Clavipectoral Fascia Descriptive Essay
Fascia is a band or sheet of connective tissue, beneath the skin.
It’s the deep fascia covering the anterior aspect of the pectoralis major muscle. It’s thin and anchored firmly to the muscle by numerous fasciculi.
- Superiorly, it’s connected to the clavicle. Inferiorly, it’s continuous with the fascia of anterior abdominal wall.
- Superolaterally, it enters over the deltopectoral groove to become continuous with the fascia covering the deltoid muscle.
- Inferolaterally, it curves round the inferolateral border of the pectoralis major to become continuous with the axillary fascia. The axillary fascia is a dense fibrous sheet that extends across the base of the axilla.
The clavipectoral fascia is a strong fascial sheet deep to the clavicular head of the pectoralis major muscle, filling the space between the clavicle and the pectoralis minor muscle.
A as observed in sagittal section of anterior axillary wall; B as viewed from front.
- Vertically, it extends from clavicle above to the axillary fascia below. Its upper part splits into 2 laminae to enclose the subclavius muscle. The posterior lamina becomes continuous with the investing layer of deep cervical fascia and gets fused with the axillary sheath. The anterior lamina gets connected to the clavicle. Its lower part splits to enclose the pectoralis minor muscle. Below this muscle it extends downwards as the suspensory ligament of axilla, that is connected to the dome of the axillary fascia. The suspensory ligament keeps the dome of axillary fascia pulled up, thus maintaining the concavity of the axilla.
- Medially, clavipectoral fascia is connected to the first rib and costoclavicular ligament and blends with external intercostal membrane of the upper 2 intercostal spaces.
- Laterally, it’s connected to the coracoid process and blends with the coracoclavicular ligament. The thick upper part of the fascia extending from first rib near costochondral junction to the coracoid process is termed costocoracoid ligament.
- The clavipectoral fascia encloses 2 muscles—subclavius and pectoralis minor.
Structures piercing the Clavipectoral Fascia
All these are as follows:
- Lateral pectoral nerve.
- Thoraco-acromial artery.
- Lymphatics from the breast to the apical group of axillary group of lymph nodes.
- Cephalic vein. The first 2 structures pass outwards, on the other hand the lower 2 structures pass inwards.
The axilla is the pyramidal space inferior to the glenohumeral joint and superior to the axillary fascia at the junction of the arm and thorax (Fig. 6.37). The axilla provides a passageway, or “distribution center,” usually protected by the adducted upper limb, for the neurovascular structures that serve the upper limb. From this distribution center, neurovascular structures pass
Figure 6.37. Location, boundaries, and contents of axilla.
A.The axilla is a space inferior to the glenohumeral joint and superior to the skin of the axillary fossa at the junction of the arm and thorax. B.Note the axilla’s three muscular walls. The small, lateral bony wall of the axilla is the intertubercular sulcus of the humerus. C.The contents of the axilla and the scapular and pectoral muscles forming its posterior and anterior walls, respectively. The inferior border of the pectoralis major forms the anterior axillary fold, and the latissimus dorsi and teres major form the posterior axillary fold. D.Superficial dissection of the pectoral region. Note that the subcutaneous platysma muscle is cut short on the right side. The severed muscle is reflected superiorly on the left side, together with the supraclavicular nerves, so that the clavicular attachments of the pectoralis major and deltoid can be observed.
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- Superiorly via the cervico-axillary canal to (or from) the root of the neck (Fig. 6.37A).
- Anteriorly via the clavipectoral triangle to the pectoral region (Fig. 6.37D).
- Inferiorly and laterally into the limb itself.
- Posteriorly via the quadrangular space to the scapular region.
- Inferiorly and medially along the thoracic wall to the inferiorly placed axio-appendicular muscles (serratus anterior and latissimus dorsi).
The shape and size of the axilla varies, depending on the position of the arm; it almost disappears when the arm is fully abducted—a position in which its contents are vulnerable. A “tickle” reflex causes most people to rapidly resume the protected position when invasion threatens.
The axilla has an apex, a base, and four walls (three of which are muscular):
- The apex of axilla is the cervico-axillary canal, the passageway between the neck and axilla, bounded by the 1st rib, clavicle, and superior edge of the scapula. The arteries, veins, lymphatics, and nerves traverse this superior opening of the axilla to pass to or from the arm (Fig. 6.37A).
- The base of axilla is formed by the concave skin, subcutaneous tissue, and axillary (deep) fascia extending from the arm to the thoracic wall (approximately the 4th rib level), forming the axillary fossa (armpit). The base of the axilla and axillary fossa are bounded by the anterior and posterior axillary folds, the thoracic wall, and the medial aspect of the arm (Fig. 6.37C).
- The anterior wall of axilla has two layers, formed by the pectoralis major and pectoralis minor and the pectoral and clavicopectoral fascia associated with them (Figs. 6.13B and 6.37B & C). The anterior axillary fold is the inferiormost part of the anterior wall that may be grasped between the fingers; it is formed by the pectoralis major, as it bridges from thoracic wall to humerus, and the overlying integument (Fig. 6.37C & D).
