The shoulder and brachial plexus Flashcards
What muscular region forms the anterior wall of the axilla?
The pectoral region. This wall is therefore made up of the pectoralis minor, subclavius and clavipectoral fascia on a deep plane and the pectoralis major with its fascia more superficially
What region forms the posterior wall of the axilla?
The scapular region- subscapularis and teres major, with the tendon of the latissimus dorsi winding around the lower border of teres major
What muscle overlies the medial wall of the axilla?
The serratus anterior
What is the name of the part of the scapular which articulates with the shoulder joint?
The glenoid cavity
Describe the various bony landmarks seen on the proximal part of the humerus
Two bony prominences are seen just distal to the head and neck of the humerus, the greater and lesser tubercles.
The tubercles can be traced down the humerus for a short way as two raised ridges called the crests of the greater and lesser tubercles
A groove is formed between the tubercles and their corresponding crests called the intertubercular groove
A short distance distal to the head of the humerus the shaft of bone narrows. What is this narrow area called. Why?
The surgical neck. It is at this point that the bone sometimes breaks (the stouter section of bone directly below the head of the humerus is called the anatomical neck)
What is the deltoid tuberosity?
A raised, roughened area distal to the surgical neck on the outer aspect of the shaft of the humerus. It is here that the deltoid muscle inserts.
What are the two bony prominences which project out of the scapula called?
The coracoid process (a beak like process which projects forwards)
The acromion- (which projects from the back of the scapula)
Describe the two points of articulation of the clavicle. What type of joints are these?
Its lateral end articulates with the acromion at the acromioclavicular joint. The medial end articulates with the manubrium of the sternum at the sternocalvicular joint. Both these joints are synovial
Which three muscles make up the pectoral region?
Deeper layer: pectoralis minor and subclavius
Superficial layer: pectoralis major
What is the origin of pectoralis minor?
The middle three true ribs (3,4,5) on the front of the chest
What is the insertion of pectoralis minor?
The coracoid process
What is the action of pectoralis minor?
a) draws the coracoid process downwards thus depressing the shoulder
b) when fixed by stabilizing the pectoral girdle, origin and insertion switch around and pec minor may act as an accessory muscle for respiration by raising the rib cage
What is the origin of the subclavius?
The first rib
What is the insertion of the subclavius?
The under-surface of the clavicle
What is the origin of the pectoralis major?
i) calvicular head: anterior surface of the inner two thirds of the clavicle
ii) sternocostal head: anterior surface of the sternum and upper six ribs
What is the insertion of the pectoralis major?
Crest of the greater tubercle. Lower fibres are inserted deep to the upper fibres
What is the action of the pectoralis major?
Adduction and medial rotation of the upper limb
What is the clinical significance of the action of the pectoralis major muscle in assessment of breast cancer?
The deep fascia on the surface of pec major forms the base on which the breast rests in females. A deeply seated breast cancer may invade the fascia and eventually the muscle. It is therefore important to be able to test the action of the muscle in such patients in order to determine whether or not such a cancer has become fixed to the muscle. This can be done by asking the patient to press both hands on her hips, tensing the muscle. The lump in the breast is then rested for mobility. If it remains fixed during this test it provides evidence that the spreading cancer has already infiltrated the underlying deep fascia and muscle.
What is the flat surface of the scapular viewed from the front called?
The subscapular fossa.
What two muscles arise from the scapula?
Subscapularis and teres major
Where does subscapularis arise?
The subscapular fossa?
Where does subscapularis insert?
The fibres converge to form a tendon which inserts onto the lesser tubercle of the humerus. As the tendon passes over the front of the shoulder joint, some of its fibres blend and fuse with the capsule of the joint
What is the action of the subscapularis?
Adduction and medial rotation of the humerus
What prevents friction between the subscapulris and the shoulder joint during movement?
The subscapular bursa- a “balloon” of synovial membrane which protrudes out of a hole in the capsule of the shoulder joint and insinuates itself between the muscle and the joint capsule to reduce friction during movement
What is the origin of teres major?
The lateral border of the posterior surface of the scapular
What is the insertion of teres major?
The crest of the lesser tubercle
What is the action of teres major?
