26. The shoulder

Question 1

What makes up the pectoral/shoulder girdle?

Answer 1

clavicle and scapula

Question 2

Which joints are present in the shoulder girdle?

Answer 2

• The shoulder joint = glenohumeral joint - represents the joint formed by the head of the humerus and the glenoid fossa of the scapula
The other joints in the shoulder girdle:
• sternoclavicular joint (articulation of sternum and clavicle)
• acromioclavicular joint (articulation of scapula and clavicle).
• scapulothoracic joint (the articulation of the scapula with the thoracic wall) is not a true joint.

Question 3

In the shoulder joint, why can the humerus be compared to a gold ball sitting on a tee?

Answer 3

The humeral head is larger than the glenoid fossa so this joint can be compared to a golf ball sitting on a tee

Question 4

What type of joint is the glenohumeral joint?

Answer 4

ball-and-socket joint (synovial)

Question 5

How is the function of the glenohumeral joint different to the hip joint?

Answer 5

the function required from the shoulder joint differs from that of the hip joint in that a large range of movement is required to position the hand in space, but it does not need to bear such a heavy load. Therefore, the shoulder has evolved to provide great flexibility and mobility at the expense of stability. As such, it is the most mobile joint in the body.

Question 6

What is the head of the humerus covered with?

Answer 6

hyaline cartilage

Question 7

What is the glenoid fossa?

Answer 7

a relatively shallow cartilage-lined socket in which the humeral head articulates

Question 8

What does the shallowness of the glenoid fossa result in?

Answer 8

shallowness of the glenoid fossa facilitates motion and flexibility but also increases the risk of a dislocation of the shoulder joint

Question 9

What is present to overcome the increased risk of dislocation brought by the shallowness of the glenoid fossa?

Answer 9

there is an additional rim of fibrocartilaginous tissue around the edge of the glenoid cavity called the glenoid labrum. This is approximately 1cm in width; its function is to deepen the socket and reduce the risk of dislocation.

Question 10

Summarise why the shoulder is such an unstable joint

Answer 10

• Large humeral head is bigger than the glenoid fossa- Shallow glenoid fossa facilities motion but increases dislocation
• Joint capsule is relatively loose
• Great flexibility and mobility at the expense of stability
• Weak ligaments

Question 11

Which part of the joint capsule of the shoulder is the weakest and why?

Answer 11

The joint capsule of the shoulder is relatively loose. Reinforcement is provided by the rotator cuff muscles, but the inferior aspect has no reinforcement so is the weakest part

Question 12

What 4 things provide stability to the glenohumeral joint?

Answer 12

• Glenoid labrum -
• Rotator cuff muscles
• Long head of biceps
• Ligaments

Question 13

which ligaments provide stability to the glenohumeral joint and at which part?

Answer 13

3 glenohumeral ligaments:

1. Superior glenohumeral ligament
2. middle glenohumeral ligament
3. inferior glenohumeral ligament

• situated at the anterior aspect of the joint

Question 14

What is the function of the glenohumeral ligaments?

Answer 14

Act to reduce the risk of anterior dislocation (the most common direction of dislocation of the shoulder)

Question 15

There are many additional ligaments to the shoulder joint other than the glenohumeral ligaments. Which of these provide stability?

Answer 15

• Conoid ligament and trapezoid ligament together forming the coracoclavicular ligament - linking the coracoid process of the scapula with the clavicle
• The coracohumeral ligament attaches the coracoid process
of the scapula to the greater tubercle of the humerus

Question 16

There are many additional ligaments to the shoulder joint other than the glenohumeral ligaments. Which of these provide tunnels through which tendons can run without bowstringing whilst the muscle is in use?

Answer 16

Transverse humeral ligament creates a tunnel between the greater and lesser tuberosities of the humerus allowing passage of the long head of the biceps

Coraco-acromial ligament providing a roof for the sub acromial space, a tunnel above the glenohumeral joint that allows passage of the supraspinatus tendon

Question 17

What is the function of the coraco-acromial ligament?

Answer 17

prevents superior dislocation of the humerus when a person falls onto their outstretched hand

Question 18

where do the extrinsic muscles of the shoulder originate and insert?

Answer 18

The extrinsic muscles of the shoulder originate from the torso and insert onto the bones of the shoulder (clavicle, scapula or humerus)

Question 19

where do the intrinsic muscles of the shoulder originate and insert?

Answer 19

The intrinsic muscles of the shoulder originate from the scapula and/or claviclen and insert onto the humerus

Question 20

What are the extrinsic muscles of the shoulder organised into and where are they found?