- The posterior wall of axilla is formed chiefly by the scapula and subscapularis on its anterior surface and inferiorly by the teres major and latissimus dorsi (Fig. 6.37B & C). The posterior axillary fold is the inferiormost part of the posterior wall that may be grasped. It extends farther inferiorly than the anterior wall and is formed by latissimus dorsi, teres major, and overlying integument.
- The medial wall of axilla is formed by the thoracic wall (1st–4th ribs and intercostal muscles) and the overlying serratus anterior (Fig. 6.37A & B).
- The lateral wall of axilla is a narrow bony wall formed by the intertubercular sulcus in the humerus.
The axilla contains axillary blood vessels (axillary artery and its branches, axillary vein and its tributaries), lymphatic vessels, and groups of axillary lymph nodes, all embedded in a matrix of axillary fat (Fig. 6.37C). The axilla also contains large nerves that make up the cords and branches of the brachial plexus, a network of interjoining nerves that pass from the neck to the upper limb (Fig. 6.38B). Proximally, these neurovascular structures are ensheathed in a sleeve-like extension of the cervical fascia, the axillary sheath (Fig. 6.38A).
Figure 6.38. Contents of axilla.
A.Note the axillary sheath enclosing the axillary artery and vein and the three cords of the brachial plexus. The innervation of the muscular walls of the axilla is also shown. The tendon of biceps brachii slides within the intertubercular sulcus B.Dissection in which most of the pectoralis major has been removed and the clavipectoral fascia, axillary fat, and axillary sheath have been completely removed. The brachial plexus of nerves surrounds the axillary artery on its lateral and medial aspects (appearing here to be its superior and inferior aspects because the limb is abducted) and on its posterior aspect (not visible from this view). Figure 6.22 is an enlarged view of part B.
The axillary artery begins at the lateral border of the 1st rib as the continuation of the subclavian artery, and ends at the inferior border of the teres major (Fig. 6.39). It passes posterior to the pectoralis minor into the arm, and becomes the brachial artery when it passes the inferior border of the teres major, at which point it usually has reached the humerus (Fig. 6.39). For descriptive purposes, the axillary artery is divided into three parts by the pectoralis minor (the part number also indicates the number of its branches):
- The first part of the axillary artery is located between the lateral border of the 1st rib and the medial border of the pectoralis minor; it is enclosed in the axillary sheath and has one branch—the superior thoracic artery (Figs. 6.38B & 6.39A; Table 6.7).
- The second part of the axillary artery lies posterior to pectoralis minor and has two branches—the thoraco-acromial and lateral thoracic arteries—which pass medial and lateral to the muscle, respectively.
- The third part of the axillary artery extends from the lateral border of pectoralis minor to the inferior border of teres major; it has three branches. The subscapular artery is the largest branch of the axillary artery. Opposite the origin of this artery, the anterior circumflex humeral and posterior circumflex humeral arteries arise, sometimes by means of a common trunk
Figure 6.39. Arteries of proximal upper limb.
Table 6.7. Arteries of Proximal Upper Limb (Shoulder Region and Arm)
|Internal thoracic||Descends, inclining anteromedially, posterior to sternal end of clavicle and first costal cartilage; enters thorax to descend in parasternal plane; gives rise to perforating branches, anterior intercostal, musculophrenic, and superior epigastric arteries|
|Thyrocervical trunk||Ascends as a short, stout trunk, giving rise to four branches: suprascapular, ascending cervical, inferior thyroid arteries, and the cervicodorsal trunk|
|Suprascapular||Thyrocervical (or as direct branch of subclavian artery)||Passes inferolaterally crossing anterior scalene muscle, phrenic nerve, subclavian artery, and brachial plexus running laterally posterior and parallel to clavicle; next it passes over transverse scapular ligament to supraspinous fossa; then lateral to scapular spine (deep to acromion) to infraspinous fossa on posterior surface of scapula|
|Superior thoracic||Runs anteromedially along superior border of pectoralis minor; then passes between it and pectoralis major to thoracic wall; helps supply 1st and 2nd intercostal spaces and superior part of serratus anterior|
|Thoraco-acromial||Curls around superomedial border of pectoralis minor; pierces costocoracoid membrane (clavipectoral fascia); divides into four branches: pectoral, deltoid, acromial, and clavicular|
|Lateral thoracic||Descends along axillary border of pectoralis minor; follows it onto thoracic wall, supplying lateral aspect of breast|
|Circumflex humeral (anterior and posterior)||Encircle surgical neck of humerus, anastomosing with each other laterally; larger posterior branch traverses quadrangular space|
|Subscapular||Descends from level of inferior border of subscapularis along lateral border of scapula, dividing within 2–3 cm into terminal branches, the circumflex scapular and thoracodorsal arteries|
|Circumflex scapular||Subscapular artery||Curves around lateral border of scapula to enter infraspinous fossa, anastomosing with suprascapular artery|
|Thoracodorsal||Continues course of subscapular artery, descending with thoracodorsal nerve to enter apex of latissimus dorsi|
|Profunda brachii (deep artery of arm)||Accompanies radial nerve along radial groove of humerus, supplying posterior compartment of arm and participating in periarticular arterial anastomosis around elbow joint|
|Superior ulnar collateral||Accompanies ulnar nerve to posterior aspect of elbow; anastomoses with posterior ulnar recurrent artery|
|Inferior ulnar collateral||Passes anterior to medial epicondyle of humerus to anastomose with anterior ulnar collateral artery|
The branches of the axillary artery are illustrated in Fig. 6.39, and their origin and course are described in Table 6.7.
