Functional Anatomy of Trapezius Muscle

Intro:

Trapezius muscle pain is one of the most common musculoskeletal problems. Patients often complain of acute or chronic neck-shoulder pain. Trapezius muscle pain is often characterized by pain, stiffness and tightness of upper fibres of Trapezius muscle, neck and sometimes around the shoulder joint. Tension headache is another common problem associated with Trapezius pain or hypertonicity or spasm.

Trapezius is a broad, flat, triangular muscle which extends over the back of neck and upper thorax. Understanding of functional anatomy is crucial to treat Trapezius muscle pain by incorporating proper stretching, and strengthening exercises.

Anatomy:

Trapezius is a diamond shaped paired muscles which laterally angles at the shoulder tips, the superior angle at the occipital protuberance and superior nuchal line, and the inferior angle at the spine of the twelfth thoracic vertebrae. Dissection studies have revealed the fascicular anatomy of Trapezius showing three definite fibres; superior (descending), middle (transverse), inferior (ascending) part.

Superior (Descending) fibres:

It originates from Occipital bone (superior nuchal line and external occipital protuberance) and the spinous process of all cervical vertebrae via the nuchal ligament. Johnson et al performed dissection study and reported that superior fibres (mainly occipital and nuchal fibres) passed downwardly but mainly transversely to insert in to the lateral third of the clavicle. Fibres from C7 and T1 passed transversely to reach the acromion and spine of scapula. Its thoracic fibres converged to the deltoid tubercle of the scapula. Volumetric studies have demonstrated that the fibres from C7, T1, and the lower half of ligamentum nuchae were the largest.

Middle (Transverse) fibres:

Originates from the broad triangular aponeurosis at the level of the T1-T4 spinous processes. These middle fibres are attached to the medial acromial margin and superior lip of the crest of the scapular spine.

Inferior (Ascending) fibres:

Originates from the spinous processes of T5-T12. These ascending fibres pass into an aponeurosis which glides over a smooth triangular surface at the medial end of the scapular spine and is attached to a tubercle at its lateral apex.

Clinical significance and actions:

  • Trapezius works with other muscles in steadying the scapula on the thorax, controlling it during the arm movement, and maintaining the level and the poise of the shoulder.
  • The occipital attachment is by a fibrous lamina, which is also adherent to the skin. The spinal attachment is by a broad triangular aponeurosis from the sixth to the fourth thoracic vertebrae, and by the tendinous fibres below the fourth thoracic vertebrae.
  • The upper fibres of Trapezius acts with levator scapula to elevate the scapula and with it the point of the shoulder. However, the study from Johnson et al 1994, have precluded the elevator action of upper and middle fibres of Trapezius muscle due to its more transverse orientation. The study has reported, “Rather the action of these fibres is to draw the scapula and clavicle backwards or to raise scapula by rotating the clavicle about the sternoclavicular joint”.
  • Acting with the serratus anterior, superior fibres of the Trapezius draws the scapula obliquely upward and rotates the glenoid cavity, so that the arm can be raised above the head.
  • Acting with the Rhomboids , Trapezius retracts the scapula, bracing back the shoulder.
  • Ascending fibres draws the scapula medially downward and supports the rotating action of the descending fibres.
  • Serratus anterior and Trapezius are opposed in scapular movement round the thorax, but combine as prime movers in lateral rotation of the scapula.
  • With the shoulder girdle fixed, Trapezius tilts the head to the same side and rotates it to the opposite side.

Innervation:

Trapezius is innervated by the spinal part of the accessory nerve (Cranial nerve XI). Sensory (proprioceptive) branches are derived from th ventral rami of C3 and C4.

Leave a Reply

Your email address will not be published. Required fields are marked *