Which pelvic bones make up the acetabulum

Sacrospinous ligament, the gemellus superior and the levator ani are inserted on the ischial spine. On the inferior side of ischial spine is the lesser sciatic notch, which contains the obturator internus tendon. The pudendal vessels and nerves pass through this area first exiting the pelvis via grater sciatic notch and then re-entering the pelvis via lesser sciatic notch. The anterior-most border of the iliac bone begins with the anterosuperior iliac spine ASIS , which gives origin to: Fascia Lata.

The iliopsoas muscle passes just medial to AIIS under which lies the iliopectineal eminence. Indirect head of the rectus femoris is attached inferior to AIIS.

The boundaries of obturator foramen is formed by the pubis superiorly, the ischium inferiorly, and the anterior horn of the acetabulum posteriorly.

Medially, the ischial and pubic rami join to form the symphyseal pubic junction. At its supero-lateral border, the obturator duct is present, which is occupied by obturator vessels and nerve. Obturator membrane covers the foramen circumferentially, which is a thick fascial structure.

The integrity of the inguinal ligament and obturator membrane prevents the separation of rami fractures during reduction and fixation of symphyseal plate. The iliosacral joint is a fibrocartilaginous joint that acts as a dual wedge in axial and antero-posterior directions [ 12 , 13 , 14 , 15 ].

It acts as a keystone during the transmission of force to the lower limbs. The joint is supported anteriorly and posteriorly by strong ligaments.

The posterior sacroiliac ligament consists of The superficial part going from the posterior iliac crest and posterior iliac spines to the posterior tubercles of the sacrum made up of several fascicles. The deep portion or interosseous ligament, which is the strongest ligament in the human body. The sacrotuberous ligament connects sacrum to the ischial tuberosity Figure 4. The sacrotuberous and sacrotuberous ligaments.

The sacrospinous ligament connects the border of sacrum and coccyx and sciatic spine deep to sacrotuberous ligament. This ligament divides the ischial area into two foramens: The Greater Sciatic Foramen: contains the piriformis muscle, superior glutei nerves, sciatic nerve, ischial vessels, and internal pudendal vessels and nerve.

The Lesser Sciatic Foramen: contains the obturator internus muscle and internal pudendal vessels. These structures exit the pelvis via greater sciatic foramen and after crossing over the sacrospinous ligament re-enters the pelvis via lesser sciatic foramen [ 13 , 14 , 15 ]. The aorta bifurcates in the lower peritoneal region into the common iliac arteries. The common iliac artery is begins at around L4 and divides at around the L5—S1 junction into the external and internal iliac arteries.

The internal iliac artery also known as hypogastric artery, branches to form the superior and inferior gluteal vessels, the obturator, the pudendal, and the coccygeal, the sacral and vesicular vessels.

The internal pudendal artery exits the pelvis underneath the piriformis and re-enters the pelvis through the lesser sciatic notch and terminates as the dorsal artery of the penis and clitoris and cavernous artery [ 16 , 17 ]. The external iliac artery just proximal to the inguinal ligament branches to form the femoral artery.

The femoral artery has three rami: urethral inferior, epigastric and iliac circumflex. The epigastric travels deep and then anastomoses with obturator vessels. The corona mortis is the anomalous connection between epigastric and obturator vessels. It can cause fatal bleeding if not identified and ligated during surgery [ 17 , 18 ] Figure 5.

Corona mortis artery. The Lumbar plexus consists of the first three lumbar anterior rami and a portion of the anterior ramus of the fourth lumbar nerve.

There are also short collateral rami, which include the hypogastric, ilioinguinal, genitofemoral, and lateral femoral cutaneous nerve. Femoral and obturator nerves are the terminal rami of lumbar plexus. The obturator nerve receives contributions from the L2, L3, and L4 trunks.

It continues into the pelvis underneath the iliopectineal line, reaches the obturator orifice. It exits the pelvis together with the obturator vessels. The femoral nerve receives contributions from the L2, L3, and L4 trunks [ 19 , 20 , 21 ]. The Sacral Plexus is formed by the coalescence of the lumbosacral trunk L5 anterior ramus with L4 anastomotic ramus and the anterior rami of the first four sacral roots.

The plexus ultimately becomes the sciatic nerve posterior tibial and peroneal nerve. The posterior branches relevant to orthopedic surgery are the superior gluteal nerve, branches to the external rotators and inferior gluteal nerve. The sciatic nerve exits the greater sciatic notch. The other variants include penetration and splitting around the muscle.

