27. The arm

Question 1

which muscles are contained in the arm?

Answer 1

The arm contains four
The arm is located between the shoulder joint and elbow joint

The arm contains fourmuscles – three in the anterior compartment (biceps brachii, brachialis, coracobrachialis), and one in the posterior compartment (triceps
brachii)

Question 2

which muscles are in the anterioir compartment of the arm, what are they innervated by and what are they supplied by?

Answer 2

B = Biceps brachii
B = Brachialis
C = Coracobrachialis

all innervated by the musculocutaneous
nerve. The arterial supply to the anterior compartment of the upper arm is via muscular branches of the brachial artery

Question 3

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

Answer 3

• two-headed muscle
• The long head of biceps brachii originates from the supraglenoid tubercle of
the scapula. short head of biceps originates from the coracoid process of the scapula
• Both heads unite to form a single muscle belly distally. Biceps brachii then inserts into the radial tuberosity via the biceps tendon and also into the deep fascia of the forearm via the bicipital aponeurosis
• Action: a strong supinator of the forearm at the radioulnar joints. It also flexes the arm at the elbow and the shoulder joints
• Innervation: Musculocutaneous nerve (C5-7 from the lateral cord of the brachial plexus)

Question 4

What is the bicipital aponeurosis

Answer 4

a thick fascial band that originates close to the
musculotendinous junction of the biceps, forms the roof of the cubital fossa and ends by blending with the deep fascia at the ulnar border of the anterior forearm.

Question 5

what is a good way to remember the movements of the biceps brachii?

Answer 5

the movements are used when opening a bottle of wine with a corkscrew: the biceps first unscrews the cork (supination) then pulls it out (flexion).

Question 6

What does the biceps tendon reflex test?

Answer 6

tests spinal cord segment C6 because this myotome is predominantly responsible for elbow flexion and for supination

Question 7

Describe rupture of the biceps tendon

Answer 7

• long head of the biceps may rupture near to its scapular origin, most commonly in patients >50 following minimal trauma.
• Typically, the patient reports hearing something “snap” in the shoulder whilst lifting.
• Characteristically, flexion of the arm at the elbow produces a firm lump in the lower part of the arm - this is the unopposed contracted muscle belly of the biceps and is called the ‘Popeye sign’.
• The patient will not notice much weakness in the upper limb because the action of the brachialis (flexion) and supinator (supination) muscles is intact, so management is
usually conservative.
• In weightlifters, the distal tendon of the biceps sometimes snaps near to its insertion instead

Question 8

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

Answer 8

• lies deep to the short head of biceps brachii in the arm
• originates from the coracoid process of the scapula
• passes through the axilla and inserts onto the medial side of the humeral shaft
• Action: flexes the arm at the shoulder and is a weak adductor of
the arm.
• Innervation: Musculocutaneous nerve

Question 9

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

Answer 9

• lies deep to the biceps brachi in the distal half of
the arm
• originates from the anterior surface of the distal half of the humeral shaft
• inserts onto the coronoid process of the ulna and the ulnar tuberosity, just distal to the elbow joint
• Action: Brachialis flexes the forearm at the elbow
• Innervation: Musculocutaneous nerve (C5-7), with contributions from the radial nerve (C5 and C6 fibres).

Question 10

What muscle forms the floor of the cubital fossa?

Answer 10

Brachialis

Question 11

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

Answer 11

• The origins of the three heads of triceps brachii :
 Long head: from the infraglenoid tubercle of the scapula.
 Lateral head: from the shaft of the humerus, superior to the radial (spiral) groove.
 Medial head: from the shaft of the humerus, inferior to the radial (spiral) groove
• Distally, the heads converge to form a single tendon that inserts onto the olecranon of the ulna
• Action: Triceps brachii extends the forearm at the elbow
• Innervation: Radial nerve

Question 12

What does the triceps reflex test for?

Answer 12

The triceps tendon reflex tests spinal cord segment C7 because this myotome is predominantly responsible for elbow extension

Question 13

What are the quadrangular and triangular spaces?

Answer 13

quadrangular and triangular spaces and the triangular interval are passageways between the muscles of the shoulder region.

Question 14

Why is the quadrangular space clinically important?

Answer 14

because it is the route via which the axillary nerve and posterior circumflex humeral artery (and vein) enter the
posterior compartment of the arm.

Question 15

What is the quadrangular space bounded by?

Answer 15

 Superiorly: the inferior margin of teres minor
 Inferiorly: the superior margin of teres major
 Medially: the long head of triceps brachii
 Laterally: the surgical neck of the humerus

Question 16

What is the triangular space the passageway for?

Answer 16

triangular space is the passageway through which the circumflex scapular
vessels enter the infraspinous fossa. No nerves pass through this
space.

Question 17

What is the triangular space bounded by?

Answer 17

 Superiorly: the inferior margin of teres minor
 Inferiorly: the superior margin of teres major
 Laterally: the long head of the triceps brachii

Question 18

What is the triangular interval bounded

Answer 18

 Superiorly: the inferior margin of teres major
 Medially: the long head of triceps brachii
 Laterally: either the shaft of the humerus or the lateral head of triceps brachii

Question 19

Which nerves are visible in the base of the triangular interval?

