Pelvic cavity - Pelvic cavity - Wikipedia

Good afternoon Today's topic is a clear synergy between basic and clinical sciences. Normal anatomy will serve as a fundamental science today, and obstetrics as a clinical science.

It is obstetricians, more than anyone else, who understand how important it is to be able to correctly determine the size of the pelvis. After all, two lives directly depend on this - the mother’s and the baby’s. It is critically important to be able to compare the key dimensions of the fetus (we will talk about them in the following articles) and the dimensions of the pelvis.

Basic information about the anatomy of the pelvis

The pelvis (pelvis) is a bony structure that houses many organs of the digestive and reproductive systems, main arteries and important nerve trunks. The pelvis also plays a huge role as a component of the musculoskeletal system, because the pelvis is also the girdle of the lower extremities. The term “pelvis” often includes muscles, ligaments, fascia and other structures that strengthen the bony base of the pelvis.

In obstetrics, the pelvis plays a crucial role, because during the birth process the fetus must move from the abdominal cavity to the outside world, and this movement takes place through the pelvis.

The bony basis of the pelvis is made up of two pelvic bones (os coxae) and the sacrum (os sacrum) with the coccyx, which connect the pelvic bones and form the pelvic cavity. If we look at the illustration it will be a little clearer.

This is the pelvis:

Here I have highlighted the sacrum and coccyx in blue, and the paired pelvic bones in yellow:

In front, the pelvic bones articulate with the help of a fibrocartilaginous disc, the interpubic disc (discus interpubicis). I've highlighted it in bright red:

Each of the pelvic bones (which are yellow) consists of three more bones - the pubis (os pubis), the ischium (os ishiaticus) and the ilium (os ilium). Let's look at a single pelvic bone:

Under the letter “A” we see the inner surface of the pelvic bone, under the letter “B” we see the outer surface. I really like this illustration from Sinelnikov’s atlas because all three bones that form the pelvic bone are clearly visible here. The ilium is painted light yellow, the pubic bone is light brown, and the ischium is light green.

The bodies of the three bones fuse to form the acetabulum, which forms the hip joint with the head of the femur. The branch of the pubis connects with the branch of the ischium and together they form the obturator foramen (foramen obturatorium). I highlighted the acetabulum in red and the obturator foramen in blue.

We will also be interested in the wing of the ilium (ala ossis ili) and the innominate (aka terminal) line (linea innominata). The innominate line, passing along the wing of the ilium, will be called the arcuate line (linea arcuata). We can see the nameless and arcuate lines only from the inside.

These are important formations for us, so I decided to highlight them in a separate picture. I highlighted the wing of the ilium in bright red, the arcuate line in blue, and the continuation of the arcuate line into the innominate line on the pubic bone in yellow.

We also need to know where the promontory of the sacrum (promontorium) is located. This is the most forward part of the pelvic surface of the sacrum. This part is located in close proximity to the place where the sacrum meets the lumbar spine.

Structure

Pelvis
The pelvis has an anterior lower, posterior and two lateral pelvic walls; and the lower wall of the pelvis, also called the pelvic floor.[2][3] The parietal peritoneum is attached here and to the abdominal wall.[4]

Small pelvis

The small pelvis (or “true pelvis”) is the space limited by the pelvic girdle and below the edge of the pelvis: between the entrance to the pelvis and the pelvic floor. This cavity is a short, curved channel, deeper on its posterior wall than on its anterior wall.[1] A little [ WHO?

] Consider this area the entire pelvic cavity.
Others[ WHO?
] define the pelvic cavity as the larger space, including the greater pelvis, just above the entrance to the pelvis.

The small pelvis is limited in front and below by the pubic symphysis and the superior branch of the pubis; above and behind the sacrum and coccyx; and on the side - a wide smooth quadrangular part of the bone corresponding to the inner surface of the body and the upper branch of the ischium, and the part of the ilium below the arcuate line.[1]

The pelvis contains the pelvic colon, rectum, bladder, and some of the genitals. rectum at the back, in the bend the sacrum and coccyx; bladder in front, pubic symphysis behind. In the female, the uterus and vagina occupy the space between these viscera.[1]

The pelvic splanchnic nerves arising in the area S2-S4 are located in the small pelvis.

