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


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

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

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The pelvis is a group of unify bones and may be thought about the first step in the linkage of the axial skeleton (bones of the head, neck, and also vertebrae) come the reduced appendages. The part of the axial skeleton directly connecting with the pelvis is the lumbar spinal column. The femur is the appendicular skeleton bone associated to the pelvis at the acetabulum, a bony ring created by the combination of 3 bones: the ilium, ischium, and also pubis. The main duty of the pelvis is support for locomotion, together it offers attachment points for muscles, tendons, and ligaments. While stubborn joints bind the axial skeleton come the pelvis, the appendicular skeleton is joined via a reasonably free-floating ball and socket joint in between the femur and also the acetabulum to permit maximal mobility that the joint.<1>

In mentioning the pelvis, a difference can it is in made in between the "pelvic spine" and also the "pelvic girdle." The pelvic girdle, additionally known together the os coxae, Latin because that “bone the the hip,” consists of the unify bones established individually as the ilium, ischium, and pubis. The ring of this girdle is closed in the anterior by the pubic symphysis in between the left and also right pubic bones, and in the posterior between the left and also right ilia and also the sacrum in ~ the sacroiliac joints. The pelvic spine is composed of the sacrum and also coccyx. With each other these two parts kind the bony pelvis.

Structure and Function

The adage “structure notifies function” ring true in the pelvis. The os coxae, or hip bones as they are well-known colloquially, room attached dorsally to the sacrum by sacroiliac ligaments. In addition to the ligaments of this joint, the interposing locations of the sacrum and also the ilium have matching, irregular border to boost joint strength. The relatively fixed joint between the sacrum and the lumbar spine is appropriate for bearing the load of the top body. In ~ the many ventral area that the pelvis, over there is a fibrocartilaginous joint in the pubic symphysis. The is amphiarthrotic, meaning that it is quite firm however allows limited movement comparable to the intervertebral joints. This enables the joint to withstand shearing forces throughout movement while quiet accommodating expansion during 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 prevent hyperextension the the hip. The ischiofemoral ligament is posterior and works to avoid over-abduction in addition to the pubofemoral ligament located medially. Every one of these ligaments connect to the acetabular labrum, i m sorry is a lip of connective tissue about the acetabulum the deepens the socket that the ball-and-socket joint to boost stability and resist dislocation.

Other ligaments of keep in mind in the acetabulum are the transverse acetabular ligament and the ligament of the head the the femur, or ligamentum teres femoris (Latin because that round ligament the the femur.) The transverse acetabular ligament is a strong band of connective fibers the traverse the acetabular notch on the inferior aspect of the acetabulum, this creates a foramen because that nutrient-supplying blood ship to go into the hip joint while still maintaining the structural integrity that the joint. Much as its surname implies, the ligament that the head the the femur is connected to the head that the femur in ~ the facility of the acetabulum. However, fairly than giving support, that is main duty is to house the artery to the head the the femur, which provides blood come the head of the femur via a branch native the obturator artery. Disruption in perfusion come the femoral head from any cause can result in degradation and even collapse of the femur inside the acetabulum. This an illness process is known as avascular necrosis or Legg-Calve-Perthes an illness in children.

There are two notches of keep in mind in the bony pelvis: the greater and also lesser sciatic notches. The better notch is on the ileum, conversely, the lesser sciatic notch is situated inferiorly ~ above the ischium just below the ischial spine. The sacrotuberous ligament runs from the sacrum to the ischial tuberosities and crosses near the higher sciatic notch to type the higher sciatic foramen. Similarly, the sacrospinous ligament runs from the sacrum come the ischial spine to form the lesser sciatic foramen. The greater sciatic foramen has multiple clinically notable structures, such together the sciatic nerve, the superior and inferior gluteal nerves, the pudendal nerve, the nerve to quadratus femoris, nerve to obturator internus, and also the superior and inferior gluteal vessels and also internal pudendal vessels. Finally, the piriformis additionally passes v this foramen. The lesser sciatic foramen consists of the tendon the obturator internus, and the pudendal nerve and also vessels comes from the higher foramen ~ above their method to the perineum and also gonads. Although rather controversial, it is considered possible for the piriformis muscle to reason nerve entrapment, known as piriformis syndrome. It presents v symptoms of sciatica and tenderness near the sciatic notch yet remains a diagnosis of exclusion.<2>

Another eye-catching structure in the os coxae is the obturator foramen. The superior and also inferior rami the the ischium and pubis skeleton come with each other to kind this ring-like framework on every side of the pelvis. This ring is covered by the obturator membrane, which pipeline a tiny opening recognized as the obturator canal through which the obturator neurovascular bundle passes. The internal and external sides of the membrane are connected to the respectively named internal and external obturator muscles responsible for external rotation that the hip and stabilization throughout ambulation.

The pelvis has both one inlet and an outlet, additionally known together the superior and also inferior apertures, as it develops somewhat that a funnel. The pelvic inlet is significant by the pelvic brim, a bony ring made up of the sacral importance 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 extending above this line form the greater, or “false” pelvis, and also the area below this line develops the lesser or “true” pelvis. The outlet the 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 anteriorly by the pubic arch the the pubic bones.

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The pelvis has a "floor" in ~ this outlet that serves lot of functions. The very first function is to contain the visceral guts in the caudal region of the pelvis and aid prevent organ prolapse with the pelvic outlet. The second role is to maintain the continence of the anus and urinary tract through numerous layers that musculature and ligaments. This pelvic floor muscle are complex and will certainly be defined further in the “Muscles” section.