Muscles Attaching the Upper Limb to the Trunk Anatomy
Three muscles connect the root of the upper limb to the chest wall and are usually dissected with the thorax. For this reason, pectoralis major and minor and serratus anterior are described with the thoracic wall (p. 31). Only the posterior group of muscles attaching the limb and its girdle to the vertebral column are described here: trapezius, latissimus dorsi, levator scapulae and the rhomboids (Fig. 3.55).
|Fig. 3.55 Attachments of trapezius, rhomboid major and minor, levator scapulae and latissimus dorsi.|
Trapezius (Fig. 3.56) is a large superficial muscle overlying the dorsum of the neck and thorax. Its upper fibres attach to the ligamentum nuchae, the external occipital protuberance and the superior nuchal line and pass downwards and laterally to the acromion of the scapula and the lateral part of the clavicle. These fibres produce elevation of the scapula as in shrugging the shoulder. When the scapula is fixed, they produce lateral flexion of the neck. The middle fibres of trapezius run horizontally from the ligamentum nuchae and upper thoracic spinous processes to the acromion and spine of the scapula and retract the scapula. Fibres of the lower part of the muscle attach to the lower thoracic spinous processes superficial to latissimus dorsi (Fig. 3.56) and pass upwards and laterally to the spine of the scapula. These fibres depress the scapula. Acting together, the upper and lower parts of trapezius produce rotation of the scapula, turning the glenoid fossa superiorly to permit full abduction of the limb (p. 117). In the neck, the anterior edge of the muscle forms the posterior boundary of the posterior triangle. The accessory nerve crosses the triangle (Fig. 7.9) and supplies the trapezius from its deep surface.
These three muscles are covered by the trapezius. Levator scapulae (Fig. 3.57) ascends from the medial border of the scapula above the root of the spine to the transverse processes of the upper four cervical vertebrae. The fibres of the rhomboids incline upwards and medially (Fig. 3.57). Rhomboid minor attaches to the medial border of the scapula at the root of its spine and to the spinous processes of the seventh cervical and first thoracic vertebrae. Rhomboid major passes between the remainder of the medial border of the scapula and the spines of the second to fifth thoracic vertebrae.
All three muscles elevate the scapula and assist in scapular rotation during adduction of the upper limb. The dorsal scapular nerve from the brachial plexus (C5) supplies the rhomboids and may innervate levator scapulae, which is also supplied by branches from the cervical plexus (C3 & C4).
Fig. 3.58 Latissimus dorsi. The anterior border lies parallel to the cut skin edge, and the thoracic attachment has been exposed by removal of trapezius.
Latissimus dorsi (Fig. 3.58) is a large triangular muscle overlying much of the dorsal aspect of the trunk. The muscle attaches to the spinous processes of the lower six thoracic vertebrae and through the lumbar fascia to the spines of the lumbar vertebrae and the sacrum. The most inferior fibres attach to the posterior part of the iliac crest. Fibres also attach to the lower four ribs and to the inferior angle of the scapula. All the fibres converge on a narrow tendon in the posterior fold of the axilla. The tendon winds round the lower border of teres major to attach to the intertubercular sulcus of the humerus.
The muscle is a powerful adductor and extensor of the humerus at the shoulder joint, particularly when the upper limb is abducted and flexed. Latissimus dorsi is also a medial rotator at the shoulder joint and assists with rotation and retraction of the scapula. In movements such as rising from an armchair, if the humerus is fixed, both muscles contract to raise the trunk. This action is particularly important in patients with paralysed lower limbs. Latissimus dorsi is supplied by a single neurovascular bundle which contains the thoracodorsal nerve (a branch of the posterior cord of the brachial plexus; Fig. 3.18) and the thoracodorsal vessels, which are branches of the subscapular vessels. In reconstructive surgery, the muscle and its overlying skin may be mobilized on this neurovascular pedicle to provide a large myocutaneous flap.