Winged scapula after mastectomy is due to injury of which nerve?

Study for the Medical Council of Canada Qualifying Examination (MCCQE) I. Engage with flashcards and multiple-choice questions with detailed feedback. Prepare confidently!

Winged scapula after mastectomy is best explained by injury to the long thoracic nerve, which supplies the serratus anterior. Serratus anterior is crucial for holding the medial border of the scapula flat against the thoracic wall and for protracting the scapula during arm elevation. When the long thoracic nerve is damaged, such as during axillary node dissection in mastectomy, serratus anterior weakens and can no longer anchor the scapula to the chest. The medial border of the scapula then protrudes outward, especially when the patient tries to push against something.

The other nerves would cause different patterns of shoulder weakness. For example, injury to the spinal accessory nerve affects the trapezius and alters shoulder elevation and scapular rotation rather than producing the classic medial winging; suprascapular nerve injury mainly weakens abduction and external rotation; dorsal scapular nerve injury weakens rhomboids, affecting scapular retraction. The prominent medial winging after chest surgery most classically points to long thoracic nerve injury.