Upper limb

Question 1

Describe the sternoclavicular joint and its structures?

Answer 1

The sternoclavicular joint is a saddle type synovial joint between the sternal end of the clavicle and manubrium of the sternum, along with part of the 1st costal cartilage. The articular surface is covered with fibrocartilage, as opposed to hyaline cartilage often found on synovial joints. The joint is composed of two compartments separated by a fibrocartilaginous articular disc. It is the only attachment of the upper limb to the axial skeleton. It has a very large degree of motility. It allows for elevation and depression of the shoulder, protraction, retraction and rotation. When engaging in elevation that involves shrugging of the shoulder or the abduction of the arm above 90 degrees. Depression involves the drooping of the shoulder and hyperextension of the arm. In rotation, moving the arm over the head allows for the passive movement of the clavicle, assisted by the coracoclavicular ligaments. The joint capsule surrounds this joint and confers a degree of stability. It has a fibrous outer layer and an inner synovial membrane. The fibrous layer extends from the epiphysis of the sternal end to the borders of the articular surface of the articular disc. The synovial membrane which lines the inner surface produces synovial fluid which reduces friction. There are four ligaments which provide stability to the joint. The anterior and posterior sternoclavicular ligaments strengthen the capsule. The interclavicular ligament spans the gap between the sternal ends reinforcing the capsule superiorly. While the costoclavicular which contains two parts separated by a bursa bind at the 1st rib and cartilage inferiorly and superiorly to the anterior and superior borders of the clavicle. This is the main ligament resisting elevation of the pectoral girdle, thus has a very significant role in providing stabilising force.

Question 2

Describe the acromioclavicular joint and its surrounding structures

Answer 2

The acromioclavicular joint is another key joint involved in the formation of the shoulder. This joint forms between the lateral end of the clavicle and the acromium of the scapula. The joint is a plane type synovial joint. It allows for gliding movements, and allows for a degree of axial rotation, and anteroposterior movement. No muscles act directly on this joint and movement is passive. The joint, just like the sternoclavicular joint also has articular surfaces which are atypically lined with fibrocartilage and divided by an articular disc. The joint capsule is formed by the loose fibrous layer enclosing two articular surfaces. Posteriorly the capsule is reinforced by fibres of the trapezius muscle. It is also lined with a synovial membrane. It contains three main ligaments. The acromioclavicular ligament runs horizontally from the acromion to the lateral end of the clavicle, reinforcing it superiorly. The coracoclavicular ligament can be further subdivided into two smaller ligaments; the conoid and trapezoid ligaments. The conoid ligament runs vertically from the coracoid process of the scapula to the conoid tubercle of the clavicle. The trapezoid ligament also runs from coracoid process but instead inserts into the trapezoid line of the clavicle. These two ligaments are very strong and essentially suspend the weight of the upper limb from the clavicle. In terms of the neurovascular supply to the joint, the joint is supplied by two arteries; the suprascapular and the thoraco-acromial arteries. The suprascapular arises from the subclavian artery at the thyrocervical trunk, while the thoraco-acromial artery arises from the axillary artery. The veins of the joint follow these arteries. The joint is innervated by articular branches of the suprascapular and lateral pectoral nerves both arising from the brachial plexus.

Question 3

Describe the body cavities

Answer 3

The body is also divided into a number of cavities each with its own unique function, primary focused on protection. The dorsal cavity is divided into a cranial and a vertebral cavity with a role in protecting of the central nervous system. The ventral cavity can be subdivided into a thoracic and an abdominopelvic cavity with a role in protection of the internal organs. The contents of the thoracic cavity include pleural cavity (with each lung); The mediastinal cavity (containing the oesophagus, trachea and thymus) and the pleaural cavity (containing the heart). The abdominopelvic cavity comprises the abdominal cavity containing the stomach, liver, gallbladder, intestines, spleen and kidneys. The pelvic cavity comprises the distal portion of the large intestine, the bladder and reproductive organs. A number of other body cavities exist; The oral cavity houses the teeth and tongue; The nasal cavity contains the sinuses; The orbital cavity contains the eyes and the middle ear contains the middle ear bones.

