TBL4 - Intrinsic Shoulder Muscles

Question 1

What are the short intrinsic shoulder muscles? Where do they attach?

Answer 1

1) The short intrinsic shoulder muscles include the rotator cuff, deltoid, and teres major muscles
2) They attach proximally on the scapula and clavicle and distally on the humerus; thus the intrinsic shoulder muscles act on the glenohumeral joint

Question 2

What are different anatomical ways the glenohumeral (shoulder) joint can move?

Answer 2

Glenohumeral joint:

1) Adduction (Towards the body sideways)
2) Abduction (Away from the body sideways)
3) Flexion
4) Extension
5) Medial Rotation
6) Lateral Rotation

Question 3

Where is the surgical neck located? Know the location of the greater tubercle, lesser tubercle, & intertubercular sulcus. Know the location of the deltoid tuberosity.

Answer 3

1) The surgical neck of the humerus is the relatively narrow part between the head and shaft
2) The lesser tubercle lies on the anterior portion of the head of the humerus. The greater tubercle lies of the lateral side of the head of the humerus. The intertubercular sulcus is a groove that lies in between the lesser and greater tubercles
3) The deltoid tuberosity lies on the lateral portion of the humeral shaft

Question 4

What are the three parts of the deltoid muscle? Where does the deltoid muscle have its proximal and distal attachments?

Answer 4

1) The three parts of the deltoid muscle are the anterior, middle, and posterior parts
2) Their proximal attachment begins at the lateral end of the clavicle and continues around to the scapular spine
3) All three parts attach distally to the deltoid tuberosity

Question 5

What nerve innervates the deltoid?

Answer 5

1) Axillary nerve (C5, C6)

2) The nerve winds around the surgical neck on the posterior surface of the humerus to reach the deltoid

Question 6

How is the axillary nerve commonly injured at the surgical neck of the humerus, and where does loss of sensation occur after the injury?

Answer 6

1) The deltoid atrophies when the axillary nerve (C5 and C6) is severely damaged
2) Because it passes inferior to the humeral head and winds around the surgical neck of the humerus, the axillary nerve is usually injured during fracture of this part of the humerus. It may also be damaged during dislocation of the glenohumeral joint, and by compression from the incorrect use of crutches
3) As the deltoid atrophies, the rounded contour of the shoulder is flattened compared to the uninjured side. This gives the shoulder a flattened appearance and produces a slight hollow inferior to the acromion
4) In addition to atrophy of the deltoid, a loss of sensation may occur over the lateral side of the proximal part of the arm, the area supplied by the superior lateral cutaneous nerve of the arm, the cutaneous branch of the axillary nerve

Question 7

What do the anterior and posterior parts of the deltoids do while a person is walking?

Answer 7

1) The anterior and posterior parts of the deltoids are used to swing the limbs during walking. The anterior part assists the pectoralis major in flexing the arm, and the posterior part assists the latissimus dorsi in extending the arm
2) The deltoid also helps stabilize the glenohumeral joint and hold the head of the humerus in the glenoid cavity during movements of the upper limb

Question 8

What causes an upper limb to be abducted 90°?

Answer 8

Simultaneous contraction of all three parts of the deltoid with assistance from the supraspinatus muscle causes abduction of the upper limb to 90°

Question 9

Where does the teres major muscle attach proximally and distally? What does the teres major muscle do?

Answer 9

1) The teres major muscle attaches proximally to the inferior angle of the scapula and distally to the medial surface of the humerus
2) The teres major (along with the anterior deltoid) is positioned to medially rotate the arm

Question 10

What divides the scapula and what is a result of this division?

Answer 10

1) The posterior surface of the scapula is unevenly divided by the thick bony spine
2) The spine demarcates the supraspinous and infraspinous fossae

Question 11

What attaches to the inferior and superior angles of the scapula?

