The atlanto-axial joint is a
joint
A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw ...
in the upper part of the
neck
The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...
between the
atlas bone
In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck. It is named for Atlas of Greek mythology because, just as Atlas supported the globe, it supports the entire head.
The atlas is ...
and the
axis bone, which are the first and second
cervical vertebrae
In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...
. It is a
pivot joint
In animal anatomy, a pivot joint (trochoid joint, rotary joint or lateral ginglymus) is a type of synovial joint whose movement axis is parallel to the long axis of the proximal bone, which typically has a convex articular surface.
According to o ...
.
Structure
The atlanto-axial joint is a joint between the
atlas bone
In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck. It is named for Atlas of Greek mythology because, just as Atlas supported the globe, it supports the entire head.
The atlas is ...
and the
axis bone, which are the first and second
cervical vertebrae
In tetrapods, cervical vertebrae (singular: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In ...
. It is a
pivot joint
In animal anatomy, a pivot joint (trochoid joint, rotary joint or lateral ginglymus) is a type of synovial joint whose movement axis is parallel to the long axis of the proximal bone, which typically has a convex articular surface.
According to o ...
.
There is a
pivot articulation between the
odontoid process
In anatomy, the axis (from Latin ''axis'', "axle") or epistropheus is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests.
The axis' defining feature is its strong odontoid process (bon ...
of the axis and the ring formed by the anterior arch and the
transverse ligament of the atlas
In anatomy, the transverse ligament of the atlas is a ligament which arches across the ring of the atlas (the topmost cervical vertebra, which directly supports the skull), and keeps the odontoid process in contact with the atlas.
Anatomy
It is co ...
.
Lateral and median joints
There are three atlanto-axial joints: one median and two lateral:
* The median atlanto-axial joint is sometimes considered a triple joint:
** one between the posterior surface of the
anterior arch of atlas
In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck. It is named for Atlas of Greek mythology because, just as Atlas supported the globe, it supports the entire head.
The atlas i ...
and the front of the
odontoid process
In anatomy, the axis (from Latin ''axis'', "axle") or epistropheus is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests.
The axis' defining feature is its strong odontoid process (bon ...
** one between the anterior surface of the ligament and the back of the odontoid process
* The lateral atlantoaxial joint involves the
lateral mass of atlas
In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck. It is named for Atlas of Greek mythology because, just as Atlas supported the globe, it supports the entire head.
The atlas i ...
and
axis
An axis (plural ''axes'') is an imaginary line around which an object rotates or is symmetrical. Axis may also refer to:
Mathematics
* Axis of rotation: see rotation around a fixed axis
* Axis (mathematics), a designator for a Cartesian-coordinat ...
.
Between the articular processes of the two bones there is on either side an
arthrodial
A plane joint (arthrodial joint, gliding joint, plane articulation) is a synovial joint which, under physiological conditions, allows only gliding movement.
Plane joints permit sliding movements in the plane of articular surfaces. The opposed sur ...
or gliding joint.
Ligaments
The ligaments connecting these bones are:
*
Articular capsules
In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint.Anterior atlantoaxial ligament
The anterior atlantoaxial ligament is a strong membrane, fixed, above, to the lower border of the anterior arch of the atlas; below, to the front of the body of the axis.
It is strengthened in the middle line by a rounded cord, which connects the ...
*
Posterior atlantoaxial ligament
The posterior atlantoaxial ligament is a broad, thin membrane attached, above, to the lower border of the posterior arch of the Atlas (anatomy), atlas; below, to the upper edges of the laminæ of the Axis (anatomy), axis.
It supplies the place of ...
*
Transverse ligament of the atlas
In anatomy, the transverse ligament of the atlas is a ligament which arches across the ring of the atlas (the topmost cervical vertebra, which directly supports the skull), and keeps the odontoid process in contact with the atlas.
Anatomy
It is co ...
Capsule
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
In anatomy, the axis (from Latin ''axis'', "axle") or epistropheus is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests.
The axis' defining feature is its strong odontoid process (bon ...
, and above to the lateral mass of the atlas near the transverse ligament.