Question 4

Describe anatomical movements in the body

Answer 4

Anatomical movements have specific terminology also. Abduction relates to movement away from the midline. Whereas adduction is movement towards the midline. Flexion decreases the angle between two body parts. Extension increases the angle between two body parts. Medial rotation is rotation towards the midline, while lateral rotation is rotation away from the midline. Protonated can be thought of as lying prone (on front face) and supinated is lying on back face. Elevation means to move superiorly, while depression is to move inferiorly. Protraction is to move anteriorly while retraction is to move posteriorly. The movements of the feet include dorsiflexion (movement of the dorsum of the foot towards the shin. While plantar flexion is the depression of the foot and elevation of the heel. Furthermore, inversion is the movement of the foot medially and eversion laterally. The hand is move specific in its movement than the feet as the thumb can move in multiple planes. Adduction and abduction of the thumb occur along the sagittal plane. Flexion and extension occur along the coronal plane. And opposition and reposition involve movement of the thumb towards the pinky finger. Circumduction is a word used to describe the movement of a distal body part of the appendicular skeleton in a circle, this is only seen in the shoulder and hip joints. Rotation is used to describe a bone revolving around its own longitudinal axis.

Question 5

What are the planes of the body?

Answer 5

All anatomical terminology is derived from the reference point known as the anatomical position. There are a number of planes of this position, sectioning it for reference. The sagittal plane is a vertical line that divides the body into left and right. The coronal plane is a vertical line dividing the body into anterior and posterior portions. The transverse plane divides the body into a superior and inferior section. Lastly, the oblique plane can be thought of as a line passing through the body at an angle.

Question 6

What terminology describes the orientation of surfaces, limb direction, and hand and feet surfaces?

Answer 6

The relationship between superior and inferior is that superior is cranial directed or above, and inferior is downward directed. Anterior and posterior relates to front and behind. Proximal means closer to the trunk and distal further from the trunk. Lateral is further from the midline and medial is closer to the midline. Superficial relates to something closer to the body surface, while deep relates to something further form the body surface. The hands and feet have respective terminology of the dorsum reflecting the upper surfaces and the palm/plantar surfaces representing the palm and sole.

Question 7

What are the 6 types of joints found in the body?

Answer 7

In total there are 6 major types of synovial joints. In pivot joints (uniaxial) a rounded process of bone fits into a bony ligamentous socket which permits rotation, an example would be the head of the radius and the radial notch of the ulna. A ball and socket joint is multiaxial, with a rounded head fitting into a concavity which allows movement in several directions, an example of this would be the acetabulum of the hip bone and the head of the femur. A plane joint is usually uniaxial which permits gliding or sliding movements, this is seen in the acromioclavicular joint. A hinge joint is uniaxial, and permits the movements flexion and extension only, that is seen in the elbow joint. A saddle joints biaxial, where two saddle-shaped heads permit movement into two planes, seen in the carpometacarpal joint. The last type of synovial joint is the condyloid joint which is biaxial and permits flexion and extension, abduction and adduction and circumduction. This is seen in the metacarpophalangeal joint. Certain joints are of particular interest. As previously notes, circumduction only occurs in the shoulder and hip joints. Interestingly, the styloid process in the hand limits abduction. The atlanto-axial joint between C1 and C2 vertebrae allows for rotation of the head. The radioulnar joint is the joint which allows for movement of the hand from supine to protonated positions.

Question 8

Describe the structure at synovial joints

Answer 8

Free movement is allowed at synovial joints. The structure of a synovial joint involved the meeting of 2 bones, with their bony articular surfaces covered respectively in hyaline cartilage. A synovial membrane surrounds this joint lining the capsule, secreting synovial fluid which nourishes the cartilage and reduces friction – with a capsule surrounding this. On the outside of the joint are the ligaments, which are tough and inelastic, providing stability to the joint and allowing attachment of the bones. Additional features of the joint include a meniscus which acts as a cushion, fat pads and bursa between the tendons to further reduce friction. Bursa are dilated synovial membranes.

Question 9

What are the classifications of joints?

Answer 9

Joints are places where bones meet and are classified according to their structure. Fibrous joints are held together by connective tissue (eg coronal sutures; syndesmosis of tibia and fibula which is similar to the interossesous membrane of the forearm – partially moveable; A dentro-alveolar syndesmosis (gomphosis) socket articulation is found between the root of the tooth and the alveolar process of the jaw). Cartilaginous joints by cartilage (hyaline or fibrocartilage) known as symphesis which include the ribcage, coxae and vertebrae. Synovial joints have an articular capsule and a synovial cavity. The joints are also classified according to the movement that they facilitate. Immovable joints include the sutures and the teeth joints. Those allowing slight movement include the epiphysis joints, vertebral joints, pubic symphysis, intervertebral disc joints (both fibro-cartilagenous) and syndesmosis joints.

