Contains a large basin. Pelvic floor, bony pelvis

Pelvis, pelvis, formed by the pelvic bones, sacrum, coccyx, and ligaments. It is divided into the large pelvis, pelvis major, and the small pelvis, pelvis minor. The border between them is the boundary line, linea terminalis, which runs from the promontory to the arcuate line and further to the pubic tubercle. The pelvic cavity is a container for internal organs, and the abdominal and thigh muscles are attached to its bones. The pelvis has two openings: the upper one, apertura pelvis superior, limited by the border line, and the lower one, apertura pelvis inferior, limited behind by the coccyx, on the sides by the ischial tuberosities, in front by the branches of the ischial and pubic bones. In the male pelvis there is: the rectum, bladder, prostate, bladder gland and vas deferens, and in women - the rectum, uterus, oviduct, bladder, ovaries, vagina.
Also in the pelvis there are blood vessels and lymphatic vessels, nodes, nerves and nerve plexuses.
There are pronounced gender differences in the structure of the pelvis. In the early childhood The pelvis is almost the same in both sexes. IN puberty Sexual characteristics of the pelvic structure are formed. The female pelvis is wider and shorter than the male one, and the latter is higher and narrower. Wings iliac bones in the female pelvis they are deployed more than in the male pelvis. The entrance to the pelvic cavity in women is larger than in men and has an elliptical shape. The pelvic cavity, cavitas pelvis, resembles a cylinder in women, and a funnel in men. The promontory, promontorium, protrudes sharply forward in the male pelvis, but protrudes less in the female pelvis. Women's buttocks are wide, flat and short, men's buttocks are narrow, high and curved. The ischial tuberosities in the female pelvis are more turned to the sides. The junction of the pubic bones forms an arc, and the lower branches of the ischial and pubic bones form a right angle. In the male pelvis, the pubic branches combine to form an acute angle.
To predict labor and prevent complications great importance have the size and shape of the pelvis.
There are external dimensions of the pelvis, dimensions of the entrance to the small pelvis and exit from it: 1) the distance between the two upper anterior spines (spinous distance) of the ilium, distantia spinamm, is 25-27 cm, and between the most distant points of the wings of the ilium, distantia cristarum - 28-30 cm;
2) distance between greater trochanter femur(trochanteric distance), distantia trochanterica - 30-32 cm;
3) the direct diameter [of the conjugate] at the entrance to the pelvis, or conjugata anatomica, is the distance between the promontory and the upper edge of the pubic symphysis and is equal to 11 cm;
4) transverse diameter, diameter transversa (the distance between the most distant points of the border line in the frontal plane) is 13 cm;
5) oblique diameter, diameter obliqua (the distance between the sacroiliac joints on one side and the iliopubic eminence on the second) is 12 cm;
6) the direct size, diameter recta, of the exit from the pelvic cavity in women (the distance between the apex of the coccyx and the lower edge of the pubic symphysis, which depends on the degree of mobility of the coccyx) is 9-12 cm;
7) the transverse size, diameter transversa, of the exit from the pelvic cavity (the distance between the inner edges of the ischial tuberosities) is 11 cm.
IN obstetric practice it is important to know the smallest anteroposterior dimension in the area pelvic inlet. This size is the real conjugate, conjugata vera - the distance between the promontory and the surface of the bottom fusion that most protrudes into the pelvic cavity. It is also called gynecological conjugate, conjugata gynaecologica, which indicates its practical significance. The size of the true conjugate of the female pelvis is on average 10.5-11 cm.
The male pelvis is 1.5-2 cm smaller than the female one. Deviations from the size of the pelvis depend on age, type of body posture, and size of the subject. Individual characteristics external difference the pelvis may touch the shape and size of the sacrum, pelvic bones and degree of prominence.
Negative influence have on the shape of the pelvis various diseases: rickets, spinal deformity and natural developmental defects.
X-ray anatomy. X-rays of the pelvic bones are carried out in three projections: posterior, direct and lateral. In the photographs in the posterior projection, all parts of the pelvic bone, the triangular shape of the buttocks, the entrance to the pelvis, the obturator foramen and the gap of the hip joint are clearly defined. In the middle between the pubic bones there is a clearing corresponding to the discus interpubicus - this is the x-ray fissure of the pubic symphysis.

The pelvis (pelvis) is formed by the connecting pelvic bones and the sacrum. It is a bone ring. The pelvis is a container for many internal organs. With the help of the pelvic bones, the torso is connected to the lower limbs. There are two sections - the large and small pelvis.

