Description

This video is about the pelvis and hip bone.

What is the Pelvis?
The pelvis is the ring-like bony structure connecting the spine to the lower limbs. Consists of the right hip bone, left hip bone, and sacrum. These form the bony pelvis, which is divided into:

Greater pelvis (false pelvis) – Located above the pelvic brim; supports abdominal organs.
Lesser pelvis (true pelvis) – Located below the brim; contains pelvic and urogenital organs.

The pelvic inlet is marked by the linea terminalis

Diameters:

Transverse diameter – Widest horizontal span, ~13 cm.
Oblique diameter – From sacroiliac joint to iliopectineal eminence, ~13.5 cm.
Anatomical conjugate – From sacral promontory to pubic symphysis, ~11–12 cm.

Hip Bone Anatomy

Ilium (Os ilium)

Iliac crest (Crista iliaca) – Palpable ridge; muscle attachment site.
Anterior superior iliac spine (Spina iliaca anterior superior) – Sartorius, inguinal ligament attachment.
Anterior inferior iliac spine (Spina iliaca anterior inferior) – Rectus femoris origin; iliofemoral ligament.
Posterior superior iliac spine (Spina iliaca posterior superior) – Posterior attachment for ligaments and fascia.
Posterior inferior iliac spine (Spina iliaca posterior inferior) – Landmark at posterior ilium border.
Iliac tubercle (Tuberculum iliacum)
Iliac fossa (Fossa iliaca) – Origin of iliacus muscle.
Arcuate line (Linea arcuata) – Internal ridge, part of pelvic brim.
Iliac tuberosity (Tuberositas iliaca) – Roughened area for sacroiliac ligament.
Auricular surface (Facies auricularis) – Articulates with sacrum at sacroiliac joint.
Gluteal surface (Facies glutea) – Outer surface for gluteal muscle origin.
Posterior gluteal line (Linea glutea posterior) – Between gluteus maximus and medius origin zones.
Anterior gluteal line (Linea glutea anterior) – Separates medius and minimus origins.
Inferior gluteal line (Linea glutea inferior) – Marks lower origin of gluteus minimus.
Supra-acetabular groove (Sulcus supraacetabularis) – Origin of reflected head of rectus femoris.

Ischium (Os ischii)

Ischial tuberosity (Tuber ischiadicum) – Origin for hamstrings and ligament attachments.
Ischial spine (Spina ischiadica) – Landmark between sciatic notches.
Greater sciatic notch (Incisura ischiadica major) – Becomes foramen via sacrospinous ligament.
Lesser sciatic notch (Incisura ischiadica minor) – Converted to foramen by sacrotuberous ligament.
Body of ischium (Corpus ossis ischii) – Forms lower part of acetabulum.
Ramus of ischium (Ramus ossis ischii) – Fuses with inferior pubic ramus; supports obturator foramen.

Pubis (Os pubis)

Pubic tubercle (Tuberculum pubicum) – Inguinal and superior pubic ligament attachment.
Pubic crest (Crista pubica) – Rectus abdominis and pyramidalis origin.
Symphysial surface (Facies symphysialis) – Forms pubic symphysis with opposite pubis.
Pecten pubis (Pecten ossis pubis) – Pectineus muscle origin, part of pelvic brim.
Obturator crest (Crista obturatoria) – Defines obturator canal path.
Superior pubic ramus (Ramus superior ossis pubis) – Forms upper part of obturator foramen.
Inferior pubic ramus (Ramus inferior ossis pubis) – Fuses with ischial ramus.

Acetabulum

Acetabular margin (Margo acetabuli) – Rim of the socket.
Acetabular notch (Incisura acetabuli) – Incomplete area bridged by ligament.
Lunate surface (Facies lunata) – Articular surface for femoral head.
Acetabular fossa (Fossa acetabuli) – Non-articular central depression.

Articulations & Ligaments

Sacroiliac joint (Articulatio sacroiliaca) – Between sacrum and ilium; strong ligamentous support.
Pubic symphysis (Symphysis pubica) – Fibrocartilaginous joint at midline.
Posterior sacroiliac ligament (Lig. sacroiliacum posterius) – Stabilizes posterior SI joint.
Anterior sacroiliac ligament (Lig. sacroiliacum anterius) – Supports anterior capsule.
Interosseous sacroiliac ligament (Lig. sacroiliacum interosseum)
Sacrotuberous ligament (Lig. sacrotuberale) – Converts sciatic notch to foramen.
Sacrospinous ligament (Lig. sacrospinale)
Superior pubic ligament (Lig. pubicum superius)
Inferior pubic ligament (Lig. pubicum inferius)
Obturator membrane (Membrana obturatoria)

