What causes winging of the scapula?

Scapular Winging: Anatomical Causes

Scapular winging results from paralysis or dysfunction of three key muscles—the serratus anterior, trapezius, or rhomboid muscles—most commonly due to nerve injury affecting the long thoracic nerve, spinal accessory nerve, or dorsal scapular nerve, respectively. 1, 2

Primary Nerve-Muscle Relationships

The anatomical basis of scapular winging depends on which stabilizing muscle is compromised:

Serratus Anterior Paralysis (Medial Winging)

• Long thoracic nerve injury causes serratus anterior paralysis, resulting in medial winging where the medial border of the scapula protrudes away from the chest wall 1, 3
• This is the most common cause of scapular winging reported in the literature 2
• The serratus anterior is critical for scapular protraction and upward rotation during arm elevation 2

Trapezius Paralysis (Lateral Winging)

• Spinal accessory nerve injury causes trapezius paralysis, producing lateral winging with drooping of the shoulder 1, 3
• The trapezius is essential for scapular elevation and rotation 2
• Conservative treatment is less effective for trapezius paralysis compared to serratus anterior dysfunction 1

Rhomboid Paralysis (Lateral Winging with Inferior Angle Rotation)

• Dorsal scapular nerve (DSN) neuropathy causes rhomboid muscle paralysis 4
• This produces winging of the medial border with lateral rotation of the inferior angle of the scapula 4
• The DSN originates from the C5 nerve root 4
• A critical anatomical finding is dynamic compression of the DSN by the proximal medial border of the scapula when the arm is elevated above 90° 4

Mechanisms of Nerve Injury

Traumatic Causes

• Direct trauma to the shoulder girdle or chest wall can damage any of these nerves 1, 3
• Surgical procedures (iatrogenic injury) are a recognized cause 1
• Acute traumatic tears of the serratus anterior, trapezius, or rhomboids directly off the scapula are under-recognized causes that differ from neurogenic etiologies 2

Atraumatic/Overuse Causes

• Repetitive overhead activities or sports can cause nerve compression 5
• Incorrect exercise technique, such as improper prone plank positioning, can cause long thoracic nerve palsy through increased scapular loading 5
• Occupations involving heavy physical work predispose to DSN compression 4
• Sports involving arm exertion (dancing, boxing, gymnastics) are risk factors for DSN neuropathy 4

Idiopathic Causes

• Many cases occur without identifiable trauma or overuse 1

Clinical Distinction Between Winging Patterns

Medial winging (serratus anterior): The medial border lifts away from the chest wall, most visible during forward arm elevation or wall push-off 1, 2

Lateral winging (trapezius): The entire scapula appears laterally displaced with shoulder drooping 1

Lateral winging with inferior angle rotation (rhomboid): The medial border wings with the inferior angle rotating laterally, particularly noticeable with arm elevation 4

Associated Conditions in Neuromuscular Disease

In the context of limb-girdle muscular dystrophy (LGMD), scapular winging can occur as part of progressive skeletal myopathy affecting the shoulder girdle musculature, with variable age of onset from childhood to the fifth decade 6

Common Pitfalls

• Overlooking traumatic muscular detachment as a cause, focusing only on neurogenic etiologies 2
• Missing dynamic compression of the dorsal scapular nerve during arm elevation above 90°, which may not be apparent at rest 4
• Attributing DSN compression solely to the middle scalene muscle when scapular compression during elevation is the actual mechanism 4
• Failing to identify the specific winging pattern (medial vs. lateral) which determines the affected nerve and muscle 1