Clinical Anatomy for Students: Problem Solving Approach Neeta V Kulkarni
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1Upper Extremity2

Pectoral Region1

The pectoral or the breast region is the name given to the front of the chest or thorax. This region contains the mammary glands, pectoral muscles, fasciae and pectoral nerves.
 
SURFACE LANDMARKS
  1. Some parts of the osteocartilaginous framework of pectoral region (Figs 1.1 and 1.2) are palpable through the skin. The sternum (breastbone) is located in the midline. All the three parts of sternum (manubrium, body and xiphoid process) are palpable. On each side, the manubrium articulates above with the clavicle and below with the first costal cartilage. The second costal cartilage articulates with the sternal angle, which is the junction of manubrium and body of sternum. The sternal angle is a very important landmark for the clinician during examination of chest, as it indicates the position of second rib from which the rest of the ribs can be counted. The body of sternum articulates with costal cartilages of the third to seventh ribs.
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    Fig. 1.1: Scheme to depict osteo-cartilaginous framework of pectoral region
  2. The clavicle or collarbone is horizontally placed in the upper part of the pectoral region. Being subcutaneous it is palpable in its entire extent. It articulates medially with the manubrium sterni at sternoclavicular joint and laterally with acromion of the scapula at acromioclavicular joint.
  3. The coracoid process of scapula projects under the lateral part of the clavicle. It can be felt 2–3 cm below the clavicle on firm pressure of the thumb in the lateral part of infraclavicular fossa or deltopectoral triangle (Fig. 1.2).
  4. The anterior axillary fold (produced by pectoralis major muscle) is a visible landmark, as it becomes prominent, when the abducted arm is adducted against resistance.
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Fig. 1.2: Surface landmarks of pectoral region
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SUPERFICIAL FASCIA
  1. The main feature of the superficial fascia is the presence of mammary glands.
  2. The platysma is seen in the upper part of the pectoral region. This is a thin subcutaneous muscle that takes origin from the deep fascia covering the upper part of pectoralis major and adjacent deltoid muscle. It crosses the clavicle to enter the neck and is inserted in the lower margin of the body of mandible partly and in to the facial muscles around the mouth (Fig. 1.3). In its course through the neck the platysma lies in the superficial fascia overlying the posterior triangle of neck. The facial nerve (seventh cranial nerve) supplies the platysma in the neck.
 
CUTANEOUS NERVES (Fig. 1.4)
  1. The skin above the sternal angle is supplied by the medial, intermediate and lateral supraclavicular nerves (C3, C4), which arise in the neck from the cervical plexus. These nerves descend to the pectoral region by crossing in front of the clavicle or frequently by piercing it. The medial supraclavicular nerve supplies the skin overlying the manubrium. The intermediate nerve supplies the skin over the upper part of pectoralis major muscle and the lateral nerve supplies the skin over the shoulder.
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    Fig. 1.3: To show origin of platysma from fascia covering pectoralis major and deltoid
  2. The anterior cutaneous branches of the second to the sixth intercostal nerves enter the pectoral region along the lateral margin of sternum after piercing the sternocostal head of pectoralis major muscle and the deep fascia. These branches are accompanied by corresponding arteries, which are the branches of internal thoracic artery. The area of supply of these nerves extends from the anterior median plane to the midclavicular line on each side. The lateral cutaneous nerves are the branches given by the intercostal nerves along a vertical line just behind the anterior axillary fold. They supply the skin beyond the midclavicular plane. It is essential to know that the first intercostal nerve does not give cutaneous branches to the pectoral region.
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    Fig. 1.4: Showing cutaneous nerves of pectoral region on right side and origin of pectoralis major muscle on left side. At the dotted green line discontinuous dermatomes (C4 and T2) meet
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    Thus, from the cutaneous nerve supply we learn that at the level of sternal angle, C4 and T2 dermatomes come close to each other (Fig. 1.5). There is interruption of the sequence of dermatomes at this site because C5 to T1 dermatomes are carried in the upper limb from the trunk during embryonic development.
 
DEEP FASCIA
The deep fascia of the pectoral region is called pectoral fascia because it covers the pectoralis major muscle. It is continuous with the periosteum of the clavicle and the sternum. It passes over the deltopectoral groove to become continuous with the fascia covering the deltoid. The upper portion of the pectoral fascia gives origin to fibers of platysma (Fig. 1.3). At the lower margin of pectoralis major the pectoral fascia and the fascia covering the latissimus dorsi are connected by the axillary fascia, which lies in the floor of the axilla. The suspensory ligament of axilla connects the axillary fascia to the clavipectoral fascia at the lower margin of pectoralis minor.
 
DELTOPECTORAL TRIANGLE (Fig. 1.4)
The boundaries of this triangle are, the upper margin of pectoralis major medially, anterior margin of deltoid laterally and the clavicle superiorly. The triangle contains the cephalic vein, deltoid branch of thoracoacromial artery and the deltopectoral lymph nodes. In its upper part the coracoid process of scapula is present.
 
PECTORALIS MAJOR
This is the largest muscle of the pectoral region. It forms the anterior axillary fold.
 
Origin (Fig. 1.4)
  1. Clavicular head takes origin from the anterior surface of the medial half of the clavicle.
  2. Sternocostal head arises from the front of the manubrium, body of the sternum and from second to sixth costal cartilages.
  3. Aponeurotic fibers arise from the aponeurosis of the external oblique muscle of the anterior abdominal wall.
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Fig. 1.5: Dermatomes of the ventral and dorsal aspect of the body
 
Insertion
Pectoralis major is inserted into the lateral lip of the intertubercular sulcus of humerus by a bilaminar U-shaped tendon (the two limbs of the U being called anterior and posterior laminae). The anterior lamina, which is formed by clavicular fibers, is inserted into the lower part of the lateral lip while the posterior lamina formed by aponeurotic fibers is inserted into the upper part of the lateral lip of the intertubercular sulcus. The sternocostal fibers form the base of the U.
 
