Pectoral and Shoulder Regions

Reading resources:

Moore and Agur, Essential Clinical Anatomy
pp 289 - 300, 302 - 306

Objectives:

At the end of this laboratory you should be able to:

    1. Identify on a skeleton the bony landmarks of the pectoral
        and shoulder regions.
    2. Identify the major ligaments of the shoulder region.
    3. Identify the pectoral muscles, their attachments and nerve supply.
    4. Identify the rotator cuff muscles..
    5. Identify the axillary artery and vein.
    6. Name the muscles that act across the shoulder joint and
        state their specific actions
_____________________

Bony landmarks

On the skeleton,  note the following bony structures and determine their corresponding position in the cadaver.
            1.  sternum
                    -suprasternal notch
                    -infrasternal notch
                    -xiphoid process
                    -sternal angle (of Lewis)

            2.  scapula
                    -coracoid process
                    -acromion
                    -subscapular fossa

            3.  humerus
                    -head
                    -greater and lesser tubercles
                    -intertubercular groove (bicipital groove)
                    -anatomical neck
                    -surgical neck

    Use a prosected specimen to study the shoulder joint.  You will not be dissecting the shoulder joint in your cadaver.  Note that the glenoid cavity is deepened by the glenoid labrum.  Observe the fibrous joint capsule (Netter, 394).  It is attached proximally to the glenoid cavity and distally to the anatomical neck of the humerus.  Observe the tendon of the long head of the biceps passing through the shoulder joint to insert into the supraglenoid tubercle.  The glenohumeral ligaments (superior, middle, and inferior) are thickenings of the front of the capsule.  They converge toward the supraglenoid tubercle.  Look for them inferior to the tendon of the long head of the biceps.  Two additional ligaments that can be observed are the coracohumeral ligament and the transversehumeralligament.

    Important ligaments connecting the clavicle and scapula are the acromioclavicular ligament and the coracoclavicularligament (Netter, 394).  Find them on the specimen.

    Identify, on the cadaver, the anterior axillaryfold and the posterior axillary fold.  The anterior axillary fold is formed by the underlying pectoral muscles; the posterior axillary fold is formed by the underlying latissimus dorsi muscle.

    Become familiar with the following lines of reference used to delineate the surface anatomy of the pectoral and axillary region:
            1.  mid-sternal line
            2.  mid-clavicular line
            3.  anterior axillary line
            4.  posterior axillary line
            5.  mid-axillary line

Reflection of skin

            1.  Make a mid-sternal incision from the suprasternal notch to the infrasternal angle.

            2.  Make another incision from the suprasternal notch along the clavicle to the tip of the shoulder.  Late in the dissection you can extend this incision down the arm to a point just above the elbow.

            3.  Make an incision from the infrasternal notch as far laterally as the mid-axillary line.  Now reflect the flap of skin outlined by the incisions 1, 2 and 3.  Remove the breast along with the flap of skin.

    Cutaneous nerves and blood vessels emerging near the sternum will not be dissected.  However, check with the atlas (Netter, 179) to see the origin of the anterior cutaneousnerves.  The perforating arterial branches supplying this area originate from the internal thoracic artery, an artery to be dissected in a subsequent dissection.

The Breast

    While the breast (mammary gland) will not be dissected in detail make note of its anatomical location (Netter, 168).  The breast is located within the superficial fascia.  It overlies two muscles, the pectoralis major and the serratus anterior.  The breast is very mobile, unless cancer has resulted in fixation of the breast to the muscle.
    Note that the breast of the female normally extends from the side of the sternum to the mid-axillary line.  Breast tissue may extend into the axilla as the axillary tail (and can be mistaken for a tumor or an enlarged lymph node).  Vertically the breast normally extends from the 2nd to the 6th rib.  In the male the nipple is usually situated in the fourth intercostal space.

Dissection of the pectoral region

     Identify the pectoralis major.  The thin fascia which covers the muscle is, as you may have guessed, named the pectoral fascia.  The pectoralis major originates from the sternum, the costal cartilages of the first seven ribs and from the medial part of the clavicle.  Note that the muscle has a dual origin (Netter, 395), a clavicular head and a sternocostal head.  Also note the insertion of this muscle into the humerus below the greater tubercle.  Clean and identify the borders of the deltoid (Netter, 395), the large muscle covering the shoulder region.  It originates from the scapula and clavicle, and inserts into the deltoid tuberosity of the humerus.

    Delineate the deltopectoral groove and expose the cephalic vein within the groove by cutting the pectoral fascia which covers it (Netter, 395).  The cephalic vein leaves the deltopectoral triangle and terminates by joining the axillary vein just below the clavicle.

    Clean the pectoral major.  Use your fingers to separate the pectoralis major from the underlying pectoralis minor.  If you are careful you will feel the medial pectoral nerve, one of the nerves that supply the pectoral muscles.  Divide the pectoralis major close to its orgin and reflect it laterally to uncover the pectoralis minor muscle (Netter, 399).

    Between the clavicle and the pectoralis minor muscle identify the thin clavipectoral fascia.  This fascia attaches to the clavicle, invests the small subclavius muscle, splits to invest the pectoralis minor, and then continues, to blend with the axillary fascia (Netter, 399b).  The clavipectoral fascia between the pectoralis minor and the clavicle is pierced by the cephalicvein, the thoracoacromial artery and vein, and the lateral pectoral nerve (Netter, 399).  Identify the subclavius muscle and note its attachments to the clavicle and first rib.

