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The zona orbicularis or annular ligament is a
ligament A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as ''articular ligament'', ''articular larua'', ''fibrous ligament'', or ''true ligament''. Other ligaments in the body include the: * Peritoneal l ...
on the
neck The neck is the part of the body on many vertebrates that connects the head with the torso. The neck supports the weight of the head and protects the nerves that carry sensory and motor information from the brain down to the rest of the body. In ...
of the
femur The femur (; ), or thigh bone, is the proximal bone of the hindlimb in tetrapod vertebrates. The head of the femur articulates with the acetabulum in the pelvic bone forming the hip joint, while the distal part of the femur articulates with ...
formed by the circular fibers of the articular capsule of the
hip joint In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...
. 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 The iliofemoral ligament is a ligament of the hip joint which extends from the ilium to the femur in front of the joint. It is also referred to as the Y-ligament (see below). the ligament of Bigelow, the ligament of Bertin and any combinations ...
, 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 In vertebrate anatomy, hip (or "coxa"Latin ''coxa'' was used by Celsus in the sense "hip", but by Pliny the Elder in the sense "hip bone" (Diab, p 77) in medical terminology) refers to either an anatomical region or a joint. The hip region is ...
when
iliopsoas muscle The iliopsoas muscle (; from lat, ile, lit=groin and grc, ψόᾱ, psóā, muscles of the loins) refers to the joined psoas major and the iliacus muscles. The two muscles are separate in the abdomen, but usually merge in the thigh. They are us ...
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