Nerve Supply
The medial pectoral (C8, T1) and lateral pectoral (C5, C6, C7) nerves supply the muscle.6
 
Actions
  1. The contraction of entire muscle produces medial rotation and adduction, of arm as for example while putting the hand on one's hip and pushing forcibly.
  2. The contraction of clavicular part alone produces flexion of arm. This part becomes prominent, when the arm is flexed against resistance, e.g. in pushing the edge of a heavy table.
  3. The contraction of sternocostal part alone produces extension of the flexed arm against resistance for example while pulling a heavy table by holding on the edge of the table.
  4. In climbing on a rope or a tree, the sternocostal part of pectoralis major and latissimus dorsi produce a very powerful movement of extension the arm from its fully flexed position.
 
Testing Function of Pectoralis Major
The subject abducts the arm to about 60° and then flexes the elbows. Then the subject attempts to bring the hands together. The examiner watches for the prominence of the anterior axillary fold (another method of testing the muscle function is by asking the subject to place hands on the hips and press firmly inwards).
 
Clinical Highlights
  1. In congenital absence of pectoralis major muscle the anterior axillary fold is absent.
  2. In fracture of clavicle (Fig. 1.6) the contraction of pectoralis major along with other adductors shifts the lateral fragment of clavicle in medial direction below the medial fragment. The sternomastoid muscle of the neck pulls the medial fragment upward. This results in overriding of the fragments.
 
PECTORALIS MINOR (Fig. 1.7)
This is a triangular muscle in the anterior wall of axilla, placed posterior to the pectoralis major. It has anterior and posterior surfaces and upper or medial and lower or lateral margins.
 
Origin
It takes origin from the outer surfaces of third, fourth and fifth ribs near the costal cartilages.
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Fig. 1.6: Fracture of right clavicle (Note: The upward displacement of medial fragment and medial displacement of lateral fragment due to muscle pull)
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Fig. 1.7: Schematic diagram showing pectoralis minor muscle and axillary lymph nodes
 
Insertion
It is inserted into the medial border and upper surface of the coracoid process of scapula.7
 
Relations
  1. The fascial relations of the muscle are as follows. It is completely enclosed in the clavipectoral fascia. From the upper margin of the muscle the fascia extends upwards for attachment to the margins of the subclavian groove on the lower surface of clavicle. From the lower margin of the muscle the fascia extends downwards as suspensory ligament of axilla.
  2. Anteriorly, muscle is related to the interpectoral lymph nodes (Rotter's nodes) and the pectoralis major muscle.
  3. The posterior relations are second part of axillary artery, axillary vein and cords of brachial plexus.
  4. Its lower (lateral) margin is related to lateral thoracic vessels and anterior group of axillary lymph nodes.
 
Nerve Supply
The medial pectoral nerve pierces the pectoralis minor and supplies it. The lateral pectoral nerve sends twigs via its communication with the medial pectoral nerve.
 
Actions
The pectoralis minor muscle helps in protraction of scapula along with serratus anterior muscle and in depression of scapula along with lower fibers of trapezius.
 
Clinical Highlights
The axillary lymph nodes are grouped into three levels, depending on their relation to pectoralis minor muscle (Fig. 1.7). Level-I nodes (anterior, posterior and lateral groups) are located below and lateral to the lower margin of the muscle. In level- II nodes the central group is located behind and the interpectoral in front of the muscle. The level -III nodes (apical group) lie above the upper margin of the muscle. In operation of mastectomy the pectoralis minor muscle is an important landmark for the surgeon.
 
SUBCLAVIUS
This is a small muscle in the uppermost part of the pectoral region. The subclavius takes origin by a narrow tendon from the first costochondral junction and is inserted into the groove on the undersurface of the middle third of clavicle.
 
Nerve Supply
The muscle receives twigs from the nerve to subclavius, which is a branch of the Erb's point of brachial plexus. This nerve contributes C5 fibers to phrenic nerve through accessory phrenic nerve.
 
Action
The subclavius steadies the clavicle during movements of the scapula at girdle joints.
 
CLAVIPECTORAL FASCIA (Fig. 1.8)
This fascia spreads across the gap between the upper margin of pectoralis minor muscle and the clavicle. In this part, it is attached medially to the first rib and laterally to the coracoid process of scapula. Above, it splits to enclose the subclavius muscle and its two layers attach to the lips of subclavian groove on the inferior surface of clavicle. Below it splits to enclose the pectoralis minor, at the lower margin of which the two layers unite to form the suspensory ligament of axilla, which become continuous with the axillary fascia.
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Fig. 1.8: Scheme to depict the disposition of clavipectoral fascia and structures piercing it
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The four structures that pierce the fascia spanning between the pectoralis minor and the clavicle are, lateral pectoral nerve, thoracoacromial artery, cephalic vein and lymphatic vessels.
 
PECTORAL NERVES
There are two pectoral nerves, medial and lateral. The medial pectoral nerve (C8, T1) arises from the medial cord of the brachial plexus. The nerve lies behind the first part of axillary artery initially but it soon curves forwards to receive a communicating ramus from the lateral pectoral nerve in front of the axillary artery. It enters the deep surface of the pectoralis minor muscle, supplies it and enters the substance of the pectoralis major muscle. The lateral pectoral nerve (C5, 6, 7) arises from the lateral cord of the brachial plexus. It travels forwards on the lateral side of axillary artery and pierces the clavipectoral fascia and the clavicular part of pectoralis major, which it supplies.