Shoulder / Pectoral Girdle Arthrology and Myology

Question 1

What are the 3 joints of the shoulder region?

Answer 1

Acromioclavicular joint
Sternoclavicular joint
Glenohumeral joint

Question 2

Description of sternoclavicular joint?

Answer 2

Articulation between medial end of clavicle and superolateral angle of manubrium of sternum and adjacent part of 1st costal cartilage: larger clavicular articular surface so that clavicle projects above manubrium.

Surfaces reciprocally concavoconvex but of different radii of curvature: congruence partly improved by fibrocartilaginous intra-articular disc.

Question 3

Description of acromioclavicular joint?

Answer 3

Flat oval articular surfaces on lateral end of clavicle and anteromedial border of acromion; both surfaces covered with fibrocartilage.

Clavicular surface faces posterolaterally, acromial surface faces anteromedially.

Question 4

Description of sternoclavicular fibrous capsule?

Answer 4

Strong fibrous capsule attaches to articular margins of clavicle and sternum, extending inferiorly onto the upper surface of 1st costal cartilage.

Reinforced by anterior, posterior and interclavicular ligs.

Complete intra-articular fibrocartilaginos disc attaches to capsule, dividing joint into 2 separate compartments.

Synovial membrane lines each compartment.

Question 5

What is the extracapsular sternoclavicular ligament and where does it attach?

Answer 5

Costoclavicular ligament:
→ passes from upper surface of 1st costal cartilage to inferior surface to inferior surface of medial end of clavicle.
→ limits elevation of clavicle as well as preventing excessive anterior/posterior movement of it’s medial end.

Question 6

Description of acromioclavicular fibrous capsule?

Answer 6

Loose fibrous capsule attaches to articular margins.

Reinforced by superior and inferior acromioclavicular ligaments.

Partial fibrocartilaginous disc attaches to superior capsule in most joints.

Synovial membrane lines all non-articular surfaces.

Question 7

Where is the extracapsular ligament at the ACJ and what is its role?

Answer 7

Coracoclavicular ligament:
Anchors lateral end of clavicle to coracoid process: conoid and trapezoid parts attach to conoid tubercle and trapezoid line respectively.

Conoid part limits forward movement and trapezoid part backward movement of clavicle → both prevent medial displacement of acromion under the lateral end of clavicle in laterally directed forces to the shoulder.

Question 8

What muscles stabilise the scapula relative to the thorax during movements of the arm?

Answer 8

trapezius
levator scapulae

Question 9

What do all the fibres of deltoid do?

Answer 9

abduction

Question 10

What do the anterior fibres of deltoid do?

Answer 10

Flexion and medial rotation

Question 11

What do the posterior fibres of deltoid do?

Answer 11

Extension and lateral rotation

Question 12

What is the action of supraspinatus?

Answer 12

Initiates the first 20 degrees of abduction

Question 13

What is the action of teres minor?

Answer 13

Laterally rotates the glenohumeral joint

Question 14

What does infraspinatus do?

Answer 14

laterally rotates the glenohumeral joint

Question 15

What does subscapularis do?

Answer 15

Medially rotates the glenohumeral joint

Question 16

What does all of pectoralis major do?

Answer 16

Adduction at the GHJ

Question 17

What do the clavicular fibres of the pectoralis major do?

Answer 17

Flexion at the glenohumeral joint

Question 18

What do the sternocostal fibres of pectoralis major do?

Answer 18

Extension (from a flexed position) at GHJ

Question 19

What do the upper fibres of trapezius do?

Answer 19

→ Laterally flex the neck to the same side when working uni-laterally and extend the neck when working bilaterally.

→ Assist in lateral scapula rotation

e.g. looking up at ceiling, resisting depression of SG when carrying bags

Question 20

What do the middle fibres of trapezius do?

Answer 20

→ Retract the shoulder girdle

e.g. opening door/any pulling activity of the upper limb

Question 21

What do the lower fibres of trapezius do?

Answer 21

→ Depress the shoulder girdle
→ Assist in lateral scapula rotation

e.g. pushing on arms of chair to help sit to stand

Question 22

What action does teres minor do?

Answer 22

→ Adduction
→ Extension
→ Medial rotation

(of GHJ)

Powerful extensor of the shoulder when in a position of flexion.

Question 23

What action does latissimus dorsi do?

Answer 23

→ Adduction
→ Extension
→ Medial rotation

(of GHJ)

Powerful extensor of the shoulder when in a position of flexion.

Question 24

What actions does serratus anterior allow?

Answer 24

→ Protraction
→ Lateral rotation

Question 25

What actions does pectoralis minor allow?

Answer 25

→ Protraction →Medial rotation

Question 26

What muscles produce lateral rotation of scapula?

Answer 26

Upper fibres trapezius → lifts clavicle and acromion Lower fibres trapezius → pulls down on medial end of spine of scapula Serratus anterior → pulls down on the inferior angle

Question 27

What muscles produce medial rotation of scapula?

Answer 27

Levator scapulae Rhomboids Pectoralis minor

Question 28

Description of glenohumeral joint?

Answer 28

The articular surface is deepened by the presence of the fibrocartilaginous glenoid labrum but remains little more than one-third that of the humeral head. Irrespective of the position of the joint, only 1/3 of the humeral head is in contact with the glenoid fossa at any one time, giving the joint its wide ROM.

Question 29

Description of glenohumeral joint capsule?

Answer 29

A loose fibrous capsule completely surrounds the joint attaching to the glenoid labrum on the scapula and to the anatomical neck and articular margin of the humeral head, except inferiorly. The anterior capsule is thickened by superior, middle and inferior glenohumeral ligaments. Rotator cuff tendons spread out and blend w/capsule. Provides little stability to joint. Tendon of long biceps passes through opening in capsule at the upper end of intertubercular groove.

Question 30

What muscles abduct the shoulder?

Answer 30

Supraspinatus Deltoid

Question 31

What muscles adduct the shoulder?

Answer 31

Coracobrachialis Pectoralis major Latissimus dorsi Teres major

Question 32

What muscles flex the shoulder?

Answer 32

Pectoralis major Deltoid (anterior fibres) Coracobrachialis

Question 33

What muscles extend the shoulder?

Answer 33

Latissimus dorsi Teres major Pectoralis major (to midline) Deltoid (posterior fibres) Triceps (long head)

Question 34

What muscles medially rotate the shoulder?

Answer 34

Subscapularis Teres major Latissimus dorsi Pectoralis major Deltoid (anterior fibres)

Question 35

What muscles laterally rotate the shoulder?

Answer 35

Teres minor Infraspinatus Deltoid (posterior fibres)