Bones of the Shoulder Girdle and Arm



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Bones of the Shoulder Girdle and Arm
The shoulder girdle consists of the clavicle and the scapula, which articulate with one another at the acromioclavicular joint.

Clavicle


The clavicle is a long, slender bone that lies horizontally across the root of the neck just beneath the skin. It articulates with the sternum and first costal cartilage medially and with the acromion process of the scapula laterally. The clavicle acts as a strut that holds the arm away from the trunk. It also transmits forces from the upper limb to the axial skeleton and provides attachment for muscles.

The medial two thirds of the clavicle is convex forward and its lateral third is concave forward

Scapula

The scapula is a flat triangular bone that lies on the posterior chest wall between the second and the seventh ribs. On its posterior surface, the spine of the scapula projects backward. The lateral end of the spine is free and forms the acromion, which articulates with the clavicle. The superolateral angle of the scapula forms the pear-shaped glenoid cavity, or fossa, which articulates with the head of the humerus at the shoulder joint. The coracoid process projects upward and forward above the glenoid cavity and provides attachment for muscles and ligaments. Medial to the base of the coracoid process is the suprascapular notch.



The anterior surface of the scapula is concave and forms the shallow subscapular fossa. The posterior surface of the scapula is divided by the spine into the supraspinous fossa above and an infraspinous fossa below. The inferior angle of the scapula can be palpated easily in the living subject and marks the level of the seventh rib and the spine of the seventh thoracic vertebra.

Humerus


The humerus articulates with the scapula at the shoulder joint and with the radius and ulna at the elbow joint. The upper end of the humerus has a head, which forms about one third of a sphere and articulates with the glenoid cavity of the scapula. Immediately below the head is the anatomic neck. Below the neck are the greater and lesser tuberosities, separated from each other by the bicipital groove. Where the upper end of the humerus joins the shaft is a narrow surgical neck. About halfway down the lateral aspect of the shaft is a roughened elevation called the deltoid tuberosity. Behind and below the tuberosity is a spiral groove, which accommodates the radial nerve.

The lower end of the humerus possesses the medial and lateral epicondyles for the attachment of muscles and ligaments, the rounded capitulum for articulation with the head of the radius, and the pulley-shaped trochlea for articulation with the trochlear notch of the ulna. Above the capitulum is the radial fossa, which receives the head of the radius when the elbow is flexed. Above the trochlea anteriorly is the coronoid fossa, which during the same movement receives the coronoid process of the ulna. Above the trochlea posteriorly is the olecranon fossa, which receives the olecranon process of the ulna when the elbow joint is extended



Parts of each bone

A. Clavicle (collar-bone)

It is a commonly fractured bone that forms the pectoral (shoulder) girdle with the scapula ,

which connects the upper limb to the axial skeleton (sternum), by articulating with the sternum

at the sternoclavicular joint and with the acromion of the scapula at the acromioclavicular

joint.

Has the medial two thirds tilted convex forward and the lateral one third flattened with a



marked concavity.

Is the first bone to begin ossification during fetal development, but it is the last one to



complete ossification , at about age 21 years.

Is the only long bone to be ossified intramembranously



Scapula (shoulder blade)

1. Spine of the scapula

Is a triangular-shaped process that continues laterally as the acromion. It divides the dorsal surface of the scapula into the upper supraspinous and lower infraspinous fossae. It provides an origin for the deltoid and an insertion for the trapezius.



2. Acromion

It is the lateral end of the spine and articulates with the clavicle. It provides an origin for the deltoid and an insertion for the trapezius.



3. Coracoid process

It provides the origin of the coracobrachialis and biceps brachii and the insertion of the

pectoralis minor. It provides an attachment site for the coracoclavicular, coracohumeral, and coracoacromial ligaments and the costocoracoid membrane.

4. Scapular notch

Is bridged by the superior transverse scapular ligament and is converted into a foramen, which permits passage of the suprascapular nerve.


5. Glenoid cavity

It is deepened by the glenoid labrum for the head of the humerus.


6. Supraglenoid and infraglenoid tubercles

They provide origins for the tendons of the long heads of the biceps brachii and triceps brachii muscles, respectively.


C. Humerus

1. Head

It has a smooth, rounded, articular surface and articulates with the scapula at the



glenohumeral joint.

2. Anatomic neck

It is an indentation distal to the head of the humerus and provides for the attachment of the

fibrous joint capsule.

3. Greater tubercle

It lies just lateral to the anatomic neck and provides attachments for the supraspinatus,

infraspinatus, and teres minor muscles.

4. Lesser tubercle

It lies on the anterior medial side of the humerus, just distal to the anatomic neck, and provides

an insertion for the subscapularis muscle.

5. Intertubercular (bicipital) groove

It lies between the greater and lesser tubercles, lodges the tendon of the long head of the

biceps brachii muscle, and is bridged by the transverse humeral ligament , which restrains

the tendon of the biceps brachii long head.

Provides insertions for the pectoralis major on its lateral lip , the teres major on its medial lip , and the latissimus dorsi on its floor.

6. Surgical neck

It is a narrow area distal to the tubercles that is a common site of fracture and is in contact with the axillary nerve and the posterior humeral circumflex artery.



7. Deltoid tuberosity

It is a V-shaped roughened area on the lateral aspect of the midshaft that marks the insertion of

the deltoid muscle.

