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


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Anatomy, Bony Pelvis and Lower Limb, Pelvis Bones

Christian Figueroa; Patrick H. Le.

Author Information

Introduction

The pelvis consists of the right and also left hip skeleton (coxal or pelvic bones) joined v the sacrum. Anteriorly, the i know well bones accomplish to kind the pubic symphysis. Posteriorly, the hip skeleton unite through the sacrum to kind the sacroiliac joints. Together, this structure creates a basin-shaped ring referred to as the bony pelvis or pelvic girdle the connects the axial and the appendicular skeleton.

Each i know well bone is composed of 3 bones: the ischium, ilium, and pubis. The Ilium is the physically biggest of the 3 pelvic bones. That is located superiorly family member to the pubis and also ischium. It is created of a wing-shaped part called the premium ala along with the worse body. The rim of the superior ala is dubbed the iliac crest. Anteriorly this crest end at the anterior premium iliac spine and posteriorly in ~ the posterior remarkable iliac spine. Inferior to this ends will certainly be your inferior equivalents.<1>

The ischium is the inferior posterior section of the i know well bone. It consists of a remarkable body and an inferior ramus. In ~ the junction posteromedial, the bone has a projection referred to as the ischial spine—the concavity between this spine and the posterior worse iliac spine from the higher sciatic notch.  The concavity in between this spine and also inferior ramus is called the lesser sciatic notch.

The pubis is the inferior, anterior portion of the i know good bone. It consists of a premium ramus, body, and inferior ramus. The exceptional ramus helps type the acetabulum. The worse ramus the the pubis fuses with the inferior ramus the the ischium. The pubis and ischium together form the obturator foramen. The human body of both the left and also right pubis sign up with to type the pubic symphysis joint.

The sacrum creates from the fusion of the five sacral vertebral bodies. On each side, it creates the sacroiliac joints together with the iliac bone.


Structure and Function

The features of the pelvic bones space locomotion, childbirth, and also support come the ab viscera. It offer to transmit the weight from the axial to the reduced appendicular skeleton. Likewise, the pelvis bear the load of the upper body when sitting. The bony structure additionally provides attachments sites for numerous abdominal, pelvic, and lower extremity muscles. It additionally provides attachment sites for external reproductive organs. Additionally, the pelvic girdle offer to safeguard the pelvic and also abdominopelvic viscera.<2>


Embryology

The pelvic bones formation requires a combination of multiple facets which enable articulation that the axial skeleton through the reduced extremities. The hip skeletal (ilium, ischium, and pubis) remain separate but attach via the triradiate cartilage in early life. Top top puberty, this bones fuse to form the acetabulum, a socket on the lateral element of the hip in i m sorry the femoral head articulates. 

The lateral key mesoderm develops the ilium, ischium, and also the pubis. This bones climate undergo endochondral ossification, similar to lengthy bones, but an early stage blastemal framework forms, which undergoes chondrification. Afterward, sites of primary ossification centers form.<3>

The sacrum experience this kind of ossification as well.


Blood Supply and Lymphatics

Vascular supply to the i know good bones originates from branches that both the external and also internal iliac arteries. Both of these come from the bifurcation of the common iliac artery, which bifurcates in ~ the level of L5-S1 vertebral level. The exterior iliac artery travels along the pelvic brim and gives turn off the worse epigastric artery and the deep circumflex iliac artery. It then transitions right into the femoral artery after passing the inguinal ligament. The interior iliac artery travels posteromedial right into the pelvis, which bifurcates right into the anterior and also posterior divisions of the interior iliac artery. The anterior department includes the umbilical, obturator, inferior vesical, uterine, vaginal, middle rectal, internal pudendal, and inferior gluteal. The posterior division consists of the iliolumbar, lateral sacral, and also superior gluteal arteries.<4>

The sacrum obtain blood it is provided from the lateral sacral and the average sacral arteries. The lateral sacral arteries are a branch the the internal iliac artery. The mean artery is a branch from the aorta ~ bifurcation right into the internal and external iliac arteries.

The lymphatic device of the pelvis has countless contributions and groups the lymph nodes. The main teams of lymph nodes room the external iliac lymph nodes, interior iliac lymph nodes, sacral lymph nodes, and the usual iliac lymph nodes.


Nerves

Innervation the the pelvis contains mainly the sacral and coccygeal plexuses.

