Joints - Sternoclavicular joint (SCJ)

Question 1

What type of joint is the SCJ?

Answer 1

It is a synovial saddle joint that connects the clavicle and the sternum.

It attaches the upper limb to the axial skeleton.

Question 2

What are the articulating surfaces of the SCJ?

Answer 2

Consists of the sternal end of the clavicle, the manubrium of the sternum and the 1st costal cartilage.

The articular surfaces are covered with fibrocartilage (as opposed to hyaline cartilage, present in the majority of synovial joints).

Question 3

What are the ligaments of the SCJ?

Answer 3

There are four and they provide stability:

1) Sternoclavicular ligaments (anterior and posterior) - these strengthen the joint capsule anteriorly and posteriorly.
2) Interclavicular ligament - the spans the gap between the sternal ends of the clavicle and reinforces the joint capsule superiorly.
3) Costoclavicular ligament - the two parts of this ligament (often separated by a bursa) bind at the 1st rib and cartilage inferiorly and to the anteiror and posterior borders of the clavicle superiorly. It is a very strong ligament and is the main stabilising force for the joint, resisting elevation of the pectoral girdle.

Question 4

What is the neurovascular supply of the SCJ?

Answer 4

1) Internal thoracic artery
2) Suprascapular artery

Innervated by the:

1) Medial supraclavicular nerve (C3 and C4)
2) Nerve to subclavius (C5 and C6).

Question 5

What are the movements of the SCJ?

Answer 5

It has a large degree of mobility. There are several movements that require joint involvement:

1) Elevation of the shoulders - shrugging the shoulders or abducting the arm over 90 degrees.
2) Depression of the shoulders - drooping shoulders or extending the arm at the shoulder behind the body.
3) Protraction of the shoulders - moving the shoulder girdle anteriorly.
4) Retraction of the shoulders - moving the shoulder girdle posteriorly.
5) Rotation - when the arm is raised over the head by flexion the clavicle rotates passively as the scapula rotates. This is trasnmitted to the clavicle by the coracoclavicular ligaments.

Question 6

What are some factors that contribute to its mobility?

Answer 6

1) Saddle joint - able to move in two axes.
2) Articular disc - allows the clavicle and the manubrium to slide over each other more freely, allowing for the rotation and movement in a third axes.

Question 7

What are some factors that contribute to its stability?

Answer 7

1) Strong joint capsule
2) Strong ligaments - particularly the costoclavicular ligament, which transfers stress from the clavicle to the manubrium (via the costal cartilage).

Question 8

Clinical relevance: dislocation of the SCJ

Answer 8

This is quite rare and requires significant force.

The costoclavicular ligament and the articular disc are highly effective at absorbing and transmitting forces away from the joint into the sternum.

There are two types of dislocation:

1) Anterior dislocation - most common - can happen following a blow to the anterior shoulder which rotates the shoulder backward.
2) Posterior dislocations - results from a force driving the shoulder forwards or from direct impact to the joint.

In yoounger people, the epiphyseal growth plate of the sternal end has not fully closed. In this population, the dislocation is usually accompanied by a fracture through the plate.