The superior thoracic artery is a small, highly variable vessel that arises just inferior to the subclavius (Fig. 6.39A). It commonly runs inferomedially posterior to the axillary vein and supplies the subclavius, muscles in the 1st and 2nd intercostal spaces, superior slips of the serratus anterior, and overlying pectoral muscles. It anastomoses with the intercostal and/or internal thoracic arteries.
The thoraco-acromial artery, a short wide trunk, pierces the costocoracoid membrane and divides into four branches (acromial, deltoid, pectoral, and clavicular), deep to the clavicular head of the pectoralis major (Fig. 6.40).
Figure 6.40. Anterior wall of axilla.
The clavicular head of the pectoralis major is excised except for its clavicular and humeral attaching ends and two cubes, which remain to identify its nerves.
The lateral thoracic artery has a variable origin. It usually arises as the second branch of the second part of the axillary artery and descends along the lateral border of the pectoralis minor, following it onto the thoracic wall (Fig. 6.38B and 6.39A); however, it may arise instead from the thoraco-acromial, suprascapular, or subscapular arteries. The lateral thoracic artery supplies the pectoral, serratus anterior, and intercostal muscles, the axillary lymph nodes, and the lateral aspect of the breast.
The subscapular artery, the branch of the axillary artery with the greatest diameter but shortest length descends along the lateral border of the subscapularis on the posterior axillary wall. It soon terminates by dividing into the circumflex scapular and thoracodorsal arteries.
The circumflex scapular artery, often the larger terminal branch of the subscapular artery, curves posteriorly around the lateral border of the scapula, passing posteriorly between the subscapularis and the teres major to supply muscles on the dorsum of the scapula (Fig. 6.39B). It participates in the anastomoses around the scapula.
The thoracodorsal artery continues the general course of the subscapular artery to the inferior angle of the scapula and supplies adjacent muscles, principally the latissimus dorsi (Fig. 6.39A & C). It also participates in the arterial anastomoses around the scapula.
The circumflex humeral arteries encircle the surgical neck of the humerus, anastomosing with each other. The smaller anterior circumflex humeral artery passes laterally, deep to the coracobrachialis and biceps brachii. It gives off an ascending branch that supplies the shoulder. The larger posterior circumflex humeral artery passes medially through the posterior wall of the axilla via the quadrangular space with the axillary nerve to supply the glenohumeral joint and surrounding muscles (e.g., the deltoid, teres major and minor, and long head of the triceps) (Fig. 6.39A & C; Table 6.7).
The axillary vein lies initially (distally) on the anteromedial side of the axillary artery, with its terminal part antero-inferior to the artery (Fig. 6.41). This large vein is formed by the union of the brachial vein (the accompanying veins of the brachial artery) and the basilic vein at the inferior border of the teres major.
Figure 6.41. Veins of axilla.
The basilic vein parallels the brachial artery to the axilla, where it merges with the accompanying veins (L. venae comitantes) of the axillary artery to form the axillary vein. The large number of smaller, highly variable veins in the axilla are also tributaries of the axillary vein.
The axillary vein has three parts, which correspond to the three parts of the axillary artery. Thus the initial, distal end is the third part, whereas the terminal, proximal end is the first part. The axillary vein (first part) ends at the lateral border of the 1st rib, where it becomes the subclavian vein. The veins of the axilla are more abundant than the arteries, are highly variable, and frequently anastomose. The axillary vein receives tributaries that generally correspond to branches of the axillary artery with a few major exceptions:
- The veins corresponding to the branches of the thoraco-acromial artery do not merge to enter by a common tributary; some enter independently into the axillary vein, but others empty into the cephalic vein, which then enters the axillary vein superior to the pectoralis minor, close to its transition into the subclavian vein.
- The axillary vein receives, directly or indirectly, the thoraco-epigastric vein(s), which is(are) formed by the anastomoses of superficial veins from the inguinal region with tributaries of the axillary vein (usually the lateral thoracic vein). These veins constitute a collateral route that enables venous return in the presence of obstruction of the inferior vena cava (see the blue box “Collateral Routes for Abdominopelvic Venous Blood”).
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