Sources:
• Kozlowski, T. (2017). Memorix Anatomy, 2nd ed.
• Standring, S. (2020). Gray’s Anatomy, 42nd edition
• Tubbs RS, Shoja MM, Loukas M. (2016). Bergman’s Encyclopedia of Human Anatomic Variation
• White TD, Folkens PA. (2005). The Human Bone Manual

Programs used: Complete Anatomy, Biorender, PowerPoint

Transcript

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This is your hip bone.
It has all these parts,

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and surface landmarks, that serve as muscle
attachments, pathways for nerves and vessels,

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and protection for the organs inside your pelvis.
The hip bone is the first topic

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in our lower limb skeletal series.
So in this video, we’re going to go through what

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is considered the pelvis, the pelvic planes, and
then break down all three parts of the hip bone,

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their surfaces and landmarks. Then we’ll talk a
little bit about the articulations around, like

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the sacroiliac joint, pubic symphysis and so on.
What’s up everyone, my name is Taim. I’m a medical

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doctor, and I make animated medical lectures to
make different topics in medicine visually easier

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to understand. If you’d like a PDF version
or a quiz of this presentation, you can

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find it on my website, along with organized
video lectures to help with your studies.

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Alright, let’s get started.
So what is the Pelvis?

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Think of the pelvis as the central bridge between
your spine and your lower limbs. Anatomically,

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the pelvis consists of three bones. The right
hip bone, the left hip bone, and the sacrum.

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Together, these three bones form the bony pelvis.
But there’s an anatomical concept that helps us

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make sense of this area, and that is the linea
terminalis, or also known as pelvic brim. This

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is a curved bony ridge that loops from the sacral
promontory at the back, along the arcuate line of

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the ilium, down to the pecten pubis, and
ends at the top of the pubic symphysis.

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This ridge forms the pelvic inlet. Everything
above the pelvic inlet is referred to as the

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greater pelvis, which is also called false
pelvis. It supports abdominal organs like the

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small intestine and sigmoid colon. Everything
below the inlet, is called the lesser pelvis,

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also known as the true pelvis, and it contains
the bladder, reproductive organs, and rectum.

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Now, if we cut the pelvis right about here, and
look at it from this view, we’ll see this sagittal

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view, as you see here the pelvic inlet starts from
the sacral promontory, curves along the arcuate

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line of the ilium, and goes all the way towards
the superior border of the pubic symphysis.

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Why am I babbling about this before I talk
about the hip bone anatomy? Let me explain.

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This opening is clinically important, especially
in obstetrics, because it defines the entrance

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to the true pelvis, the space a fetus must pass
through during vaginal delivery. And to assess if

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that passage is even possible, we study a set of
diameters of the pelvic inlet. These dimensions

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are part of standard obstetric evaluation, they
help estimate whether labor is likely to progress

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normally or if a C-section might be required.
Now, I’ll go through some of the important ones

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here, and I’ll cover them in more
detail in the PDF written version

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that goes along with this video.
First is the transverse diameter,

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this is the widest horizontal span of the pelvic
inlet. It goes from one side of the pelvic brim

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to the other, and it’s usually about 13
centimeters in an average female pelvis.

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Next is the oblique diameter, it runs diagonally,
from the sacroiliac joint on one side to the

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iliopectineal eminence on the
opposite side. Its length is

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slightly longer, roughly 13.5 centimeters.
And then there’s the anatomical conjugate, which

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is the straight line from the sacral promontory
to the upper border of the pubic symphysis.

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This one’s critical, because it reflects the
anteroposterior diameter of the pelvic inlet. It

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typically measures around 11 to 12 centimeters.
But clinically, we often estimate the obstetric

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conjugate instead, since the anatomical conjugate
can’t be measured directly during a pelvic exam.

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Now if we look from underneath, from the inferior
view, we can see another important boundary,

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and that’s the pelvic outlet. This is the
lower opening of the true pelvis. What’s

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really interesting about the pelvic outlet
is that it’s divided into two triangles. The

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urogenital triangle at the front, and the
anal triangle at the back. These triangles

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aren’t just shapes for your visual memory,
they reflect the orientation of muscles,

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fascia, and clinical zones. For example, when a
woman is giving birth, sometimes a surgical cut

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has to be done to enlarge the vaginal opening and
facilitate delivery, this is called episiotomies.

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And this is performed in the perineal region
that lies right across these triangles.

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So, that’s the pelvis, it’s the bony ring
formed by the right and left hip bones and

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the sacrum, divided into a greater
and lesser part by the pelvic brim,

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and functionally defined by its inlet and outlet.
Now let’s go ahead and isolate the hip bone.

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The hip bone itself consists of three
fused parts, the ilium, the pubis,

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and the ischium. Let’s go through the major
landmarks of each, starting with the ilium.

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The ilium is generally divided into the
Ala of the ilium, and the body. Ala is

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the wing of the ilium, and the body is
the smaller caudal part of the ilium.

