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StatPearls . Endowment Island (FL): StatPearls Publishing; 2022 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 left hip skeleton (coxal or pelvic bones) joined v the sacrum. Anteriorly, the i know good bones satisfy to form the pubic symphysis. Posteriorly, the hip skeleton unite v the sacrum to form the sacroiliac joints. Together, this structure forms a basin-shaped ring dubbed the bony pelvis or pelvic girdle that connects the axial and the appendicular skeleton.

Each hip bone consists of three bones: the ischium, ilium, and also pubis. The Ilium is the physically largest of the 3 pelvic bones. That is located superiorly loved one to the pubis and also ischium. The is composed of a wing-shaped part called the exceptional ala along with the inferior body. The in salt of the premium ala is referred to as the iliac crest. Anteriorly this crest end at the anterior exceptional iliac spine and also posteriorly at the posterior premium iliac spine. Inferior to these ends will certainly be your inferior equivalents.<1>

The ischium is the inferior posterior part of the hip bone. It is composed of a superior body and also an worse ramus. In ~ the junction posteromedial, the bone has actually a projection called the ischial spine—the concavity in between this spine and also the posterior worse iliac spine native the greater sciatic notch.  The concavity between this spine and inferior ramus is dubbed the lesser sciatic notch.

The pubis is the inferior, anterior portion of the i know good bone. It is composed of a exceptional ramus, body, and also inferior ramus. The superior ramus helps kind the acetabulum. The worse ramus the the pubis fuses with the worse ramus of the ischium. The pubis and ischium together form the obturator foramen. The 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 every side, it develops the sacroiliac joints along with the iliac bone.


Structure and Function

The attributes of the pelvic bones space locomotion, childbirth, and support to the abdominal viscera. It offer to transmit the load from the axial come the lower appendicular skeleton. Likewise, the pelvis bear the weight of the upper body as soon as sitting. The bony structure also provides attachment sites for plenty of abdominal, pelvic, and lower extreme muscles. It also provides attachments sites for external reproductive organs. Additionally, the pelvic girdle serves to defend the pelvic and abdominopelvic viscera.<2>


Embryology

The pelvic bones formation entails a combination of multiple facets which allow articulation that the axial skeleton through the lower extremities. The hip bones (ilium, ischium, and pubis) stay separate but attach via the triradiate cartilage in at an early stage life. ~ above puberty, these bones fuse to kind the acetabulum, a socket ~ above the lateral aspect of the i know good in which the femoral head articulates. 

The lateral bowl mesoderm develops the ilium, ischium, and also the pubis. These bones climate undergo endochondral ossification, comparable to long bones, but an early stage blastemal framework forms, which experience chondrification. Afterward, web page of primary ossification centers form.<3>

The sacrum undergoes this kind of ossification as well.


Blood Supply and Lymphatics

Vascular it is provided to the i know good bones comes from branches that both the external and also internal iliac arteries. Both of these come from the bifurcation of the typical iliac artery, i m sorry bifurcates in ~ the level that L5-S1 vertebral level. The outside iliac artery travels follow me the pelvic brim and gives turn off the inferior epigastric artery and the deep circumflex iliac artery. It then transitions into the femoral artery after ~ passing the inguinal ligament. The interior iliac artery travel posteromedial into the pelvis, i beg your pardon bifurcates into the anterior and also posterior departments of the inner iliac artery. The anterior division includes the umbilical, obturator, inferior vesical, uterine, vaginal, middle rectal, internal pudendal, and inferior gluteal. The posterior department consists the the iliolumbar, lateral sacral, and superior gluteal arteries.<4>

The sacrum obtain blood supply from the lateral sacral and the average sacral arteries. The lateral sacral arteries space a branch that the inner iliac artery. The typical artery is a branch native the aorta after ~ bifurcation right into the internal and external iliac arteries.

The lymphatic mechanism of the pelvis has many contributions and also groups that lymph nodes. The main groups of lymph nodes are the exterior iliac lymph nodes, internal iliac lymph nodes, sacral lymph nodes, and the usual iliac lymph nodes.


