Search databaseBooksAll DatabasesAssemblyBiocollectionsBioProjectBioSampleBioSystemsBooksClinVarConserved DomainsdbGaPdbVarGeneGenomeGEO DataSetsGEO ProfilesGTRHomoloGeneIdentical Protein internet CatalogNucleotideOMIMPMCPopSetProteinProtein ClustersProtein family ModelsPubChem BioAssayPubChem CompoundPubChem SubstancePubMedSNPSRAStructureTaxonomyToolKitToolKitAllToolKitBookgh Bookshelf. A organization of the national Library of Medicine, national Institutes the Health.

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

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


Anatomy, Abdomen and Pelvis, skeletal (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 considered the very first step in the link of the axial skeleton (bones the the head, neck, and also 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 skeletal bone linked to the pelvis in ~ the acetabulum, a bony ring created by the blend of three bones: the ilium, ischium, and also pubis. The main role of the pelvis is support for locomotion, as it gives attachment points because that muscles, tendons, and ligaments. While stiff joints tie the axial skeleton to 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 allow 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, likewise known as the os coxae, Latin for “bone that the hip,” is composed of the unify bones determined individually together the ilium, ischium, and also pubis. The ring of this girdle is closed in the anterior through the pubic symphysis in between the left and also right pubic bones, and in the posterior in between the left and also right ilia and also the sacrum at 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 informs function” rings true in the pelvis. The os coxae, or hip bones as they are well-known colloquially, room attached dorsally to the sacrum through sacroiliac ligaments. In enhancement to the ligaments the this joint, the interposing locations of the sacrum and also the ilium have matching, irregular border to rise joint strength. The fairly fixed joint between the sacrum and also the lumbar spine is appropriate for bearing the fill of the top body. At the most ventral area that the pelvis, over there is a fibrocartilaginous joint in the pubic symphysis. It is amphiarthrotic, definition that that is rather firm but allows restricted movement comparable to the intervertebral joints. This permits the share to stand up to shearing forces throughout movement while still accommodating expansion throughout labor.

Three significant ligaments stabilize the femur in the acetabulum, one because that each component of the os coxae. The iliofemoral ligament is the most anterior and has a “Y” appearance. It works to prevent hyperextension the the hip. The ischiofemoral ligament is posterior and also works to stop over-abduction along with the pubofemoral ligament situated medially. Every one of these ligaments attach to the acetabular labrum, i beg your pardon is a lip the connective tissue around the acetabulum that deepens the socket the the ball-and-socket joint to boost stability and also resist dislocation.

Other ligaments of note in the acetabulum room the transverse acetabular ligament and the ligament that the head of the femur, or ligamentum teres femoris (Latin because that round ligament the the femur.) The transverse acetabular ligament is a strong band that connective fibers the traverse the acetabular notch top top the inferior aspect of the acetabulum, this creates a foramen because that nutrient-supplying blood ship to get in the hip joint while still maintaining the structural integrity that the joint. Much as its name implies, the ligament the the head that the femur is linked to the head that the femur at the center of the acetabulum. However, rather than providing support, its main function is to house the artery to the head of the femur, which provides blood come the head of the femur via a branch from the obturator artery. Disruption in perfusion come the femoral head from any type of cause can an outcome in degradation and even please of the femur within the acetabulum. This condition process is well-known as avascular necrosis or Legg-Calve-Perthes condition in children.

There space two notches of note in the bony pelvis: the greater and also lesser sciatic notches. The better notch is ~ above the ileum, conversely, the lesser sciatic notch is located inferiorly ~ above the ischium just below the ischial spine. The sacrotuberous ligament runs from the sacrum to the ischial tuberosities and crosses close to the greater sciatic notch to type the greater sciatic foramen. Similarly, the sacrospinous ligament operation from the sacrum to the ischial spine to form the lesser sciatic foramen. The greater sciatic foramen contains multiple clinically noteworthy structures, such as the sciatic nerve, the superior and inferior gluteal nerves, the pudendal nerve, the nerve to quadratus femoris, nerve come obturator internus, and also the superior and also inferior gluteal vessels and also internal pudendal vessels. Finally, the piriformis additionally passes with this foramen. The lesser sciatic foramen consists of the tendon that obturator internus, and also the pudendal nerve and also vessels comes from the better foramen ~ above their way to the perineum and gonads. Although somewhat controversial, it is considered feasible for the piriformis muscle to reason nerve entrapment, well-known as piriformis syndrome. The presents through symptoms of sciatica and also tenderness close to the sciatic notch but remains a diagnosis the exclusion.<2>

Another eye-catching framework in the os coxae is the obturator foramen. The superior and also inferior rami of the ischium and also pubis bones come together to form this ring-like framework on every side that the pelvis. This ring is extended by the obturator membrane, which pipeline a little opening well-known as the obturator canal v which the obturator neurovascular bundle passes. The internal and also external political parties of the membrane are associated to the respectively called internal and external obturator muscle responsible for exterior rotation the the hip and also stabilization throughout ambulation.

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

See more: Many Market Trends Are Intensified By A, _____ Instinct Among Investors

The pelvis has a "floor" at this outlet the serves multiple functions. The very first function is come contain the visceral offal in the caudal region of the pelvis and aid prevent body organ prolapse with the pelvic outlet. The second function is to maintain the continence the the anus and urinary tract through several layers of musculature and also ligaments. These pelvic floor muscle are complicated and will be described further in the “Muscles” section.