The zona orbicularis or annular ligament is a
ligament
A ligament is a type of fibrous connective tissue in the body that connects bones to other bones. It also connects flight feathers to bones, in dinosaurs and birds. All 30,000 species of amniotes (land animals with internal bones) have liga ...
on the
neck
The neck is the part of the body in many vertebrates that connects the head to the torso. It supports the weight of the head and protects the nerves that transmit sensory and motor information between the brain and the rest of the body. Addition ...
of the
femur
The femur (; : femurs or femora ), or thigh bone is the only long bone, bone in the thigh — the region of the lower limb between the hip and the knee. In many quadrupeds, four-legged animals the femur is the upper bone of the hindleg.
The Femo ...
formed by the circular fibers of the
articular capsule of the
hip joint
In vertebrate anatomy, the hip, or coxaLatin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) (: ''coxae'') in medical terminology, refers to either an anatomical region or a joint o ...
. It is also known as the orbicular zone, ring ligament, and zonular band.
Structure
The zona orbicularis forms a ring around the neck of the femur.
The articular capsule is much thicker above and in front of the joint, where the greatest amount of resistance is required, and thin and loose behind and below the joint.
The capsule consists of two sets of fibers, circular and longitudinal. The circular fibers, the zona orbicularis, are most abundant at the lower and back part of the capsule where they form a sling or collar around the femoral neck. Anteriorly, they blend with the deep surface of the
iliofemoral ligament, and gain an attachment to the
anterior inferior iliac spine.
[''Gray's Anatomy'' (1918), 7a3]
Function
The zona orbicularis and proximal hip joint capsule are poorly understood. Recent studies seem to confirm that the proximal to middle part of the articular capsule, including the zona orbicularis, acts biomechanically as a locking ring wrapped around the femoral neck and thus is a key structure for hip stability in distraction.
[Ito H. ''et al'' (2009)] It tightens the joint capsule of the
hip when
iliopsoas muscle contracts.
Additional images
File:Gray342.png, Front view of hip joint with capsular ligament largely removed
Zona orbicularis used as arthroscopic landmark for iliopsoas muscle.
Notes
References
*
* (Abstract)
{{Authority control
Ligaments of the lower limb