8. Spiral groove

It contains the radial nerve, separating the origin of the lateral head of the triceps above and

the origin of the medial head below.

9. Trochlea

It is the medial articular surface, shaped like a spool, and articulates with the trochlear notch



of the ulna .

10. Capitulum

It is the lateral articular surface, globular in shape, and articulates with the head of the radius.

P.21

11. Olecranon fossa

It is a posterior depression above the trochlea of the humerus that houses the olecranon of the

ulna on full extension of the forearm.

12. Coronoid fossa

It is an anterior depression above the trochlea of the humerus that accommodates the coronoid process of the ulna on flexion of the elbow.



13. Radial fossa

It is an anterior depression above the capitulum that is occupied by the head of the radius

during full flexion of the elbow joint.

14. Lateral epicondyle

It projects from the capitulum and provides the origin of the supinator and extensor muscles of

the forearm.

15. Medial epicondyle

It projects from the trochlea and has a groove on the back for the ulnar nerve and superior ulnar

collateral artery.It provides attachment sites for the ulnar collateral ligament, the pronator teres, and the common tendon of the forearm flexor muscles.

The Axilla

The axilla, or armpit, is a pyramid-shaped space between the upper part of the arm and the side of the chest. It forms an important passage for nerves, blood, and lymph vessels as they travel from the root of the neck to the upper limb. The upper end of the axilla, or apex, is directed into the root of the neck and is bounded in front by the clavicle, behind by the upper border of the scapula, and medially by the outer border of the first rib. The lower end, or base, is bounded in front by the anterior axillary fold (formed by the lower border of the pectoralis major muscle), behind by the posterior axillary fold (formed by the tendon of latissimus dorsi and the teres major muscle), and medially by the chest wall.

Walls of the Axilla

The walls of the axilla are made up as follows:


  • Anterior wall: By the pectoralis major, subclavius, and pectoralis minor muscles

  • Posterior wall: By the subscapularis, latissimus dorsi, and teres major muscles from above down

  • Medial wall: By the upper four or five ribs and the intercostal spaces covered by the serratus anterior muscle

  • Lateral wall: By the coracobrachialis and biceps muscles in the bicipital groove of the humerus

The base is formed by the skin stretching between the anterior and posterior walls The axilla contains the principal vessels and nerves to the upper limb and many lymph nodes.
Key Muscles in the Axilla

Pectoralis Minor

The pectoralis minor is a thin triangular muscle that lies beneath the pectoralis major. It arises from the third, fourth, and fifth ribs and runs upwards and laterally to be inserted by its apex into the coracoid process of the scapula. It crosses the axillary artery and the brachial plexus of nerves. It is used when describing the axillary artery to divide it into three parts


Table 9-1 Muscles Connecting the Upper Limb to the Thoracic Wall



Clavipectoral Fascia

The clavipectoral fascia is a strong sheet of connective tissue that is attached above to the clavicle. Below, it splits to enclose the pectoralis minor muscle and then continues downward as the suspensory ligament of the axilla and joins the fascial floor of the armpit.

Contents of the Axilla

The axilla contains the axillary artery and its branches, which supply blood to the upper limb; the axillary vein and its tributaries, which drain blood from the upper limb; and lymph vessels and lymph nodes, which drain lymph from the upper limb and the breast and from the skin of the trunk, down as far as the level of the umbilicus. Lying among these structures in the axilla is an important nerve plexus, the brachial plexus, which innervates the upper limb. These structures are embedded in fat.

Axillary Artery

The axillary artery begins at the lateral border of the first rib as a continuation of the subclavian and ends at the lower border of the teres major muscle, where it continues as the brachial artery. Throughout its course, the artery is closely related to the cords of the brachial plexus and their branches and is enclosed with them in a connective tissue sheath called the axillary sheath. If this sheath is traced upward into the root of the neck, it is seen to be continuous with the prevertebral fascia.
First Part of the Axillary Artery

This extends from the lateral border of the first rib to the upper border of the pectoralis minor.

Relations


  • Anteriorly: The pectoralis major and the skin. The cephalic vein crosses the artery

  • Posteriorly: The long thoracic nerve (nerve to the serratus anterior)

  • Laterally: The three cords of the brachial plexus

  • Medially: The axillary vein

Second Part of the Axillary Artery

This lies behind the pectoralis minor muscle.

Relations


  • Anteriorly: The pectoralis minor, the pectoralis major, and the skin

  • Posteriorly: The posterior cord of the brachial plexus, the subscapularis muscle, and the shoulder joint

  • Laterally: The lateral cord of the brachial plexus.

  • Medially: The medial cord of the brachial plexus and the axillary vein.

Third Part of the Axillary Artery

This extends from the lower border of the pectoralis minor to the lower border of the teres major.


Relations



  • Anteriorly: The pectoralis major for a short distance; lower down the artery it is crossed by the medial root of the median nerve.

  • Posteriorly: The subscapularis, the latissimus dorsi, and the teres major. The axillary and radial nerves also lie behind the artery

  • Laterally: The coracobrachialis, the biceps, and the humerus. The lateral root of the median and the musculocutaneous nerves also lie on the lateral side.

  • Medially: The ulnar nerve, the axillary vein, and the medial cutaneous nerve of the arm

Branches of the Axillary Artery

From the first part:



  • The highest thoracic artery is small and runs along the upper border of the pectoralis minor.

From the second part:

  • The thoracoacromial artery immediately divides into terminal branches.

