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

radius In classical geometry, a radius (: radii or radiuses) 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 radius of a regular polygon is th ...

, 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 b ...

of the

ulna The ulna or ulnar bone (: ulnae or ulnas) is a long bone in the forearm stretching from the elbow to the wrist. It is on the same side of the forearm as the little finger, running parallel to the Radius (bone), radius, the forearm's other long ...

.''

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 had multiple revised editions, and the current edition, the 42nd (October 2020 ...

'' (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'' (commonly abbreviated TA) is the international standard for human anatomy, human anatomical terminology. It is developed by the Federative International Programme on Anatomical Terminology (FIPAT) a program of the Inter ...

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

Structure

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 Motion, the process of movement, is described using specific anatomical terminology, anatomical terms. Motion includes movement of Organ (anatomy), organs, joints, Limb (anatomy), limbs, and specific sections of the body. The terminology used de ...

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 relativ ...

. 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 has ...

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.

Clinical significance

Children whose proximal radial

epiphyseal plate The epiphyseal plate, 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, with ma ...

has not finished fusing may suffer dislocations of this joint, called ''

pulled elbow A pulled elbow, also known as nursemaid's elbow or a radial head subluxation, is when the ligament that wraps around the radial head slips off. Often a child will hold their arm against their body with the elbow slightly bent. They will not mov ...

'' or ''Nursemaid's elbow''. A common cause of this dislocation is a caregiver sharply jerking a child by the arm, for example when grabbing the child away from traffic or some other danger.

Additional images

References

External links

* {{Authority control Ligaments of the upper limb