7 Pectoral Region and Axilla
THE UPPER LIMB
Pectoral Region and Axilla
Learning Objectives
By the end of the course students will be able to:
- Identify the muscles of the pectoral region, their fascia, nerve, and blood supply
- Describe the lymphatic drainage of the upper limb and the major lymphatic nodes of the axilla.
- Recall the concept of the axilla as a space, its boundaries, and its contents.
- Illustrate or describe the brachial plexus, including its parts, the nerves arising from it, and their specific origins and areas of distribution.
- Predict the functional and cutaneous loss that might result in the back, posterior shoulder, pectoral region, or cutaneous upper limb, given an injury to a specific site in the brachial plexus.
- Predict where the brachial plexus might be injured, given a functional or cutaneous loss in the back, posterior shoulder, pectoral region or cutaneous upper limb.
- Identify the axillary artery and vein, their major branches. Identify their relationships to each other, the brachial plexus, and the pectoralis minor muscle.
- Identify prominent bony features of the humerus, cubital fossa, and associated prominences of the scapula, radius, and ulna as given in the lab manual.
Reference: Moore, Clinically Oriented Anatomy, chapter 6
Particularly Relevant Blue Boxes in Moore:
●Paralysis of the Serratus Anterior, p. 709-710
● Injury to Thoracodorsal Nerve p. 710
●Arterial Anastamoses Around the Scapula, p. 726-727
●Enlargement of Axillary Lymph Nodes, p. 728
●Brachial Plexus Injuries, pp. 729-730
To access the Netter Presenter Database click here
To access the Primal Pictures software click here
Check out the Primal Pictures model of the Pectoral Region and Axilla
To check out Gray’s Photographic Dissector on the Pectoral Region click here
THE UPPER LIMB
Introduction (Moore 672-673)
The upper extremity is specialized to combine great mobility and delicacy of movements with considerable strength. The upper limb consists of a SHOULDER, ARM, FOREARM, and HAND (Netter 398); the SHOULDER, ELBOW and WRIST JOINTS separate these components. The bones of the upper limb include: the CLAVICLE and SCAPULA of the shoulder girdle, the HUMERUS of the arm, the RADIUS and ULNA of the forearm, and 27 bones of the hand. The bones of the hand are grouped into the CARPALS, METACARPALS, and PHALANGES
The sternoclavicular joint between the clavicle and the sternum serves as the upper extremity’s only bony connection to the body. The bone of the shoulder girdle, the scapula, is freestanding and embedded within a sea of shoulder muscles. It is able to move freely in all directions, allowing the shoulder much of its mobility (Netter 406).
The humerus is attached to the scapula in a very loose ball-and-socket joint. Also called the gleno-humeral articulation, this joint further enhances the mobility of the upper extremity.
OSTEOLOGY OF THE UPPER LIMB ( Moore 673-683)
Refer to these diagrams (Netter 404, 405, 406) and locate the following:
SCAPULA
Spine Glenoid fossa Subscapular fossa Supraspinatus fossa Infraspinatus fossa
Inferior angle Medial and lateral edges Acromion Coracoid process Suprascapular notch
Supraglenoid tubercle Infraglenoid tubercle
HUMERUS
Head Anatomical neck Surgical Neck
Greater tubercle Lesser tubercle medial, lateral epicondyles
Olecranon fossa capitulum trochlea
Spiral groove
ULNA
Head ulnar tuberosity styloid process
Olecranon coranoid process
RADIUS
Head styloid process radial tuberosity
The CLAVICLE (Netter 404) is a strut that suspends the scapula and the rest of the upper limb. This bone keeps the upper limb at a more functional distance from the body. Also note the sternal and acromial articulations that play an important role in the upper limb.