Big pelvis

The large pelvis (or “false pelvis”) is the space limited by the pelvic girdle above and in front of the edge of the pelvis. It is bounded on both sides by the ilium; in front it is incomplete, with a wide gap between the anterior borders of the ilia, which is filled with muscles and fascia of the anterior abdominal wall; behind - a deep notch on both sides between the ilium and the base of the sacrum which is filled with the thoracolumbar fascia and associated muscles.[1]

It is usually considered part of the abdominal cavity (hence why it is sometimes called the false pelvis).[6] A little [ WHO?

] consider this region to be part of the pelvic cavity,[
citation needed
] while others reformulate the classification issue as the combination abdomen and pelvis.

The large pelvis supports the intestines (specifically the ileum and sigmoid colon), and transfers some of its weight to the anterior wall of the abdominal cavity.[1]

The femoral nerve from L2-L4 is found in the pelvis but not in the pelvis.

Ligaments

Arteries

• internal iliac artery
• median sacral artery
• ovarian artery

Nerves

• sacral plexus
• splanchnic nerves
• femoral nerve (large pelvis)

Sections of the pelvis

There are two sections of the pelvis - large and small. They are not separated by any tangible membrane, diaphragm or other formations. Organs that are located in the pelvic cavity can move higher - for example, a full bladder changes its location, the uterus during pregnancy also stretches and shifts. However, for calculations and a more accurate idea of ​​the topography of organs and vessels, the pelvis is usually divided into large and small.

If you pick up a specimen of a whole pelvis, you, without knowing a single anatomical structure, will most likely correctly show the boundary of the division of the large and small pelvis. Let's try to do this with illustrations.

The border dividing the small pelvis runs from the promontory of the sacrum along the arcuate lines of the wings of the ilium, then along the crests of the pubic bones (forming the innominate line), and finally converges at the upper inner edge of the pubic symphysis.

Look, it's very simple:

Accordingly, everything that is higher is the large pelvis, everything that is lower is the small pelvis. You have probably heard the phrases “pelvic ultrasound”, “pelvic organs”. So, the organs that are located in the pelvis in women include:

• Uterus
• Ovaries
• Fallopian tubes
• Bladder
• Rectum;
• Vagina.

In men, the pelvic organs are:

• Bladder
• Rectum
• Prostate.

Dimensions of a large pelvis

In general, the large pelvis is not the main object of study for an obstetrician. It is much more important to get as much information as possible about the small pelvis. The fetus will definitely be able to push through the large pelvis, but what will happen in the small pelvis is the most important problem.

However, it is simply necessary to know the four sizes of the large pelvis, because they can indirectly be used to judge the size of the small pelvis. Let's look at these sizes.

Distantia spinarum

Distantia spinarum is the distance between the right and left spina iliaca anterior superior. Don't know what it is? Ho-ho, you probably don’t visit my website very often, because I periodically, in different topics, touch on this anatomical formation. Look, on the wing of the ilium there are two protrusions in front and behind. These are the awns, in front - the anterior upper and anterior lower, in the back - the posterior upper and posterior lower. We are now interested in the anterior superior spine, let's mark it on the right and left:

This spine protrudes very well just under the skin. You can definitely feel it if you step back a couple of centimeters from the navel and then move laterally, towards the edge of the body.

The spina iliaca anterior superior is a rather important anatomical formation. The sartorius muscle begins from this spine, the upper edge of the inguinal ligament is attached to it, it is a reference point for a bunch of operations on the abdominal organs and much more.

So, to get distantia spinarum, we just need to measure the distance between these two spines. This size usually falls within the range of 25-26 cm.

Pay attention to the clue in the name itself - spinarum comes from the word spina (iliaca). By the name alone you can guess where this size is carried out.

Distantia cristarum

Now let's move back a little from our spina iliaca anterior superior. We will move along the upper edge of the iliac wing. By the way, the upper edge is called the iliac crest (crista iliaca), it is slightly thickened and rounded. Let's mark it:

As you understand, the front edge of the crista iliaca is the spina iliaca anterior superior, with which we measured the previous size.

To measure distantia cristarum, we need to select the most distant areas of the crista iliaca on both pelvic bones. In our case, it's something like this:

Accordingly, distantia cristarum will be measured here:

On average, distantia cristarum is 28-29 cm.