Answer 11

1) The teres major attaches to the inferior angle of the scapula
2) The levator scapulae attaches to the superior angle of the scapula

Question 12

What muscles attach proximally to the supraspinous and infraspinous fossae of the scapula? Where do these muscles attach distally?

Answer 12

1) The supraspinatus muscle attaches proximally to the supraspinous fossa
2) The infraspinatus muscle attaches proximally to the infraspinous fossa
3) Both the supraspinatus and infraspinatus muscles attach distally on the greater tubercle of the humerus

Question 13

What is the function of the subacromial bursa?

Answer 13

1) The fluid-filled subacromial bursa cushions the supraspinatus tendon as it courses between the humeral head and osseoligamentous coraco-acromial arch toward the greater tubercle
2) In general, the subacromial - subdeltoid bursae decrease friction and allow free motion of the rotator cuff relative to the coracoacromial arch and the deltoid muscle.

Question 14

What innervates the supraspinatus and infraspinatus muscles?

Answer 14

1) The supraspinatus muscle is innervated by the Suprascapular nerve (C4, C5, C6)
2) The infraspinatus muscle is innervated by the Suprascapular nerve (C5, C6)

Question 15

What are the functions of the supraspinatus and infraspinatus muscles?

Answer 15

1) The supraspinatus muscle induces the first 15° of abduction (assists deltoid abduction) & acts with rotator cuff muscles
2) The infraspinatus muscle laterally rotates the arm & acts with rotator cuff muscles

Question 16

Where does the teres minor muscle proximally and distally attach to?

Answer 16

1) The teres minor muscle attaches proximally to the lateral border of the scapula
2) The teres minor muscle attaches distally to the greater tubercle

Question 17

What innervates the teres minor muscle? What is the function of the teres minor muscle and what other muscle does it work with to do so?

Answer 17

1) The Axillary nerve (C5, C6) innervates the teres minor muscle
2) The teres minor muscle laterally rotates the arm by working synergistically with the infraspinatus muscle

Question 18

Where does the subscapularis muscle attach proximally and distally?

Answer 18

1) The subscapularis muscle covers the anterior surface of the scapula
2) It attaches proximally to the subscapular fossa (most of anterior surface of the scapula)
3) It attaches distally to the lesser tubercle of the humerus
4) it is positioned to medially rotate the arm

Question 19

What innervates the subscapularis muscle?

Answer 19

The upper and lower subscapular nerves (C5, C6, C7) innervate the subscapularis muscle

Question 20

What does the subscapularis muscle do?

Answer 20

The subscapularis muscle medially rotates arm; as part of rotator cuff, helps hold head of humerus in glenoid cavity

Question 21

Why is the upper limb pulled into medial rotation after an avulsion fracture of the greater tubercle?

Answer 21

1) An avulsion fracture of the greater tubercle of the humerus is seen most commonly in middle-aged and elderly people. A small part of the tubercle is “avulsed” (torn away)
2) Muscles (especially the subscapularis) that remain attached to the humerus pull the limb into medial rotation

Question 22

What is the painful arc syndrome?

Answer 22

1) Deposition of calcium in the supraspinatus tendon is common. This causes increased local pressure that often causes excruciating pain during abduction of the arm; the pain may radiate as far as the hand
2) The calcium deposit may irritate the overlying subacromial bursa, producing an inflammatory reaction known as subacromial bursitis
3) As long as the glenohumeral joint is adducted, no pain usually results because in this position the painful lesion is away from the inferior surface of the acromion
4) In most people, the pain occurs during 50–130° of abduction (painful arc syndrome) because during this arc the supraspinatus tendon is in intimate contact with the inferior surface of the acromion

Question 23

How is degenerative tendinitis of the rotator cuff tested?

Answer 23

1) To test for degenerative tendonitis of the rotator cuff, the person is asked to lower the fully abducted limb slowly and smoothly
2) From approximately 90° abduction, the limb will suddenly drop to the side in an uncontrolled manner if the rotator cuff (especially its supraspinatus part) is diseased and/or torn