ARTERIAL SUPPLY OF THE UPPER LIMB – GENERAL PLAN (Moore 715-717; 736)
|
As the subclavian artery crosses the first rib and descends into the axilla, it is renamed the AXILLARY ARTERY (Netter 414). When it crosses the lower edge of the teres major muscle and reaches the arm, it is renamed the BRACHIAL ARTERY (Netter 420) . In the forearm, the artery divides to form the RADIAL ARTERY laterally and the ULNAR ARTERY medially. The radial and ulnar arteries end in the palm of the hand by forming the PALMAR ARCHES. |
In this region of the body, we can see the great vessels as they exit the heart carrying oxygen rich blood. The aorta gives off vessels to the head, neck, and upper extremities before it descends through the abdomen to supply the lower limbs. Blood goes to the head and neck via the carotid arteries. The UPPER LIMBS are supplied by the SUBCLAVIAN ARTERIES, which ascend from the heart through the thorax, loop over the first rib, and ascend into the axilla region (Netter 420).Evaluation of arterial blood pressure in the upper limb is demonstrated in this video (from the New England Journal of Medicine’s series of Videos in Clinical Medicine)
VENOUS RETURN
The deep veins of the arm parallel the brachial artery and its branches. The radial and ulnar veins of the forearm join to form two or three brachial veins (venae comitantes) which anastamose freely about the brachial artery. The venae comitantes join with the basilic vein in the region of the teres major muscle to form the axillary vein.
The superficial veins (Netter 402, 403) of the arm lie in the subcutaneous tissue. The cephalic vein passes anterior to the lateral epicondyle along the anterior aspect of the arm to the deptopectoral triangle. This site is commonly used for a surgical cut-down to insert an intravenous cannula. It pierces the clavipectoral fascia and joins the axillary vein just distal to the first rib.
The basilic vein passes anterior to the medial epicondyle and lies just medial to the biceps brachii along the arm. It penetrates the brachial fascia with the medial antebrachial cutaneous nerve, where it joins the brachial veins near the teres major muscle to form the axillary vein.
The median cubital vein is a connecting vein and runs between the cephalic vein in the forearm through the cubital fossa to join the basilic vein in the arm. It is subject to large variation. For example, the median cubital vein may be replaced by median cephalic and median basilic veins that join in the cubital fossa (a diamond-shaped region in teh anterior elbow) to fom a median forearm vein. It lies superficial to the bicipital aponeurosis, enabling it to be immobilized by the thumb of a phebotomist for venipuncture.
Clinical Note: The median cubital vein is ofen a site for venous puncture in order to obtain a sample of bllod or to administer medication. A video demonstrating peripher venous cannulation is found here (from the New England Journal of Medicine’s series of Videos in Clinical Medicine)
PECTORAL REGION (Netter 412; Moore 697-709)
The pectoral region is composed of the pectoralis major, pectoralis minor, and subclavius muscles.
The pectoral fascia encloses the pectoralis major muscle, while a deep fascia known as the clavipectoral fascia encloses the pectoralis minor and subclavius muscles. On the anterior aspect of the pectoral region is the breast region.
Deep to pectoralis major is the pectoralis minor muscle. The pectoralis minor passes from the anterior thoracic wall to the coracoid process (see Table 6.3 of Moore).
The delto-pectoral groove is found on the antero-lateral surface of arm and merges with the apex of the delto-pectoral triangle. The borders of the delto-pectoral triangle are formed by the clavicle, deltoid, and pectoralis major(clavicular head). Within the delto-pectoral groove, the cephalic vein and the small deltoid artery (branch of the thoracoacromial artery), run between the borders of the deltoid and pectoralis major muscles.
|
The pectoralis major muscle (Netter 409) is divided into clavicular and sternocostal muscle heads. The pectoralis muscle has a wide and broad origin, but has a relatively short (2″ – 3″) insertion point on the bicipital groove of the humerus. The lateral pectoral nerve innervates the clavicular head, while the medial pectoral nerve innervates the sternocostal head. The main function of this muscle is internal rotation and adduction of the humerus (“hugging” motion). |
The pectoralis minor (Netter 412, 415) is a small muscle that lies deep to the pectoralis major. The pectoralis minor serves as an important landmark in the upper limb. It divides the axillary artery into three parts (discussed later) and is one of the borders of the axilla region. It originates near the costochondral junction on the 3rd to 5th ribs, but can sometimes extend from the 2nd to the 6th rib. It inserts onto the supero-medial surface of the coracoid process. It is innervated by the medial pectoral nerve and functions in drawing the scapula forward and downward to depress the shoulder.