  • The lateral thoracic artery runs along the lower border of the pectoralis minor

From the third part:

  • The subscapular artery runs along the lower border of the subscapularis muscle.

  • The anterior and posterior circumflex humeral arteries wind around the front and the back of the surgical neck of the humerus, respectively

  • Axillary Vein

  • The axillary vein is formed at the lower border of the teres major muscle by the union of the venae comitantes of the brachial artery and the basilic vein. It runs upward on the medial side of the axillary artery and ends at the lateral border of the first rib by becoming the subclavian vein.

  • The vein receives tributaries, which correspond to the branches of the axillary artery, and the cephalic vein.

The Breasts

Location and Description

The breasts are specialized accessory glands of the skin that secrete milk. They are present in both sexes. In males and immature females, they are similar in structure. The nipples are small and surrounded by a colored area of skin called the areola. The breast tissue consists of a system of ducts embedded in connective tissue that does not extend beyond the margin of the areola.

Puberty

At puberty in females, the breasts gradually enlarge and assume their hemispherical shape under the influence of the ovarian hormones. The ducts elongate, but the increased size of the glands is mainly from the deposition of fat. The base of the breast extends from the second to the sixth rib and from the lateral margin of the sternum to the midaxillary line. The greater part of the gland lies in the superficial fascia. A small part, called the axillary tail , extends upward and laterally, pierces the deep fascia at the lower border of the pectoralis major muscle, and enters the axilla.



Each breast consists of 15 to 20 lobes, which radiate out from the nipple. The main duct from each lobe opens separately on the summit of the nipple and possesses a dilated ampulla just before its termination. The base of the nipple is surrounded by the areola. Tiny tubercles on the areola are produced by the underlying areolar glands.

The lobes of the gland are separated by fibrous septa that serve as suspensory ligaments Behind the breasts is a space filled by loose connective tissue called the retromammary space .

Young Women

In young women the breasts tend to protrude forward from a circular base.

Pregnancy

Early


In the early months of pregnancy, there is a rapid increase in length and branching in the duct system .The secretory alveoli develop at the ends of the smaller ducts and the connective tissue becomes filled with expanding and budding secretory alveoli. The vascularity of the connective tissue also increases to provide adequate nourishment for the developing gland. The nipple enlarges, and the areola becomes darker and more extensive as a result of increased deposits of melanin pigment in the epidermis. The areolar glands enlarge and become more active.

Late


During the second half of pregnancy, the growth process slows. The breasts, however, continue to enlarge, mostly because of the distention of the secretory alveoli with the fluid secretion called colostrum.

Postweaning

Once the baby has been weaned, the breasts return to their inactive state. The remaining milk is absorbed, the secretory alveoli shrink, and most of them disappear. The interlobular connective tissue thickens. The breasts and the nipples shrink and return nearly to their original size. The pigmentation of the areola fades, but the area never lightens to its original color.

Postmenopause

After the menopause, the breast atrophies Most of the secretory alveoli disappear, leaving behind the ducts. The amount of adipose tissue may increase or decrease. The breasts tend to shrink in size and become more pendulous. The atrophy after menopause is caused by an absence of ovarian estrogens and progesterone.

Blood Supply

Arteries

The branches to the breasts include the perforating branches of the internal thoracic artery and the intercostal arteries. The axillary artery also supplies the gland via its lateral thoracic and thoracoacromial branches.

Veins

The veins correspond to the arteries.



Lymph Drainage

The lymph drainage of the mammary gland is of great clinical importance because of the frequent development of cancer in the gland and the subsequent dissemination of the malignant cells along the lymph vessels to the lymph nodes.

The lateral quadrants of the breast drain into the anterior axillary or pectoral group of nodes (situated just posterior to the lower border of the pectoralis major muscle). The medial quadrants drain by means of vessels that pierce the intercostal spaces and enter the internal thoracic group of nodes (situated within the thoracic cavity along the course of the internal thoracic artery). A few lymph vessels follow the posterior intercostal arteries and drain posteriorly into the posterior intercostal nodes (situated along the course of the posterior intercostal arteries); some vessels communicate with the lymph vessels of the opposite breast and with those of the anterior abdominal wall.
Lymph Drainage and Carcinoma of the Breast

The importance of knowing the lymph drainage of the breast in relation to the spread of cancer from that organ cannot be overemphasized. The lymph vessels from the medial quadrants of the breast pierce the second, third, and fourth intercostal spaces and enter the thorax to drain into the lymph nodes alongside the internal thoracic artery. The lymph vessels from the lateral quadrants of the breast drain into the anterior or pectoral group of axillary nodes. It follows, therefore, that a cancer occurring in the lateral quadrants of the breast tends to spread to the axillary nodes. Thoracic metastases are difficult or impossible to treat, but the lymph nodes of the axilla can be removed surgically.

Approximately 60% of carcinomas of the breast occur in the upper lateral quadrant. The lymphatic spread of cancer to the opposite breast, to the abdominal cavity, or into lymph nodes in the root of the neck is caused by obstruction of the normal lymphatic pathways by malignant cells or destruction of lymph vessels by surgery or radiotherapy. The cancer cells are swept along the lymph vessels and follow the lymph stream. The entrance of cancer cells into the blood vessels accounts for the metastases in distant bones.