Distantia trochanterica

This size very roughly refers to the size of the pelvis. In many textbooks and in many departments, apparently observing traditions, distantia trochanterica is included in the dimensions of the pelvis, however, the values ​​​​changed here have no special relation to the pelvis.

Here we measure the distance between the greater trochanters of the femur. By the way, you can study the structure of the femur in detail here (not at all difficult). I took a good picture from that article showing how the femur attaches to the pelvis, here it is:

Let's highlight the trochanters of the femurs:

Let's connect these two trochanters of the femurs and get distantia trochanterica, which is normally 31-32 cm, this is the largest size of all that we study.

Here, too, the name indicates to us the points between which we need to measure the distance, because the greater trochanter in Latin sounds like trochanter major.

Conjugata externa

We studied and remembered all the transverse dimensions of the large pelvis. Now we are left with the last size - conjugata externa, that is, the external conjugate. This size is obtained by measuring the distance from the fossa under the spinous process of the fifth lumbar vertebra to the outer edge of the pubic symphysis.

You can find the fifth lumbar vertebra by palpation because it is the last lumbar vertebra before the sacrum. The second way to find this vertebra is to identify the diamond of Michaelis and palpate its upper angle. I will prepare a special article on the topography of the back, where I will tell you in more detail about the Michaelis rhombus.

This is how the measurement of this illustration looks on the patient (illustration from Savelyeva’s textbook). This is a rather small picture, but in it we can clearly see the projection of the pelvis onto the patient, the measuring device and the points themselves for measuring the external conjugate.

Now look at the preparation of the pelvis in the sagittal plane. This is a cool illustration, but it is not from Sinelnikov and not from Zolotko, oddly enough. This seems to be Samusev's textbook, and the outer conjugate here is indicated by the number 2:

The outer conjugate is 20-21 cm.

Lower limb belt

In the skeleton of the pelvic girdle, the right and left pelvic bones are connected to each other (by means of pubic fusion) and each of the pelvic bones and the sacrum to form the sacroiliac joint. The bony pelvis formed as a result of these connections ensures the distribution and transfer of body weight to the bones of the lower limb and protection of the pelvic organs.

The pelvic bone is generally irregular in shape; on its outer surface there is an acetabulum (acetabulum) (Fig. 40, 43) - a spherical depression that serves to connect the head of the femur to the pelvic bone and is limited by the articular lunate surface (fasies lunata) (Fig. 40). Both the pubis and ilium, as well as the ischium, participate in the formation of the acetabulum. Their relative position relative to the acetabulum helps to highlight these bones on the body of the pelvic bone.

In the structure of the pubic bone (Fig. 39), located anteriorly below the acetabulum, there is a body (corpus ossis pubis) (Fig. 41), an upper branch (r. superior ossis pubis) (Fig. 40, 41) and an inferior branch (r. inferior ossis pubis) (Fig. 40, 41) of the pubic bone. The body of the pubis is involved in the formation of the acetabulum. On the upper edge of the superior branch of the pubic bone there is a pubic crest (crista pubica) (Fig. 40, 41) and a pubic tubercle (tuberculum pubicum) (Fig. 40, 42), on the lower edge there is an obturator crest (crista obturatoria) (Fig. 41 ), in the posterior section of which there is an anterior obturator tubercle (tuberculum obturatorium anterius) (Fig. 41). On the inner side of each of the pubic bones, at the place where its upper branch passes into the lower one, there is a rough (symphysial) surface (facies symphysialis) (Fig. 41) of an oval shape. The latter serves to connect with the other pubic bone to form the pubic fusion (symphisis ossium pubis).