Question 10

Describe the osteology of the clavicle

Answer 10

The clavicle contains an acromial and sternal end, with a trapezoid line, conoid tubercle and impression for the costoclavicular ligament. The sternal end is an enlarged quadrangular area which articulates with the manubrium of the sternum and forms the sternoclavicular joint. The acromial end faces laterally and attaches to the acromium of the scapula. The shaft of the clavicle extends between these two ends. The trapezoid line is the attachment site of the trapezoid ligament whereas the conoid tubercle allows for attachment of the conoid ligament – these are both found on the posterior aspect of the acromial end of the clavicle. The groove for the subclavius is also visible on the shaft which is the attachment site of the subclavius muscle to the 1st rib. The impression for the costoclavicular ligament found near the sternal end, this is also known to be the costal tuberosity.

Question 11

Describe the osteology of the scapula

Answer 11

The scapula contains a lateral and medial border on its posterior aspect, with the infraspinous fossa inferior to the spine which lead to the acromion. The spine is the attachment site of the deltoid and trapezoid muscles. Beneath the acromium is the inferior scapular notch which allows for passageway of the suprascapular nerve and artery. The supraspinous fossa is beneath the suprascapular angle and notch and leads to the coracoid process. The glenoid cavity is the attachment site of the head of the humerus forming the glenohumeral joint. The small raised area above this cavity is the supraglenoid tubercle which is the origin site of the long head of the biceps. On the anterior aspect of the scapula the subscapular fossa is visible as is the inferior angle.

Question 12

Describe the osteology of the humerus

Answer 12

The humerus has a semi rounded proximal end which articulates with the scapula. The proximal end is composed of greater and lesser tubercles separated by an intertubercular sulcus. The anatomical neck forms the head which is involved in the joint whilst inferior to this is the surgical neck. The deltoid tuberosity is the attachment site of the deltoid. Anteriorly and distally, the medial epicondyle is medial to the trochlea, the coronoid fossa, the capitulum, the radial fossa and the lateral supracondylar ridge. The posterior aspect moving laterally from the medial epicondyle is beside the trochlea, the olecranon fossa, the medial supracondylar ridge then the lateral epicondyle. It is important to consider that the surgical neck of the humeral is where the head meets the body or shaft of the humerus, whereas the anatomical neck is where the head meets the tubercles (forms the joint). The greater tubercle is the attachment point for the supraspinatus, infraspinatus and teres minor muscles. These muscles are significant as along with the subscapularis which attaches to the lesser tubercle, they form the rotator cuff muscles.

Question 13

Describe the glenohumeral joint and its structures

Answer 13

The glenohumeral joint is formed from the articulation between the head of the humerus and the glenoid fossa of the scapula. Both surfaces are covered with hyaline cartilage unlike the clavicle joints which have fibrocartilage. Hyaline cartilage is typical for a synovial type joint. Inherent instability results from the disproportion in surface sizes between the head of the humerus and the smaller glenoid fossa. As a result of this, to reduce dislocation of the arm the glenoid cavity is deepened by a fibrocartilaginous rim called the glenoid labrum. The joint capsule, a fibrous sheath – encloses the joint. It extends from the anatomical neck of the humerus to the border of the glenoid fossa.

Question 14

Describe the motility of the glenohumeral joint and the joint capsule

Answer 14

The lax nature of the glenohumeral joint capsule permits greater motility in the joint. As a ball and socket joint a wide range of movement is possible. Extension is permitted through the posterior deltoid, the latissimus dorsi and the teres major; Flexion from both heads of the biceps, the pectoralis major, the anterior deltoid and the coracobrachialis; Abduction, the first 15 degrees of which is permitted by the supraspinatus, and the middle fibres of the deltoid permit the following 15-90 degrees of rotation, then above 90 which is allowed through rotation of the scapula with action of the trapezius and serratus anterior; Adduction which is produced from contraction of pectoralis major, latissimus dorsi and teres major; Medial rotation from contraction of the subscapularis, the pectoralis major, latissimus dorsi, teres major and the anterior deltoid; and lateral rotation from contraction of the infraspinatus and the teres minor. The synovial membrane on the inner surface of the capsule produces synovial fluid which permits these movements and reduces friction. To further reduce this friction, two bursa are present (a synovial fluid filled sac acting as a cushion between tendons and other joint structures), these are; The subacromial bursa located inferiorly to the deltoid and the acromion and superiorly to the supraspinatus tendon and joint capsule – supporting the deltoid an supraspinatus; and the subscapular bursa between the subscapularis tendon and the scapula which reduced wear and tear on the tendon during movement.

