The annular ligament (orbicular ligament) is a strong band of fibers that encircles the head of the

radius In classical geometry, a radius ( : radii) of a circle or sphere is any of the line segments from its center to its perimeter, and in more modern usage, it is also their length. The name comes from the latin ''radius'', meaning ray but also the ...

, and retains it in contact with the

radial notch The radial notch of the ulna (lesser sigmoid cavity) is a narrow, oblong, articular depression on the lateral side of the coronoid process; it receives the circumferential articular surface of the head of the radius. It is concave from before bac ...

of the

ulna The ulna (''pl''. ulnae or ulnas) is a long bone found in the forearm that stretches from the elbow to the smallest finger, and when in anatomical position, is found on the medial side of the forearm. That is, the ulna is on the same side of t ...

.'' Gray's Anatomy'' (1918), see infobox Per '' Terminologia Anatomica 1998'', the spelling is "anular", but the spelling "annular" is frequently encountered. Indeed, the most recent version of ''

Terminologia Anatomica ''Terminologia Anatomica'' is the international standard for human anatomical terminology. It is developed by the Federative International Programme on Anatomical Terminology, a program of the International Federation of Associations of Anatomi ...

'' (2019) uses "annular" as the preferred English spelling.

Anatomy

The annular ligament is attached by both its ends to the anterior and posterior margins of the radial notch of the ulna, together with which it forms the

articular surface 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- ...

that surrounds the head and neck of the radius. The ligament is strong and well defined, yet its flexibility permits the slightly oval head of the radius to rotate freely during pronation and supination. The head of the radius is wider than the bone's neck, and, because the annular ligament embraces both, the radial head is "trapped" inside the ligament which thus acts to prevent distal displacement of the radius. It helps to stabilise the proximal radial head, and the radioulnar joint. Superiorly, the ligament is supported by attachments to the radial collateral ligament and the fibrous capsule of the elbow joint. Inferiorly, a few fibres attached to the neck of the radius support a fold of the synovial membrane without interfering with the movements at the joint. The fibrocartilage on the upper part of the ligament is continuous with the hyaline cartilage of the radial notch. At the posterior attachment the ligament widens to reach above and below the radial notch. A thickened band which extends from the inferior border of the annular ligament below the radial notch to the neck of the radius is known as the

quadrate ligament In human anatomy, the quadrate ligament or ligament of Denucé is one of the ligaments of the proximal radioulnar joint in the upper forearm. Structure The quadrate ligament is a fibrous band attached to the inferior border of the radial notch on ...

Clinical significance

Children who have not finished fusing their proximal radial

epiphyseal plate The epiphyseal plate (or epiphysial plate, physis, or growth plate) is a hyaline cartilage plate in the metaphysis at each end of a long bone. It is the part of a long bone where new bone growth takes place; that is, the whole bone is alive, wit ...

may suffer dislocations of this joint, called '' pulled elbow'' or ''Nursemaid's elbow''. This frequently happens when parents sharply jerk their children by their arms, e.g. the act of grabbing a child away from traffic.

Additional images

References

External links

* {{Authority control Ligaments of the upper limb