Answer 20

The extrinsic muscles of the shoulder are all sited on the back of the trunk and are organised into two layers – a superficial layer and a deep layer

Question 21

Which muscles are part of the superfical layer of extrinsic muscles of the shoulder?

Answer 21

trapezius and latissimus dorsi

They are situated in the upper back, deep to the trapezius muscle

Question 22

Which muscles are part of the deep layer of extrinsic muscles of the shoulder?

Answer 22

levator scapulae, rhomboid major, rhomboid minor

Question 23

Describe the trapezius:
• Describe its shape and location 
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 23

• broad, flat, triangular muscle and is the most superficial of all the back muscles
• originates from the external occipital protuberance of the skull, the nuchal ligament and the spinous processes of C7-T12
• insert onto the clavicle, acromion and the spine of the scapula
• actions: upper fibres of the trapezius elevate the scapula and rotate it during abduction of the arm above 90°. The middle fibres of trapezius retract the scapula and the lower fibres pull the scapula inferiorly
• Innervation:
- motor innervation is from the spinal accessory nerve (cranial nerve).
-also receives proprioceptor (position-sense) fibres from the C3 and C4 spinal nerves.

Question 24

How do you test the power of the trapezius muscle clinically?

Answer 24

you can ask the patient to shrug their shoulders whilst you attempt to push them back down

Question 25

Describe the Latissimus Dorsi:
• Describe its shape and location 
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 25

• covers a wide area on the lower back. At their origin, the superior fibres of latissimus dorsi lie deep to the inferior fibres of trapezius
• originates from the spinous processes of T6-T12, the iliac crest, thoracolumbar fascia and the inferior three rib
• fibres converge into a tendon that inserts into the intertubercular sulcus of the humerus
• Actions: extends, adducts and medially rotates the upper limb
• Innervation: Thoracodorsal nerve

Question 26

Describe the Levator Scapulae:
• Describe its shape and location 
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 26

• a small strap-like muscle. It lies deep to the trapezius muscle and superior to rhomboid minor
• originates from the transverse processes of the C1-C4 vertebrae
• inserts on the medial border of the scapula
• Actions: elevates the scapula
• Innervation: Dorsal scapular nerve

Question 27

Describe the Rhomboid Minor:
• Describe its shape and location 
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 27

• smaller muscle and is situated superiorly to rhomboid major
• originates from the spinous processes of the C7-T1 vertebrae
• inserts onto the medial border of the scapula, at the level of the spine of the scapula
• Actions: retracts the
scapula and rotates the medial border, such that the glenoid fossa is rotated inferiorly. It therefore helps return it to its anatomical position following previous abduction of the arm above 90°.
• Innervation: Dorsal scapular nerve

Question 28

Describe the Rhomboid Minor:
• Describe its shape and location 
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 28

• originates from the spinous processes of the T2-T5 vertebrae
• inserts onto the medial border of the scapula, between the scapular spine and the inferior angle of the scapula
• Actions: retracts the scapula and rotates the medial border, such that the glenoid fossa is rotated inferiorly. It therefore helps return it to its anatomical position following previous abduction of the arm above 90°.
• Innervation: Dorsal scapular nerve.

Question 29

What are the intrinsic muscles of the shoulder?

Answer 29

the deltoid, teres major, and the four rotator cuff muscles (supraspinatus, infraspinatus, subscapularis and teres minor).

Question 30

Where do the intrinsic muscles all originate and insert?

Answer 30

all originate from the scapula and/or clavicle, and insert onto the humerus

Question 31

Describe the Deltoid:
• Describe its shape and location 
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 31

• a triangular muscle, shaped like the Greek letter delta
• originates from the anterior border and upper surface of the lateral third of the clavicle, and from the acromion and spine of the scapula
• inserts into the deltoid tuberosity on the lateral surface of the humerus
• Actions:
 Anterior fibres – flex and medially rotate the arm at the shoulder.
 Middle fibres – abduct the arm from 15-90°
 Posterior fibres – extend and laterally rotate the arm at the
shoulder
•

Question 32

Describe the Teres Major:
• Describe its shape and location 
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 32

• originates from the posterior surface of the inferior angle of the scapula
• passes anterior to the long head of triceps to insert onto the medial lip
of the intertubercular groove of the humerus
• Actions: adducts and extends the arm at the shoulder and also medially rotates the arm
• Innervation: Lower subscapular nerve.

Question 33

What are rotator cuff muscles?