Question 15

Describe the ligaments of the glenohumeral joint

Answer 15

The ligaments play a vital role in supporting this joint. The majority of which are thickenings of the joint capsule. The glenohumeral ligaments can be subdivided into the superior, middle and inferior bands which run from the glenoid fossa to the anatomical neck of the humerus stabilising the anterior aspect of the joint; the coracohumeral ligament runs from the base of the coracoid process of the scapula to the greater tubercle of the humerus supporting the superior aspect of the joint capsule; the transverse humeral ligament runs over the two tubercles of the humerus which holds the long head of the biceps brachii within the intertubercular groove; and lastly the coracoacromial ligament which is not a thickening of the capsule by instead runs from the acromion to the coracoid process froming the coraco-acromial arch overlying the shoulder joint and preventing superior displacement of the humerus.

Question 16

Describe the neurovascular supply of the glenohumeral joint

Answer 16

In terms of neurovascular supply to the glenohumeral joint the arterial supply is from the anterior and posterior circumflex humeral arteries as well as the suprascapular artery. Branches of these arteries from an anastamotic network around the joint. The nerve supply if from the axillary, the suprascapular and the lateral pectoral nerves dericed from C5 and C6 of the brachial plexus, for this reason an upper brachial plexus injury (Erbs palsy) will affect shoulder joint function. Factors that contribute to the motility of this joint include the type of joint, the disproportion in size of the surfaces, the laxity of the joint capsule; alternatively the factors which contrtibute to the inherent stability of the joint include the rotator cuff muscles which pull the head of the humerus into the glenoid cavity, the glenoid labrum which deepens the cavity as well as the ligaments which reinforce the capsule and the coracoacromial ligament forming the arch helping to prevent superior displacement.

Question 17

Describe the muscles which contribute to shoulder formation

Answer 17

In terms of the muscles which contribute to the formation of the shoulder, a number of muscles connect the scapular to the humerus in the arm, these are the teres major, the rotator cuff muscles (supraspinatus, infraspinatus, teres major and subscapularis) and the deltoid muscle. The deltoid is a large triangular shaped muscle which attaches from its base to the scapula and the clavicle, with its apex attached to the deltoid tuberosity of the humerus. Its main role is abduction of the arm beyond the initial 10 degrees carried out by the supraspinatus with its innervating nerve being the axillary nerve, a branch of the posterior cord of the brachial plexus. Anterior muscles which help to form the shoulder include the pectoralis major and minor and the serratus anterior. While the superficial muscles of the back involved in forming the shoulder are the trapezius, the latissimus dorsi, the rhomboid major and minor and the levator scapulae. The serratus anterior is supplied by the long thoracic nerve. This originates from C5,C6 and C7, enters the axilla via the lateral border of the first rib behind the axillary vessels and the brachial plexus, and decends over the lateral surface of the serratus anterior. Of all these muscles described which compose the shoulder, five muscles are involved in the movement of the shoulder girdle. Elevation is caused by the rhomboids, trapezius and the levator scapulae. Depression is caused by the trapezius and the pectoralis minor. Retraction by the rhomboids, the trapezius and levator scapular. Protraction by the serratus anterior and the pectoralis minor. Upward rotation by the trapezius, serratus anterior and the rhomboids, and downward rotation by the rhomboids, the pectoralis minor and the levator scapulae.