    Note that the pectoralis minor muscle is a key structure in the axillary region.  Identify the axillary artery and axillary vein deep to the muscle (Netter, 400).  For convenience, the axillary artery is divided into three parts with respect to the pectoralis minor muscle:  the first part superior to the muscle, the second part deep to the muscle, and the third part inferior to the muscle.  Surrounding the axillary artery are parts of the brachialplexus of nerves.  Identify the medial cord, the lateralcord, and the posterior cord of the brachial plexus.  These structures take their names from their position relative to the axillary artery.  Branches of the axillary artery and nerves of the brachial plexus will be studied in the next lab.

    Now TURN THE CADAVER OVER.  Using the scapel cut the deltoid from the spine and acromion of the scapula.  The deltoid can now be reflected anteriorly providing access to the supraspinatusmuscle and infraspinatus muscle.  Identify and clean the teres major and teres minor muscles (Netter, 397).  Note their attachments to the lower part of the scapula, below infraspinatus.  The teres minor inserts into the greater tubercle of the humerus - it adducts and arm and rotates it laterally.  The teres major inserts into the lesser tubercle.  Teres major is an adductor, medial rotator and extensor of the arm.

    Four muscles surround the shoulder joint forming the 'rotator cuff' of muscles:  supraspinatus, infraspinatus, teres minor, and subscapularis (Netter, 396).  Subscapularis will be identified in the cadaver during the next lab.  It is a medial rotator of the shoulder joint.

    Finally, identify and clean the long head of the tricepsmuscle.  The long head originates from the infraglenoid tubercle of the scapula.  Note that the long head of the triceps runs between the teres minor and the teres major.  The teres minor runs posterior to the triceps; the teres major runs anterior to the long head.   Separate the long head of the triceps from the lateral head to observe the large radial nerve and the deep brachial artery in the radial (spiral) groove of the humerus.  Because the nerve lies against the humerus here, it is susceptible to damage from fractures of the humerus.
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Review questions

1.    What is the angle of Lewis?
2.    Which ribs articulate at the sternal angle?
3.    What reference line lies vertically mid-way between the anterior and posterior axillary folds?
4.    Which nerves enter the superficial fascia at the mid-axillary line?
5.    Which nerves enter the superficial fascia at the lateral borders of the sternum?
6.    What name is given to the ventral primary rami which pass between the ribs from the intervertebral foramina to the
       sternum?
7.    What is the function of the intercostal nerves in addition to giving origin to cutaneous nerves?
8.    What vessels accompany the intercostal nerves?
9.    What is the usual position of the nipple with respect to the thoracic wall of the male?
10.  What are the boundaries of the deltopectoral triangle?
11.  What structures lies within the deltopectoral triangle?
12.  What fascia covers the pectoralis major?
13.  What fascia passes from the clavicle to invest the pectoralis minor?
14.  Why is the lateral pectoral nerve so named, when it appears to lie medial to the medial pectoral nerve?
15.  What is the blood supply to the pectoral muscles?
16.  What structures pierce the clavipectoral fascia?
17.  What are the anatomical sites to which lymph from the breast may flow?
18.  What is the axillary tail of the breast?  Why is this important to know?
19.  Which muscles form the 'rotator cuff' of the shoulder?  On what bony landmarks on the humerus to the rotator cuff
        muscles insert?
20.  Where is the rotator cuff the weakest?  Is this clinically relevant?
21.  Which muscles contribute to abduction of the arm?
22.  What is the difference between a shoulder dislocation and a shoulder 'separation'?
23.   What action of the upper limb would be impaired after rupture of the supraspinatus tendon?
 

Answers

1.    The sternal angle; formed by the junctions of the manubrium and body of the sternum.
2.    The second pair of ribs, by their costal cartilages.
3.    The mid-axillary line.
4.    The lateral cutaneous branches of the ventral primary rami of the thoracic spinal nerves.
5.    The anterior cutaneous branches of the ventral primary rami.
6.    Intercostal nerves.
7.    They innervate the intercostal nerves.
8.    The intercostal arteries and veins.  Most of these arteries come from the aorta.
9.    In the fourth intercostal space.
10.  Medial border of deltoid, lateral border of pectoralis major, and the inferior border of the clavicle.
11.  Cephalic vein
12.  Pectoral fascia
13.  Clavipectoral fascia.
14.  The lateral pectoral nerve is so named because it arises from the lateral cord of the brachial plexus.
15.  Pectoral branches of the thoracoaromial trunk, and branchesof the lateral thoracic and internal thoracic arteries.
16.  Cephalic vein, thoracoacromial artery and vein, pectoral nerves.
17.  To axillary nodes, to nodes along the internal thoracic artery, to lymphatics of the opposite breast, and to abdominal
        viscera.  These routes provide sites for the spread of breast cancer.
18.  The axillary tail is the normal breast tissue which extends into the axilla.  This tissue can be mistaken for a tumor.
19.  Supraspinatus, infrapinatus, teres minor, and subscapularis.  Supraspinatus, infraspinatus, and teres minor insert on or
        below the greater tubercle of the humerus. Subscapularis on the lesser tubercle.
20.  The rotator cuff is weakest inferiorly. Shoulder dislocations occur most frequently through the inferior part of the rotator
       cuff.
21. Supraspinatus, deltoid.  Abduction of the arm beyond the horizontal requires rotation of the scapula as well.  Serratus
       anterior and trapezius contribute to rotation of the scapula.

Comments or questions may be directed to:Dr. J. Vriend