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


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

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

Author Information


The pelvis is a group of fused bones and also may be thought about the first step in the linkage of the axial skeleton (bones that the head, neck, and also vertebrae) to the lower appendages. The part of the axial skeleton directly interacting with the pelvis is the lumbar spinal column. The femur is the appendicular skeletal bone linked to the pelvis in ~ the acetabulum, a bony ring formed by the blend of 3 bones: the ilium, ischium, and pubis. The main role of the pelvis is assistance for locomotion, together it gives attachment points for muscles, tendons, and ligaments. While stiff joints bind the axial skeleton to the pelvis, the appendicular skeleton is join via a fairly free-floating ball and also socket joint in between the femur and also the acetabulum to enable maximal mobility of the joint.<1>

In pointing out the pelvis, a distinction can it is in made in between the "pelvic spine" and also the "pelvic girdle." The pelvic girdle, additionally known as the os coxae, Latin for “bone that the hip,” consists of the fused bones figured out individually together the ilium, ischium, and pubis. The ring the this girdle is closed in the anterior by the pubic symphysis between the left and also right pubic bones, and also in the posterior between the left and right ilia and the sacrum at the sacroiliac joints. The pelvic spine is composed of the sacrum and coccyx. Together these two parts form the bony pelvis.

Structure and Function

The adage “structure educates function” rings true in the pelvis. The os coxae, or i know good bones as they are known colloquially, are attached dorsally to the sacrum through sacroiliac ligaments. In addition to the ligaments that this joint, the interposing areas of the sacrum and also the ilium have matching, irregular contours to rise joint strength. The relatively fixed joint in between the sacrum and also the lumbar spine is appropriate for bearing the load of the top body. In ~ the many ventral area of the pelvis, over there is a fibrocartilaginous share in the pubic symphysis. It is amphiarthrotic, an interpretation that it is rather firm however allows limited movement similar to the intervertebral joints. This allows the joint to withstand shearing forces during movement while tho accommodating expansion throughout labor.

Three major ligaments stabilize the femur in the acetabulum, one for each component of the os coxae. The iliofemoral ligament is the most anterior and also has a “Y” appearance. It works to avoid hyperextension the the hip. The ischiofemoral ligament is posterior and works to protect against over-abduction along with the pubofemoral ligament located medially. Every one of these ligaments connect to the acetabular labrum, i m sorry is a lip the connective tissue about the acetabulum that deepens the socket of the ball-and-socket joint to boost stability and also resist dislocation.

Other ligaments of keep in mind in the acetabulum are the transverse acetabular ligament and the ligament of the head of the femur, or ligamentum teres femoris (Latin because that round ligament of the femur.) The transverse acetabular ligament is a strong band of connective fibers the traverse the acetabular notch top top the inferior aspect of the acetabulum, this creates a foramen for nutrient-supplying blood vessels to get in the hip joint while still preserving the structural integrity the the joint. Much as its name implies, the ligament of the head that the femur is linked to the head of the femur in ~ the center of the acetabulum. However, quite than providing support, that is main role is to house the artery to the head the the femur, which gives blood come the head of the femur via a branch native the obturator artery. Disruption in perfusion to the femoral head from any cause can result in degradation and even collapse of the femur within the acetabulum. This condition process is known as avascular necrosis or Legg-Calve-Perthes disease in children.

There room two notches of keep in mind in the bony pelvis: the greater and lesser sciatic notches. The greater notch is ~ above the ileum, whereas the lesser sciatic notch is located inferiorly ~ above the ischium just listed below the ischial spine. The sacrotuberous ligament runs from the sacrum to the ischial tuberosities and crosses near the greater sciatic notch to kind the greater sciatic foramen. Similarly, the sacrospinous ligament runs from the sacrum come the ischial spine to type the lesser sciatic foramen. The greater sciatic foramen has multiple clinically remarkable structures, such as the sciatic nerve, the superior and also inferior gluteal nerves, the pudendal nerve, the nerve come quadratus femoris, nerve to obturator internus, and the superior and inferior gluteal vessels and also internal pudendal vessels. Finally, the piriformis likewise passes through this foramen. The lesser sciatic foramen includes the tendon the obturator internus, as well as the pudendal nerve and also vessels comes from the better foramen ~ above their means to the perineum and also gonads. Although rather controversial, it is considered possible for the piriformis muscle to reason nerve entrapment, well-known as piriformis syndrome. It presents through symptoms the sciatica and tenderness close to the sciatic notch however remains a diagnosis of exclusion.<2>

Another eye-catching structure in the os coxae is the obturator foramen. The superior and inferior rami of the ischium and also pubis bones come with each other to kind this ring-like structure on each side that the pelvis. This ring is extended by the obturator membrane, which pipeline a little opening recognized as the obturator canal v which the obturator neurovascular bundle passes. The internal and also external political parties of the membrane are connected to the respectively called internal and also external obturator muscles responsible for exterior rotation the the hip and stabilization throughout ambulation.

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

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The pelvis has actually a "floor" at this outlet that serves lot of functions. The first function is come contain the visceral offal in the caudal an ar of the pelvis and help prevent organ prolapse with the pelvic outlet. The second function is to maintain the continence the the anus and urinary street through number of layers of musculature and also ligaments. These pelvic floor muscle are complex and will certainly be described further in the “Muscles” section.