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 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 t ...

and the axis bone, which are the first and second cervical vertebrae. It is a pivot joint.

Structure

The atlanto-axial joint is a joint between the

and the axis bone, which are the first and second cervical vertebrae. It is a pivot joint. 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 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 and the front of the odontoid process ** 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 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 * Anterior atlantoaxial ligament *

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, 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

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: 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, 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 "therapeu ...

, 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 ...

. Surgery may be used in severe cases, and may have good outcomes.

Abnormal widening

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. 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

* {{Authority control Joints Joints of the head and neck Bones of the vertebral column