The large pelvis (pelvis major) is delimited from the lower pelvis by a boundary line. The border line (linea terminalis) runs through the promontory of the sacrum, along the arcuate lines of the iliac bones, the crests of the pubic bones and the upper edge of the pubic symphysis. The large pelvis is limited from behind by the body of the V lumbar vertebra, from the sides by the wings of the ilium. Large pelvis in front bone wall does not have.

The small pelvis (pelvis minor) is limited posteriorly by the pelvic surface of the sacrum and the ventral surface of the coccyx. On the side, the walls of the pelvis are the inner surface of the pelvic bones (below the boundary line), the sacrospinous and sacrotuberous ligaments. The anterior wall of the pelvis is the upper and lower branches of the pubic bones, the pubic symphysis.

The small pelvis has an inlet and an outlet. The upper aperture (opening) of the pelvis (apertura pelvis superior) is limited by the border line. The exit from the small pelvis - the lower aperture of the pelvis (apertura pelvis inferior) is limited from behind by the coccyx, from the sides by the sacrotuberous ligaments, the branches of the ischial bones, the ischial tuberosities, the lower branches of the pubic bones, and in front by the pubic symphysis. The obturator foramen, located in the lateral walls of the pelvis, is closed by a fibrous obturator membrane (membrana obturatoria). Spreading over the obturator groove, the membrane limits the obturator canal (canalis obturatorius). Vessels and a nerve pass through it from the pelvic cavity to the thigh. In the lateral walls of the pelvis there are also large and small sciatic foramina. The greater sciatic foramen (foramen ischiadicum majus) is bounded by the greater sciatic notch and the sacrospinous ligament. The lesser sciatic foramen (foramen ischiadicum minus) is formed by the lesser sciatic notch, sacrotuberous and sacrospinous ligaments.

The structure of the pelvis is related to a person’s gender. The superior aperture of the pelvis vertical position In women, the body forms an angle of 55-60° with the horizontal plane. The pelvis in women is lower and wider, the sacrum is wider and shorter than in men. The promontory of the sacrum in women protrudes less forward. The ischial tuberosities are more turned to the sides, the distance between them is greater than in men. The angle of convergence of the lower branches of the pubic bones in women is 90° (pubic arch), in men it is 70-75° (subpubic angle).

For forecasting birth process It is important to know the size of a woman’s pelvis. Practical significance They have the sizes of both small and large pelvis. The distance between the two upper and anterior iliac spines (distantia spinarum) in women is 25-27 cm. The distance between the most distant points of the wings of the iliac bones (distantia cristarum) is 28-30 cm.

The direct size of the entrance to the small pelvis (true, or gynecological, conjugate - conjugata vera, s. gynaecologica) is measured between the promontory of the sacrum and the most posteriorly protruding point of the pubic symphysis. This size is 11 cm.

The transverse diameter (diameter transversa) of the entrance to the pelvis - the distance between the most distant points of the border line - is 13 cm.

The oblique diameter (diameter obliqua) of the entrance to the pelvis is 12 cm. It is measured between the sacroiliac joint of one side of the pelvis and the iliopubic eminence of the other side.

In men and women, the pelvis forms a bony ring through which body weight is distributed lower limbs, but in women the pelvis has some features that are adapted for childbirth. The pelvis consists of four bones: the sacrum, the coccyx and two pelvic or innominate bones. The pelvic bones are attached to the sacrum via the sacroiliac synchondrosis and to each other via the pubic symphysis.

Hip bone

Each pelvic bone is formed by the fusion of the ilium, ischium and pubis. Connecting with each other, these bones form the acetabulum.

The ilium has an upper section, the wing, and a lower section, the body. The place where they connect has an arcuate shape - an arcuate line. There are several projections on the wing of the ilium: in front - the anterior superior iliac spine, slightly below it - the anterior inferior iliac spine; behind - the posterior superior iliac spine and the posterior inferior iliac spine.