Adduction and medial rotation of the humerus (origin and insertion in the same plabe as subscapularis therefore action is the same)
What is the origin of latissimus dorsi?
Lower thoracic and lumbar spinous processes (T7-S2), posterior part of the iliac crests
What is the insertion of latissimus dorsi?
Intertubercular groove of the humerus
What is the action of latissimus dorsi?
Adducts and medially rotates the humerus.
It is the great climbing muscle- in climbing with the hands gripping a fixed point above, the muscle draws the whole trunk upwards
What is the posterior fold?
The posterior wall of the axilla which has a rounded appearance because of the relationship between the tendon of latissimus dorsi and the lower border of teres major
What is the origin of serratus anterior?
The first eight ribs. Arises by digitations from the anterior ends
What is the insertion of the serratus anterior?
Medial/vertebral border of the scapula
What is the action of serratus anterior?
Holds the medial border of the scapula against the chest wall
Can pull the scapula forward around the chest wall in an action called protraction
If the pectoral girdle is fixed, the muscle can also act as an accessory muscle of respiration
What is a winged scapular? When does it occur?
The serratus anterior holds the medial edge of the scapula close against the chest wall. If it is paralysed the medial border of the scapula splays out from its bed- a condition called winging of the scapula. This condition is occasionally found after operations for cacinoma of the brest when there have been injuries to the nerve supply of the muscle, the long thoracic nerve
What is the origin of the deltoid?
Outer margins of the lateral part of the clavicle, acromion, spine of the scapula
What is the insertion of the deltoid?
The deltoid tuberosity of the humerus
How is friction between the deltoid muscle and the underlying shoulder joint prevented?
the subacromial bursa
What is the action of the deltoid muscle?
Anterior fibres flex the arm
Posterior fibres extend the arm
The fibres in the middle which directly overlie the shoulder joint make up the chief abductor muscle of the arm
What nerves and vessels are found in the axilla?
- The brachial plexus
- The axillary artery (a continuation of the subclavian artery)
- The axillary vein (renamed the subclavian vein when it reaches the root of the neck)
What nerve roots supply the upper limb
The ventral rami of the 5th, 6th, 7th and 8th cervical spincal nerves and part of the ventral ramus of the 1st thoracic spinal nerve
Describe the route taken by the ventral rami which supply the upper limb
The ventral rami emerge from between the scalenus anterior and medius in the neck. Here they immediately enter the posterior triangle of the neck, where they fuse to form 3 trunks- the upper middle and lower trunks. At this level four branches are given off. Then, a short distance behind the clavicle, the upper, middle and lower trunks reorganise themselves to form the lateral, medial and posterior cords of the brachial plexus. These lie in the axilla arranged round the axillary artery (they are named according to their relationship to the axillary artery).
What boundaries define the posterior triangle of the neck?
The sternocleidomastoid muscle, the clavicle and the trapezius
What four branches are given off from the upper, middle and lower trunks?
- Dorsal scapular
- Suprascapular
- Long thoracic nerve
- Nerve to subclavius
What muscles are supplied by the dorsal scapular nerve?
levator scapulae and rhomboids
What muscles are supplied by the suprascapular nerve?
Supraspinatus and infraspinatus
What muscle is supplied by the long thoracic nerve? What is the clinical significance of this nerve?
Serratus anterior
The LTN is vulnerable during operations on carcinoma of the breast. If it is damaged there is paralysis of serratus anterior and winging of the scapular
What group of muscles do each of the cords of the brachial plexus supply?
Lateral and medial cords supply flexor aspects of the limb
Posterior cord supplies extensor aspects of the limb
What muscles are supplied by the lateral and medial pectoral nerves?
Lateral- pectoralis major
Medial- pectoralis minor (some fibres also aid in the supply of pec major)
(N.B. lateral pectoral nerve arises from lateral cord; medial pectoral nerve arises from medial cord)
What nerves arise from the lateral cord?
Lateral pectoral nerve
Musculocutaneous nerve
What is supplied by the musculocutaneous nerve?
biceps
coracobrachialis
How does the median nerve arise?
It is a continuation of the lateral cord but also receives a contribution from the medial cord
What muscles are supplied by the median nerve?
The flexor muscles below the elbow
How does the ulnar nerve arise? What muscles are supplied by the ulnar nerve?
