| Atlanto-axial joint | |
|---|---|
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| Details | |
| System | Skeletal |
| Identifiers | |
| Latin | articulatio atlantoaxialis mediana, articulatio atlantoaxialis lateralis |
| MeSH | D001268 |
| FMA | 25524 |
| Anatomical terminology | |
The atlanto-axial joint is a joint in the upper part of the neck between the atlas bone and the axis bone, which are the first and second cervical vertebrae. It is a pivot joint.
The atlanto-axial joint is a joint between the atlas bone and the axis bone, which are the first and second cervical vertebrae. It is a pivot joint that provides 40 to 70% of axial rotation of the head. [1]
There is a pivot articulation between the odontoid process of the axis and the ring formed by the anterior arch and the transverse ligament of the atlas.
There are three atlanto-axial joints: one median and two lateral: [2]
The ligaments connecting these bones are:
The atlantoaxial articular capsules are thick and loose, and connect the margins of the lateral masses of the atlas with those of the posterior articular surfaces of the axis.
Each is strengthened at its posterior and medial part by an accessory ligament, which is attached below to the body of the axis near the base of the odontoid process, and above to the lateral mass of the atlas near the transverse ligament.
Because of its proximity to the brain stem and importance in stabilization, fracture or injury to the atlanto-axial joint can cause serious problems. Common trauma and pathologies include (but are not limited to):
The dens: significant depression on the skull can push the dens into the brainstem, causing death. The dens itself is vulnerable to fracture due to trauma or ossification.
Transverse ligament: Should the transverse ligament of the atlas fail due to trauma or disease, the dens is no longer anchored and can travel up the cervical spine, causing paralysis. If it reaches the medulla death can result. Alar ligaments: stress or trauma can stretch the weaker alar ligaments, causing an increase in range of motion of approximately 30%.
Posterior atlanto-occipital membrane: genetic traits can sometimes result in ossification, turning the groove into a foramen.
Osteoarthritis may occur at the atlanto-axial joint. [5] This involves classic pathophysiology, such as loss of articular cartilage, osteophytes visible with radiography, and bone thickening with a narrow joint space. [5] Conservative management is usually effective, involving analgesics. [5] Surgery may be used in severe cases, and may have good outcomes. [5]
A widening of the atlanto-axial joint, as measured between the posterior surface of the anterior arch of atlas and the front of the odontoid process, indicates an injury to the transverse atlantal ligament. [6] Normally, this atlanto-dental distance is less than 2 mm, sometimes a maximum of 3 mm is accepted in men and 2.5 mm in women. [6]
In vertebrate anatomy, ribs are the long curved bones which form the rib cage, part of the axial skeleton. In most tetrapods, ribs surround the thoracic cavity, enabling the lungs to expand and thus facilitate breathing by expanding the thoracic cavity. They serve to protect the lungs, heart, and other vital organs of the thorax. In some animals, especially snakes, ribs may provide support and protection for the entire body.
In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck.
The clavicle, collarbone, or keybone is a slender, S-shaped long bone approximately 6 inches (15 cm) long that serves as a strut between the shoulder blade and the sternum (breastbone). There are two clavicles, one on the left and one on the right. The clavicle is the only long bone in the body that lies horizontally. Together with the shoulder blade, it makes up the shoulder girdle. It is a palpable bone and, in people who have less fat in this region, the location of the bone is clearly visible. It receives its name from Latin clavicula 'little key' because the bone rotates along its axis like a key when the shoulder is abducted. The clavicle is the most commonly fractured bone. It can easily be fractured by impacts to the shoulder from the force of falling on outstretched arms or by a direct hit.
In humans and other primates, the knee joins the thigh with the leg and consists of two joints: one between the femur and tibia, and one between the femur and patella. It is the largest joint in the human body. The knee is a modified hinge joint, which permits flexion and extension as well as slight internal and external rotation. The knee is vulnerable to injury and to the development of osteoarthritis.
In anatomy, the temporomandibular joints (TMJ) are the two joints connecting the jawbone to the skull. It is a bilateral synovial articulation between the temporal bone of the skull above and the condylar process of mandible below; it is from these bones that its name is derived. The joints are unique in their bilateral function, being connected via the mandible.
The tibia, also known as the shinbone or shankbone, is the larger, stronger, and anterior (frontal) of the two bones in the leg below the knee in vertebrates ; it connects the knee with the ankle. The tibia is found on the medial side of the leg next to the fibula and closer to the median plane. The tibia is connected to the fibula by the interosseous membrane of leg, forming a type of fibrous joint called a syndesmosis with very little movement. The tibia is named for the flute tibia. It is the second largest bone in the human body, after the femur. The leg bones are the strongest long bones as they support the rest of the body.
In anatomy, the axis is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests. The spinal cord passes through the axis.
The radius or radial bone is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna. The ulna is longer than the radius, but the radius is thicker. The radius is a long bone, prism-shaped and slightly curved longitudinally.
In tetrapods, cervical vertebrae are the vertebrae of the neck, immediately below the skull. Truncal vertebrae lie caudal of cervical vertebrae. In sauropsid species, the cervical vertebrae bear cervical ribs. In lizards and saurischian dinosaurs, the cervical ribs are large; in birds, they are small and completely fused to the vertebrae. The vertebral transverse processes of mammals are homologous to the cervical ribs of other amniotes. Most mammals have seven cervical vertebrae, with the only three known exceptions being the manatee with six, the two-toed sloth with five or six, and the three-toed sloth with nine.
The talus, talus bone, astragalus, or ankle bone is one of the group of foot bones known as the tarsus. The tarsus forms the lower part of the ankle joint. It transmits the entire weight of the body from the lower legs to the foot.
The lateral parts of the occipital bone are situated at the sides of the foramen magnum; on their under surfaces are the condyles for articulation with the superior facets of the atlas.
The atlanto-occipital joint is an articulation between the atlas bone and the occipital bone. It consists of a pair of condyloid joints. It is a synovial joint.
In anatomy, the transverse ligament of the atlas is a broad, tough ligament which arches across the ring of the atlas posterior to the dens to keep the dens in contact with the atlas. It forms the transverse component of the cruciform ligament of atlas.
The posterior longitudinal ligament is a ligament connecting the posterior surfaces of the vertebral bodies of all of the vertebrae of humans. It weakly prevents hyperflexion of the vertebral column. It also prevents posterior spinal disc herniation, although problems with the ligament can cause it.
The tectorial membrane of atlanto-axial joint is a tough membrane/broad, strong band representing the superior-ward prolongation of the posterior longitudinal ligament.
The occipital condyles are undersurface protuberances of the occipital bone in vertebrates, which function in articulation with the superior facets of the atlas vertebra.
The cruciate ligament of the atlas is a cross-shaped ligament in the neck forming part of the atlanto-axial joint. It consists of the transverse ligament of atlas, a superior longitudinal band, and an inferior longitudinal band.
The following outline is provided as an overview of and topical guide to human anatomy:
The vertebral column, also known as the spinal column, spine or backbone, is the core part of the axial skeleton in vertebrate animals. The vertebral column is the defining and eponymous characteristic of the vertebrate endoskeleton, where the notochord found in all chordates has been replaced by a segmented series of mineralized irregular bones called vertebrae, separated by fibrocartilaginous intervertebral discs. The dorsal portion of the vertebral column houses the spinal canal, an elongated cavity formed by alignment of the vertebral neural arches that encloses and protects the spinal cord, with spinal nerves exiting via the intervertebral foramina to innervate each body segments.
Each vertebra is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal segment and the particular species.