical candidacy, particularly if:

   • Multiple positive tests suggest full-thickness tear 4
   • Patient has functional limitations 6
   • Acute traumatic onset in younger patients 6

Treatment Options Based on Tear Characteristics

For repairable full-thickness tears:

• Surgical rotator cuff repair is the standard approach 6
• Routine acromioplasty is NOT required at time of repair—two level II studies showed no benefit in postoperative functional outcomes (ASES scores, Constant-Murley scores, DASH scores) 6

For irreparable rotator cuff tears:

• Options include partial repair, debridement, or muscle transfers (latissimus dorsi or teres major) 6
• All options show improvement in pain and function at 3-4 years, though no comparative studies establish superiority of one technique 6
• Complications may include temporary complex regional pain syndrome and cosmetic biceps deformity 6

Critical Pitfalls to Avoid

• Never rely on the drop arm test alone—sensitivity is too low (38%) to rule out disease if negative 3
• Do not assume normal active external rotation means intact teres minor—poor correlation exists between teres minor involvement and loss of active external rotation 2
• Avoid ordering MRI without clinical examination—imaging has limitations including motion artifact, soft tissue density issues, and difficulty distinguishing infraspinatus from teres minor 2
• Do not perform acromioplasty routinely during rotator cuff repair for Bigliani type II or III acromions—evidence shows no functional benefit 6

Special Consideration for Teres Minor Assessment

The teres minor is critical for outcomes of reverse shoulder arthroplasty and tendon transfers, making its assessment essential in massive rotator cuff tears 2. An external rotation lag sign >40° is the most accurate clinical indicator of teres minor dysfunction (100% sensitivity, 92% specificity) 2.