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You are watching: Which bone is not part of the os coxae?

StatPearls . Sweetheart Island (FL): StatPearls Publishing; 2021 Jan-.


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Anatomy, Abdomen and also Pelvis, bones (Ilium, Ischium, and also Pubis)

Anna M. Wobser; Zachary Adkins; Randy W. Wobser.

Author Information

Introduction

The pelvis is a group of unify bones and also may be thought about the very first step in the link of the axial skeleton (bones that the head, neck, and vertebrae) come the reduced appendages. The component of the axial skeleton directly connecting with the pelvis is the lumbar spinal column. The femur is the appendicular skeleton bone linked to the pelvis at the acetabulum, a bony ring created by the combination of three bones: the ilium, ischium, and pubis. The main duty of the pelvis is assistance for locomotion, together it provides attachment points for muscles, tendons, and ligaments. While stubborn joints bind the axial skeleton to the pelvis, the appendicular skeleton is joined via a relatively free-floating ball and also socket joint in between the femur and also the acetabulum to permit maximal mobility of the joint.<1>

In pointing out the pelvis, a distinction can be made in between the "pelvic spine" and also the "pelvic girdle." The pelvic girdle, likewise known together the os coxae, Latin for “bone the the hip,” is composed of the fused bones determined individually as the ilium, ischium, and also pubis. The ring the this girdle is closed in the anterior by the pubic symphysis in between the left and right pubic bones, and also in the posterior in between the left and right ilia and also the sacrum in ~ the sacroiliac joints. The pelvic spine consists of the sacrum and coccyx. With each other these 2 parts kind the bony pelvis.


Structure and also Function

The adage “structure notifies function” rings true in the pelvis. The os coxae, or i know well bones together they are known colloquially, are attached dorsally to the sacrum through sacroiliac ligaments. In enhancement to the ligaments that this joint, the interposing areas of the sacrum and the ilium have actually matching, irregular border to rise joint strength. The reasonably fixed joint in between the sacrum and the lumbar spine is best for bearing the fill of the top body. At the many ventral area of the pelvis, over there is a fibrocartilaginous joint in the pubic symphysis. That is amphiarthrotic, definition that it is quite firm but allows restricted movement comparable to the intervertebral joints. This allows the joint to stand up to shearing forces throughout movement while tho accommodating expansion throughout labor.

Three major ligaments stabilize the femur in the acetabulum, one because that each part of the os coxae. The iliofemoral ligament is the many anterior and has a “Y” appearance. It functions to avoid hyperextension that the hip. The ischiofemoral ligament is posterior and also works to stop over-abduction along with the pubofemoral ligament located medially. All of these ligaments attach to the acetabular labrum, which is a lip of connective tissue roughly the acetabulum the deepens the socket that the ball-and-socket joint to increase stability and also resist dislocation.

Other ligaments of note in the acetabulum are the transverse acetabular ligament and the ligament the the head the the femur, or ligamentum teres femoris (Latin because that round ligament of the femur.) The transverse acetabular ligament is a strong band that connective fibers that traverse the acetabular notch top top the inferior facet of the acetabulum, this create a foramen for nutrient-supplying blood ship to go into the hip share while still maintaining the structure integrity of the joint. Lot as its surname implies, the ligament that the head the the femur is connected to the head that the femur in ~ the center of the acetabulum. However, fairly than providing support, that main role is to residence the artery come the head of the femur, which offers blood to the head that the femur via a branch native the obturator artery. Disruption in perfusion to the femoral head from any kind of cause can result in degradation and even please of the femur inside the acetabulum. This an illness process is well-known as avascular necrosis or Legg-Calve-Perthes an illness in children.

There room two notches of keep in mind in the bony pelvis: the greater and also lesser sciatic notches. The better notch is ~ above the ileum, vice versa, the lesser sciatic notch is situated inferiorly on the ischium just below the ischial spine. The sacrotuberous ligament operation from the sacrum come the ischial tuberosities and also crosses close to the higher sciatic notch to kind the better sciatic foramen. Similarly, the sacrospinous ligament runs from the sacrum to the ischial spine to type the lesser sciatic foramen. The better sciatic foramen includes multiple clinically significant structures, such as the sciatic nerve, the superior and inferior gluteal nerves, the pudendal nerve, the nerve to quadratus femoris, nerve come obturator internus, as well as the superior and also inferior gluteal vessels and internal pudendal vessels. Finally, the piriformis additionally passes through this foramen. The lesser sciatic foramen contains the tendon of obturator internus, as well as the pudendal nerve and also vessels coming from the greater foramen on their means to the perineum and gonads. Although somewhat controversial, it is considered possible for the piriformis muscle to cause nerve entrapment, well-known as piriformis syndrome. That presents v symptoms of sciatica and tenderness close to the sciatic notch however remains a diagnosis the exclusion.<2>

Another eye-catching framework in the os coxae is the obturator foramen. The superior and also inferior rami that the ischium and pubis skeleton come together to form this ring-like framework on each side that the pelvis. This ring is spanned by the obturator membrane, which pipeline a tiny opening recognized as the obturator canal with which the obturator neurovascular bundle passes. The internal and external sides of the membrane are linked to the respectively called internal and external obturator muscle responsible for exterior rotation that the hip and also stabilization throughout ambulation.

The pelvis has both an inlet and also an outlet, also known together the superior and inferior apertures, together it creates somewhat the a funnel. The pelvic inlet is significant by the pelvic brim, a bony ring consisted of of the sacral prominence posteriorly, the arcuate heat of the ilium laterally, and the pectineal heat of the pubis and pubic symphysis anteriorly. The wings of the ilium extending over this line form the greater, or “false” pelvis, and the area below this line creates the lesser or “true” pelvis. The outlet that the pelvis is marked posteromedially by the coccyx, posterolaterally by the sacrotuberous ligaments connecting the sacrum come the ischial tuberosities, laterally by the ischial bones, and also anteriorly by the pubic arch of the pubic bones.

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The pelvis has a "floor" at this outlet that serves lot of functions. The an initial function is to contain the visceral guts in the caudal region of the pelvis and aid prevent organ prolapse v the pelvic outlet. The second duty is to preserve the continence of the anus and also urinary tract through number of layers that musculature and also ligaments. This pelvic floor muscle are complicated and will certainly be defined further in the “Muscles” section.