The trapezius covers the posterior neck and upper thorax. Its three parts coordinate scapular movement for full shoulder elevation — the lower trapezius depresses and rotates the scapula as the upper and middle elevate and retract it.
| Origin | External occipital protuberance, superior nuchal line, nuchal ligament, spinous processes C7-T12 |
|---|---|
| Insertion | Spine of scapula, acromion, lateral third of clavicle |
| Nerve Supply | Accessory nerve (CN XI) — motor; C3, C4 — proprioceptive |
| Blood Supply | Transverse cervical artery |
| Actions | Upper fibres: elevate scapula and extend head; Middle fibres: retract scapula; Lower fibres: depress scapula and rotate glenoid upward |
|---|
CN XI palsy causes shoulder droop, loss of retraction, and inability to elevate the arm above 90 degrees due to lost scapular upward rotation. Trapezius is frequently divided in posterior cervical surgery. Used as a musculocutaneous flap for posterior neck reconstruction.
Upper fibres at neck-shoulder junction; middle at interscapular space; lower along lower thoracic spine during resisted shoulder movements.
Accessory nerve injury producing trapezius paralysis with shoulder drop, superior scapular winging, and loss of arm elevation, managed by CN XI repair or Eden-Lange transfer.
