How to test for winging of the scapula due to trapezius, serratus anterior, and rhomboid muscle weakness?

Testing for Scapular Winging by Muscle Etiology

To differentiate the cause of scapular winging, use the shoulder flexion resistance test (SFRT) for serratus anterior dysfunction, observe winging patterns during arm elevation for trapezius weakness, and assess scapular position at rest for rhomboid involvement.

Serratus Anterior Testing (Medial Winging)

The shoulder flexion resistance test (SFRT) should replace the traditional wall push-up test as it is 100% sensitive and 100% specific for serratus anterior dysfunction, compared to the wall push-up test which has 0% specificity. 1

SFRT Technique:

• Resist the patient's shoulder flexion with the elbow fully extended at three positions: 30°, 60°, and 100° 1
• Positive test: increased medial winging of the scapula during resistance 1
• This test accurately identifies long thoracic nerve palsy causing serratus anterior paralysis 1

Wall Push-Up Test Limitations:

• While the wall push-up test is 100% sensitive, it produces false positives in 90% of cases because any cause of scapulothoracic abnormal motion will produce winging during this maneuver 1
• The wall push-up test cannot differentiate between serratus anterior dysfunction and other causes of winging 1

Clinical Pattern:

• Medial winging occurs with serratus anterior paralysis 2
• Winging may be present in neutral position and shoulder extension but paradoxically absent during wall push-up in some traumatic serratus anterior tears 3

Trapezius Testing (Lateral Winging)

Trapezius weakness produces lateral winging and is best identified by observing difficulty maintaining arm elevation above horizontal, along with visible weakness and atrophy of both the sternocleidomastoid and upper trapezius muscles. 4

Clinical Assessment:

• Have the patient elevate their arm above 90° and observe for inability to maintain this position 4
• Examine for combined weakness and atrophy of the sternocleidomastoid and upper trapezius muscles, indicating spinal accessory nerve (CN XI) injury 4
• Lateral winging is generated by trapezius paralysis 2

Important Consideration:

• Trapezius palsy is frequently missed and must be considered as a differential diagnosis in any scapular winging case 5
• Consider skull base pathology if combined nerve palsies involving CN IX, X, and XI are present 4

Rhomboid Testing (Lateral Winging)

Rhomboid paralysis produces lateral winging similar to trapezius weakness and is assessed by observing scapular position at rest and during active shoulder motion. 2

Clinical Pattern:

• Lateral winging occurs with rhomboid paralysis 2
• Rhomboid dysfunction often accompanies other scapulothoracic muscle impairments 5

Diagnostic Algorithm

1. Initial observation: Determine if winging is medial or lateral

   • Medial winging → suspect serratus anterior 2
   • Lateral winging → suspect trapezius or rhomboid 2

2. Perform SFRT: Resist shoulder flexion at 30°, 60°, and 100° with elbow extended 1

   • Positive SFRT with medial winging → serratus anterior dysfunction confirmed 1
   • Negative SFRT with medial winging → consider traumatic serratus tear or other causes 3

3. Assess arm elevation: Have patient elevate arm above horizontal 4

   • Inability to maintain elevation with lateral winging → trapezius weakness 4
   • Check for sternocleidomastoid and trapezius atrophy → CN XI injury 4

4. Confirm with electrodiagnostic studies: Electromyography helps characterize nerve injury and muscle function 5

Common Pitfalls

• Do not rely solely on the wall push-up test, as it cannot differentiate between causes of winging and produces 90% false positives 1
• Do not miss trapezius palsy, which is frequently overlooked but requires different management than serratus anterior dysfunction 5
• Do not assume all medial winging is neurogenic, as traumatic serratus anterior muscle tears can occur and may show different patterns on wall push-up testing 3
• Do not attempt immediate surgical intervention, as most serratus anterior paralysis cases spontaneously resolve within 24 months 2

Advanced Imaging Considerations

• MRI with and without IV contrast is the preferred imaging for CN XI pathology evaluation when trapezius weakness is suspected 4
• MRI and electromyography are essential components of thorough evaluation for surgical planning 5