In patients with localized cancer of the breast, most surgeons do a simple mastectomy or a lumpectomy, followed by radiotherapy to the axillary lymph nodes and/or hormone therapy. In patients with localized cancer of the breast with early metastases in the axillary lymph nodes, most authorities agree that radical mastectomy offers the best chance of cure. In patients in whom the disease has already spread beyond these areas (e.g., into the thorax), simple mastectomy, followed by radiotherapy or hormone therapy, is the treatment of choice.

Radical mastectomy is designed to remove the primary tumor and the lymph vessels and nodes that drain the area. This means that the breast and the associated structures containing the lymph vessels and nodes must be removed en bloc. The excised mass is therefore made up of the following: a large area of skin overlying the tumor and including the nipple; all the breast tissue; the pectoralis major and associated fascia through which the lymph vessels pass to the internal thoracic nodes; the pectoralis minor and associated fascia related to the lymph vessels passing to the axilla; all the fat, fascia, and lymph nodes in the axilla; and the fascia covering the upper part of the rectus sheath, the serratus anterior, the subscapularis, and the latissimus dorsi muscles. The axillary blood vessels, the brachial plexus, and the nerves to the serratus anterior and the latissimus dorsi are preserved. Some degree of postoperative edema of the arm is likely to follow such a radical removal of the lymph vessels draining the upper limb.

A modified form of radical mastectomy for patients with clinically localized cancer is also a common procedure and consists of a simple mastectomy in which the pectoral muscles are left intact. The axillary lymph nodes, fat, and fascia are removed. This procedure removes the primary tumor and permits pathologic examination of the lymph nodes for possible metastases.

Lymph Nodes of the Axilla
The axillary lymph nodes (20-30 in number) drain lymph vessels from the lateral quadrants of the breast, the superficial lymph vessels from the thoracoabdominal walls above the level of the umbilicus, and the vessels from the upper limb.
The lymph nodes are arranged in six groups.
1. Anterior (pectoral) group: Lying along the lower border of the pectoralis minor behind the pectoralis major, these nodes receive lymph vessels from the lateral quad rants of the breast and superficial vessels from the anterolateral abdominal wall above the level of the umbilicus.
2. Posterior (subscapu1ar group: Lying in front of the subscapularis muscle, these nodes receive superficial lymph vessels from the back, down as far as the level of the iliac crests.
3. Lateral group: Lying along the medial side of the axillary vein, these nodes receive most of the lymph vessels of the upper limb (except those superficial vessels draini ng the lateral side).
4. Central group: Lying in the center of the axilla in the axillary fat, these nodes receive lymph from the above three groups.
5. Infraclavicular (deltopectoral) group: These nodes are not strictly axillary nodes because they are located outside the axilla. They lie in the groove between the deltoid and pectoralis major muscles and receive superficial lymph vessels from the lateral side of the hand, forearm, and arm.
6. Apical group: Lying at the apex of the axilla at the lateral border of the first rib, these nodes receive the efferent lymph vessels from all the other axillary nodes.
The apical nodes drain into the subclavian lymph trunk. On the left side this trunk drains into the thoracic duct and on the right side it drains into the right lymph trunk. Alternatively, the lymph trunks may drain directly into one of the large veins at the root of the neck.
Brachial Plexus

The brachial plexus is formed in the posterior triangle of the neck by the union of the anterior rami of the fifth, sixth, seventh, and eighth cervical and the first thoracic spinal nerves.

The plexus can be divided into roots, trunks, divisions, and cords. The roots of C5 and 6 unite to form the upper trunk, the root of C7 continues as the middle trunk, and the roots of C8 and TI unite to form the lower trunk. Each trunk then divides into anterior and posterior divisions. The anterior divisions of the upper and middle trunks unite to form the lateral cord, the anterior division of the lower trunk continues as the medial cord, and the posterior divisions of all three trunks join to form the posterior cord.
The roots, trunks, and divisions of the brachial plexus reside in the lower part of the posterior triangle of the neck. The cords become arranged around the axillary artery in the axilla. Here, the brachial plexus and the axillary artery and vein are enclosed by a sheath of fascia called the axillary sheath.

Cords of the Brachial Plexus All three cords of the brachial


plexus lie above and lateral to the first part of the axillaty artery.The cords of the plexus have the relationship to the second part of the axillary artery that is indicated by their names.
Most branches of the cords that form the main nerve trunks of the upper limb continue this relationship to the artery in its third part.
The branches of the different parts of the brachial plexus are as follows:

Roots
1. Dorsal scapular nerve (C5)


2. Long thoracic nerve (C5, 6, and 7)

Upper trunk


1. Nerve to subclavius (C5 and 6).

2. Suprascapular nerve (supplies the supraspinatus and infraspinatus muscles)

Lateral cord
1. Lateral pectoral nerve
2. Musculocutaneous nerve
3. Lateral root of median nerve
Medial cord


  1. Medial pectoral nerve.

  2. Medial cutaneous nerve of arm

  3. Medial cutaneous nerve of forearm.

  4. Ulnar nerve.

  5. Medial root of median nerve.
    Posterior cord
    1. Upper subscapular nerves

2. lower subscapular nerves
3. Thoracodorsal nerve
4.Axillary nerve
5. Radial nerve

Branches of the Brachial Plexus Found in the Axilla: The nerve to the subclavius (C5 and 6): supplies the subclavius muscle. It is important clinic ally because it may give a contribution (C5) to the phrenic nerve; this branch, when present, is referred to as the accessory phrenic nerve.