Clinical significance
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
In anatomy, the transverse ligament of the atlas is a ligament which arches across the ring of the atlas (the topmost cervical vertebra, which directly supports the skull), and keeps the odontoid process in contact with the atlas.
Anatomy
It is co ...
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
Medulla or Medullary may refer to:
Science
* Medulla oblongata, a part of the brain stem
* Renal medulla, a part of the kidney
* Adrenal medulla, a part of the adrenal gland
* Medulla of ovary, a stroma in the center of the ovary
* Medulla of t ...
death can result.
Alar ligaments
In anatomy, the alar ligaments are ligaments which connect the dens (a bony protrusion on the second cervical vertebra) to tubercles on the medial side of the occipital condyle.
They are short, tough, fibrous cords that attach on the skull an ...
: 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.
Arthritis
Osteoarthritis
Osteoarthritis (OA) is a type of degenerative joint disease that results from breakdown of joint cartilage and underlying bone which affects 1 in 7 adults in the United States. It is believed to be the fourth leading cause of disability in the w ...
may occur at the atlanto-axial joint.
This involves classic
pathophysiology
Pathophysiology ( physiopathology) – a convergence of pathology with physiology – is the study of the disordered physiological processes that cause, result from, or are otherwise associated with a disease or injury. Pathology is the ...
, such as loss of
articular cartilage
Hyaline cartilage is the glass-like (hyaline) and translucent cartilage found on many joint surfaces. It is also most commonly found in the ribs, nose, larynx, and trachea. Hyaline cartilage is pearl-gray in color, with a firm consistency and has ...
,
osteophytes
Osteophytes are exostoses (bony projections) that form along joint margins. They should not be confused with enthesophytes, which are bony projections that form at the attachment of a tendon or ligament. Osteophytes are not always distinguished ...
visible with
radiography
Radiography is an imaging technique using X-rays, gamma rays, or similar ionizing radiation and non-ionizing radiation to view the internal form of an object. Applications of radiography include medical radiography ("diagnostic" and "therapeut ...
, and bone thickening with a narrow joint space.
Conservative management Conservative management is a type of medical treatment defined by the avoidance of invasive measures such as surgery or other invasive procedures, usually with the intent to preserve function or body parts. For example, in appendicitis, conservati ...
is usually effective, involving
analgesics
An analgesic drug, also called simply an analgesic (American English), analgaesic (British English), pain reliever, or painkiller, is any member of the group of drugs used to achieve relief from pain (that is, analgesia or pain management). It i ...
.
Surgery
Surgery ''cheirourgikē'' (composed of χείρ, "hand", and ἔργον, "work"), via la, chirurgiae, meaning "hand work". is a medical specialty that uses operative manual and instrumental techniques on a person to investigate or treat a pat ...
may be used in severe cases, and may have good outcomes.
Abnormal widening
![Normal atlanto-dental joint on X-ray](https://upload.wikimedia.org/wikipedia/commons/8/86/Normal_atlanto-dental_joint_on_X-ray.jpg)
A widening of the atlanto-axial joint, as measured between the posterior surface of the
anterior arch of atlas
In anatomy, the atlas (C1) is the most superior (first) cervical vertebra of the spine and is located in the neck. It is named for Atlas of Greek mythology because, just as Atlas supported the globe, it supports the entire head.
The atlas i ...
and the front of the
odontoid process
In anatomy, the axis (from Latin ''axis'', "axle") or epistropheus is the second cervical vertebra (C2) of the spine, immediately inferior to the atlas, upon which the head rests.
The axis' defining feature is its strong odontoid process (bon ...
, indicates an injury to the transverse atlantal ligament.
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.
References
Bibliography
*Dalley, Arthur F; Moore, Keith L. Clinically Oriented Anatomy Fourth Edition. Baltimore. Lippincott Williams & Wilkins, 1992.
*Saladin, Kenneth S. Anatomy &Physiology: the Unity of Form and Function. New York. McGraw Hill, 2007.
External links
*
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Joints
Joints of the head and neck
Bones of the vertebral column