MSK 16 - Functional Anatomy of the Shoulder

Question 1

Be able to label the osteology of the scapula, distal humerus + clavicle.

Answer 1

Make sure you know the following prominences:

• Glenoid cavity (fossa), supraglenoid + infraglenoid tubercles (on lateral view)
• Spine, acromion, supraspinous + infraspinous fossa (on posterior view).

Question 2

What two structures does the clavicle articulate with?

Answer 2

• Sternal end with manubrium of sternum (AKA: sternoclavicular joint)
• Acromial end with acromion of scapula (AKA: acromiovclavicular joint)

Question 3

What does the head of the humerus articulate with?

Where does the anatomical neck, surgical neck + greater/less tubercles lie?

Answer 3

• The glenoid cavity of the scapula
• Anatomical neck separates head from tubercles
• The two tubercles are separated by a deep grove called the intertubercular sulcus
• The surgical neck lies between the tubercles and the shaft of the humerus - most likely to be fractures (surgical neck > anatomical neck)

Question 4

Which joint is the shoulder joint?
What type of joint is it?
How stable/mobile is it?

Answer 4

• The glenohumeral joint (articulation between glenoid fossa and humerus)
• A synovial/ball + socket joint (humerus covered in hyaline cartilage). Most mobile in the body, but least stable (commonly dislocated)

Question 5

What factors allow the glenohumeral joint to be very mobile?

What is the role of the glenoid labrum?

Answer 5

• Shallow glenoid fossa
• Dissproportion of articular surfaces (4:1 ratio of humerus to glenoid fossa)
• Lax capsule - particularly inferiorly
• Glenoid labrum is a fibrocartilaginous rim around the edge of the glenoid fossa which deepens glenoid cavity by 1cm - increasing stability.

Question 6

Apart from the glenoid labrum, what else provides stability to the shoulder joint?

Answer 6

• Joint capsule, Intracapsular ligaments + extracapsular ligaments (static stabilisers)
• Rotator cuff muscles, deltoid, coracobrachialis, long head of biceps + triceps (dynamic stabilisers)

Question 7

What are the 3 intracapsular ligaments of the glenohumeral joint that provide stability?
Where do they run to and from?

Answer 7

1) Superior glenohumeral ligament (SGHL)
2) Middle glenohumeral ligament (MGHL)
3) Inferior glenohumeral ligament (IGHL)

• Fibrous bands running from glenoid labrum to humerus which reinforce joint capsule anteriorly. (only seen inside the capsule)

Question 8

What are the 3 extracapsular ligaments of the glenohumeral joint that provide stability?

Answer 8

1) Coracoacromial ligament (CAL) - from coracoid to acromium.
2) Coracohumeral ligament (CHL) - from coracoid to greater tubercle of humerus
3) Transverse humeral ligament (THL) - holds tendon of long head of biceps in place

Question 9

What are the 4 main rotator cuff muscles?

Where do the rotator cuff muscles run from and to?

Answer 9

1) Supraspinatus 2) Infraspinatus 3) Teres minor 4) Subscapularis - pneumonic = SITS.

1-3) Arise on dorsal (back) aspect of scapula and insert onto greater tubercle of humerus
4) Arises from ventral (front) aspect of scapula and inserts into lesser tubercle of humerus

Question 10

What is the overall function of the rotator cuff muscles?

What are the actions of the 4 main rotator cuff muscles?

Answer 10

• Stabilise shoulder joint + hold head of humerus into glenoid cavity.

1) S - first 15 degrees of abduction
2) I - lateral/external rotation of arm
3) T - Lateral rotation of arm
4) S - Internal rotation of arm

Question 11

What are the main movements of the shoulder joint?

Answer 11

• Flexion + Extension
• Medial + Lateral Rotation
• Abduction + adduction
• Circumduction

Question 12

What muscles carry out abduction of the shoulder?

Answer 12

• First 15 degrees = supraspinatus - suprascapular nerve
• 15-90 degrees = deltoid central fibres - axillary nerve
• 90-150 degrees = rotation of scapula at scapulothoracic joint - trapezius + serratus anterior.

Question 13

What muscles are responsible for adduction of the shoulder?

Answer 13

1) Pectoralis Major (medial + lateral pectoral nerve)
2) Latissimus dorsi (thoracodorsal nerve)
3) Teres major (lower sub-scapular nerve)

Question 14

Which muscles are responsible for flexion of the shoulder?

Answer 14

1) Anterior fibres of deltoid
2) Coracobrachialis
3) Clavicular head of pec major
4) Biceps brachii

Question 15

Which muscles are responsible for extension of the shoulder?

Answer 15

1) Posterior fibres of deltoid
2) Latissimus dorsi
3) Teres major

Question 16

Which muscles are responsible for internal + external rotation of shoulder/arm?

Answer 16

Internal:

1) Sternocostal head of pec major
2) Subscapularis
3) Teres Major
4) Latissimus dorsi

External:

1) Infraspinatus
2) Teres minor

Question 17

What are the 3 muscles of the anterior compartment of the arm?
What are the actions of these 3 muscles?

Answer 17

• Think BBC - 1) Biceps brachii, brachialis + coracobrachialis

B = strong supinator, flexor of elbow 
B = flexes forearm at elbow
C = weak flexor + adductor of shoulder

Question 18

Describe the anatomy of the anterior compartment arm muscles

Answer 18

Biceps Brachii = 2 heads, long head into supraglenoid tubercle, short into coracoid process.

Brachialis = lies deep to biceps brachii, inserts into coranoid process of ulna

Coracobrachialis = coracoid process of scapula to medial side of humeral shaft.

Question 19

What muscle is in the posterior compartment of the arm and what is its action?

Answer 19

• Triceps brachii

- Extends forearm at the elbow

Question 20

What is the subacromial space?

What 4 structures run through it?

Answer 20

• Space between the acromion of scapula and head of humerus.

- 1) Subacromial bursa 2) Supraspinatus tendon 3) Capsule 4) long head of biceps tendon

Question 21

What 3 arteries supply the shoulder joint?

What 3 nerves supply the shoulder joint?

Answer 21

• Anterior circumflex, posterior circumflex + suprascapular artery
• Axillary, suprascapular + lateral pectoral nerve (from C5/C6 of brachial plexus)