| Trapezius | |
|---|---|
 The trapezius muscle (pl.: trapezii) is a surface muscle ofback, shown in red above and below. | |
 | |
| Details | |
| Origin | Medial one-third of superior nuchal line,external occipital protuberance,spinous processes ofvertebrae C7-T12,Nuchal ligament[1] |
| Insertion | Posterior border of the lateral one-third of theclavicle,acromion process, andspine of scapula |
| Artery | Superficial branch of transverse cervical artery orsuperficial cervical artery[2] |
| Nerve | Accessory nerve (motor) cervical spinal nerves C3 and C4 (motor and sensation)[3] |
| Actions | Rotation,retraction, elevation, and depression ofscapula |
| Antagonist | Serratus anterior muscle,latissimus dorsi,pectoralis major |
| Identifiers | |
| Latin | musculus trapezius |
| TA98 | A04.3.01.001 |
| TA2 | 2226 |
| FMA | 9626 |
| Anatomical terms of muscle | |
Thetrapezius[4] is a large pairedtrapezoid-shaped surfacemuscle that extends longitudinally from theoccipital bone to the lowerthoracic vertebrae of thespine and laterally to the spine of thescapula. It moves the scapula and supports thearm.
The trapezius has three functional parts:
The trapezius muscle resembles atrapezium, also known as a trapezoid, or diamond-shapedquadrilateral. The word "spinotrapezius" refers to the human trapezius, although it is not commonly used in modern texts. In other mammals, it refers to a portion of the analogous muscle.
Thesuperior orupper (or descending) fibers of the trapezius originate from thespinous process of C7, theexternal occipital protuberance, the medial third of thesuperior nuchal line of theoccipital bone (both in the back of the head), and theligamentum nuchae. From this origin, they proceed downward and laterally to be inserted into the posterior border of the lateral third of theclavicle.
The middle fibers, or transverse of the trapezius arise from thespinous process of the seventh cervical (both in the back of the neck), and the spinous processes of the first, second, and thirdthoracic vertebrae. They are inserted into the medial margin of theacromion, and into the superior lip of the posterior border of thespine of the scapula.
Theinferior orlower (or ascending) fibers of the trapezius arise from the spinous processes of the remaining thoracic vertebrae (T4–T12). From this origin, they proceed upward and laterally to converge near the scapula and end in anaponeurosis, which glides over the smooth triangular surface on the medial end of the spine, to be inserted into a tubercle at the apex of this smooth triangular surface.
At its occipital origin, the trapezius is connected to the bone by a thin fibrous lamina, firmly adherent to the skin. The superficial and deepepimysia are continuous with an investing deep fascia that encircles the neck and also contains bothsternocleidomastoid muscles.
At the middle, the muscle is connected to the spinous processes by a broad semi-ellipticalaponeurosis, which reaches from the sixth cervical to the third thoracic vertebræ and forms, with that of the opposite muscle, a tendinous ellipse. The rest of the muscle arises by numerous short tendinous fibers.
It is possible to feel the muscles of the superior trapezius as they become active by holding a weight in one hand in front of the body and, with the other hand, touching the area between the shoulder and the neck.[citation needed]
Motor function is supplied by theaccessory nerve.[5] Sensation, including pain and the sense of joint position (proprioception), travel via theventral rami of thethird (C3) andfourth (C4) cervicalspinal nerves.[5] Since it is a muscle of the upper limb, the trapezius is not innervated bydorsal rami, despite being placed superficially in the back.
Contraction of the trapezius muscle can have two effects: movement of the scapulae when the spinal origins are stable, and movement of the spine when the scapulae are stable.[5] Its main function is to stabilize and move the scapula.[5]
The upper fibers elevate the scapulae, the middle fibers retract the scapulae, and the lower fibers depress the scapulae.[5]
In addition to scapular translation, the trapezius induces scapular rotation. The upper and lower fibers tend to rotate the scapula around thesternoclavicular articulation so that theacromion and inferior angles move up and the medial border moves down (upward rotation). The upper and lower fibers work in tandem withserratus anterior to upwardly rotate the scapulae, and work in opposition to thelevator scapulae and therhomboids, which effect downward rotation.
An example of trapezius function is anoverhead press. When activating together, the upper and lower fibers also assist the middle fibers (along with other muscles such as therhomboids) with scapular retraction/adduction.
The trapezius also assists in abduction of the shoulder above 90 degrees by rotating the glenoid upward. Injury to cranial nerve XI will cause weakness in abducting the shoulder above 90 degrees.
When the scapulae are stable, a co-contraction of both sides can extend the neck.
Dysfunction of the trapezius can result inwinged scapula, sometimes further specified as "lateral winging"[6] and in an abnormal mobility or function of the scapula (scapular dyskinesia).[7] There are multiple causes of trapezius dysfunction.
Trapezius palsy, due to damage of thespinal accessory nerve, is characterized by difficulty with armadduction andabduction, and associated with a drooping shoulder, and shoulder andneck pain.[8] Intractable trapezius palsy can be surgically managed with anEden–Lange procedure.
The trapezius muscle is one of the commonly affected muscles infacioscapulohumeral muscular dystrophy (FSHD). The lower and middle fibers are affected initially, and the upper fibers are commonly spared until late in the disease.[9]
Although rare, underdevelopment or absence of the trapezius has been reported to correlate to neck pain and poor scapular control that are not responsive tophysical therapy.[10] Absence of the trapezius has been reported in association withPoland syndrome.[11]
It is mainly used in throwing, with thedeltoid muscle androtator cuff.
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This article incorporates text in thepublic domain frompage 432 of the 20th edition ofGray's Anatomy(1918)