Question 18

What is the axilla

Answer 18

In terms of the muscles which contribute to the formation of the shoulder, a number of muscles connect the scapular to the humerus in the arm, these are the teres major, the rotator cuff muscles (supraspinatus, infraspinatus, teres major and subscapularis) and the deltoid muscle. The deltoid is a large triangular shaped muscle which attaches from its base to the scapula and the clavicle, with its apex attached to the deltoid tuberosity of the humerus. Its main role is abduction of the arm beyond the initial 10 degrees carried out by the supraspinatus with its innervating nerve being the axillary nerve, a branch of the posterior cord of the brachial plexus. Anterior muscles which help to form the shoulder include the pectoralis major and minor and the serratus anterior. While the superficial muscles of the back involved in forming the shoulder are the trapezius, the latissimus dorsi, the rhomboid major and minor and the levator scapulae. The serratus anterior is supplied by the long thoracic nerve. This originates from C5,C6 and C7, enters the axilla via the lateral border of the first rib behind the axillary vessels and the brachial plexus, and decends over the lateral surface of the serratus anterior. Of all these muscles described which compose the shoulder, five muscles are involved in the movement of the shoulder girdle. Elevation is caused by the rhomboids, trapezius and the levator scapulae. Depression is caused by the trapezius and the pectoralis minor. Retraction by the rhomboids, the trapezius and levator scapular. Protraction by the serratus anterior and the pectoralis minor. Upward rotation by the trapezius, serratus anterior and the rhomboids, and downward rotation by the rhomboids, the pectoralis minor and the levator scapulae.

Question 19

What are the four walls of the axilla

Answer 19

. It has four boundaries with these structures helping to form this pyramidal space. The anterior wall is the lateral part of the pectoralis major, the underlying pectoralis minor and the subclavius muscles as well as the clavipectoral fascia. The posterior wall is formed from the scapula, the subscapularis, the teres major and the inferior latissimus dorsi. The medial wall is formed from ribs 1-4 of the thoracic wall and the respective intercoastal muscles and the overlying serratus anterior muscle. Finally the lateral wall is formed from a narrow bony wall formed by the intertubercular groove of the humerus.

Question 20

Describe the passage in the axilla

Answer 20

With its four walls it has its inlet which forms the apex, and the floor which forms the base. It is at the axillary inlet at the apex where the arteries, veins, lymphatics and nerves traverse this superior opening and pass to or from the arm, making the cervico-axillary canal a vital point for distribution of the neurovascular structures. At this inlet the axillar vein, artery and trunks of the brachial plexus pass through. From this distribution centre the passing of the neurovascular structures has a number of possible passage ways; superiorly the structures can pass through the cervico-axillary canal to or from the root of the neck; anteriorly they can pass through the clavipectoral triangle to the pectoral region; inferiorly and laterally into the limb itself; posteriorly via a space called the quadrangular space to the scapular region; or inferiorly and medially along the thoracic wall to the inferiorly placed axioappendicular muscles which are the latissimus dorsi and the serratus anterior.

Question 21

Describe the contents of the axilla

Answer 21

The base of the axilla is formed from concave skin, subcutaneous tissue and the deep fascia. Specifically, the contents of the axilla include the axillary artery and its branches, the axillary vein and its tributaries, lymph vessels and nodes, the cords and branches of the brachial plexus and the proximal heads of the biceps and coracobrachialis – all these are embedded in fat tissue. More proximally, these structures and ensheathed in the axillary sheath, a sleeve-like extension of the cervical fascia.

Question 22

Describe the quadrangular space

Answer 22

The quadrangular space is bounded superiorly by the teres minor, inferiorly by the teres major, medially by the long head of the triceps and laterally by the surgical neck of the humerus. Within this space it transmits the axillary nerve and the posterior circumflex humeral vessels.

Question 23

Describe the triangular space

Answer 23

The triangular space an inferior border formed by the teres major, a superior border formed by the teres minor, and a lateral border formed by the long head of the triceps. This space contains the scapular circumflex vessels but not any major nerve

Question 24

Describe the triangle interval

Answer 24

The triangular interval is formed superiorly by the teres major, laterally by the humerus and medially by the long head of the triceps. This interval allows for passage of the radial nerve and the profunda brachii artery.

Question 25

Describe the origin of blood flow to the upper limb

Answer 25

The blood supply of the upper limb originated from oxygenated blood pumped out of the aorta. The ascending aorta forms the aortic arch of the brachiocephalic trunk, the left common carotid and left subclavian. From the brachiocephalic trunk arises the right subclavian, this forms the axillary artery which will in turn from the brachial artery in the upper arm.