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Right here at the top, we have this broad,
curved edge we call the iliac crest. This is

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the one that’s easily palpable on the sides
of your hips. If we trace the crest forward,

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we get to the anterior superior iliac spine.
And this spine serves as attachment site for

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the tensor fasciae latae, sartorius muscle, and
the inguinal ligament. This is also the landmark

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we use when measuring leg length clinically.
If we rotate the ilium to the back,

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we now see the posterior aspect of the iliac
crest. What’s fascinating here is that the

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crest is divided into three zones, the outer
lip, the intermediate zone, and the inner lip.

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Why do we bother naming these? Because different
muscle groups attach to different parts of this

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crest. And you can see here, for example, how
the abdominal muscles sit on distinct regions.

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The external oblique inserts on the outer lip, the
internal oblique anchors to the intermediate zone,

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and the transversus abdominis, the deepest
of the three, originates from the inner lip.

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Other examples are the thoracolumbar fascia which
attaches medially, blending with the inner lip

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as it anchors into the lumbar spine. We can see
the gluteus maximus attaching to the outer lip,

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while the gluteus medius sits a bit higher up on
the gluteal surface but still near the crest. And

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there is the tensor fasciae latae which continues
its course along the anterior part of the iliac

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crest, blending into the iliotibial tract.
So that was the crest.

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Another structure we can appreciate along
the crest is the tuberculum of the iliac

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crest. It serves as the thickest part of the
crest and it’s actually where the iliotibial

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tract attaches. I talked about these muscles
in the video about the muscles of the thigh.

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If we now look posteriorly, we can see
the posterior superior iliac spine. Just

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below that is the posterior inferior iliac
spine. Both of these spines contribute to

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the posterior border of the auricular surface,
but if we now rotate back to the anterior view.

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Just below the anterior superior iliac spine,
we’ve got the anterior inferior iliac spine.

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This serves as the origin point for the rectus
femoris muscle, one of the quadriceps muscles.

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It’s also the site where part of the iliofemoral
ligament attaches, which is a crucial stabilizer

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of the hip joint that resists hyperextension.
Just medial to that, we see the iliac fossa.

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This broad surface is where the iliacus muscle
originates. You can see how it sits right in the

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fossa, joining with the psoas major further down
to form the iliopsoas, the strongest hip flexor.

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If we follow along the inner surface, there’s
a curved bony ridge known as the arcuate line.

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This marks the boundary between the ala
and the body of the ilium, and forms part

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of the pelvic brim we talked about earlier.
Just behind this area is the iliac tuberosity,

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a roughened patch of bone where the strong
ligaments of the sacroiliac joint attach.

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Directly below it is the auricular surface,
shaped like an ear, and this is the actual

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articular surface that connects with the sacrum.
Now if we go back to the posterior view again,

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this broad outer surface of the ilium is called
the gluteal surface. And there are three lines

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running across this surface, the posterior gluteal
line, the anterior gluteal line, and the inferior

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gluteal line. The reason we have these is because
this this is where the gluteal muscles originate,

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gluteus maximus, medius, and minimus. And
to help us map out their zones of origin,

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we have three lines running across this surface
The posterior gluteal line separates the area

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where the gluteus maximus originates from
that of the gluteus medius. The anterior

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gluteal line marks the border between
gluteus medius and gluteus minimus. And

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the inferior gluteal line defines the lower
boundary of where gluteus minimus arises.

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Another landmark in this region that we can
point out is the supra-acetabular groove.

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This little depression just above the
acetabulum serves as the origin point

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for the reflected head of rectus femoris.
And that brings us to the acetabulum, the

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socket of the hip joint. It’s composed of several
parts. The acetabular margin forms the rim,

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and at the bottom you have the acetabular notch,
which remains incomplete until bridged by the

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transverse acetabular ligament. The lunate surface
is the curved, articular part that the femoral

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head actually contacts, and the acetabular fossa
is the central, non-articular area filled with fat

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and the ligament of the head of the femur. All of
these help form the hip joint, where the head of

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femur goes right within the acetabulum.
So that was everything we are going to

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cover for the ilium.
Now, let’s move on to

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the next part of the hip bone, the pubis.
The pubis is divided into three main parts, the

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superior pubic ramus, the body, and the inferior
pubic ramus. Let’s start here with the body.

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On the anterior surface of the body, we can find
the pubic tubercle. This small projection serves

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as an important attachment point for both the
inguinal ligament and the superior pubic ligament.

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Just medial to the tubercle is the pubic crest,
and right next to it is the symphysial surface.

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The pubic crest is a ridge that provides insertion
for the rectus abdominis, and just lateral to

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that, origin for the pyramidalis muscle. The
symphysial surface, the flat articular area,

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contributes to the pubic symphysis, which
unites the two pubic bones at the midline.

