How to clinically differentiate winging of the scapula due to weakness of the serratus anterior, trapezius, and rhomboid muscles?

Clinical Differentiation of Scapular Winging by Muscle Etiology

The shoulder flexion resistance test (SFRT) at 30°, 60°, and 100° with elbow extended is the most specific and accurate examination to diagnose serratus anterior dysfunction, while observing scapular position during arm elevation and resistance testing differentiates trapezius versus rhomboid weakness. 1

Serratus Anterior Weakness (Medial Winging)

Clinical Presentation

• Medial border of scapula wings away from chest wall, most prominent with the scapula in neutral position and during shoulder flexion 1, 2
• Winging increases with forward arm elevation and pushing movements 2
• Patient has difficulty elevating arm above 90° and experiences pain with overhead activities 2

Specific Physical Examination Maneuvers

Shoulder Flexion Resistance Test (SFRT) - This is the gold standard test with 100% sensitivity and 100% specificity for serratus anterior dysfunction 1:

• Resist shoulder flexion with elbow fully extended at three positions: 30°, 60°, and 100°
• Positive test shows dramatic winging during resistance at these angles 1

Wall Push-Up Test (WPUT) - This test should NOT be used as it has 0% specificity 1:

• While traditionally taught, WPUT produces 45 false positives out of 50 patients with scapulothoracic abnormal motion 1
• The test is 100% sensitive but completely non-specific, making it clinically useless for determining the cause of winging 1

Associated Findings

• Long thoracic nerve injury is the most common neurogenic cause 2
• Electromyography shows denervation of serratus anterior if neurogenic 1, 3
• Traumatic tears of serratus anterior off the scapula are under-recognized causes 2

Trapezius Weakness (Lateral Winging)

Clinical Presentation

• Lateral winging with superior and lateral displacement of the inferior scapular angle 2
• Scapula rotates downward and the shoulder droops 2
• Winging becomes more prominent during arm abduction and elevation 2

Specific Physical Examination Maneuvers

• Shoulder shrug test: Patient cannot elevate shoulder against resistance 2
• Arm abduction test: Observe scapular position during active abduction - the scapula fails to rotate upward normally and wings laterally 2
• Patient has difficulty maintaining arm elevation above horizontal 2

Associated Findings

• Spinal accessory nerve (CN XI) injury is the most common neurogenic cause 4, 2
• Weakness and atrophy of both sternocleidomastoid and upper trapezius muscles may be present 4
• MRI with and without IV contrast of head, orbit, face, and neck is the preferred imaging to evaluate CN XI pathology 4

Rhomboid Weakness

Clinical Presentation

• Medial border winging similar to serratus anterior palsy, but with distinct differences 2
• Winging is less prominent than with serratus anterior dysfunction 2
• Scapula drifts laterally away from midline during rest 2

Specific Physical Examination Maneuvers

• Scapular retraction test: Patient cannot pull scapula toward spine against resistance 2
• Arms akimbo position: Have patient place hands on hips and push elbows backward - observe for inability to retract scapula 2
• Winging improves (not worsens) with arm elevation, opposite to serratus anterior palsy 2

Key Differentiating Feature

• Unlike serratus anterior palsy where winging increases with forward flexion, rhomboid weakness shows improvement of winging during arm elevation because the trapezius can partially compensate 2

Critical Diagnostic Algorithm

1. First, perform SFRT (not wall push-up) to definitively rule in or out serratus anterior dysfunction 1

   • If positive at 30°, 60°, and 100° resistance: serratus anterior dysfunction confirmed 1
   • If negative: proceed to evaluate trapezius and rhomboids 1

2. Observe scapular position during active arm elevation 2:

   • Lateral winging with downward rotation = trapezius weakness 2
   • Medial winging that improves with elevation = rhomboid weakness 2

3. Test specific muscle function 2:

   • Shoulder shrug against resistance for trapezius 2
   • Scapular retraction against resistance for rhomboids 2

4. Obtain electromyography if neurogenic cause suspected to differentiate nerve injury from primary muscle pathology 1, 3

5. Consider MRI if traumatic muscle tear suspected, as acute tears of serratus anterior, trapezius, and rhomboids are under-recognized causes 2

Common Pitfalls to Avoid

• Never rely on wall push-up test alone - it cannot differentiate causes of winging and has zero specificity 1
• Do not miss trapezius palsy - it is frequently misdiagnosed and requires different treatment than serratus anterior dysfunction 3
• Consider traumatic muscle detachment in addition to neurogenic causes - these require different surgical management 2
• Examine for combined nerve palsies - CN IX, X, and XI may be involved together in skull base pathology 4
• Patients with scapular winging should be referred immediately to specialized centers if spontaneous recovery does not occur 3