long thoracic nerve

**Origin and course:** The nerve arises from the ventral rami of C5, C6, and C7, the "wings" roots of the plexus ("C5, 6, 7 raise the wings to heaven"). It comes off the roots, above the clavicle and before the trunks form. It passes through the middle scalene, then descends posterior to the brachial plexus and axillary vessels. It runs down the superficial surface of the serratus anterior along the midaxillary line (lateral thoracic wall). This long, superficial course makes it vulnerable.

**Function:** It innervates only the serratus anterior. The muscle protracts the scapula and holds its medial border against the thoracic wall. It also rotates the scapula upward, so the arm can be abducted above 90°. It works with the trapezius for this movement.

**Clinical significance:** - **Injury:** The usual causes are axillary lymph node dissection or mastectomy, stab wounds, a blow to the lateral chest wall, and heavy backpack carrying. Other causes are prolonged traction in sports or surgery, and thoracic surgery. Parsonage-Turner syndrome (neuralgic amyotrophy) can also affect it. - **Presentation:** Medial winging of the scapula, in which the medial border lifts off the chest wall. Winging worsens when the patient pushes against a wall. The patient has difficulty abducting the arm above the horizontal, because the scapula cannot rotate upward. Pain is usually minimal. - **Differentiate from spinal accessory (CN XI) injury:** CN XI injury paralyzes the trapezius and causes lateral winging, with shoulder droop and weakness of shrugging and of abduction above 90°. Dorsal scapular nerve injury (rhomboids) can also cause mild winging. - **Mnemonic:** "Break the long thoracic nerve and the scapula wings (Bells of Serratus)." The nerve has the "Long" course, so it is easily injured. - **Management:** Mostly conservative (observation, physical therapy), because most cases recover over months. Nerve transfer or muscle transfer is rarely needed for persistent cases.

**High-yield associations:** - Branches directly from the roots (with the dorsal scapular nerve, C5), not from a trunk, cord, or branch. - Lies on the superficial surface of the serratus anterior. It is at risk during axillary dissection, so surgeons preserve it. - In the exam, "winged scapula after mastectomy" means long thoracic nerve.