After exiting through greater sciatic notch, it courses behind the obturator internus, under the gluteal sling to enter the thigh. The sciatic nerve is a vital structure that is encountered during posterior approaches to the acetabulum. Due to proximity of sciatic nerve and its branches to the posterior part of acetabulum, fractures and dislocations in this area have very high incidence of sciatic nerve injury.

Most common to be involved is the peroneal division of sciatic nerve [ 21 , 22 ] Figure 6. The greater sciatic notch is divided by the piriformis.

The classification and subsequent treatment of acetabular fractures are based on imaging studies that have been derived from a thorough understanding of the anatomy of the innominate bone [ 17 , 18 , 19 ].

These columns are connected to the sacroiliac articulation by a thick strut of bone lying above the greater sciatic notch known as the sciatic buttress. The radiographic anatomy of the acetabulum can be determined using AP pelvis and two degree oblique radiographs as proposed by Judet and Letournel.

Therefore, three radiographic projections of the pelvis that are used to evaluate the fractures of acetabulum are as follows: The antero-posterior view of the pelvis. These plain films are interpreted based on the understanding of normal radiographic landmarks of the acetabulum, and disruption of these landmarks represents a fracture involving that portion of the bone.

They are generated by the tangency of the applied x-ray beam to a region of cortical bone. There are six basic landmarks Figure 7 Iliopectineal line. Radiographic landmarks on AP radiograph of hip. The Iliopectineal Line is the major landmark of the anterior column.

The pelvic brim is represented by anterior three-quarters of the iliopectineal line. The posterior quarter of this line is formed by the tangency of the x-ray beam to the internal cortical surface of the sciatic buttress and the internal part of the roof of the greater sciatic notch.

The Ilioischial Line is considered a radiographic landmark of the posterior column. It is formed by the tangency of the x-ray beam to the posterior portion of the quadrilateral surface.

The Radiographic Tear drop is not a true anatomic structure. It represents a radiographic finding and consists of a medial and lateral limb. The lateral limb represents the inferior aspect of the anterior wall in the acetabulum whereas the medial limb is formed by the obturator canal and the antero inferior portion of the quadrilateral surface.

Dissociation of the teardrop and the ilioischial line indicates a fracture of the quadrilateral surface. The Roof of the Acetabulum is a radiographic landmark that results from the tangency of the x-ray beam to a narrow portion of the subchondral bone of the superior acetabulum. Dissociation of the radiographic line of the roof indicates a fracture involving the superior acetabulum. The Anterior Rim of the Acetabulum represents the lateral margin in the anterior wall of the acetabulum and is contiguous with the inferior margin of the superior pubic ramus.

The anterior rim is typically medial to the posterior rim and has a characteristic undulation in its midcontour in the AP pelvis view. The Posterior Rim of the Acetabulum represents a lateral margin in the posterior wall of the acetabulum. Inferiorly, the posterior rim is contiguous with the thickened condensation of the posterior horn of the acetabulum and approximates a straight line, being more vertical than the anterior wall.

This view is obtained by rotating the patient so that the injured hemipelvis is tilted 45 degrees away from the x-ray beam. Structures visible on this view are greater and lesser sciatic notches, anterior rim of acetabulum and iliac wing in its largest dimension.

This is the best view to see the fractures involving posterior column. Fractures of the anterior column traversing the iliac wing can also be detected.

This view is obtained by rotating the patient so that the injured hemipelvis is rotated 45 degrees toward the x-ray beam. This view shows the obturator foramen in its largest dimension and profiles the anterior column.

The posterior rim of the acetabulum is best visualized in the obturator oblique view. Posterior subluxation of femoral head can be detected by comparing the relationship of the femoral head with the posterior wall on the normal hip and the injured hip on the obturator oblique view.

A dislocated hip will become more obvious in the obturator oblique view, and this view has been advocated for routine evaluation of all posterior fracture dislocations of the hip joint. It is prudent not to delay the reduction of a known dislocated hip Figure 8. A obturator oblique view and B iliac oblique view. Dynamic stress views under general anesthesia have also been used in acetabular fractures.

They serve as a clinical measure of dynamic stability and congruence of the hip thus helps in assessing the need for operative treatment in small and intermediate fractures of the posterior acetabular wall.

This stress examination is most applicable to the fractures of posterior wall. Each fracture pattern in the classification of Letournel and Judet has typical radiographic characteristics. These fracture patterns are described with respect to the disruption or intactness of the radiographic landmarks. In the operating room, the three standard views can be obtained with fluoroscopy. This problem is compounded, because as human pelvises became smaller, the heads of infants became larger to accommodate increased brain size.