Answer 19

The radial nerve and profunda brachii artery are visible in the base of the triangular interval as they wind around the humerus in the radial (spiral) groove.

Question 20

What is a bursa?

Answer 20

A bursa is a fluid filled sac that provides a cushion between a tendon and a bone (or ligament) to allow a smooth gliding action of the tendon.

Question 21

Where is the subacromial bursa found, what does it separate and what is its function?

Answer 21

a lies under the acromion .
It separates the supraspinatus tendon from the overlying coraco acromial ligament, the acromion, the coracoid process and from the deep surface of the deltoid muscle.
It acts like a cushion, reducing friction as the supraspinatus tendon passes under these structures.

Question 22

Where is the subscapular bursa located and what is its function?

Answer 22

located between the tendon of subscapularis and the neck of the scapula. It protects the tendon of the subscapularis muscle as it passes inferior to the root of the coracoid process and over the neck of the scapula.

Question 23

What is the subacromial spce?

Answer 23

The space between the coraco-acromial arch (formed by the coracoid process, coraco-acromial ligament and acromion) and the head of the humerus

Question 24

What is found in the subacromial space

Answer 24

 Subacromial bursa
 Supraspinatus tendon
 Joint capsule
 Long head of biceps

Question 25

Where does the tendon of the long head of the biceps brachii lie?

Answer 25

lies within the cavity of the shoulder joint(intertubercular sulcus). It acquires a tubular sleeve of synovium as it enters the joint, which surrounds
it up to its insertion on the supraglenoid tubercle of the scapula

Question 26

Which muscles carry out abduction of the shoulder?

Answer 26

• The first 90° of abduction occurs at the glenohumeral joint. Of this:
 0-15° is carried out by supraspinatus (suprascapular nerve)
 15-90° is carried out by deltoid (axillary nerve) (figure 7.42a and here)
• Above 90°, abduction occurs at the scapulothoracic ‘joint’ through rotation of the
scapula. The muscles responsible for this are trapezius (upper fibres only) and serratus anterior

Question 27

Which muscles carry out adduction of the shoulder?

Answer 27

 Pectoralis major – sternal head (medial and lateral pectoral nerves)
 Latissimus dorsi (thoracodorsal nerve)
 Teres major (lower subscapular nerve)

Question 28

Which muscles carry out flexion of the shoulder?

Answer 28

 Anterior fibres of deltoid (axillary nerve)
 (Clavicular head of) pectoralis major (medial and lateral pectoral nerves)
 Coracobrachialis (musculocutaneous nerve)
 Biceps brachii (musculocutaneous nerve)

Question 29

Which muscles carry out Extension of the shoulder?

Answer 29

 Posterior fibres of deltoid (axillary nerve)
 Latissimus dorsi (thoracodorsal nerve)
 Teres major (lower subscapular nerve)

Question 30

Which muscles carry out internal rotation of the shoulder?

Answer 30

 Subscapularis (upper and lower subscapular nerves)
 Teres major (lower subscapular nerve)
 (Sternal head of) pectoralis major (medial and lateral pectoral nerves)
 Latissimus dorsi (thoracodorsal nerve)

Question 31

Which muscles carry out External rotation of the shoulder?

Answer 31

 Infraspinatus (suprascapular nerve)

 Teres minor (axillary nerve)

Question 32

which group of muscles are the most important stabiliser of the shoulders?

Answer 32

The rotator cuff muscles

Question 33

What is the mnemonic to remember rotator cuff muscles?

Answer 33

Muscles of the rotator cuff = mnemonic SITS

S = Supraspinatus
I = Infrapinatus
T = Teres minor
S = Subscapularis

Question 34

summarise the innervations and actions of the rotator cuff muscles

Answer 34

 Supraspinatus: Suprascapular nerve (C5,6) – first 15° of abduction
 Infraspinatus: Suprascapular nerve (C5,6) – lateral (external) rotation
 Teres Minor: Axillary nerve (C5,6) – lateral rotation and adduction
 Subscapularis: Upper and lower subscapular nerves (C5,6) – medial (internal) rotation

Question 35

Which myotome is responsible for shoulder abduction and external (lateral) rotation?

Answer 35

C5

Question 36

How do the rotator cuff muscles provide stability to shoulder joint?

Answer 36

The 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 37

What are the 5 static stabilisers (provide stability at rest) of the shoulder joint?

Answer 37

 Congruency of the humeral head and glenoid cavity
 Glenoid labrum, provides circumferential stability
 Joint capsule
 Glenohumeral ligaments, provide stability anteriorly
 Extra-capsular ligaments e.g. coracoacromial arch provides stability superiorly; coracohumeral ligament provides stability superiorly
 Negative intra-articular pressure (holds the humeral head in place by suction)

Question 38

What are the 2 dynamic stabilisers (provide stability during motion) of the shoulder joint?

Answer 38

 Rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis) – provide stability anteriorly, posteriorly and superiorly
 Extrinsic muscles that cross the shoulder joint:
o biceps brachii (long head) – provides stability superiorly
o triceps brachii (long head) – provides stability inferiorly
o deltoid – provides stability superiorly, anteriorly and posteriorly
o pectoralis major – provides stability anteriorly;
o coracobrachialis – provides stability anteriorly

Question 39

Which part of the joint is the least well supported?

Answer 39

Inferior aspect