What are the most common neurogenic causes of winging of the scapula?
1. Long thoracic nerve palsy:
The long thoracic nerve innervates the serratus anterior muscle.
Serratus anterior weakness leads to the most pronounced winging, which is accentuated with forward flexion of the arms and decreased with the arms at rest.
The superior (medial) angle of the scapula is displaced closer to the midline, whereas the inferior angle swings laterally and away from the thorax.
2. Spinal accessory nerve palsy:
The spinal accessory nerve innervates the trapezius muscle.
Trapezius muscle weakness leads to mild winging of the scapula at rest, which is accentuated by arm abduction to 90° and decreased by forward flexion to 90°.
The superior (medial) angle of the scapula is displaced away from the midline, but the inferior angle is medially rotated.
The shoulder is lower on the affected side because of atrophy of the trapezius muscle.
3. Dorsal scapular nerve palsy:
The dorsal scapular nerve innervates the rhomboid muscle. Weakness of this muscle produces minimal winging at rest, which is accentuated by slowly lowering the arm from the forward overhead position and decreased by elevation of the arms overhead.
The superior (medial) angle is displaced away from the midline, and the inferior angle is laterally displaced.
In addition, there are many nonneurogenic causes of winging of the scapula, including myopathies and muscular dystrophy (e.g., facioscapulohumeral muscle dystrophy).
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