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

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

, and retains it in contact with the radial notch 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 ''Gray's Anatomy'' is a reference book of human anatomy written by Henry Gray, illustrated by Henry Vandyke Carter, and first published in London in 1858. It has gone through multiple revised editions and the current edition, the 42nd (Octo ...

'' (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 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 Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relati ...

and

supination Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relati ...

. 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 Fibrocartilage consists of a mixture of white fibrous tissue and cartilaginous tissue in various proportions. It owes its inflexibility and toughness to the former of these constituents, and its elasticity to the latter. It is the only type of ...

on the upper part of the ligament is continuous with the

hyaline 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 h ...

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