The long thoracic nerve (C5, 6, and 7):

Arises from the roots of the brachial plexus in the neck and enters the axilla by passing down over the lateral border of the first rib behind the axillary vessels and brachial plexus. It descends over the lateral surface of the serratus anterior muscle, which it supplies.

The lateral pectoral nerve: arises from the lateral cord of the brachial plexus and supplies the pectoralis major muscle.

The musculocutaneous nerve:

Arises from the lateral cord of the brachial plexus, supplies the coracobrachialis muscle, and leaves the axilla by piercing that muscle.

The lateral root of the median nerve: is the direct continuation of the lateral cord of the brachial plexus. It is joined by the medial root to form the median nerve trunk, and this passes downward on the lateral side of the axillary artery. The median nerve gives off no branches in the axilla.

The medial pectoral nerve:

Arises from the medial cord of the brachial plexus, supplies and pierces the pectoralis minor muscle, and supplies the pectoralis major muscle.

The medial cutaneous nerve of the arm (TI):

Arises from the medial cord of the brachial plexus and is joined by the intercostobrachial nerve (lateral Cutaneous branch of the second intercostal nerve). It supplies the skin on the medial side of the arm.

The medial cutaneous nerve of the forearm: arises from the medial cord of the brachial plexus and descends in front of the axillary artery.
The ulnar nerve (C8 and TI):

Arises from the medial cord of the brachial plexus and descends in the interval between the axillary artery and vein. The ulnar nerve gives off no branches in the axilla.

The medial root of the median nerve:

Arises from the medial cord of the brachial plexus and crosses in front of the third part of the axillary artery to join the lateral root of the median nerve.

The upper and lower subscapular nerves

Arise from the posterior cord of the brachial plexus and supply the upper and lower parts of the subscapularis muscle. In addition, the lower subscapular nerve supplies the teres muscle.


The thoracodorsal nerve: arises from the posterior cord of the brachial plexus and runs downward to supply the latissimus dorsi muscle.

The axillary nerve:

Is one of the terminal branches of the Posterior cord of the brachial plexus. It turns backward and passes through the quadrangular space. Having given off a branch to the shoulder joint, it divides into anterior and posterior branches.

The radial nerve: is the largest branch of the brachial plexus and lies behind the axillary artery. It gives off branches to the long and medial heads of the triceps muscle and the posterior cutaneous nerve of the arm. The latter branch is distributed to the skin on the middle of the back of the arm.



The back and the scapular region

MUSCLES
Trapezius


The trapezius is a large, flat, triangular muscle that extends over the back of the neck and thorax.

• Origin: From the medial third of the superior nuchal line of the occipital bone, the external occipital protuberance, and the ligamentum nuchae: from the spine of the seventh cervical vertebra and the spines and supraspinous ligaments of all the thoracic vertebrae.


• Insertion: The upper fibers are directed downward and laterally into the lateral third of the clavicle; the middle fibers are directed horizontally into the acromion and the upper border of the spine of the scapula; the lowest fibers are directed upward and laterally and are inserted on the medial end of the spine of the scapula.
• Nerve supply: Motor fibers from the spinal part of the accessory nerve (cranial nerve XI) and sensory fibers from the third and fourth cervical nerves.

• Action: The trapezius muscle suspends the shoulder girdle from the skull and the vertebral column. The upper fibers elevate the scapula. The middle fibers pull the scapula medially. The lower fibers pull the medial border of the scapula downward so that the glenoid cavity faces upward and forward.


Knowing that the scapula rotates around the point of attachment of the coracoid process to the clavicle by the coracoclavicular ligament, it is easy to understand that the superior and inferior fibers of the trapezius assist the serratus anterior muscle in rotating the scapula when the arm is raised above the head.

Subscapularis

• Origin: From the subscapular fossa on the anterior surface of the scapula.


• Insertion: Its fibers converge and are inserted on the lesser tuberosity of the humerus.

• Nerve supply: The upper and lower subscapular nerves, branches of the posterior cord of the brachial plexus.

• Action: Medially rotates the arm and acts with the other short muscles around the shoulder joint in helping to stabilize this joint.

Latissimus Dorsi

The latissimus dorsi is a large, flat, triangular muscle that extends over the lumbar region and the lower part of the thorax.


• Origin: From the posterior part of the iliac crest, the lumbar fascia, and the spines of the lower six thoracic vertebrae (deep to the trapezius), from the lower three or four ribs, and sometimes by a few fibers from the inferior angle of the scapula.
• Insertion: Its tendon wraps around the lower border of the teres major muscle and is inserted into the floor of the bicipital groove of the humerus.

• Nerve supply: The thoracodorsal nerve, a branch of the posterior cord of the brachial plexus.


• Action: It extends, adducts, and medially rotates the arm.

Teres Major

• Origin: From the lower third of the lateral border of the scapula.


• Insertion: Into the medial lip of the bicipital groove of the humerus.

• Nerve supply: Lower subscapular nerve from the posterior cord of the brachial plexus.


• Action: It medially rotates and adducts the arm.

Serratus Anterior

The serratus anterior is a large, thin muscle that covers the lateral chest wall.

