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You are watching: Which bones form the three main divisions of the pelvis?

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


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Anatomy, Abdomen and Pelvis, Bones (Ilium, Ischium, and Pubis)

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

Author Information

Introduction

The pelvis is a group of fprovided bones and also may be taken into consideration the first action in the link of the axial skeleton (bones of the head, neck, and vertebrae) to the reduced appendages. The part of the axial skeleton straight interacting through the pelvis is the lumbar spinal column. The femur is the appendicular skeletal bone associated to the pelvis at the acetabulum, a bony ring created by the fusion of three bones: the ilium, ischium, and also pubis. The primary function of the pelvis is assistance for locomovement, as it gives attachment points for muscles, tendons, and also ligaments. While stiff joints bind the axial skeleton to the pelvis, the appendicular skeleton is joined by means of a fairly free-floating ball and socket joint between the femur and also the acetabulum to allow maximal mobility of the joint.<1>

In pointing out the pelvis, a difference have the right to be made in between the "pelvic spine" and also the "pelvic girdle." The pelvic girdle, likewise known as the os coxae, Latin for “bone of the hip,” consists of the foffered bones established individually as the ilium, ischium, and pubis. The ring of this girdle is closed in the anterior by the pubic symphysis between the left and right pubic bones, and also in the posterior in between the left and also best ilia and also the sacrum at the sacroiliac joints. The pelvic spine consists of the sacrum and also coccyx. With Each Other these 2 parts form the bony pelvis.


Structure and Function

The adage “structure increates function” rings true in the pelvis. The os coxae, or hip bones as they are well-known colloquially, are attached dorsally to the sacrum by sacroiliac ligaments. In addition to the ligaments of this joint, the interposing areas of the sacrum and also the ilium have matching, ircontinuous contours to increase joint strength. The relatively fixed joint between the sacrum and also the lumbar spine is best for bearing the fill of the top body. At the a lot of ventral location of the pelvis, tright here is a fibrocartilaginous joint in the pubic symphysis. It is amphiarthrotic, interpretation that it is fairly firm but enables restricted movement equivalent to the intervertebral joints. This enables the joint to stand up to shearing forces in the time of movement while still accommodating development during labor.

Three major ligaments stabilize the femur in the acetabulum, one for each component of the os coxae. The iliofeethical ligament is the many anterior and has actually a “Y” appearance. It functions to proccasion hyperextension of the hip. The ischiofeethical ligament is posterior and functions to proccasion over-abduction together with the pubofemoral ligament situated medially. All of these ligaments affix to the acetabular labrum, which is a lip of connective tconcern approximately the acetabulum that deepens the socket of the ball-and-socket joint to rise stcapability and stand up to displace.

Other ligaments of note in the acetabulum are the transverse acetabular ligament and also the ligament of the head of the femur, or ligamentum teres femoris (Latin for round ligament of the femur.) The transverse acetabular ligament is a strong band of connective fibers that traverse the acetabular notch on the inferior facet of the acetabulum, this creates a foramen for nutrient-offering blood vessels to enter the hip joint while still preserving the structural integrity of the joint. Much as its name implies, the ligament of the head of the femur is linked to the head of the femur at the facility of the acetabulum. However, fairly than giving support, its major attribute is to residence the artery to the head of the femur, which provides blood to the head of the femur via a branch from the obturator artery. Disruption in perfusion to the feethical head from any kind of reason have the right to bring about deterioration and also collapse of the femur inside the acetabulum. This condition process is recognized as avascular necrosis or Legg-Calve-Perthes disease in children.

Tright here are two notches of note in the bony pelvis: the higher and also lesser sciatic notches. The higher notch is on the ileum, whereas the lesser sciatic notch is located inferiorly on the ischium simply listed below the ischial spine. The sacrotuberous ligament runs from the sacrum to the ischial tuberosities and crosses close to the greater sciatic notch to develop the higher sciatic foramales. Similarly, the sacrospinous ligament runs from the sacrum to the ischial spine to create the lesser sciatic foramen. The better sciatic foramales includes multiple clinically significant structures, such as the sciatic nerve, the premium and inferior gluteal nerves, the pudendal nerve, the nerve to quadratus femoris, nerve to obturator internus, as well as the remarkable and inferior gluteal vessels and also internal pudendal vessels. Finally, the piriformis additionally passes through this foramales. The lesser sciatic foramales has the tendon of obturator internus, and also the pudendal nerve and also vessels coming from the better foramales on their means to the perineum and also gonads. Although somewhat controversial, it is taken into consideration feasible for the piriformis muscle to cause nerve entrapment, recognized as piriformis syndrome. It presents via symptoms of sciatica and also tenderness near the sciatic notch but continues to be a diagnosis of exemption.<2>

Anvarious other eye-recording framework in the os coxae is the obturator foramen. The exceptional and also inferior rami of the ischium and pubis bones come together to form this ring-prefer structure on each side of the pelvis. This ring is extended by the obturator membrane, which leaves a small opening known as the obturator canal through which the obturator neurovascular bundle passes. The internal and also outside sides of the membrane are associated to the respectively named inner and outside obturator muscles responsible for exterior rotation of the hip and stabilization throughout ambulation.

The pelvis has actually both an inlet and an outlet, additionally recognized as the exceptional and also inferior apertures, as it develops somewhat of a funnel. The pelvic inlet is marked by the pelvic brim, a bony ring comprised of the sacral prestige posteriorly, the arcuate line of the ilium laterally, and also the pectineal line of the pubis and also pubic symphysis anteriorly. The wings of the ilium extfinishing over this line form the better, or “false” pelvis, and also the area below this line creates the lesser or “true” pelvis. The outlet of the pelvis is noted posteromedially by the coccyx, posterolaterally by the sacrotuberous ligaments connecting the sacrum to 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 multiple functions. The first feature is to contain the visceral organs in the caudal area of the pelvis and also aid prevent organ prolapse through the pelvic outlet. The second feature is to preserve the continence of the anus and also urinary tract with a number of layers of musculature and ligaments. These pelvic floor muscles are complicated and will certainly be defined further in the “Muscles” area.