The trapezius is a broad, flat muscle covering the upper back. It is named for the trapezoid shape that these paired muscles create. It has 3 major sections that originate on the axial skeleton and insert on the pectoral girdle, making it an extrinsic back muscle.
Each of its sections has a distinctive function and pain patterns. The upper section is similar in attachment, function and referral patterns to the sternocleidomastoid. The middle and lower sections are similar to each other in attachment and pain patterns. Because of this, this text deals with each of those sections individually.
In general, the trapezius retracts the scapula. It acts to suspend and stabilize the shoulder girdle for use of the upper extremity. It also retracts and stabilizes the scapula so that extrinsic chest muscles can expand the rib cage during labored breathing and for labored breathing.
The upper trapezius connects the occiput and upper cervical vertebrae to the clavicle through the lower cervical vertebrae, first rib, and manubrium.
Origin -the medial third of the superior nuchal ridge and ligamentum nuchae from C1-C5
Insertion – posterior edge of the lateral clavicle
Function – draws the lateral clavicle medially toward the spine, rotating the scapula upward or laterally flexing the cervical vertebrae
The middle trapezius connects the lower cervical and upper thoracic vertebrae to the scapula through the upper ribs, sternum, manubrium, and clavicle.
Origin – the spinous processes and superior ligaments of the vertebrae C6-T3
Insertion – acromion and spine of the scapula
Function – adduction and retraction of the scapula
The lower trapezius connects the lower thoracic vertebrae to the scapula through the ribs, sternum, manubrium, and clavicle.
Origin – the spinous processes and superior ligaments of T4-T12
Insertion – the root of the scapula
Function – stabilize the scapula during movement of the upper extremity; may adduct or upwardly rotate the scapula