A wing scapula and resulting weak shoulder are common complaints. The three principal muscles concerned with fixation and movement of the scapula have overlapping functions.
Trapezius Muscle: Spinal Accessory Nerve, C3 and C4 The trapezius pulls the scapula upward. This was demonstrated in the "shoulder shrug" when
you examined the eleventh cranial nerve (see "How to Test the Spinal Accessory Nerve" in Chapter 9). It also pulls the medial edge of the scapula toward the midline (adduction). Therefore, if only trapezius weakness is the cause of the wing scapula, the scapula is lower and more lateral when the shoulder is at rest.
Ask the patient to abduct his arm away from his trunk against resistance. The downward and lateral displacement of the scapula will be more obvious and the winging is most obvious at the lower edge.
Ask the patient to put his anns horizontally straight in front of him as though pushing the wall (flexion); the winging disappears (compare with serratus anterior palsy).
Rhomboids: Dorsal Scapular Nerve, C5 These muscles pull the medial edge of the scapula upward and toward the midline. You "brace" the shoulders with your rhomboids.
To see normal rhomboid function, ask the patient to put his hand on his hip and push his elbow backward against the resistance of the examiner's hand. Watch and feel the medial edge of the scapula move toward the midline and upward.
In rhomboid weakness this action produces winging, and the medial edge of the scapula moves laterally and downward.
Serratus Anterior: Long Thoracic Nerve, C5 to C7 This muscle pulls the scapula away from the midline and also forward.
When the serratus is weak, inspection of the back at rest shows the inferior angle of the scapula is slightly winged and the medial edge is pulled toward the midline.
Abduction of the arm against resistance reduces the winging. Pushing the horizontally flexed arm against the wall increases the winging, and the inferior angle of the scapula is lifted off the chest wall.
Remember: The best test to identify scapula winging resulting from trapezius weakness is abduction of the arm against resistance; to test that caused by serratus anterior weakness, use flexion (with the arm horizontal, pushing forward against the wall).
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