The ilium is located superiorly posterior to the acetabulum, in the formation of which it also participates. The structure of the ilium includes a short and massive body of the ilium (corpus ossis ilii) (Fig. 40, 41) and a wing (ala ossis ilii) (Fig. 40, 41), under which an arcuate line (linea arcuata) runs on the inner surface. (Fig. 41). The upper edge of the wing - the iliac crest (crista iliaca) (Fig. 41, 42) - has two protrusions on its anterior and posterior edges. These protrusions are called, respectively, the upper anterior (spina iliaca anterior superior) (Fig. 40, 41, 42) and the lower anterior (spina iliaca anterior inferior) (Fig. 40, 41, 42) iliac spines and the upper posterior (spina iliaca posterior superior) (Fig. 40, 41) and the lower posterior iliac spine (spina iliaca posterior inferior) (Fig. 40, 41). The inner surface of the wing forms an extensive iliac fossa (fossa iliaca) (Fig. 41, 42) with a smooth, gently descending surface. The gluteal surface of the wing has anterior (linea glutea anterior) (Fig. 40), posterior (linea glutea posterior) (Fig. 40) and lower (linea glutea inferior) (Fig. 40) gluteal lines that serve as places of muscle attachment. On the sacropelvic surface of the wing there is an ear-shaped surface (facies auricularis) (Fig. 41), through which the ilium articulates with the iliac tuberosity (tuberositas iliaca) (Fig. 41) and the sacrum. With the sacrum, the iliac bones form a semi-joint (articulatio sacroiliaca).

The ischium is located inferiorly posterior to the acetabulum. The structure of the ischium also includes a body (corpus ossis ischii) (Fig. 40, 41), which participates in the formation of the acetabulum, and a branch (r. ossis ischii) (Fig. 40, 41). At the junction of the body and the branch of the ischium there is a massive thickening - the ischial tubercle (tuber ischiadicum) (Fig. 40), above which is the ischial spine (spina ischiadica) (Fig. 41, 42). On both sides of the ischial spine there are the major (incisura ischadica major) (Fig. 40, 41) and minor (incisura ischadica minor) (Fig. 40) sciatic notches. The bodies and branches of the ischium and pubis, closing, form the boundaries of the obturator foramen (foramen obturatum) (Fig. 40, 41, 43).

The coccyx, sacrum and pelvic bones connected to each other constitute the bony pelvis (pelvis). It contains the organs of the digestive and genitourinary systems, large vessels and nerves. This bony skeleton of the pelvis is divided into upper and lower sections - the large and small pelvis.

The large pelvis (pelvis major) (Fig. 43) has an open front wall, limited on the sides by the wings of the ilium, and behind by the base of the sacrum and the lower lumbar vertebrae. The border line (linea terminalis) (Fig. 43), which is the lower border of the pelvis, runs along the crest of the pubic bone and the arcuate line of the ilium. Below the boundary line is the small pelvis (pelvis minor) (Fig. 43), which is a cylindrical cavity. The lateral walls of the small pelvis are formed by the lower part of the bodies of the iliac bones, the ischial bones, the anterior walls - by the pubic bones, and the posterior walls - by the sacrum and coccygeal bones. Connecting at an angle, the pubic bones form the subpubic angle (angulus subpubicus) in men (Fig. 43), and the pubic arch (arcus pubis) in women (Fig. 43). The midpoints of the direct diameters of the inlet and outlet of the small pelvis are connected by the pelvic axis (axis pelvis).

At the junction of the large pelvis and the small one, the upper pelvic opening (apertura pelvis superior) is formed. The lower opening of the pelvis (apertura pelvis inferior) is bordered on the sides by the ischial tuberosities, in front by the pubic symphysis and lower branches of the pubic bones, and behind by the coccygeal bone.

Sexual dimorphism is especially noticeable in the structure of the bony base of the pelvis. This is explained by the fact that in women, the structure and method of connecting the pelvic bones are designed, in addition to purely mechanical tasks, to ensure the successful completion of childbirth. In particular, during pregnancy, the internal cavity of the small pelvis can increase due to loosening of the cartilaginous interpubic disc and, accordingly, expansion of the symphysis.

The female pelvis is wider and lower, with the wings of the ilium turned to the sides. The lower branches of the pubic bones converge in a wide arc, and the small pelvis has the shape of a wide cylinder. The upper aperture of the small pelvis is close in shape to oval, the symphysis is wider and lower located than in the male pelvis.

The male pelvis, compared to the female one, is higher and narrower, with less developed wings of the iliac bones. The lower branches of the pubic bones converge at an acute angle, the pelvic cavity from below noticeably narrows, the opposite ischial tuberosities and spines are located closer to each other. The upper and lower apertures of the male pelvis differ significantly in size and shape from the corresponding apertures of the female due to the more noticeably protruding promontory of the sacral bone, as well as due to the coccyx, which more sharply protrudes into the lumen of the outlet of the small pelvis.

