The Sternoclavicular Joint
The sternoclavicular joint is a saddle type synovial joint (sometimes called a double-plane joint) between the clavicle and the manubrium of the sternum. It is the only attachment of the upper limb to the axial skeleton. Despite its strength, it is a very mobile joint and can function more like a ball-and-socket type joint.
In this article we will look at the anatomy of the sternoclavicular joint, as well as its important clinical considerations.
The sternoclavicular joint consists of the sternal end of the clavicle, the manubrium of the sternum, and part of the 1st costal cartilage. The articular surfaces are covered with fibrocartilage (as opposed to hyaline cartilage, present in the majority of synovial joints). The joint is separated into two compartments by a fibrocartilaginous articular disc.
The joint capsule consists of a fibrous outer layer, and inner synovial membrane. The fibrous layer extends from the epiphysis of the sternal end of the clavicle, to the borders of the articular surfaces and the articular disc. A synovial membrane lines the inner surface and produces synovial fluid to reduce friction between the articulating structures.
The ligaments of the sternoclavicular joint provide much of its stability. There are four major ligaments:
- Sternoclavicular ligaments (anterior and posterior) – these strengthen the joint capsule anteriorly and posteriorly.
- Interclavicular ligament – this spans the gap between the sternal ends of each clavicle and reinforces the joint capsule superiorly.
- Costoclavicular ligament – the two parts of this ligament (often separated by a bursa) bind at the 1st rib and cartilage inferiorly and to the anterior 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.
The sternoclavicular and interclavicular ligaments can be considered to be thickenings of the joint capsule.
Arterial supply to the sternoclavicular joint is from the internal thoracic artery and the suprascapular artery.
The joint is supplied by the medial supraclavicular nerve (C3 and C4) and the nerve to subclavius (C5 and C6).
The sternoclavicular joint has a large degree of mobility. There are several movements that require joint involvement:
- Elevation of the shoulders – shrugging the shoulders or abducting the arm over 90º
- Depression of the shoulders – drooping shoulders or extending the arm at the shoulder behind the body
- Protraction of the shoulders – moving the shoulder girdle anteriorly
- Retraction of the shoulders – moving the shoulder girdle posteriorly
- Rotation – when the arm is raised over the head by flexion the clavicle rotates passively as the scapula rotates. This is transmitted to the clavicle by the coracoclavicular ligaments
The costoclavicular ligament acts as a pivot for movements of the clavicle. You can feel this if you palpate the sternal end of your clavicle and shrug your shoulders, you should feel the sternal end moving inferiorly.
Mobility and Stability
The sternoclavicular joint is required to accommodate the movements of the upper limb, and thus has a high degree of mobility. However, it also requires much stability, as it is the only connection between the upper limb and the axial skeleton.
Here we will consider the factors which contribute to both its mobility and its stability.
- Type of joint – being a saddle joint it can move in two axes.
- Articular disc – this allows the clavicle and the manubrium to slide over each other more freely, allowing for the rotation and movement in a third axis.
- Strong joint capsule.
- Strong ligaments – particularly the costoclavicular ligament, which transfers stress from the clavicle to the manubrium (via the costal cartilage).
Clinical Relevance: Dislocation of the Sternoclavicular Joint
A dislocation of the sternoclavicular joint 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 major types of dislocation:
- Anterior dislocations are the most common and can happen following a blow to the anterior shoulder which rotates the shoulder backwards.
- Posterior dislocations normally result from a force driving the shoulder forwards or from direct impact to the joint.
In younger people, the epiphyseal growth plate of the sternal end of the clavicle has not fully closed. In this population, the dislocation is usually accompanied by a fracture through the plate.