Ulnar nerve is a continuation of the medial cord and supplies flexor muscles below the elbow
What are the branches of the medial cord?
- Medial pectoral nerve
- Medial cutaneous nerve of the arm
- Medial cutaneous nerve of the forearm
What are the branches of the posterior cord?
Upper and lower subscapular nerves
Thoracodorsal nerve
What is supplied by the upper and lower subscapular nerves?
Subscapularis and teres major
What is supplied by the thoracodorsal nerve?
Latissimus dorsi
What are the terminal branches of the posterior cord?
Axillary and radial nerves
What is the route taken by the axillary nerve? What muscle does it supply?
It passes between the subscaularis and teres major then curls round the back of the humerus. It then lies deep to the deltoid muscle which it supplies
What is supplied by the radial nerve?
The extensor aspect of the humerus
What happens to the axillary artery after it leaves the axilla?
It leaves the axilla at the lower border of the teres major and is then renamed the brachial artery
Where does the axillary vein lie in relation to the axillary artery?
Medial to the axillary artery and the surround cords of the brachial plexus
What is supplied by the branches of the axillary artery?
The scapular muscles
The chest wall
The female breast
What branch of the axillary artery supplies the female breast?
Lateral thoracic branch
What arteries form a loop around the neck of the humerus? Which nerve runs with these arteries?
The circumflex humeral branches form a vasular arrangement around the sirgical neck of the humerus, The posterior one accompanies the axillary nerve to the back of the humerus.
What artery accompanies the thoracodorsal nerve?
The subscapular artery
What is the blood supply to the subclavian muscles. Why is this important?
The subclavian muscles receive a dual blood supply from the branches of the axillary artery, and from the subclavian artery in the root of the neck. This is important as if there is a blockage in the first part of the axillary artery, a bypass may develop through the scapular network of vessels, which may be sufficient to maintain a viable blood supply to the limb
What are the three groups of lymph nodes in the axilla?
Lateral group- lies laterally along the axillary vessels and receieve lymph from the upper limb lymphatics
Pectoral/anterior group- lies anteriorly between the anterior and medial walls of the axilla. Upper nodes of this group receive lymph from the breast
Subscapular/posterior group- lie in the posterior wall of the axilla along the subscapular vessels. Receive lymph from the scapular region and back
Describe the path taken by lymph which drains into the axilliary lymph nodes
All three groups connect with central nodes which lie in the fat of the axilla. Lymph from the central nodes drains into the apical nodes at the apex of the axilla. The efferents from these form the subclavian lymph trunk which usually empties into the subclavian vein
How is the glandular tissue of the breast divided?
The divisions of the gland are called lobes. There are about 15 lobes in each breast. The lobes are further divided into lobules.
How does milk leave the breast?
Milk is produced in the lobes. Milk from each lobe passes towards the nippe through a lactiferous duct. Just beneath the nipple each duct expands to form a lactiferous sinus before opening onto the nipple.
Where does the blood supply to the breast come from?
The perforating branches of the internal thoracic artery and the lateral thoracic branch of the axillary artery
Where does the lymph from the breast drain to?
Most drains to the axillary nodes. From the deep part of the gland, lymphatic drainage follows branches of the internal thoracic artery to nodes that lie along this vessel- the internal thoracic nodes. Lymphatics then follow the intercostal artery back to the aorta where they drain into paraaortic nodes
What is the clinical significance of lymphatic drainage of the breast?
Cancer of the breast often spreads via the lymphatic system. Thus cancer may spread to the axillary nodes, as evidenced by a hard lump in the axilla, or may spread into the thoracic cavity via the internal thoracic and para-aortic nodes.
Describe the posterior surface of the scapula
From behind, the scapula is divided into upper and lower parts by a bony spine- the scapula spine, which ends laterally as the acromion. The section of scapula above the spine is the supraspinous fossa, while the section below the spine is the infraspinous fossa.
Which three muscles can be seen on the back of the scapula?
Supraspinatus (in the supraspinous fossa)
Infraspinatus and teres minor in the infraspinous fossa
What is the origin of supraspinatus?
Supraspinous fossa
What is the insertion of supraspinatus?
Greater tubercle of the humerus. Some of its fibres fuse with the capsule of the shoulder joint
What is the clinical significance of supraspinatous?