Makes up the lower and posterior third of the pelvic bone. It has a body, which participates in the formation of the acetabulum, and branches. The body and the branch form an angle between themselves, at the top of which there is a thickening - the ischial tuberosity. The ischial ramus joins the inferior ramus of the pubis. On the posterior surface, the branch of the ischium has a protrusion - the ischial spine. The ischium is involved in the formation of the lesser sciatic notch.

pubic bone forms the anterior wall of the pelvis and consists of a body and two branches: the upper, horizontal and the lower, descending. The lower branches of the pubic bones form an angle - the pubic arch. The body of the pubis is involved in the formation of the acetabulum. At the junction of the ilium and pubic bones there is an iliopubic elevation. Along the top edge upper branch The pubic bone has a bony ridge that ends in the pubic tubercle. Both pubic bones are attached to each other via the pubic symphysis. The pubic symphysis has a cavity inside that is filled with fluid and increases during pregnancy. Relaxation of the symphysis begins in the first half of pregnancy and is especially pronounced during the last 3 months. Regression of such relaxation begins immediately after childbirth and is completely completed after 3-5 months.

The sacrum consists of 5-6 vertebrae that are motionlessly connected to each other and has a uniformly concave anterior surface. The first vertebra of the sacral bone is connected to the fifth with the help of cartilage lumbar vertebra, forming a protrusion - a cape. The sacrum is connected to each of the pelvic bones by flat cartilaginous sacroiliac joints, which have some mobility, and two ligaments: the sacroosteal and sacrohumpy.

The sacrospinal ligament runs from the posterior surface of the sacrum to the ischial spine, the sacrohumpy ligament runs from the posterior surface of the sacrum to the ischial tuberosity. These ligaments bend around the lesser and greater sacrosciatic notches and form the greater and lesser sciatic foramina.
The coccygeal bone is usually formed by 4-5 fused vertebrae, and is attached to the distal end of the sacrum via a movable coccygeal joint. During childbirth, thanks to this joint, the tailbone can deviate by 1-1.5 cm.

Pelvic floor(perineum) is a group of fascia and muscles that supports the pelvic organs and is located in the area between the thighs from the tailbone to the pubic bone. The perineum is limited in front by the pubic symphysis, on the sides by the ischial tuberosities, and behind by the coccyx. Bottom surface the levator anus muscle forms upper limit crotch. The floor of the perineum consists of skin and two layers of superficial fascia - the superficial subcutaneous fat layer (Camper's fascia) and the deep membranous layer (Collis' fascia). A transverse line drawn through the center of the perineum divides it into the anterior and posterior parts, or triangles - the urogenital (genitourinary diaphragm) and anal triangles (pelvic diaphragm).

Pelvic diaphragm(anal triangle) is wide but thin muscle layer, which forms lower limit abdominal (and pelvic) cavity and consists of a wide funnel-shaped belt of fascia and muscles, extending from the symphysis to between the walls of the pelvis. The pelvic diaphragm consists of 3 groups of muscles and fascia that cover:

Elevator anus muscles;
Coccygeus muscle;
External sphincter of the anus.

These structures are evolved remnants of the tail muscles of lower animals. The levator anus muscle is the longest and strongest of all the muscles and forms a wide muscular belt extending from the posterior surface of the superior ramus of the pubis, inner surface ischium and between these two formations from the obturator fascia. Muscle fibers are distributed in several directions: in the urethra, vagina and rectum, forming functional fibers around them. The levator anus muscle is divided into three paired components, which are named according to their anatomical location: the pubococcygeus, ischiorectalis and iliococcygeus muscles.

An important space of the pelvic diaphragm is the ischiorectal (ischial-anal) fossa - the space between the skin and the levator anus muscle on both sides anal canal containing adipose tissue, bounded by Collis's fascia. The ischiorectal fossa at the back is combined with the same one on the opposite side, forming a “horseshoe”.

Urogenital diaphragm

The urogenital diaphragm (urogenital triangle) is a strong muscular sheath that occupies the area between the symphysis and the ischial tuberosities and passes through the triangular anterior part of the pelvic outlet. The urogenital diaphragm is located outside and inferior to the pelvic diaphragm and is formed by two spaces, or layers: superficial and deep.

The superficial space of the perineum is limited by the deep fascia of the perineum and includes 3 pairs of muscles:

ischiocavernosus muscle;
Bulbocavernosus, or bulbospongiosus muscle;
Superficial transverse perineal muscle.

In this space are the bulbs of the vestibule of the vagina and large vestibules glands (Bartholin's glands). The ischiocavernosus muscle runs from the medial surface of the ischial tuberosities under the pubic arch to the crura of the clitoris.

