MSK Muscles of the pectoral and shoulder region

Question 1

Name the muscles of the pectoral region

Answer 1

Pectoralis major
Pectoralis minor
Serratus anterior

Question 2

What are the attachments and actions of the pectoralis major?

Answer 2

Fan shaped muscle:
The clavicular head attaches to the clavicle
The sternocostal head attaches to the sternum and ribs
Both heads attach to the intertubecular groove of humerus

Actions:
Adduct and medial rotate humerus at shoulder
Clavicular head also performs flexion

Question 3

What is the innervation of pec major and minor?

Answer 3

Pec major - medial and lateral pectoral nerves
Pec minor - medial pectoral nerve
(derived from brachial plexus)

Question 4

What are the attachments and actions of the pectoralis minor?

Answer 4

Triangular shaped muscle:
Originates from ribs 3-5
Attach to coracoid process of scapula (forms a bridge where vessels pass underneath to reach arm)

Actions:
Depresses the shoulder

Question 5

What are the attachments and actions of the serratus anterior?

Answer 5

Consists of several strips:
Originates from ribs 2-8
Attach to costal surface of medial border of scapula

Actions:
Holds scapula against ribcage
Rotates scapula so arm can abduct over 90 degrees

Question 6

What is the innervation of serratus anterior?

Answer 6

Long thoracic nerve

Question 7

What is the difference between extrinsic and intrinsic shoulder muscles?

Answer 7

Extrinsic - originate from torso and attach to shoulder bones, located at the back
Intrinsic - originate from scapula or clavicle and attach to humerus

Question 8

Name deep and superficial extrinsic shoulder muscles

Answer 8

Superficial:

• trapezius
• latissimus dorsi

Deep:

• levator scapulae
• rhomboid major
• rhomboid minor

Question 9

What are the attachments and actions of the trapezius?

Answer 9

Broad, flat, triangular muscle:
Originates from skull and spinous processes of C7-T12
Attaches to clavicle, acromion and scapula spine

Actions:
Upper fibres elevate scapula and rotate it during arm abd
Lower fibres retract scapula and pull it inferiorly

Question 10

What is the innervation of the trapezius and how would you test this?

Answer 10

Innervated by accessory nerve
Also proprioreceptor fibres from C3-4

Surgeries such as lymph node biopsy or cannulation to jugular vein can cause trauma to the accessory nerve
To test the nerve the patient is asked to shrug

Question 11

What are the attachments and actions of the latissimus dorsi?

Answer 11

Broad origin from spinous processes of T6-12, iliac crest, inferior 3 ribs
Attaches to intertubecular groove of humerus

Actions:
Extends, adducts and medial rotates upper limb

Question 12

What is the innervation of the latissimus dorsi?

Answer 12

Thoracodorsal nerve

Question 13

What are the attachments and actions of the levator scapulae?

Answer 13

Small strap-like muscle:
Originated from transverse processes of C1-4
Attaches to medial border of scapula

Actions:
Elevates scapula

Question 14

What is the innervation of the levator scapulae?

Answer 14

Dorsal scapular nerve

Question 15

What are the attachments and actions of the rhomboid major?

Answer 15

Originated from spinous processes of T2-5
Attaches to medial border of scapula

Actions:
Retracts and rotates scapula

Question 16

What are the attachments and actions of the rhomboid minor?

Answer 16

Originates from spinous processes of C7-T1
Attaches to medial border of scapula

Actions:
Retracts and rotates scapula

Question 17

What is the innervation of rhomboid major and minor?

Answer 17

Dorsal scapular nerve

Question 18

Name the intrinsic shoulder muscles

Answer 18

Teres major
Deltoid

Rotator cuff muscles:
Subscapularis
Supraspinatus
Infraspinator
Teres minor

Question 19

What are the attachments and actions of the deltoid?

Answer 19

Originates from spine of scapula and clavicle
Attaches to deltoid tuberosity of humerus

Actions:
Anterior fibres flex arm
Posterior fibres extend arm
Middle fibres are major abductor of arm (takes over from supraspinatus which does the first 15 degrees)

Question 20

What is the innervation of the deltoid?

Answer 20

Axillary nerve

Question 21

What are the attachments and actions of teres major?

Answer 21

Forms inferior border of quadrangular space

Originates from posterior surface of scapula
Attaches to intertubecular groove of humerus

Actions:
Adducts and medially rotates arm

Question 22

What is the innervation of teres major?

Answer 22

Lower subscapular nerve

Question 23

What is the collective function of the rotator cuff muscles?

Answer 23

They originate from the scapula and attach to the humeral head
Their resting tone acts to pull the humeral head into the glenoid fossa, giving the joint a lot of stability

Question 24

What are the attachments and actions of supraspinatus?

Answer 24

Originates from supraspinous fossa and attaches to greater tubercle

Actions:
Abducts arm 0-15 degrees
Assists deltoid for 15-90 degrees

Question 25

What are the attachments and actions of infraspinatus?

Answer 25

Originates from infraspinous fossa and attaches to greater tubercle

Actions:
Laterally rotates arm

Question 26

What are the attachments and actions of subscapularis?

Answer 26

Originates from sub scapular fossa and attaches to less tubercle

Actions:
Medially rotates arm

Question 27

What are the attachments and actions of teres minor?

Answer 27

Originates from lateral border of scapula and attaches to greater tubercle

Actions:
Laterally rotates arm

Question 28

What is the innervation of the rotator cuff muscles?

Answer 28

Supra/infraspinatus - suprascapular nerve
Subscapularis - upper and lower sub scapular nerves
Teres minor - axillary nerve

Question 29

What is the cause and treatment of rotator cuff tendonitis?

Answer 29

Inflammation of the rotator cuff tendons due to repetitive use of the shoulder
Supraspinatus tendon most affected because it rubs over the coerce-acromial arch during abduction, causing inflammation

Rest, analgesia (pain relief), physiotherapy
More severe - steroid injections, surgery