The sacral plexus derives indigenous the L4-S4 nerve roots, and it sits on the interior surface of the piriformis muscle—most that the sacral nerves stemming indigenous the sacral plexus leave through the better sciatic notch. The sciatic nerve develops out the the sacral plexus and can be compressed by the muscle, leading to radicular pain under the leg. This kind of entrapment neuropathy through the compression from the piriformis muscle is referred to as piriformis muscle syndrome.<5><6>

The coccygeal plexus develops from the S4-S5 nerve roots, and also it lies follow me the coccygeus muscle top top the pelvic surface.

The autonomic system additionally provides innervation to the pelvis, which mostly courses via the inferior hypogastric plexus. This plexus is make of the nerve yarn from the sorry splanchnic nerves, parasympathetic splanchnic nerves, and also hypogastric nerves. The autonomic nerves are travel come the guts via their corresponding splanchnic nerve group.


Muscles

The pelvic bones room an attachments for plenty of different muscle teams involving the abdomen, pelvis, perineum, and also lower extremities.  The muscles restricted to the pelvis include the muscle of the pelvic wall surface and the pelvic diaphragm.

Along the anterolateral wall surface of the true pelvis lies the obturator internus muscle. This muscle extends from the bony surfaces of the pelvis right into the lesser sciatic foramen and inserts top top the greater trochanter. The muscle receive innervation indigenous the nerve to the obturator internus (L5-S2). The serves as an external rotator that the hip and also strengthens the hip joint.

Along the posterolateral surface ar of the true pelvis lies the piriformis muscle. This muscle extends native the bony surfaces of the sacrum and pelvis into the greater sciatic foramen, with its insertion on the better trochanter of the femur. The muscle receives innervation indigenous the anterior rami of S1 and S2. It additionally serves together an outside rotator that the hip and also strengthening the hip joint.<7>

The pelvic diaphragm is composed of the coccygeus muscles and the levator ani muscles.

The coccygeus muscle is the many posterior and also superior of the pelvic diaphragm muscles. It extends native the ischial spines to attach to the lateral surface ar of the coccyx and also inferior sacral segment. Its innervation originates from branches the the S4 and also S5 spinal nerves. That serves as the support for the pelvic viscera and also flexes the coccyx.

The levator ani deserve to subdivide into different muscle teams (pubococcygeus, puborectalis, and iliococcygeus), however margins space ill-defined. These muscle groups prolong from the anterior bony surfaces of the pelvis to connect to the perineal body, anococcygeal ligament, and walls of the viscera close to the pelvic floor. The muscles space innervated nerve to levator ani, worse anal nerve, and also coccygeal plexus. They serve as support for the pelvic viscera.<8>


Physiologic Variants

Physiologic variants that the bony pelvis exist in between males and females. The masculine pelvis is typically thicker and heavier 보다 the lighter and thinner pelvis that the female. Males likewise tend to have a narrower pelvic opening than females.

Most physiological differences lie in sports of the pelvic girdle. There are four types described.


The gynecoid pelvis screens an oval shape with a broad transverse diameter. This different is the most common type and gives adequate cavity room for a female to give birth.  
The android display screens a heart-shaped inlet and also is most common in males.
The platypelloid display screens a vast inlet transversely but brief in the anterior-posterior axis. This type provides obstacles for a mrs to give birth.

Surgical Considerations

The diameter the the pelvic ring is a surgical consideration that an OB/GYN should take right into account when planning their patient"s birth. The ability of vaginally delivering a baby is restricted to the anatomical framework of the woman’s pelvis. This anteroposterior diameter the the pelvic inlet have to be assessed radiographically or with pelvic examination. A diagonal conjugate is measure up instead throughout the pelvic examination because of the i can not qualify to measure up a true anteroposterior diameter. The distance in between the ischial spines is additionally considered because this an are is the narrowest part of the pelvic canal. A cesarean section will be abdominal muscle option if the anatomical structure renders vaginal birth difficult.<9>


Clinical Significance

Fractures the the pelvis are not common, but they often involve multiple skeletal of the pelvis or may incorporate the i know good joint. Many pelvic fractures happen due to straight trauma (ex. Auto accident) or a fall from significant heights. In addition, civilization with currently osteoporosis are more prone to fractures of the pelvis.

The severity that the fracture determines the require for surgery. If the pelvis is broken in many places and also is taken into consideration unstable, intervention may be understood necessary. Certain species of fractures might be life-threatening.<10>

Open book fractures once the two pubic bones are separated, and the pelvis is currently anteriorly open. This case can be life-threatening as result of the exposed vessels and viscera of the pelvis.

Vertical shear fractures take place when the fracture allows half of the pelvis to shift upwards. This problem can it is in dangerous early out to far-reaching blood loss.

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When fifty percent the fracture is displaced inwards, lateral crush fractures can additionally represent life-threatening cases involving damage to the vessels and also viscera.