Dimensions and planes of the small pelvis

As I already said, the most important numbers in obstetrics are the size of the small pelvis. It is the ratio of the sizes of the small pelvis and the fetus that is the most important sign by which the doctor can predict the course of labor and develop the correct obstetric tactics.

We sorted everything out pretty quickly with the large basin, but the small basin is not so simple. Here, in addition to dimensions, there are also planes. More precisely, the entire small pelvis is divided into planes, but in the planes there are dimensions.

So, the small pelvis is divided into four planes:

• Entrance plane
• Wide part
• Narrow part
• Exit plane

Let's study each of these planes one by one.

Entrance plane

The pelvic inlet plane is the plane that separates the greater pelvis and the lesser pelvis. That is, this is the same border that we have already examined:

In the entry plane we need to remember three dimensions.

True conjugate

Direct size/true conjugate (conjugata vera), also known as obstetric or gynecological, is the distance from the most protruding part of the promontory of the sacrum to the middle of the inner edge of the pubic arch. In some sources, the second reference point is not the middle of the upper edge of the pubic arch, but the part of the pubic arch that most protrudes inward.

Let's mark it on our pelvis model:

This diagram has a significant flaw, because it seems as if the anterior border of the true conjugate is the upper edge of the pubic arch, which is not at all the case. A cut in the sagittal plane will help us establish the truth here; here the number 1 indicates the true conjugate:

The size of a true conjugate is 11 cm, which is the smallest size of all that exist in this plane.

Transverse size

The transverse size of the inlet to the pelvis is the distance between the most distant points of the innominate line. We know very well where the nameless line is, so we can easily mark this size:

This is a great size because it is very easy to remember. This is the largest size of all in the small pelvis - as much as 13.5 cm.

Oblique size

In fact, it's not one, but two identical sizes. But they are also very simple. To carry out this measurement, we need to find the places where the sacrum articulates with the pelvic bones and connect it with the iliosacral eminences lying on the opposite side. We haven't covered these anatomical structures yet, so I decided to highlight them. I highlighted the areas where the sacrum articulates with the pelvis in blue, and the iliopubic eminences in yellow.

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Now let's connect these objects crosswise to get two oblique dimensions:

Each oblique dimension is 12 cm. Oblique dimensions should be named based on the side of the articulation of the pelvis and sacrum. Accordingly, the right oblique dimension extends from the right joint of the pelvis and sacrum, and the left oblique dimension departs from the left.

Plane of the wide part

The flatness of the wide part is generally a real gift among all these planes and sizes. It's just a 12.5 by 12.5 square. To draw the boundaries of the wide plane, we need to draw a circle that starts from the middle of the distance between the 2nd and 3rd sacral vertebrae, then moves to the middle of the smooth plates covering the acetabulum, and closes in front on the inner middle of the surface of the pubic arch.

Straight size

The straight size of the wide part is the distance from the middle between the 2nd and 3rd sacral vertebrae to the middle of the inner surface of the pubic arch. This is slightly lower than the front point of the direct dimension of the entry plane. I've highlighted the straight size of the wide part here:

As you remember, the straight size of the wide part is 12.5 cm.

Transverse dimension of the wide part

It will be very difficult for me to show this size. The fact is that the transverse size of the wide part is the distance between the points of the right and left acetabulum that are most distant from each other. Let me remind you that the acetabulum is the socket into which the head of the femur fits to form the hip joint.

The Internet is full of drawings in which we can admire the outside of the acetabulum. For example, here is this drawing - here I have highlighted the acetabulum in red:

In order to draw this measurement, we need to look at the pelvis from the front and slightly below, and connect the most protruding parts of this cavity. I found this drawing of the pelvis and tried to roughly mark on it the transverse dimension of the plane of the wide part:

The transverse dimension of the wide part is 12.5 cm.

Plane of the narrow part

We still have quite a bit left - two planes and four sizes. The penultimate plane is the narrow part. We can draw its boundaries if we begin to draw the oval from the place where the sacrum meets the coccyx, then we pass along the ischial spines and close the oval at the lower edge of the pubic symphysis.

By the way, have you noticed a pattern yet? By the boundaries of the plane you can learn about the direct and transverse dimensions; this does not only work here.

This is a very approximate diagram of the narrow part, probably the obstetricians will throw their curettes and mirrors at me - in the frontal plane at an angle it is quite difficult to show the narrow part accurately.