The subclavius muscle is a small triangular muscle that lies between the clavicle and the 1st rib. It arises from the 1st rib, close to the costochondral junction, and ascends laterally to insert onto the medial 2/3rds of the inferior surface of the clavicle. This area of insertion is known as the subclavian groove. The nerve to subclavius, which comes off of the brachial plexus just before the upper trunk is formed, innervates this muscle. The subclavius muscle acts to stabilize the clavicle at the sternoclavicular joint. In cases of a fractured clavicle, this muscle serves as a cushion to prevent jagged bone edges from lacerating the vessels (subclavian vessels) that pass below it.
The clavipectoral fascia (Netter 412 is a thickened fascia that lies below the clavicular head of the pectoralis major muscle. It fills in the space between the clavicle and the pectoralis minor. Laterally, the fascia is attached to the coracoid process. Medially, it fuses with the external intercostal membranes of the upper two intercostal spaces and also attaches to the 1st rib. Between the 1st rib and the coracoid process, the fascia thickens to form the costocoracoid ligament. Superiorly, the clavipectoral fascia splits to enclose the subclavius muscle and then attaches to the clavicle anteriorly and posteriorly (in relation to the subclavian groove). Inferiorly, the fascia splits to enclose the pectoralis minor muscle. At the lower border of pectoralis minor, the fascia fuses again and descends to attach to the axillary fascia. This results in the formation of the suspensory ligament of the axillary fascia.
The pectoral fascia is a deep fascia enclosing the pectoralis major muscle. Superiorly, it is attached to the clavicle and postero-inferiorly it extends to the scapular region to form the axillary fascia. In the axilla, the pectoral fascia is pierced by the axillary tail of Spence at the level of the 3rd intercostal space.
THE AXILLA (Netter 417; Moore 713-730)
The AXILLA is the space posterior and inferior to the clavicle by which the major nerves and vessels enter and leave the arm.
Note that the nerves descend from the cervical spinal roots into the arm and the vessels ascend from the thorax and arch over the first rib into the arm.
Axilla Borders:
The axilla is a pyramidal-shaped area with four sides, a base, and an apex. The base of this region is the axillary skin fold (the concave armpit). The apex is the space between the clavicle, scapula, and first rib.
The four sides are:
Medial: serratus anterior muscle and lateral thoracic wall
Anterior: anterior axillary fold comprised of the pectoralis major and pectoralis minor muscles
Lateral: intertubercular groove of the humerus (between insertions of pectoralis major, teres major, and latissimus dorsi muscles)
Posterior: posterior axillary fold comprised of the subscapularis, teres major and latissimus dorsi muscle masses
|
The axillary artery (Netter 414) passes through the axilla and the axillary vein lies immediately anterior to the artery. The lateral, posterior, and medial cords of the brachial plexus also pass through the axilla and are named as they relate to the second portion of the axillary artery. The clavipectoral fascia is subdivided into: 1) fascia for subclavius muscle, 2) the costocoracoid membrane/ligament, 3) fascia for pectoralis minor muscle, and 4) the suspensory ligament, which attaches to axillary skin fold.
|
Axillary Artery and its Branches (Netter 414; Moore 715-718)
The subclavian artery emerges from the thoracic region and passes below the clavicle before passing into the upper extremity. As the vessel passes over the first rib, it is renamed the axillary artery. This vessel continues down the upper extremity to the lower border of teres major muscle where it is renamed the brachial artery. The pectoralis minor muscle serves an anatomical marker, separating the axillary artery into three segments: proximal (or 1st), deep (or 2nd), and distal (or 3rd).
The first segment of the axillary artery is found proximal to the border of the pectoralis minor muscle. This segment has one branch, the supreme or superior thoracic artery.
The second segment is found deep to the body of the pectoralis minor muscle. It has two branches, the thoraco-acromial artery and the lateral thoracic artery. The thoraco-acromial artery typically has four branches: pectoral, clavicular, deltoid, and acromial. The lateral thoracic artery runs along the superficial surface of the serratus anterior muscle, alongside the long thoracic nerve.