• Origin: From the outer surfaces of the upper eight ribs.
• Insertion: Into the medial border of the scapula. A great part of this muscle is inserted in the region of the inferior angle.
• Nerve supply: The long thoracic nerve, which arises from roots C5, 6, and 7 of the brachial plexus.
• Action: It draws the scapula forward around the thoracic wall and, because of the greater pull exerted on the inferior angle, rotates it so that the inferior angle passes laterally and forward and the glenoid cavity is raised upward and forward; in this action the muscle is assisted by the trapezius. This rotation of the scapula takes place when the arm is raised from the horizontal abducted position upward to a vertical position above the head. This muscle is also used when the arm is pushed forward in the horizontal position as in a forward punch.

Levator Scapulae

• Origin: From the transverse processes of the upper four cervical vertebrae.
• Insertion: Into the medial border of the scapula opposite the supraspinous fossa.

• Nerve supply: From the third and fourth cervical nerves and from the dorsal scapular nerve (C5).

• Action: It raises the medial border of the scapula. When it acts in conjunction with the middle fibers of the trapezius and with the rhomboids, it pulls the scapula medially arid upward, that is, it braces the shoulder backward.

Rhomboid Minor

• Origin: From the lower part of the ligamentum nuchae and the spines of the seventh cervical and first thoracic vertebrae.

• Insertion: Into the medial border of the scapula opposite the root of the spine.

• Nerve supply: From the dorsal scapular nerve (C5).
• Action: With the rhomboid major and levator scapulae, it elevates the medial border of the Scapula and pulls it medially.

Rhomboid Major

• Origin: From the second to the fifth thoracic spines and the corresponding supraspinous ligaments.
• Insertion: Into the medial border of the scapula opposite the infraspinous fossa.

• Nerve supply: From the dorsal scapular nerve (C5).


• Action: With the rhomboid minor and levator scapulae, it elevates the medial border of the scapula and pulls it medially.
Deltoid
The deltoid muscle is thick and triangular and covers the shoulder joint. It forms the rounded contour of the shoulder.
• Origin: Anterior fibers arise from the lateral third of the anterior border of the clavicle. Middle fibers arise from the lateral border of the acromion. Posterior fibers arise from the lower border of the spine of the scapula.

• Insertion: its fibers converge to be inserted into the deltoid tuberosity, on the middle of the lateral surface of the shaft of the humerus.


• Nerve supply: From the axillary nerve (C5 and 6).
• Action: With the help of the supraspinatus muscle, the del- told abducts the upper limb at the shoulder joint. The main effort is undertaken by the strong multipennate middle (acromial) fibers; the weaker anterior and posterior fibers serve as stays and prevent the arm from swaying forward or backward. For every 30 of abduction of the arm, a 2° abduction occurs in the shoulder joint and 1° occurs by rotation of the scapula. At about 1200 of abduction the greater tuberosity of the humerus hits the lateral edge of the acrormion. Elevation of the arm above the head is accomplished by rotating the scapula, which is brought about by the contract ion of the trapezius and serratus anterior muscles.
lii addition, the anterior fibers of the deltoid can flex and medially rotate the arm, and the posterior fibers can extend and laterally rotate the arm.

Supraspinatus

• Origin: From the supraspinous fossa of the scapula.
• Insertion: Into the upper facet of the greater tuberosity of the humerus and into the capsule of the shoulder joint.
• Nerve supply: Suprascapular nerve.

• Action: It assists the deltoid muscle in the abduction of the arm at the shoulder joint by fixing the head of the humerus against the glenoid cavity.

Infraspinatus

• Origin: From the infraspinous fossa of the scapula.


• Insertion: Into the middle facet of the greater tuberosity of the humerus and into the capsule of the shoulder joint.
• Nerve supply: Suprascapular nerve.

• Action: It laterally rotates the arm and stabilizes the shoulder joint.

Teres Minor

• Origin: From the upper two-thirds of the lateral border of the scapula.


• Insertion: Into the lower facet of the greater tuberosity of the humerus and into the capsule of the shoulder joint.
• Nerve supply: A branch of the axillary nerve.
• Action: It laterally rotates the arm and stabilizes the shoulder joint.

ROTATOR CUFF

Four muscles the supraspinatus, the Infraspinatus, the teres minor, and the Subscapularis form what is termed the rotator cuff. The tone of these muscles assists in holding the head of the humerus in the glenoid cavity of the scapula during movements at the shoulder joint. Therefore, they assist in stabilizing the shoulder joint. The cuff lies on the anterior, superior, and posterior aspects of the joint. The cuff is deficient inferiorly, and this is a site of potential weakness.

Quadrangular Space

The quadrangular space is an intermuscular space bounded above by the subscapularis and capsule of the shoulder joint and below by the teres major muscle. It is bounded medially by the long head of the triceps and laterally by the surgical neck of the humerus.
The axillary nerve and the posterior circumflex humeral vessels pass backward through this space.

Nerves
Spinal Part of the Accessory Nerve (Cranial Nerve Xl)


The spinal part of the accessory nerve runs downward in the posterior triangle of the neck on the levator scapulae muscle. It is accompanied by branches from the anterior rami of the third and fourth cervical nerves. The accessory nerve runs beneath the anterior border of the trapezius muscle at the junction of its middle and lower thirds and, together with the cervical nerves, supplies the trapezius muscle.

Suprascapular Nerve

The suprascapular nerve arises from the upper trunk of the brachial plexus (C5 and 6) in the posterior triangle in the neck. It runs downward and laterally and passes beneath the suprascapular ligament, which bridges the suprascapular notch, to reach the supraspinous fossa. It supplies the supraspinatus and infraspinatus muscles and [he shoulder joint.

