Which sign indicates weakness of the serratus anterior muscle leading to scapular winging?

Which sign indicates weakness of the serratus anterior muscle leading to scapular winging?

• A. Liver disease
• B. Injury to the long thoracic nerve
• C. Muscular dystrophy
• D. Weakness of the serratus anterior muscle

Answer: (D)

The sign being tested is weakness of the serratus anterior muscle, because this muscle normally anchors the medial border of the scapula to the rib cage and keeps the scapula flat against the thorax. When the serratus anterior is weak, the scapula cannot be held tightly to the chest wall and tends to protrude, especially when the arm is pushed forward or against resistance—this is scapular winging. In practice, you can think of the action that reveals this weakness: asking someone to push against a wall or reach forward will show the medial border of the scapula sticking out as the muscle fails to stabilize it. Injury to the long thoracic nerve can cause this weakness, but the observable sign you’re looking for is the impaired strength of the serratus anterior itself. Choices like liver disease or muscular dystrophy don’t specifically explain scapular winging due to serratus anterior weakness, whereas the presence of weakness in this muscle directly accounts for the winging phenomenon.

The sign being tested is weakness of the serratus anterior muscle, because this muscle normally anchors the medial border of the scapula to the rib cage and keeps the scapula flat against the thorax. When the serratus anterior is weak, the scapula cannot be held tightly to the chest wall and tends to protrude, especially when the arm is pushed forward or against resistance—this is scapular winging.

In practice, you can think of the action that reveals this weakness: asking someone to push against a wall or reach forward will show the medial border of the scapula sticking out as the muscle fails to stabilize it. Injury to the long thoracic nerve can cause this weakness, but the observable sign you’re looking for is the impaired strength of the serratus anterior itself.

Choices like liver disease or muscular dystrophy don’t specifically explain scapular winging due to serratus anterior weakness, whereas the presence of weakness in this muscle directly accounts for the winging phenomenon.