The bulbocavernosus, or bulbospongiosus muscle, which is also called the sphincter of the vagina, begins behind the tendon center of the perineum, passes from both sides of the vestibule of the vagina to the dorsal surface of the clitoris into the lower fascia of the urogenital diaphragm and forms the medial border of the superficial space of the perineum. The superficial transverse perineal muscle runs transversely from the front of the ischial tuberosities to the tendon center of the perineum.

Deep crotch space(triangular ligament) - a closed space between the upper and lower fascia of the genitourinary diaphragm, on the sides - the places where this fascia enters the ischiopubic branches, which includes the following muscle groups:

Sphincter urethra;
Deep transverse perineal muscle.

Sphincter of the urethra starts from the pubisciatic branches, goes medially to the urethra, covers its distal section, as well as the anterior and posterior walls of the vagina. In women, it is poorly developed due to the fact that it is perforated by two openings: the urethra and the vagina.

Deep transverse perineal muscle consists of transverse muscle fibers that pass along the posterior edge of the urethral sphincter and enter the central tendon center of the perineum. Unlike men, in women this muscle plays a very minor role in the mechanism of urinary continence.

The blood supply to the perineum is carried out by the internal pudendal artery and its branches: the inferior rectal and posterior labial arteries.
Innervation of the perineum occurs due to the pudendal nerve (from the second, third and fourth sacral segments) and its branches.

Clinical correlations

The ischial spines are of great obstetric importance, since the distance between them is usually equal to the smallest diameter of the pelvic cavity. They are also a guide for the advancement of the presenting part of the fetus along the axis of the birth canal. When a woman is positioned in the dorsal lithotomy position during childbirth, due to the mobility of the sacroiliac joints, the diameter of the pelvic outlet can increase by 1.5-2 cm. This circumstance is the main argument for placing a woman in this position during childbirth.

During childbirth, all layers of the perineal muscles form a wide muscular canal, which is a continuation of the bone birth canal. The paired levator anus muscle has important to maintain abdominal and pelvic organs, distributions intra-abdominal pressure along with the diaphragm and muscles abdominal wall(for example, with), control of urine and feces, as well as for the process of childbirth (significant stretching of the imbricate-composed muscle fibers during the advancement of the fetus with their subsequent contraction). When this muscle contracts, the genital opening, rectum and vagina are compressed.

The presence of adipose tissue in the ischiorectal fossa facilitates stretching of the anal canal during defecation and the vaginal canal during the second stage of labor. It can become a site of blood accumulation when postpartum hemorrhage(hematoma) or pus from abscesses and can hold up to 1 liter of liquid. Such abscesses can spread to the opposite side of the pelvis.

Female pelvis in obstetrics

The bony pelvis creates a solid foundation for the soft tissues of the birth canal and determines its direction and size. The bones of the female pelvis are thinner, the plane of the entrance to the small pelvis usually has the shape of a transversely narrowed oval, while the plane of the entrance to the male pelvis is funnel-shaped. The female pelvis is lower, wider and more spacious compared to the male; the pubic symphysis is shorter. The cavity of the female pelvis towards the exit becomes wider due to the flatness of the iliac bones, a greater distance between the ischial tuberosities and a large subpubic angle (90-100 ° compared to 70-75 ° in men).

From an obstetric point of view female pelvis divided into two parts. The boundary between them is the boundary line. It runs along the inner surface of each ilium from the sacroiliac joint at the iliopubic eminence and divides the pelvis into two parts: the upper (large pelvis) and the lower (lesser, or true pelvis).

The large pelvis cannot serve as a guide for the capacity of the small pelvis, but it is easily accessible for measurement, and therefore some of its dimensions are used to roughly estimate the size of the small pelvis:

Interspinous distance - the distance between the anterior superior spines of the iliac bones (25-26 cm);
Intercrest distance - the distance between the most distant points of the iliac crests (28-29 cm);
Interacetabular distance - the distance between the most distant points hip joints(30-31 cm);
External conjugate - Baudeloc's conjugate, external obstetric conjugate - the distance from the fossa between the spinous processes of the last lumbar and first sacral vertebrae to the most protruding point of the symphysis (20-21 cm).

Small(real) pelvis

He has highest value for childbirth. It is bounded above by the promontory of the sacrum, the border line and the upper edge of the pubic bones, and below by the outlet of the pelvis. The anterior wall in the symphysis area is about 5 cm long, the posterior wall (in the sacral area) is about 10-12 cm. The lateral walls of the pelvis are represented by the inner surfaces of the ischial bones. When a woman is in an upright position top part The pelvic canal is directed down and back, and the lower one forms an arc and goes down and forward. Lateral walls of the pelvis adult woman have a somewhat converging direction. The descending branches of the pubic bones in the normal female pelvis form a circular arch (subpubic angle 90-100 °), which allows the passage of the fetal head.