Axillary Nerve

The axillary nerve arises from the posterior cord of the brachial plexus (C5 and 6) in the axilla. It passes backward and enters the quadrangular space with the posterior circumflex humeral artery. As the nerve passes through the space, it comes into close relationship with the inferior aspect of the capsule of the shoulder joint and with the medial side of the surgical neck of the humerus. It terminates by dividing into anterior and posterior branches.
Branches
The axillary nerve has the following branches:
1. An articular branch to the shoulder joint.
2. An anterior terminal branch, which winds around the surgical neck of the humerus beneath the deltoid muscle; it supplies the deltoid and the skin that covers its lower part.
3. A posterior terminal branch, which gives off a branch to the teres minor muscle and a few branches to the deltoid, then emerges from the posterior border of the deltoid as the upper lateral cutaneous nerve of the arm.
It is thus seen that the axillary nerve supplies the shoulder joint, two muscles, and the skin covering the lower half of the deltoid muscle.

ARTERIAL ANASTOMOSIS AROUND THE SHOULDER JOINT


The extreme mobility of the shoulder joint may result in kinking of the axillary artery and a temporary occlusion of its lumen. To compensate for this, an important arterial anastomosis exists between the branches of the subclavian artery and the axillary artery, thus ensuring that an adequate blood flow takes place into the upper limb irrespective of the position of the arm.

Branches from the Subclavian Artery:

1. The suprascapular artery.

2. The transverse cervical artery with its dorsal scapular branch

Branches from the Axillary Artery

1. The subscapular artery and its circumflex scapular.

2. The anterior circumflex humeral artery.
3. The posterior circumflex humeral artery.
Both the circumflex arteries form an anastomosing circle around the surgical neck of the humerus.

The arm

SKIN of the arm

Cutaneous nerves

The sensory nerve supply to the skin over the point of the shoulder to halfway down the deltoid muscle is from the supraclavicular nerves (C3 and 4). The skin over the lower half of the deltoid is supplied by the upper lateral cutaneous nerve of the arm, a branch of the axillary nerve (C5 and 6). The skin over the lateral surface of the arm below the deltoid is supplied by the lower lateral cutaneous nerve of the arm, a branch of the radial nerve (C5 and 6). The skin of the armpit and the medial side of the arm is supplied by the medial cutaneous nerve of the arm (TI) and the intercostobrachial nerves (T2). The skin of the back of the arm is supplied by the posterior cutaneous nerve of the arm, a branch of the radial nerve (C8).



Superficial veins

The superficial veins of the arm lie in the superficial fascia.


The cephalic vein ascends in the superficial fascia on the lateral side of the biceps and, on reaching the infraclavicular fossa, drains into the axillary vein.

The basilic vein ascends in the superficial fascia on the medial side of the biceps. Halfway up the arm, it pierces the deep fascia and at the lower border of the teres major joins the venae comitantes of the brachial artery to form the axillary vein.

FASCIAL COMPARTMENTS OF THE ARM

The arm is enclosed in a sheath of deep fascia. Two fascial septa, one on the medial side and one on the lateral side, extend from this sheath and are attached to the medial and lateral supracondylar ridges of the humerus, respectively. By this means the arm is divided into an anterior and a posterior fascial compartments.



The Anterior Fascial Compartment

Muscles
Biceps Brachii

• Origin: The long head from the supraglenoid tubercle of the scapula; the short head from the tip of the coracoid process of the scapula.


The tendon of the long head crosses the humeral head within the capsule of the shoulder joint and emerges from the joint surrounded by a synovial sheath and lying in the bicipital groove of the humerus. It is joined in the middle of the upper arm by the short head.
• Insertion: Into the posterior part of the tuberosity of the radius and, by the bicipital aponeurosis, in to the deep fascia on the medial aspect of the forearm.

• Nerve supply: Musculocutaneous nerve.

• Action: The biceps is a strong supinator of the forearm. The biceps also is a powerful flexor of the elbow joint and a weak flexor of the shoulder joint.

Coracobrachialis


• Origin: from the tip of the coracoid process.
• Insertion: Into the middle of the medial side of the shaft of the humerus.

• Nerve supply: Musculocutaneous nerve.

• Action: It flexes the arm and is also a weak adductor.

Brachialis


• Origin: From the front of the lower half of the humerus.
• Insertion: into the anterior surface of the coronoid process of the ulna.
• Nerve supply: Musculocutaneous nerve. A small part of the muscle that arises behind the deltoid tuberosity, and is therefore located in the posterior compartment, is supplied by the radial nerve.
• Action: It is a strong flexor of the elbow joint.

Structures Passing Through the Anterior Fascial Compartment

Brachial Artery:

begins at the lower border of the teres major muscle as a continuation of the axillary artery. It provides the main arterial supply to the arm. It terminates opposite the neck of the radius by dividing into the radial and ulnar arteries.

Branches


1. The profunda artery arises near the beginning of the brachial artery and follows the radial nerve into the spiral groove of the humerus.
2. The superior ulnar collateral artery arises near the middle of the upper arm and follows the ulnar nerve.
5. The inferior ulnar collateral artery arises near the termination of the artery and takes part in the anastomosis around the elbow joint.

