A complete long thoracic nerve injury would primarily affect which functional task?

A complete long thoracic nerve injury would primarily affect which functional task?

• A. Putting hand in the back pocket
• B. Bending toward the involved side
• C. Taking a deep breath
• D. Reaching forward above head

Answer: (A)

The long thoracic nerve innervates the serratus anterior, a muscle that keeps the scapula pressed against the thoracic wall and helps protract and upwardly rotate the shoulder blade during arm movements. When this nerve is completely injured, the serratus anterior becomes very weak, and the scapula tends to wing (the medial border lifts away from the thorax). Movements that place the arm behind the body, such as putting the hand in the back pocket, rely heavily on the scapula staying stable and properly positioned as the arm moves in that behind-the-back plane. With the scapula unstable, this behind-the-back motion becomes especially difficult and is the most affected function. Bending toward the involved side involves mostly trunk and spinal control, not primarily the scapular stabilization that serratus anterior provides. Taking a deep breath is mainly a thoracic and diaphragmatic/intercostal function, not driven by serratus anterior. Reaching forward above the head does require scapular upward rotation and stability, but the behind-the-back task is more dependent on preserving scapular position when the arm moves in that direction, making it the best reflection of a complete long thoracic nerve injury’s effect.

The long thoracic nerve innervates the serratus anterior, a muscle that keeps the scapula pressed against the thoracic wall and helps protract and upwardly rotate the shoulder blade during arm movements. When this nerve is completely injured, the serratus anterior becomes very weak, and the scapula tends to wing (the medial border lifts away from the thorax). Movements that place the arm behind the body, such as putting the hand in the back pocket, rely heavily on the scapula staying stable and properly positioned as the arm moves in that behind-the-back plane. With the scapula unstable, this behind-the-back motion becomes especially difficult and is the most affected function.

Bending toward the involved side involves mostly trunk and spinal control, not primarily the scapular stabilization that serratus anterior provides. Taking a deep breath is mainly a thoracic and diaphragmatic/intercostal function, not driven by serratus anterior. Reaching forward above the head does require scapular upward rotation and stability, but the behind-the-back task is more dependent on preserving scapular position when the arm moves in that direction, making it the best reflection of a complete long thoracic nerve injury’s effect.