The Shoulder Joint

Question 1

What is another name for the shoulder joint?

Answer 1

Glenohumeral joint

Question 2

What type of joint is the shoulder joint?

Answer 2

A ball and socket joint between the scapula and humerus

Question 3

Is the shoulder more mobile or stable?

Answer 3

It is one of the most mobile joints in the human body, at the cost of joint stability

Question 4

What are the articulating surfaces of the shoulder joint?

Answer 4

The shoulder joint is formed by the articulation of the head of the humerus with the glenoid fossa of the scapula.

Question 5

What are both of the articulating surfaces covered with?

Answer 5

Hyaline Cartilage - this is typical for a synovial type joint

Question 6

What is the problem associated with the head of the humerus being much larger than the glenoid fossa?

Answer 6

This gives the joint inherent instability

Question 7

How is the disproportion in surfaces reduced?

Answer 7

The glenoid fossa is deepened by a fibrocartilage rim called the glenoid labrum

Question 8

Describe the joint capsule of the shoulder joint

Answer 8

The joint capsule is a fibrous sheath which encloses the structures of the joint. It extends from the anatomical neck of the humerus to the border of the glenoid fossa. The joint capsule is lax, permitting greater mobility (particularly abduction). The synovial membrane lines the inner surface of the joint capsule, and produces synovial fluid to reduce friction between the articular surfaces.

Question 9

What is a bursa and what is its function?

Answer 9

The function is to reduce friction in the shoulder joint. There are several synovial bursae present. A bursa is a synovial fluid filled sac, which acts as a cushion between tendons and other joint structures.

Question 10

Name the clinically important bursae in the shoulder joint and describe their locations

Answer 10

Subacromial - located inferiorly to the deltoid and acromion, and superiorly to the supraspinatus tendon and the joint capsule. It supports the deltoid and supraspinatus muscles. Inflammation of the bursa is the cause of several shoulder problems.
Subscapular - located between the subscapularis tendon and the scapula. It reduces wear and tear on the tendon during movement at the shoulder joint

Question 11

What is the function of the ligaments of the shoulder joint?

Answer 11

In the shoulder joint, the ligaments play a key role in stabilising the bony structures. The majority of the ligaments are thickenings of the joint capsule.

Question 12

Name the ligaments of the shoulder joint

Answer 12

Glenohumeral ligament (superior, middle and inferior) - consists of three bands, which runs with the joint capsule from the glenoid fossa to the anatomical neck of the humerus. They act to stabilise the anterior aspect of the joint. 
Coroacohumeral ligament - attaches the base of the coracoid process to the greater tubercle of the humerus. It supports the superior part of the joint capsule 
Transverse humeral ligament - spans the distance between the two tubercles of the humerus. It holds the tendon of the long head of the biceps in the intertubercular groove 
Coracoacromial ligament - it is not a thickening of the joint capsule, unlike the others. It runs between the acromion and coracoid process of the scapula, forming the coraco-acromial arch. This structure overlies the shoulder joint, preventing superior displacement of the humeral head.

Question 13

Describe the neuromuscular supply of the shoulder joint

Answer 13

Arterial supply to the shoulder joint is via the anterior and posterior circumflex humeral arteries, and the suprascapular artery. Branches from these arteries form an anastomotic network around the joint.
The joint is supplied by the axillary, suprascapular, and lateral pectoral nerves. These nerves are derived from roots C5 and C6 of the brachial plexus. Therefore an upper brachial plexus injury (Erb’s palsy) will affect shoulder joint function.

Question 14

Name the factors that contribute to the mobility of the shoulder joint

Answer 14

Type of joint - it’s a ball and socket joint
Bony surfaces - shallow glenoid fossa and large humeral head (golf ball and tee)
Laxity - the joint capsule is very lax

Question 15

Name the factors that contribute to the stability of the shoulder joint

Answer 15

Rotator cuff muscles - these muscles surround the shoulder joint, attaching to the tubercles of the humerus, whilst also fusing with the joint capsule. The resting tone of these muscles acts to ‘pull’ the humeral head into the glenoid cavity
Glenoid labrum - this is a fibrocartilaginous ridge surrounding the glenoid cavity. It deepens the cavity, reducing the risk of dislocation
Ligaments - the ligaments act to reinforce the joint capsule, and forms the coraco-acromial arch