Musculocutaneous Nerve:

It runs downward and laterally, pierces the coracobrachialis muscle, and then passes downward between the biceps and brachialis muscles. It appears at the lateral margin of the biceps tendon and pierces the deep fascia just above the elbow. It runs down the lateral aspect of the forearm as the lateral cutaneous nerve of the forearm.

Branches


1. Muscular branches to the biceps, coracobrachialis, and brachialis.
2. Cutaneous branches. The lateral cutaneous nerve of the forearm supplies the skin of the front and lateral aspects of the forearm down as far as the root of the thumb.

3. Auricular branches to the elbow joint.

Median Nerve

It runs downward on the lateral side of the brachial artery. Halfway down the upper arm, it crosses the brachial artery and continues downward on its medial side.

The nerve, like the artery, is therefore superficial, but at the elbow it is crossed by the bicipital aponeurosis.

The median nerve has no branches in the upper arm, except for a small vasomotor nerve to the brachial artery.

Ulnar Nerve

It runs downward on the medial side of the brachial artery as far as the middle of the arm. Here, at the insertion of the coracobrachialis, the nerve pierces the medial fascial septum, accompanied by the superior ulnar collateral artery, and enters the posterior compartment of the arm; the nerve passes behind the medial epicondyle of the humerus. The ulnar nerve has no branches in the anterior compartment of the arm.

Radial Nerve

On leaving the axilla, the radial nerve immediately enters the posterior compartment of the arm and only enters the anterior compartment just above the lateral epicondyle.



The Posterior Fascial Compartment of the Arm

Muscle of the Posterior Fascial Compartment

Triceps
• Origin: Long head from the infraglenoid tubercle of the scapula; lateral head from the upper half of the posterior surface of the shaft of the humerus above the spiral groove; medial head from the posterior surface of the lower half of the shaft of the humerus below the spiral groove.

• Insertion: The common tendon is inserted into the upper surface of the olecranon process of the ulna.

• Nerve supply: Radial nerve.

• Action: This muscle is a strong extensor of the elbow joint.

Structures Passing Through the Posterior Fascial Compartment

Radial nerve:

Winds around the back of the arm in the spiral groove on the back of the humerus between the heads of the triceps. It pierces the lateral fascial septum above the elbow and continues downward into the cubital fossa in front of the elbow, between the brachialis and the brachioradialis muscles. In the spiral groove the nerve is accompanied by the profunda vessels, and it lies directly in contact with the shaft of the humerus.

Branches


1. in the axilla: Branches are given to the long and medial heads of the triceps, and the posterior cutaneous nerve of the arm is given off.
2. in the spiral groove: Branches are given to the lateral and medial heads of the triceps and to the anconeus. The lower lateral cutaneous nerve of the arm supplies the skin over the lateral and anterior aspects of the lower part of the arm. The posterior cutaneous nerve of the forearm runs down the middle of the back of the forearm as far as the wrist.

  1. In the anterior compartment of the arm: After the nerve has pierced the lateral fascial septum, it gives branches to the brachialis, the brachioradialis, and the extensor Carpiradialis longus muscles. It also gives articular branches to the elbow joint.

Ulnar Nerve:

Having pierced the medial fascial septum halfway down the upper arm; the ulnar nerve descends behind the septum, covered posteriorly by the medial head of the triceps. The nerve is accompanied by the superior ulnar collateral vessels. At the elbow, it lies behind the medial epicondyle of the humerus on the medial ligament of the elbow joint. It continues downward to enter the forearm between the two heads of origin of the flexor carpiulnaris.



Branches

The ulnar nerve has an articular branch to the elbow joint.



Profunda Brachii Artery

The profunda brachii artery arises from the brachial artery near its origin. It accompanies the radial nerve through the spiral groove, supplies the triceps muscle, and takes part in the anastomosis around the elbow joint.

Branches


  1. Radial collateral artery.

  2. Middle collateral artery.

Superior and Inferior Ulnar Collateral Arteries

Ulnar collateral arteries arise from the brachial artery and take part in the anastomosis around the elbow joint.



Cubital fossa

Cubital fossa is the triangular area between pron. teres, brachiorad. And a line joining the humeral epicond.

The roof is formed by the deep fascia of forearm, reinforced on the medial side by the bicipital aponeurosis. Infront of the bicipital aponeurosis lies the median cubital v. with the medial cut. N. of forearm; separating these structures from the underlying med. N. and brachial a.

Is the triangular area between pron. teres, brachiorad. And a line joining the humeral epicond.

The roof is formed by the deep fascia of forearm, reinforced on the medial side by the bicipital aponeurosis. Infront of the bicipital aponeurosis lies the median cubital v. with the medial cut. N. of forearm; separating these structures from the underlying med. N. and brachial a.

The floor is formed in the main by brach. M. and below by the supin. As it claps the neck of the radius.

The contents of fossa, from med. To lat. Side are:

Med. N., brach. A., tendon of biceps, and further lat. The radial N. and its post. Inteross. Br. Which are only seen when brachioradialis is retracted laterally.

The brachial art. is palpated med. To the tendon to define the position for placing the stethoscope when taking the Blood Pressure.

The post. Inteross. N. gives branches to ext. carpi rad. Brevis & supinator before disappearing from the fossa by passing between the two heads of origin of Supinator M. in the ext. compartment.



The superficial branch of the radial N. passes down the forearm under cover of brachioradialis.


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