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Anatomy of the sternoclavicular and acromioclavicular joints


Anatomy of the sternoclavicular and acromioclavicular joints

Figure 1:  Ligaments of the A. Sternoclavicular joint. B. Acromioclavicular joint.



Joints are structures in which bones meet to either permit movement, or provide stability.

There are plenty of them in our upper limbs.

We’ve got the:sternoclavicular; the acromioclavicular; and the glenohumeral joints in the pectoral girdle; the elbow; the proximal and distal radioulnar joints in the forearm; the wrist joint; and the joints of the hand, which include the carpometacarpal, the intermetacarpal, the metacarpophalangeal, and interphalangeal joints.

So let’s get acquainted with the first two of these joints!

First up, there’s the sternoclavicular joint, which is the only bony articulation attaching the upper limb to the axial skeleton.

It involves the clavicular notch of the manubrium, the medial end of the clavicle, and a small part of the first costal cartilage.

It is a saddle synovial type of joint, named so because the manubrial articulating surface is concave and the clavicular articulating surface is convex, so they fit together the same way that a cowboy sits on his horse’s saddle.

The joint has an articular disc that is firmly attached to the anterior and posterior fibrous joint capsule by the anterior and posterior sternoclavicular ligaments, as well as the interclavicular ligament.

Like any other synovial joint, the articular surfaces of the sternoclavicular joint are covered by the fibrous joint’s capsule which has 4 ligamentous thickenings, simply called ligaments, lined internally by a thin layer of synovial membrane.

The ligaments of the fibrous capsule are the anterior and the posterior sternoclavicular ligaments, which reinforce the joint capsule anteriorly and posteriorly; the interclavicular ligament which strengthens the sternoclavicular joint superiorly; and finally, there is the costoclavicular ligament, which anchors the inferior surface of the medial end of the clavicle to the 1st rib and its costal cartilage, providing stability to the sternoclavicular joint by limiting the elevation of the pectoral girdle.

And second, there’s the acromioclavicular joint.

It lies between the lateral end of the clavicle and the tip of the acromion of the scapula.

It’s a plane type of synovial joint, meaning its articular surfaces are almost flat.