Question 26

Describe the location of the 3 parts of the axillary artery

Answer 26

The axillary artery is the name derived to the artery as it reaches the lateral border of the first rib until it reaches the inferior border of the teres major. Throughout its course the artery is closely related to the cords of the brachial plexus and their branches is enclosed with them in the axillary sheath. Tracing this sheath upwards to the root in the neck shows it is continuous with the prevertebral fascia. The pectoralis minor muscle separates the axillary artery into 3 parts. The first part is ascribed to the artery as it is proximal to pectoralis minor, located at the medial aspect of the muscle and at the lateral margin of the first rib. The second part is ascribed to the part which passes posterior to the pectoralis minor. The third part is the artery name as it passes distally to the muscle from the lateral margin until it reaches the inferior border of the teres major and is then called the brachial artery.

Question 27

Describe the branches of the axillary artery

Answer 27

There are different branches of the axillary artery. The first part has one branch which forms the superior thoracic artery. The second part has two branches which from the thoraco-acromial artery and the lateral thoracic artery. The third branch of the axillary artery has three branches, the subscapular artery and the anterior and posterior circumflex humeral arteries.

Question 28

Describe the pathways of the veins in the upper limb

Answer 28

The venous supply can be subdivided into the deep and superficial veins. The deep veins include the subclavian and axillary vein, the brachial (inbetween cephalic and basilic), radial, ulnar and deep palmar venous arch. Whereas the superficial and visable veins are the cephalic (lateral), basilic (medial), the median cubital which joints these two, the superficial palmar venous arch and the digitial veins.

In the upper arm the basilic vein forms the axillary vein which then forms the subclavian vein. The axillary vein runs alongside the artery, so it is ascribed this name as it passes from the inferior border of the teres major until it reaches the lateral border of the first rib. Generally, all the tributaries of the axillary vein follow the branches of the axillary artery, other tributaries include the cephalic vein (more lateral) and the brachial vein (more medial).

Question 29

Describe the origin and function of the nerves of the upper limb

Answer 29

The nerves of the upper limb are formed from the anterior rami of the last 4 cervical (C1-C4) and the first thoracic (T1) nerves. These originate in the neck and pass laterally and inferiorly over the first rib and enter the axilla forming a network of nerves known as the biracial plexus. The nerves which enter the upper limb have important roles in motor innervation of the muscles of the upper limb, sensory innervation of the skin and deep structures such as the joints. Furthermore, the sympathetic vasomotor nerves influence the diameters of the blood vessels, while the sympathetic secretomotor nerves supply the sweat glands.

Question 30

Describe the orientation and location of the parts of the brachial plexus

Answer 30

The brachial plexus can be described medially to laterally with the roots forming the trunks, which form the divisions and cords, which then terminate in nerves. The roots and the trunks of the plexus are orientated supraclavicularly, the divisions postclavicularly, and the cords and branches infraclavicularly. The brachial plexus is found proximal posterior to the subclavian artery into the neck and its more distal regions surround the axillary artery. The roots of the plexus will often pass through the gap between the anterior and middle scalene muscles. These attach superiorly the first rib, inferiorly to the clavicle and form the scalene muscle triangle, with the medial border formed by the anterior scalane muscle, the lateral border by the middle scalene muscle and the inferior border formed by the bound first rib. Through this region the brachial plexus and axillary artery pass.

Question 31

Describe the formation of the roots and trunks of the brachial plexus

Answer 31

With the component parts of the bracial plexus known to be the roots, trunks, divisions cords and the terminal branches, it is important to know how each is derived. The roots of the plexus are formed by C5-C8 and T1. Close to their origin, the roots receive gray rami comunicans from the adjacent paravertebral ganglion of the sympathetic trunk. These carry postganglionic sympathetic fibres onto the roots for distribution to the periphery. The trunks are formed from the union of these roots; C5 and C6 unite to form the superior trunk; C7 forms the continuous middle trunk; and C8 and T1 unite to form the inferior trunk. The inferior trunk lies on rib 1 posteriorly to the subclavian artery, while the middle and superior trunks are more superior in position. The roots and trunks enter the neck by passing through the scalene triangle. Each of these trunks divide into either anterior or posterior divisions as the plexus passes through the cervicoaxillary canal posteriorly to the clavicle. The anterior division support the anterior flexor compartments of the upper limb, while the posterior divisions supply the posterior extensor compartments. None of the peripheral nerves originate directly from the divisions of the brachial plexus.

