1.5. Joints of the Thorax
The Main Thoracic Joints
There are five main types of joints in the thorax:
1. Chondrosternal joint
This occurs between the sternum and costal cartilage. It permits expansion of the thoracic cavity. Note that in some literature, these are referred to as sternocostal joints instead (however, I feel this is not a particularly accurate way to desceibe them so here I chosen to call them chondrosternal, or sternochondral, joints.
2. Costochondral joint
This occurs between a rib and a costal cartilage. Allows minimal movement.
3. Costovertebral joint
There are three of these:
- The superior costal facet articulates with the rib head.
- The inferior costal facet articulates with the rib head.
- The transverse costal facet articulates with the tubercle of the rib.
4. Sternal symphysis
This is between the manubrium and sternal body. It permits some movement between these bones. See Section 1.4. for more info.
5. Sternoclavicular joint
This is considered in more depth when studying the limbs. However, you should know that it is bilateral and occurs where the medial end of the clavicle articulates with the sternum. See the accompanying diagram.
Note that joints throughout the body can be classified by their structure or function:
Structurally, joints can be classified as:
Fibrous - these joints all have fibrous connections, e.g. mesenchyme or ligaments between the bones.
Cartilaginous - these joints have cartilage between them.
Synovial - these joints are surrounded by a capsule with fluid inside.
There are three subtypes of fibrous joints: suture, syndesmosis and gomphosis. A suture is found between the bones in the cranium - here, the bones are close together with little mesenchyme in-between. There is only one example of a syndesmosis in the human body - this is the inferior tibiofibular joint. Here, the bones are further apart compared to the suture and have more mesenchyme in-between. An example of a gomphosis is the periodontal ligament attaching a tooth to its bony sockett.
There are two subtypes of cartilaginous joint: primary and secondary. A primary cartilaginous joint is also called a synchondrosis. Hyaline cartilage alone connects the bones. In the thorax, the costochondral joints are primary cartilaginous joints. A secondary cartilaginous joint is also called a symphysis. Hyaline cartilage AND fibro-cartilage connect the bones, allowing slight movement. In the thorax, the sternal symphysis is an example of a symphysis joint.
In a synovial joint, an articular capsule surrounds the ends of the connecting bones, which have hyaline cartilage and are bathed in synovial fluid. Synovial joints in the thorax include most of the chondrosternal joints, the costovertebral joints and the sternoclavicular joints.
Functionally, joints can be classified as:
Synarthrosis (an immovable joint, e.g. the sutures between the bones of the cranium).
Amphiarthrosis (a joint that provides only a little movement, e.g. intervertebral joints).
Diarthrosis (a joint that provides considerable movement, e.g. any synovial joint).