0:10:08.240,0:10:13.600
Running along the upper border of the superior
pubic ramus is the pecten pubis, also known as

0:10:13.600,0:10:19.280
the pectineal line. This surface is the origin
of the pectineus muscle, and it’s also where

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both the lacunar ligament and pectineal ligament
are found. If you wanna know more about them,

0:10:24.160,0:10:29.520
see my topography of the hip video, so we can
focus on the bony landmarks in this video.

0:10:29.520,0:10:33.520
If we rotate the view a bit,
we can see the obturator crest,

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which is this raised bony margin just above
the obturator foramen. The obturator crest

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helps define the path for the obturator nerve
and vessels, which pass through a small opening

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in the obturator membrane, that’s the fibrous
sheet covering most of the obturator foramen.

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So, that was all the structures
I wanted to show for the pubis.

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Let’s now move on to the next
part, which is the ischium.

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The ischium consists of two parts, the body
and the ramus of the ischium. And here,

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from the medial view, you can see that the body
of the ischium is quite large. It spans the

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upper portion and forms part of the acetabulum.
One of the first landmarks we should highlight

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here is the ischial tuberosity. This is a really
important surface because it serves as a common

0:11:16.880,0:11:22.400
origin or insertion for multiple muscles and
ligaments. These include the sacrotuberous

0:11:22.400,0:11:28.160
ligament, ischiofemoral ligament, and several
muscles, semitendinosus, semimembranosus,

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long head of biceps femoris, adductor
magnus, quadratus femoris, and inferior

0:11:33.040,0:11:38.560
gemellus. So when you hear someone say that the
hamstrings originate from the ischial tuberosity,

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this is the exact spot they’re talking about.
In this same region, we can also identify the

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lesser sciatic notch, the greater sciatic notch,
and the ischial spine that sits between them.

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These are part of the topographical landscape
of the posterior pelvis. I go over this in

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more detail in the video on pelvic topography,
but the key idea is that these structures are

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transformed by ligaments, the sacrotuberous and
sacrospinous ligaments, into two passageways:

0:12:06.160,0:12:11.520
the greater sciatic foramen and the lesser
sciatic foramen. These foramina are gateways

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for important nerves and vessels that
travel to and from the gluteal region.

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Alright, so that was everything I
wanted to cover for the ischium.

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Now, the last thing I wanted to talk
about are the articulations of the pelvis.

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The first one is the sacroiliac joint. This
joint is formed between the auricular surface

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of the sacrum and the auricular surface of
the ilium. These surfaces interlock tightly,

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and the joint is surrounded by a short but
extremely strong capsule. It’s further reinforced

0:12:42.480,0:12:47.680
by several ligaments. The main ones you’ll see
here are the posterior sacroiliac ligament and

0:12:47.680,0:12:54.160
the anterior sacroiliac ligament, but there’s
also a deep interosseous sacroiliac ligament.

0:12:54.160,0:12:58.880
This last one sits between the bones and is one
of the strongest ligaments in the entire body,

0:12:58.880,0:13:03.680
it plays a role in stabilizing
the sacroiliac joint under load.

0:13:03.680,0:13:09.440
The next articulation is right here, the pubic
symphysis. This is a cartilaginous joint that

0:13:09.440,0:13:14.960
unites the two pubic bones at the midline.
It’s supported by the superior pubic ligament,

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running across the top, and the inferior pubic
ligament, down here at the bottom. These ligaments

0:13:20.640,0:13:26.000
work together to provide stability during
movements like walking and changes in posture.

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Other important ligaments in the region include
the sacrotuberous ligament and the sacrospinous

0:13:31.040,0:13:35.840
ligament. These were mentioned earlier, but
just to recap, they span between the sacrum

0:13:35.840,0:13:40.720
and the ischium, and they help convert the
greater and lesser sciatic notches into the

0:13:40.720,0:13:45.840
greater sciatic foramen and the lesser sciatic
foramen, respectively. Forming passageways

0:13:45.840,0:13:52.400
for structures entering or leaving the pelvis.
Lastly, let’s not forget the obturator membrane,

0:13:52.400,0:13:56.320
which spans most of the obturator
foramen, leaving just a small canal

0:13:56.320,0:14:00.560
called the obturator canal, through which
the obturator nerve and vessels pass.

0:14:00.560,0:14:05.040
So that wraps up everything I wanted to
cover about the pelvis and hip bone. I

0:14:05.040,0:14:08.480
really hope all of that made sense.
The next video is going to be about

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the joint that sits right about in this area, the
hip joint. So if you want to learn more about how

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the femur interacts with the acetabulum and what
ligaments and movements are involved, go ahead and

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click on the next video, and I’ll see you there.
If you want a handmade PDF version of this

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lecture, take a quiz to test your knowledge,
or access an organized list of all my videos,

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you can find everything on my website.
Thanks for watching! See you in the next one.