Answer 33

• a group of four muscles that originate from the
scapula and attach to the humeral head.
• the resting tone of these
muscles acts to ‘pull’ the humeral head into the glenoid fossa. This
gives the glenohumeral joint a large amount of dynamic stability.
• the rotator cuff muscles also have their own individual actions

Question 34

Describe the Supraspinatus:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 34

• originates from the supraspinous fossa of the scapula
• inserts onto the greater tubercle of the humerus
• Actions: Supraspinatus abducts the arm from 0-15°, and assists deltoid in abducting the arm from 15-90
• Innervation: Suprascapular nerve

Question 35

Describe the Infraspinatus:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 35

• originates from the infraspinous fossa of the scapula
• inserts onto the greater tubercle of the humerus, between the insertions of supraspinatus and teres minor
• Action: Infraspinatus laterally rotates the arm
• Innervation: Suprascapular nerve

Question 36

Describe the Subscapularis:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 36

• originates from the subscapular fossa
• inserts onto the lesser tubercle of the humerus
• Actions: Subscapularis medially (internally) rotates the arm
• Innervation: Upper and lower subscapular nerves

Question 37

Describe the Teres Minor:
• Where does it originate
• Where does it insert
• What is its action
• What is it innervated by

Answer 37

• originates from the posterior surface of the scapula
• inserts onto the greater tubercle of the humerus
inferior to the insertion of infraspinatus
• Actions: Teres minor laterally rotates the arm.
• Innervation: Axillary nerve (C5,6 from the posterior cord of the brachial plexus)

Question 38

What does the anterior and posterior rotator cuff muscles insert into?

Answer 38

posterior muscles insert into the greater tubercle. Anterior muscle (subscapularis) insert into the lesser tubercle

Question 39

How do the rotator cuff muscles stabilise the joint?

Answer 39

Insertions of the rotator cuff muscles blend to form a tendinous ‘cuff’ which fuses with the joint capsule and strengthens it. In addition, the tone in the rotator cuff muscles holds the head of the humerus close to the glenoid cavity

Question 40

Where does the right subclavian artery arise from?

Answer 40

brachiocephalic trunk

Question 41

What is the left subclavian artery a direct branch of?

Answer 41

the arch of the aorta

Question 42

When does the subclavian artery become known as the axillary artery?

Answer 42

When the subclavian artery (on either side of the body) crosses the lateral border of the first rib to enter the axilla, it becomes known as the axillary artery

Question 43

Describe the branches of the axillary artery

Answer 43

• The axillary artery passes behind the pectoralis minor muscle and at the level of the surgical neck of the humerus, gives off the anterior and posterior circumflex humeral arteries.
• These encircle the neck of the humerus to supply the shoulder region.
• There is also an arterial anastomosis (connection between vessels) around the margin of the scapula.
• The subscapular artery arises from the third part of the axillary artery to form part of this anastomosis, anastomosing with branches of the suprascapular artery and transverse cervical artery

Question 44

What is the arterial supply of the shoulder joint derived from?

Answer 44

from the anterior and posterior circumflex humeral arteries and the suprascapular artery

Question 45

When does the axillary artery become known as the brachial artery?

Answer 45

The axillary artery becomes the brachial artery at the inferior border of the teres major muscle

Question 46

Describe the route and branches of the brachial artery

Answer 46

• Immediately distal to the teres major, the brachial artery gives rise to the profunda
brachii (deep brachial artery), which travels with the radial nerve in the radial (spiral) groove of the humerus and supplies the structures in the posterior compartment of the arm (e.g. triceps brachii).
• The profunda brachii terminates by contributing to an anastomotic network around the elbow joint.
• The brachial artery then descends in the anterior compartment of the arm.
• As it passes through the cubital fossa, underneath the brachialis muscle, the brachial artery terminates by bifurcating into the radial and ulnar arteries.
• In the proximal arm, the median nerve lies immediately lateral to the brachial artery.
• Distally, the median nerve crosses to the medial side of the brachial artery

Question 47

Which areas does the brachial artery supply?

Answer 47

It provides the main supply blood supply to the arm and forearm.

Question 48

Where is the brachial pulse palpated?

Answer 48

The brachial pulse is palpated in the cubital fossa, medial to the tendon of biceps
brachii

Question 49

What is the relationship between the brachial plexus and the axillary artery?

Answer 49

The cords of the brachial plexus lie in close relationship with the axillary artery, and are named according to their anatomical relationship with the second part (middle section) of this artery i.e. the medial cord is medial to the second part of the axillary artery, the lateral cord is lateral to it and the posterior cord is posterior

Question 50

What is the nerve supply to the shoulder joint?

Answer 50

The nerve supply to the shoulder joint is derived from the axillary nerve, suprascapular nerve and the lateral pectoral nerve. These are all branches of the brachial plexus with the nerve roots C5 and C6. The C5 dermatome overlies the
shoulder