|
The third segment of the axillary artery is found distal to the border of the pectoralis minor muscle and has three branches: 1) subscapular artery, 2) anterior humeral circumflex artery, and 3) posterior humeral circumflex artery. The subscapular artery has two branches, the scapular circumflex and the thoracodorsal. The scapular circumflex artery passes through the medial triangular space to supply the posterior scapular region while the thoracodorsal supplies the latissimus dorsi muscle. The posterior humeral circumflex artery passes through the quadrangular space, accompanied by the axillary nerve, to supply the deltoid muscle. Many arterial anastamoses occur around the scapula and these are described in the Blue Box on page 726 of Moore and in the next chapter. |
Veins of The Axillary Region
The axillary vein (Netter 181, 186 ) lies medial to the axillary artery. This vein is formed by the joining of the basilic vein and the brachial veins near the distal margin of the teres major muscle. It receives veins that correspond to the branches of the axillary artery with much variability. It becomes the subclavian vein at teh distal edge of thr first rib. The cephalic vein lies in the deltopectoral grove together with the deltoid branch of the thoracoacromial artery. Although it is useful for the insertion of venous lines, it is absent in approximately 10% of the population. It terminates in the axillary vein just distal to the clavicle.
Clinical Note:
Central venous line catheterization is a procedure in which a cather is inserted into the axillary vein, subclavian vein or internal jugular vein in order to administer medication or fluids or to measure the central venous pressure. A video demonstrating this procedure is found here (from the New England Journal of Medicine’s series of Videos in Clinical Medicine)
Lymphatic Drainage in the Axilla (Netter 178; Moore 719-721)Within the axilla, there are five sets of lymph nodes that drain specific regions. The pectoral nodes drain the anterior thorax including the breast, while the subscapular nodes drain the posterior thorax. The lateral (humeral) nodes drain the proximal extremity and the central nodes receive drainage from the pectoral, subscapular, and lateral lymph nodes. The apical nodes have efferent ducts, which form the subclavian lymphatic trunk that returns lymph to the venous system in the neck region. In addition, parasternal nodes are present along the mid-line and serve as a connection to the other side of the body.
Lymphatics also pass through the diaphragm to reach upper abdominal organs (e.g., liver).
Due to the extensive lymphatic and venous system of breast (see a discussion of the Breast in the Appendix, below), metastatic spread of cancer from the breast can readily occur. Metastatic cancer in the breast may pass: l) through axillary nodes and then up into the cervical region, 2) to the contralateral side of the body through the parasternal nodes, and 3) to upper abdominal organs through the liver.
|
Clinical Considerations Breast Cancer Detection and Surgical Treatment Breast cancer occurs in the upper lateral quadrant of the breast in about 60% of cases. In advanced stages of breast cancer, a palpable mass is usually present. As a tumor mass enlarges, it attaches to Cooper’s ligaments within the breast. When this happens, the ligaments shorten and this results in dimpling of the overlying skin. As a result, the skin will have the appearance of an orange skin or peel; this is known as peau d orange. The mass may also attach to and shorten the lactiferous ducts, which would produce a retracted or inverted nipple. Cancerous cells may also block superficial vessels draining the skin of the breast, leading to edema of the skin. Due to the excessive breast lymphatic and venous network that communicates with many parts of the body, breast cancer can easily spread. The posterior intercostal veins of the breast communicate with the vertebral veins that drain the brain. This venous communication may serve as a route for the spread of breast cancer cells. Breast cancer can spread into the abdominal region through the parasternal group of lymph nodes because of their communication with the subperitoneal lymph nodes. Breast cancer can also spread to the pelvis and affect the uterus through a route known as the pathway of Gerota. This pathway is not well defined or understood. Cancer cells may also spread from one breast to the other, through the inter-communicating lymphatic vessels. If cancer cells infiltrate the pectoralis major muscle, adhesion of the breast to the pectoralis major will result. A modified radical mastectomy involves excision of the entire breast and axillary lymph nodes, with preservation of the pectoralis major and minor muscles. |
NERVE SUPPLY – The Brachial Plexus (Netter 416, Moore 721-724)
The upper limb is innervated by the nerve fibers of the BRACHIAL PLEXUS.The brachial plexus is formed from the ventral primary rami of spinal nerves C5, C6, C7, C8, and T1. It descends infero-laterally through the axilla, where its many fibers group and regroup in a complicated, but orderly fashion, as shown in the figure below.
The five TERMINAL BRANCHES of the brachial plexus pass out of the axilla and descend into the arm. These terminal branches provide motor and sensory innervation to the structures of the arm and shoulder. There is an innervation pattern for the upper limb, as there was for the lower limb. Nerves from the brachial plexus can be categorized as either preaxial or postaxial nerves. Preaxial nerves supply muscles that flex, while postaxial nerves supply muscles that act to extend. This organization is related to the development of the limbs and their division into anterior and posterior compartments. The flexors and extensors are located in the anterior and posterior compartments, respectively. The ulnar and median nerves supply preaxial muscles and are formed from the anterior divisions of the brachial plexus. The radial nerve, however, supplies postaxial extender muscles and is formed from the posterior divisions of the brachial plexus.