Question 32

Describe the cords of the brachial plexus

Answer 32

Of the three cords which are formed, they originate directly from the anterior or posterior divisions. Two of these lie anteriorly and one posteriorly. The lateral cord is formed form the union of the superior and middle trunk (C5-C7). The medial is formed form the continuation of the anterior division of the inferior trunk (C8-T1). The posterior cord is formed from the union of the posterior divisions of the the superior, middle and inferior trunks (C5-T1). All of these cords are found within the axilla.

Question 33

Describe the non-cord branches of the brachial plexus

Answer 33

The first two branches found in the plexus are within the root region. The dorsal scapular nerve branches directly from C5 and innervates the rhomboid major and minor muscles. The long thoracic nerve is formed in the root region of the plexus from the union of C5-C7 which innervate the serratus anterior. There are two further branches of the plexus in the trunk region within the superior trunk. The first of these is the suprascapular nerve (C5-C6) which innervates the supraspinatus and the infraspinatus muscles on the posterior of the scapula. The second of these is the nerve to the subclavius (C5-C6) which innervates the subclavius muscle bound to the scapula. Following this trunk region, with there being no branches as the nerves divide, the next branches are found from the lateral, medial and posterior cords.

Question 34

Describe the anterior branches of the cords of the brachial plexus

Answer 34

the lateral cord branches to form; the lateral pectoral nerve- which serves the pectoralis major muscle; the musculocutaneous nerve - which serves the coracobrachialis, the biceps, the brachialis, all three flexors in the anterior compartment of the arm and terminates as the lateral cutaneous nerve of the forearm; and the lateral root of the median nerve – the largest terminal branch of the lateral cord which passes medially and joins a similar branch from the medial cord forming the median nerve. The medial cord branches include; the medial pectoral nerve which serves the pectoralis major and minor; the medial brachial cutaneous nerve which serves the medial third of the distal arm; the medial antebrachial cutaneous nerve which serves the medial surface of the forearm to the wrist; the ulnar nerve which innervates the dorsal and palmar surfaces of the medial one and a half fingers; and finally the median nerve when union occurs with the lateral cord. It has a sensory role to the skin of the hand, serving the palmar aspect of the radial three and one half fingers and the dorsal aspect of the radial three and one half nail beds; furthermore, it supplies all the muscles of the front of the forearm except for the flexor carpi ulnaris and the ulnar half of the flexor digitorum profundus, as well as four small muscles of the hand (Lateral two lumbricals, opponens pollcis, abductor pollicis brevis and flexor pollicis brevis). The brachial artery is very closely related to the median nerve formed by the plexus. In proximal regions of the upper limb, the median nerve is immediately lateral to this artery. Distally in the limb, the median nerve crosses the medial aspect of the brachial artery and lies anteriorly to the elbow joint. Over the third part of the axillary artery, a characteristic M shape is formed from the musculocutaneous nerve (laterally located), (the lateral root of the median nerve, the median nerve, the root of the median nerve – forming the V shape) and the ulnar nerve (medially located).

Question 35

Describe the posterior branching of the brachial plexus

Answer 35

The branches of the posterior cord include; the superior subscapular nerve – which supplies the subscapularis muscle; the thoracodorsal nerve which supplies the latissimus dorsi; the inferior subscapular nerve which serves the subscapularis and the teres major; the axillary nerve – supplying the deltoid and the teres minor; and final the radial nerve which passes into the arm and forearm. All of these then branches bar the radial nerve innervates muscles associated with the posterior wall of the axilla.

Question 36

Describe some of the conditions which result from damage to the brachial plexus

Answer 36

Damage to any of the nerves of the brachial plexus will result in characteristic symptoms in patients. Damage to the long thoracic nerve will result in winging of the scapula. Upper lesions of the brachial plexus will result in a condition known as Erb’s Palsy – this is characterised by the ‘waiters tip’ which is caused by excessive displacement of the head to the opposite side with depression of the shoulder on the same side; this often occurs in infants during a delivery facing complications, or in adults after a significant blow or fall to the shoulder. Conversely, lower lesions to the brachial plexus present a condition known as Klumpke’s Palsy, characterised by a claw hand. This is caused by traction injuries from somebody falling from a height grasping something to break the fall, or from a baby’s upper limb being pulled excessively during delivery. This causes damage to the C8 and T1 roots which affect the ulnar and median nerves.