Muscles retracting the pectoral(shoulder) girdle

Rhomboid minor

Rhomboid major

Trapezius

Rhomboid minor

Rhomboid minor is a small quadrilateral muscle whose fibres run obliquely downwards and laterally from the spinous processes of C7 and T1 and the supraspinous ligament between them and the lower part of the ligamentum nuchae, to attach the medial border of the smooth triangular area at the base of the spine of the scapula.

Rhomboid major

Rhomboid major, although larger than rhomboid minor, may be continuous with it. It arises by tendinous slips from the spinous processes of T2 to T5 inclusive and the intervening supraspinous ligament. The muscle fibres run obliquely downwards and laterally to attach to a medial border of the scapula between the base of the spine and the inferior angle.

Both rhomboids lie superficial to the long back muscles, being themselves covered by trapezius, except for the lower border of rhomboid major which forms the floor of the “triangle of auscultation”.

Nerve supply

Both rhomboid muscles are supplied by the dorsal scapular nerve, root value C5.

Action

The rhomboids act principally to retract the scapula but are also active, however, in medial rotation of the pectoral girdle. In addition they also act as important stabilizers of the scapula when other muscle groups are active.

Palpation

With the subject’s hand placed in the small of the back(to relax trapezius), the rhomboids can be palpated through trapezius when the hand is moved backwards. Contraction of the rhomboids can be felt(and occasionally be seen) between the medial border of the scapula and the vertebral column.

Trapezius

Trapezius is a large, flat triangular sheet of muscle extending from the skull and spine medially to the pectoral girdle laterally. It is the most superficial muscle in the upper back and with its fellow of the opposite side it forms a trapezium, hence its name.

The medial attachment of trapezius runs from the medial third of the superior nuchae line and external occipital protuberance of the occipital bone, the ligamentum nuchae, the spinosus processes of C7 to T12 inclusive and the intervening supraspinous ligament. The majority of this attachment is by direct muscular slips, however a triangular aponeurosis exists in trapezius between C6 and T3 which corresponds to a hollow seen in the living subject.

From this extensive central attachment the upper fibres of trapezius run downwards and laterally, the middle fibres almost horizontally, and the lower fibres upwards and laterally to form a continuous line of attachment to the clavicle and scapula. The upper fibres descend to the posterior border of the lateral third of the clavicle, while the middle fibres pass to the medial border of the acromion and upper border of the crest of the spine of the scapula, being separated from the smooth area on the medial part of the spine by a small bursa. The lower-most fibres converge to a tendon which attaches to the tubercle on the inferior edge at the medial end of the spine of the scapula.

The upper free edge of trapezius forms the posterior border of the posterior triangle of the neck, while the lower free border forms the medial boundary of the triangle of auscultation. This latter triangle is an area of the chest wall free of bony obstruction by the scapula and thinly covered by muscle. Its other boundaries are the upper border of latissimus dorsi below and the medial border of the scapula laterally.

Nerve supply

Trapezius receives its motor supply via the spinal part of the accessory nerve(XI) which enters it from the posterior triangle. It also receives sensory fibres from the ventral rami of C3,4 via the cervical plexus. The skin over trapezius is supplied by the dorsal rami of C3 – T12.

Action

Trapezius has an important function in stabilizing the scapula as a base for movements of the upper limb. The middle horizontal fibres pull the scapula backwards towards the midline, that is retraction, and may be aided by the upper and lower fibres contracting together to produce a “resolved” force towards the midline. The upper fibres of trapezius elevate the pectoral girdle and maintain the level of the shoulders against the effect of gravity, or when a weight is being carried in the hand. When both left and right muscles contract they can extend the neck, but when acting singularly the upper fibres produce lateral(side) flexion of the neck. The lower fibres pull down the medial part of the scapula and thus lower the shoulder, especially against resistance, for example when using the arms to get out of a chair. The upper and lower fibres working together produce lateral rotation of the scapula about a point towards the base of the spine. Trapezius is thus important in the overall function of the upper limb as its action increases the possible range of movement.

Paralysis of trapezius, particularly its upper part, results in the scapula moving forwards around the chest wall with the inferior angle moving medially. The usually smooth curve of its upper border between the occiput and the acromion process may become markedly angulated.

Palpation

To demonstrate and palpate all three parts of trapezius, the subject should abduct both arms to 90°, flex the elbows to 90° and then rotate them laterally so that the fingers are pointing upwards.

In this position the three sets of fibres can be readily palpated; in a lean subject the contraction of the various parts of the muscle can be seen. For the lower fibres of trapezius the contraction can be further enhanced by asking the subject to clasp his or her hands together above the head and pull hard.

Soft tissue techniques are often applied to the upper muscular fibres of trapezius in the presence of muscle spasm secondary to neck pain, with the aim of inducing relaxation. Deep transverse frictions can also be applied to the tendinous attachment of trapezius on the superior nuchal line when this is the site of a lesion causing pain in the neck or occipital region.