Anatomy and actions of the trapezius muscle.

Dissection studies revealed the fascicular anatomy of the trapezius. Its occipital and nuchal fibres passed downwards but mainly transversely to insert into the clavicle. Fibres from C7 and T1 passed transversely to reach the acromion and spine of the scapula. Its thoracic fibres converged to the deltoid tubercle of the scapula. Volumetric studies demonstrated that the fibres from C7, T1, and the lower half of ligamentum nuchae were the largest. The essentially transverse orientation of the upper and middle fibres of trapezius precludes any action as elevators of the scapula as commonly depicted. Rather the action of these fibres is to draw the scapula and clavicle backwards or to raise the scapula by rotating the clavicle about the sternoclavicular joint. By balancing moments the trapezius relieves the cervical spine of compression loads.