Since the pelvis is vital for both efficient locomotion and childbirth, natural selection has been forced to strike a compromise between a wide pelvis to facilitate birthing large-brained infants and having a narrow pelvis to increase locomotive efficiency. This compromise has been referred to as the obstetrical dilemma. Thus, the female pelvis has evolved to be as wide as possible, to make childbirth easier, without becoming so wide as to make bipedal locomotion too inefficient.

Additionally, the female pubic symphysis, which is the cartilaginous joint connecting the left and right side of the pelvis, is remodeled by hormones released during pregnancy, allowing it to stretch during childbirth. Male pelves are not constrained by the issue of childbirth, and thus are narrower and more optimal for bipedal locomotion.

Wider hips in females cause an increased valgus angle, which is the angle between the femur and lower leg. This increases the risk of torsional knee injuries. The Male Pelvis : The male pelvis is narrower than that of the female, as can be seen by the less than 90 degree angle of the pubic arch. The Female Pelvis : The female pelvis is wider than that of the male, as can be seen by the greater than 90 degree angle of the pubic arch.

Privacy Policy. Skip to main content. Skeletal System: Parts of the Skeleton. Search for:. The Hip. Ilium The ilium is the uppermost and largest bone of the pelvis. Learning Objectives Describe the ilium. Key Takeaways Key Points The ilium articulates with the ischium, sacrum, and pubis. The ilium is divisible into the body and the ala, or wing. The body and ala are separated by the arcuate line on the posterior surface and the margin of the acetabulum on the inferior surface.

The iliac crest is on the upper margin of the ala. The external surface of the ilium is partly articular relating to a joint and partly non-articular. Bi-iliac width is an anatomical term referring to the widest measure of the pelvis between the outer edges of the upper iliac bones. Key Terms acetabulum : A concave structure formed from three bones in the pelvis that articulates with the femoral head to form the hip joint.

It consists of hip bone, sacrum, and coccyx. Ischium The ischium forms the lower and posterior portion of the hip bones of the pelvis.

Learning Objectives Describe the ischium. Key Takeaways Key Points The ischium articulates with the ilium and the pubis.

The ischium is divided into the body, superior ramus of the ischium, and inferior ramus of the ischium. The ischial tuberosity, which supports weight when sitting, is located on the ischium.

Key Terms ischium : The most inferior of the three bones that make up each side of the pelvis. Pubis The pubis is the lowest and most anterior portion of the hip bones of the pelvis. Learning Objectives Describe the pubic bone. Key Takeaways Key Points The most anterior portion of the pubis, the pubic symphysis, is where the two hip bones of the pelvis are fused together.

The pubis has a body, a superior ramus, and an inferior ramus. The body of the pubis contributes to the lunate surface and acetabular fossa in the acetabulum. Key Terms pubic symphysis : A cartilaginous joint between the two bones of the pubis.

False and True Pelves The false greater pelvis is larger and superior to the true lesser pelvis where the pelvic inlet is located. Learning Objectives Describe the differences between false and true pelves. Key Takeaways Key Points Some believe that the false pelvis is actually part of the abdominal cavity and therefore that the true pelvis is the only true portion of the pelvis. The true pelvis contains the pelvic inlet and is a short, curved canal, deeper on its posterior than on its anterior wall.

The false pelvis supports the intestines specifically, the ileum and sigmoid colon and transmits part of their weight to the anterior wall of the abdomen. Key Terms true pelvis : Bounded in front and below by the pubic symphysis and the superior rami of the pubis; above and behind, by the sacrum and coccyx; and laterally, by a broad, smooth, quadrangular area of bone, corresponding to the inner surfaces of the body and superior ramus of the ischium, and the part of the ilium below the arcuate line.

Comparison of Female and Male Pelves The female pelvis has evolved to its maximum width for childbirth and the male pelvis has been optimized for bipedal locomotion. Learning Objectives Apply the diagnostic criteria to determine whether a pelvis is male or female.

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Edit article. View revision history Report problem with Article. Citation, DOI and article data. Bannai, M. Reference article, Radiopaedia. URL of Article. Gross anatomy All three bones of the pelvis the ilium , ischium , and pubis together form the acetabulum. The column principle The column principle divides the acetabulum into the anterior and posterior columns and becomes important when considering acetabular fractures and their management.

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