Rupture of it’s tendon may occur with injury
Its tendon is prone to calcific degeneration
What nerve supplies supraspinatous? How does this nerve reach the muscle?
Supplied by suprascapular nerve
Reaches the muscle via the scapular notch in the upper border of the scapula
What is the action of supraspinatus?
Abduction of the arm from the side of the body- it is important for initiation of this movement
What is the origin of infraspinatus?
Infraspinous fossa
What is the insertion of infraspinatus?
Greater tubercle of the humerus. Some of its fibres fuse with the capsule of the shoulder joint
What nerve supplies infraspinatous? How does this nerve reach the muscle?
Supplied by suprascapular nerve
Reaches the muscle via the spinoglenoid notch- at the lateral end of the scapula spine
What is the action of infraspinatus?
Lateral rotation of the arm (n.b. it’s position corresponds with that of the subscapualris on the front of the scapula and it has the opposite action)
What is the origin of teres minor
Infraspinous fossa
What is the insertion of teres minor?
Greater tubercle of the humerus.
What is the action of teres minor?
Lateral rotation of the arm
What is the nerve supply of teres minor?
axilliary nerve
What is the origin of the trapezius?
A long linear origin taking in the back of the skull, the ligamentum nuchae and the cervical and thoracic spines
What is the insertion of the trapezius?
The upper fibres insert into the lateral third of the clavical
The lower fibres insert onto the acromion and spine of the scapula
What is the nerve supply of the trapezius?
The spinal accessory nerve (CN XI)
What are the three joints of the shoulder region?
Sternoclavicular joint
Acrominoclavicular joint
Shoulder joint
What type of joint is the sternoclavicular joint?
Ball and socket, synovial joint
What structures resist displacement of the sternocalvicular joint?
- The costoclavicular ligament
- The joint capsule
- An articular disc which attaches to the clavicle above and the first rib below which therefore prevents extreme displacement of the medial end of the clavicle
Why are the coracoclavicular ligaments important?
These ligaments support the weight of the upper limb, taking the stress of the acromioclavicular joint
What type of the joint is the acromioclavicular joint?
A sliding joint which allows only a little gliding movement between its surfaces
How does the head of the humerus articulate with the glenoid cavity of the scapula?
Via a synovial ball and socket joint. The glenoid cavity is pear shaped and at first appears too small to accept the head of the humerus. However, its articular surface is deepened slightly by a rim of fibrous tissue called the labrum glenoidale
What bones does the capsule of the shoulder joint attach to?
The labrum of the scapula
Around the anatomical neck of the humerus
What ligaments are in place to strengthen the capsule of the shoulder joint?
The coracohumeral ligament
The coracoacromial ligament
Where does the coracohumeral ligament attach? What is its action
Passes from the coracoid process to the greater tubercle. It prevents excessive external rotation of the shoulder
What is the function of the coracoacromial ligament?
With the coracoid process and acromion it forms a strong arch above the joint, preventing any upward displacement
What muscle tendon is found inside the shoulder joint capsule?
The long head of the biceps- it also aids in stabilising the joint
Which bursa does not communicate with the synovia of the shoulder joint?
The subacromial bursa
What muscles make up the rotator cuff?
Supraspinatus
Infraspinatus
Teres minor
Subscapularis
What aspect of the shoulder joint is unsupported? What is the clinical relevance of this?
The inferior aspect. If the shoulder joint is dislocated, it usually does so through this weak inferior aspect
What nerve may be injured by dislocation of the shoulder?
The axillary nerve
What factors stabilise the shoulder joint?
The rotator cuff muscles
The overhanging coracoacromial arch
What factors contribute to the freedom of movement at the shoulder joint?
The large rounded area of the head of the humerus in comparison with the small shallow glenoid
The lax capsule surrounding the joint
What muscles allow flexion of the shoulder joint?
Anterior fibres of the deltoid aided by pec major
What muscles allow extension of the shoulder joint?
Posterior fibres of the deltoid aided by latissimus dorsi
What muscles allow abduction of the shoulder joint?
Supraspinatus initially then deltoid takes over
What muscles allow adduction of the shoulder joint?
Pec major and latissimus dorsi