Nerves

Innervation the the pelvis has mainly the sacral and also coccygeal plexuses.

The sacral plexus derives from the L4-S4 nerve roots, and it sits on the interior surface of the piriformis muscle—most of the sacral nerves stemming from the sacral plexus leave through the better sciatic notch. The sciatic nerve creates out that the sacral plexus and also can it is in compressed by the muscle, resulting in radicular pain down the leg. This kind of entrapment neuropathy by the compression indigenous the piriformis muscle is called piriformis muscle syndrome.<5><6>

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

The autonomic system likewise provides innervation to the pelvis, which largely courses via the inferior hypogastric plexus. This plexus is made of the nerve yarn from the sympathetic splanchnic nerves, parasympathetic splanchnic nerves, and also hypogastric nerves. The autonomic nerves room travel to the organs via their equivalent splanchnic nerve group.


Muscles

The pelvic bones room an attachment for numerous different muscle teams involving the abdomen, pelvis, perineum, and lower extremities.  The muscles minimal to the pelvis incorporate 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 surface of the pelvis into the lesser sciatic foramen and inserts on the higher trochanter. The muscle receive innervation native the nerve to the obturator internus (L5-S2). It serves together an outside rotator of the hip and also strengthens the i know well joint.

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

The pelvic diaphragm consists of the coccygeus muscles and the levator ani muscles.

The coccygeus muscle is the most posterior and also superior the the pelvic diaphragm muscles. That extends indigenous the ischial spines to affix to the lateral surface of the coccyx and also inferior sacral segment. The innervation comes from branches the the S4 and S5 spinal nerves. It serves together the support for the pelvic viscera and flexes the coccyx.

The levator ani have the right to subdivide into different muscle groups (pubococcygeus, puborectalis, and also iliococcygeus), however margins space ill-defined. These muscle groups expand from the anterior bony surfaces of the pelvis to attach to the perineal body, anococcygeal ligament, and also walls that the viscera near the pelvic floor. The muscles room innervated nerve to levator ani, worse anal nerve, and 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 male pelvis is frequently thicker and also heavier than the lighter and also thinner pelvis the the female. Males additionally tend to have actually a narrower pelvic opening 보다 females.

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


The gynecoid pelvis screens an oval shape with a large transverse diameter. This variant is the many common kind and provides adequate cavity an are for a female to provide birth.  
The android screens a heart-shaped inlet and also is most common in males.
The platypelloid displays a wide inlet transversely but brief in the anterior-posterior axis. This type provides obstacles for a female to offer birth.

Surgical Considerations

The diameter the the pelvic ring is a surgical factor to consider that one OB/GYN need to take into account once planning your patient"s birth. The capability of vaginally carrying a baby is minimal to the anatomical structure of the woman’s pelvis. This anteroposterior diameter that the pelvic inlet should be assessed radiographically or through pelvic examination. A diagonal line conjugate is measure up instead throughout the pelvic examination due to the inability to measure up a true anteroposterior diameter. The distance in between the ischial spines is additionally considered due to the fact that this space is the narrowest part of the pelvic canal. A cesarean ar will be abdominal option if the anatomical structure renders vaginal birth difficult.<9>


Clinical Significance

Fractures of the pelvis are not common, however they regularly involve multiple skeleton of the pelvis or may incorporate the i know good joint. Most pelvic fractures occur due to direct trauma (ex. Automobile accident) or a fall from far-reaching heights. In addition, world with currently osteoporosis are much more prone to fractures that the pelvis.

The severity that the fracture determines the need for surgery. If the pelvis is fractured in multiple places and also is thought about unstable, intervention may be deemed necessary. Certain varieties of fractures might be life-threatening.<10>

Open book fractures once the 2 pubic bones are separated, and also the pelvis is currently anteriorly open. This case can be life-threatening as result of the exposed vessels and also viscera the the pelvis.

Vertical shear fractures occur when the fracture allows half of the pelvis to change upwards. This condition can be dangerous early out to far-reaching blood loss.

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When half the fracture is displaced inwards, lateral to like fractures can likewise represent life-threatening cases involving damages to the vessels and viscera.