Straight size

We draw the direct measurement, as you might have guessed, from the junction of the sacrum to the coccyx to the lower edge of the pubic symphysis. I tried to depict this pelvis in the frontal plane, the dotted line is the part of the size that passes under the symphysis:

The direct size of the narrow part of the small pelvis is 11.5 cm.

Transverse size

The main landmark for transverse size is the ischial spine. The ischial spines are small bony projections on the back sides of the sit bones. In order to draw a transverse dimension, we need to connect the ischial spines of the right and left ischial bones. The transverse size of the narrow part is 10.5 cm.

I find it difficult to draw this dimension in the illustration, where we see the pelvis in a horizontal plane. If I get a good photo of the pelvis from behind, then I will supplement this article with the missing diagram.

Pelvic exit plane

This is the very last plane of the pelvis. I know you are already tired, but we only have two sizes left to remember to complete this extremely important topic.

So, the plane of exit from the pelvis is drawn from the top of the coccyx, then it passes along the ischial tuberosities, and rises slightly upward to close at the lower edge of the pubic arch.

Straight size

The direct size of the outlet from the pelvis has one interesting feature. This is the distance from the top of the coccyx (that is, its lowest part) to the lower edge of the pubic arch, which is 9.5 cm for a woman not during childbirth. However, during childbirth, the bony base of the pelvis is stretched due to the movable coccyx, which moves back, and in this case this size reaches 11-11.5 centimeters. That is, the mobility of the coccyx gives as much as two additional centimeters for the fetus, which is trying to leave the pelvis through the exit plane.

In this figure, the direct size of the outlet from the pelvis is indicated by the number 4:

Transverse size

The transverse dimension of the pelvic outlet is the line that connects the ischial tuberosities of the right and left ischial bones. On the sagittal section of the pelvis, we can clearly see this small bony protrusion:

If you try to draw this dimension in the figure, where we see the pelvis in the frontal plane, it will turn out something like this:

The transverse size of the pelvic outlet is 11 cm.

Measurements

The pelvis can be divided into four main types by measuring the diameters of the pelvis and the conjugates at the pelvic inlet and outlet, as well as the oblique diameters.

Female pelvic cavity
Pelvic measurements[7]

Differences between the female and male pelvis

Knowing the basic dimensions and patterns of the structure of the pelvis is very important, because this helps to make a very accurate prognosis in terms of pregnancy and childbirth. Let's look at the pelvis we used as the main illustration:

Such a pelvis clearly indicates big problems with pregnancy and childbirth, because it is a male pelvis.

Why can we confidently say that this is so? There are several signs that indicate the gender of the pelvis. In our case, we see the male pelvis because:

1. The angle formed by the pubic arch is right. In more typical versions of the male pelvis, it is sharp. For women, this thing is stupid;
2. The wings of the ilium are located vertically and narrowly. In women they are much wider and lower, where these wings are more “open”;
3. The promontory of the sacrum protrudes more forward at the male pelvis. Therefore, from above, the pelvic cavity in a woman looks like an oval, and in men it looks like Mickey Mouse. Although women also look like Mickey Mouse, only fatter.

Let's look at the female pelvis to see these differences:

In the illustration with the female pelvis, I highlighted the distinctive features, numbering them according to the list above:

But in this illustration you can see a fat and thin Mickey Mouse - a man on the left and a woman on the right:

Recommendations

1. ^ a b c d f g This article incorporates public domain text from the 20th edition of
   Gray's Anatomy
   (1918)
2. Moore, Keith L. et al (2010) Clinically Oriented Anatomy
   6th ed, chapter 3
   Pelvis and perineum
   , p.339
3. Richard S. Snell Clinical Anatomy by Region
   ,
   Pelvic Cavity
   p.242
4. Tank, P. (2013) Grant Dissector
   15th ed., Ch.4
   Belly
   , p.99
5. "Anatomy of the female pelvis - D. El-Movafi." Retrieved 2007-12-03.
6. Drake et al (2009) Gray Anatomy for Students, 2nd Edition, Chapter 5 Pelvis and Perineum
   -
   General Description
   , p.406
7. Platzer, Werner (2004). Color Atlas of Human Anatomy, Vol.
   1: musculoskeletal system (5th ed.). Time. p. 190. ISBN 3-13-533305-1.