The spinal nerves C5 through T1 make up the ROOTS of the brachial plexus. These five roots combine to form three TRUNKS: upper, middle, and lower. Each trunk then divides into a posterior and anterior DIVISION. All three posterior divisions join to form the Posterior CORD. The anterior divisions of the upper and middle trunks combine to form the Lateral CORD and the anterior division of the lower trunk continues on as the Medial CORD. The cords are named by their position as it relates to the second segment of the axillary artery (lateral, posterior, and medial). Five large terminal branches arise from the cords: 1) musculocutaneous nerve, 2) axillary nerve, 3) radial nerve (from posterior cord), 4) median nerve (from both lateral and medial cords), and 5) ulnar nerve (from medial cord).
The “Rule of FIVES” is a helpful mnemonic for remembering the brachial plexus. It is formed from 5 roots (starting with C5 through Tl); it passes through 5 stages in formation (ventral roots, trunks, divisions, cords, and terminal branches); and it gives rise to 5 major terminal branches (musculocutaneous, axillary, radial, median, and ulnar). We will discuss the function of the terminal branches later in the syllabus.
Clinical Correlation: Lesions to the Brachial Plexus – IMPORTANT!
1. Injury to the Roots
A. Nerve root compression is most commonly the result of cervical spondylosis, a condition in which the patient first complains of pain in the arm or shoulder in a dermatomal distribution, followed by progressive muscular weakness.
B. Trauma to the roots produces not only complete paralysis of the upper limb but also winging of the scapula because of paralysis of the serratus anterior muscle innervated by the long thoracic nerve. In addition, patients may experience weakness of scapular rotation owing to involvement of the dorsal scapular nerve to the rhomboids.
2. Injury to the trunks and cords produces distinct syndromes.
A. Upper trunk injury (Erb Duchenne paralysis) is the most common problem. Violent downward displacement of the arm, such as results from being thrown from a horse, may tear the 5th and 6th roots of the upper trunk.
1. Patients lose function of all nerves that receive contributions from the anterior an posterior division of the upper trunk.
2. Loss of abduction, radial flexion and external rotation causes the upper limb to hang by the side in internal rotation or “waiters tip” position“
3. Involvement of the lateral pectoral nerve results in inability to touch the opposite shoulder (due to paralysis of the pectoralis major muscle)
B. Middle trunk injury by itself, is rare, but it may occur as the result of an attempted intrascalene anesthetic block
C. Lower Trunk injury (Klumpke paralysis) is less common but may be caused by violent or prolonged upward displacement of the arm, dislocation of he shoulder, apical tumors of the lung, a cervical rib or scalene compression syndrome.
1. Function is lost in all nerves derived from the anterior and posterior divisions of the lower trunk
2. Injury results in loss of ulnar flexion of the wrist and paralysis of many of the intrinsic muscles of the hand
3. Involvement of the medial pectoral nerve produces inability to adduct the arm in the lowered position against resistance (due to paralysis of pectoralis minor and the sternocostal head of pectoralis major.
D. Cord injuries
1. Injury to the posterior cord (aka. Saturday Night or crutch palsy) or to the radial nerve results in loss o fthe extensor muscles of the arm, forearm and wrist (wrist drop)
2. Thoracodorsal nerve injury produces paralysis of the latissimus dorsi muscle
3. Axillary nerve injury results in deltoid and teres minor paralysis (loss of shoulder abduction and weakend external rotation) with loss of sensation over the deltoid muscle
3. Scalene (thoracic outlet syndrome) can be produced by spasm of the anterior and middle scalene muscles or by a cervical rib that restricts the size of the thoracic outlet
1. Spasm can compress portions of the brachial plexus, most commonly the lower trunk, causing pain along th emedial border of the arm and atrophy of some of the small muscles of the hand
2. Spasm may also compress the subclavian artery, causing ischemia of the arm, which in turn can result in loss of nerve function and subsequent muscular paralysis
APPENDIX: THE BREAST (Netter 179, 180)
The breast is a modified sudoriferous (sweat) gland, specifically an apocrine gland. It is a paired gland found in both males and females. In males and immature females, the breast is rudimentary. During puberty in females the breast undergoes developmental changes, but it attains its final development in late pregnancy and during lactation.
