Joints of spine, thorax and skull

The joints of the spine, thorax, and skull encompass all the connections between the bones that compose them. These joints can be mobile, semi-mobile, or immobile, depending on their anatomical and functional role.

The joints of the skull are numerous and of different types. They can be divided into four groups:

• The sutures of the head and cranial synchondroses, which connect the various bones forming the skull. Initially fibrous and cartilaginous, these joints ossify with age and are replaced by synostoses.

• The temporomandibular joint, which connects the mandible to the temporal bone of the skull. It is a synovial joint of the condylar type. Primarily intended for mastication, it has great functional importance and varies specifically according to dietary habits.

• The hyoid joints, part of which intrinsically connect the different parts of the hyoid bone. The other part attaches each suspension arch to the styloid process of the temporal bone—these are known as temporohyoid joints.

• The atlanto-occipital joint, the only extrinsic joint of the skull, connects the occipital condyles to the cranial cavities of the atlas (the first cervical vertebra).

The joints of the spine are present throughout its entire length and are organized similarly to the bones they connect, allowing for both mobility and stability. They also play a role in protecting the spinal cord. These joints include:

• The atlantoaxial joint, which connects the atlas and axis (the second cervical vertebra). It is sometimes considered an extrinsic joint of the skull.

• The intervertebral symphysis, which connect adjacent vertebral bodies.

• The joints of articular processes, which unite the vertebral arches of adjacent vertebrae.

The joints of the thorax allow the ribs to connect themselves to the sternum and the spine. They can be divided into five groups:

• The costovertebral joints, which connect the ribs to the thoracic vertebrae.

• The costochondral joints, which connect the bony and cartilaginous parts of the ribs.

• The intrachondral joints, which connect the costal cartilages to each other.

• The sternocostal joints, which connect the costal cartilages to the sternum.

• The sternal synchondroses, which connect the various parts of the sternum.