The female breast is located atop the superficial fascia of the anterior thoracic wall. It overlies the pectoralis major muscle, serratus anterior muscle, and the aponeurosis of the external oblique abdominus muscle. The breast’s upper lateral quadrant extends into the axilla as the axillary tail of Spence.
ANATOMICAL RELATIONS OF THE BREAST
The base of the breast is related to the pectoral fascia, the pectoralis major, the serratus anterior, and the aponeurosis of the external oblique abdominis muscle. The breast is separated from the pectoral fascia and the pectoralis major by an areolar space, also known as the submammary or retromammary space. This space allows for the independent movement of the breast over the pectoral fascia and the pectoralis major muscle.
STRUCTURE OF THE BREAST
The breast is structurally designed to produce milk for a newborn. The breast is comprised of several components:
1. The skin
2. Parenchyma
3. The Stroma
THE SKIN
The skin has the following features:
1. The nipple or mammary papilla: This is a cylindrical or conical projection, which lies slightly below the center of the breast. It forms the apex of the breast and in nulliparous females (women who have not given birth) it typically lies over the 4th intercostal space. The nipple is transversed by 15-20 lactiferous ducts, which discharge milk to the surface of the skin.
The nipple also contains non-striated myocytes (smooth muscle cells), which are arranged circularly and longitudinally. Upon stimulation, either by sucking or by tactile stimulation, the circular smooth muscle cells contract. This causes erection of the nipple and allows the lactiferous duct to open in lactating mothers. When the longitudinal smooth muscle cells contract, this causes the nipple to flatten. When the nipple flattens, the lactiferous ducts close and prevent the outflow of milk in a lactating mother.
2. The Areola: This is a highly pigmented area of skin that surrounds the base of the nipple. In caucasian females it is a rose pink color, while in blacks and other melanized races, it is darker and highly pigmented. During pregnancy, the pigmentation of the areola increases and becomes darker in color. After pregnancy, it never returns to its original color.
THE PARENCHYMA
The parenchyma is the milk producing or glandular tissue of the breast and contains about 15-20 lobes. Each lobe contains clusters of lobules and each lobule contains clusters of alveoli. The lobes are drained by lactiferous ducts, which open into the rough ended tip of the nipple. At the base of the areola, the lactiferous ducts expand, forming the lactiferous sinus. This sinus acts as a reservoir for milk during lactation.
THE STROMA
The stroma acts as the supporting tissue of the breast. It is made up of both fibrous and adipose tissue and is enclosed by subcutaneous tissue. From the subcutaneous tissue, septa emerge to attach the skin and the lobes to the pectoral fascia. This results in the formation of the suspensory ligament of Cooper. Adipose tissue gives the breast its smooth contour and the volume of adipose tissue is the main determinant in breast size.
Blood Supply to the Breast (Netter 180)
The breast is supplied by several arterial sources that include:
- Perforating branches of the internal thoracic artery
- Pectoral branch of the thoracoacromial artery
- Lateral branches of the posterior intercostal artery
- Lateral thoracic artery
Venous Drainage of the Breast
The breast is drained by a series of veins, which closely correspond with the arterial network. Around the base of the nipple, veins form an anastomosis known as the circulus venosus. From this anastomotic network, veins emerge into the surrounding tissue. Superficial veins drain fluid from the cutaneous tissues into the internal thoracic vein and the superficial veins of the inferior neck region. Deep veins drain into the axillary vein, the anterior intercostal veins, and the posterior intercostal veins.
Lymphatic Drainage of the Breast
1. Superficial set of lymphatic vessel drains the skin of the breast, except the nipple and areola
2. Deep set of the lymphatic vessels drains the parenchyma, stroma, nipple, and areola of the breast.
About 75% of breast lymph drains into the axillary lymph nodes, 20% into the parasternal lymph nodes, and about 5% drains into the posterior intercostal nodes. The lymph of one breast can also drain into the opposite breast, by passing through the intermammary cleft.
Pectoral Region and Axilla quiz – click here