In the pelvis there are 4 conventional planes that help to navigate in determining the location of the presenting part of the fetus during childbirth:

The plane of entry into the pelvis;

The plane of the widest part of the pelvic cavity (passes through the largest diameter of the pelvis);

The plane of the narrow part of the pelvic cavity (passes through the small diameter of the pelvis);

The plane of exit of the small pelvis.

The plane of entrance to the small pelvis is limited posteriorly by the promontory and wings of the sacrum; on the sides - by the border line, in front - by the symphysis and the upper (horizontal) branches of the pubic bones. The configuration of the entrance to the female pelvis in 50% of women is more round than oval (gynecoid type of pelvis). In the plane of the entrance to the pelvis, 4 diameters have obstetric significance: straight (antero-posterior, true conjugate), transverse and two oblique.

Straightdiameter- true conjugate (internal obstetric conjugate) - the most important anteroposterior diameter, which is the smallest distance between the promontory and the internal superior edge (10-11 cm). The distance between the promontory of the sacrum and the upper edge of the symphysis (the anteroposterior diameter of the anterior opening of the pelvis) is called the anatomical conjugate and is equal to 11.5 cm.

Transversediameter- the distance between the most distant points of the intermediate line (13-13.5 cm).

Obliquediameter- the distance between the sacroiliac joint on one side and the iliopubic eminence on the opposite side (12-12.5 cm). The right diameter is measured from the right sacroiliac joint, the left - from the left.

The plane of the wide part of the pelvic cavity is limited in front by the middle of the inner surface of the symphysis, on the sides by the middle of the hip sockets, and behind by the communication of the II and III sacral vertebrae. In the wide part of the small pelvis, the straight (12.5 cm) and transverse (12.5 cm) diameters are determined.

The plane of the narrow part of the pelvic cavity is limited in front by the lower edge of the pubic symphysis, on the sides by the spines of the ischial bones, and behind by the sacrococcygeal joint. In this plane, straight (11.5 cm) and transverse (10.5 cm) diameters are also distinguished.

The plane of exit of the small pelvis is limited in front by the lower edge of the pubic arch, on the sides by the ischial tuberosities, and behind by the apex of the coccyx. It has a straight diameter of 9.5 cm, but when the coccyx deviates, it can increase by 1.5-2 cm and equals 11-11.5 cm; and transverse diameter (between the ischial tuberosities), which is 11 cm (at least 8 cm). In the plane of the exit of the pelvis, the anal sagittal diameter is also distinguished (a segment of direct diameter from the apex of the coccyx to the point of intersection with the transverse diameter), which in normal pelvis should not be less than 7.5 cm. If the narrow part of the pelvic cavity or pelvic outlet is narrowed, the prognosis vaginal birth depends on the size of the anal sagittal diameter.

So, in the plane of the entrance to the pelvis, the largest is the transverse diameter; in the wide part of the pelvic cavity, the straight and transverse diameters are the same (this plane has no special obstetric significance); in the narrow part of the pelvic cavity and in the exit plane, the largest are straight diameters. These provisions are important for understanding the biomechanism of childbirth with a normal pelvis.

Pelvicaxis, or leading line of the pelvis, connecting the midpoints of the straight diameters of all planes of the small pelvis and is directed down and back when entering the pelvis, and down and forward when exiting.

The angle of inclination of the pelvis is formed between the plane of the entrance to the pelvis and the horizontal line when the woman is in a vertical position and is 45-60 ° (at non-pregnant women- 45-46 °).

Classification of pelvis types

A line drawn through the transverse diameter of the plane of the entrance to the pelvis divides it into anterior and posterior segments. The shape of these segments is taken into account when classifying pelvic types. Thus, the nature of the posterior segment determines the type of pelvis, the anterior segment determines the tendency that helps to identify mixed types pelvis

Gynecoid pelvis. The posterior sagittal diameter is slightly smaller than the anterior sagittal diameter, the sides of the posterior segment are rounded and wide. Considering that the transverse diameter of the pelvic inlet is almost the same as the anteroposterior one, the pelvic inlet has almost rounded shape or oval. The pelvic walls are straight, the ischial spines do not protrude and the distance between them exceeds 10 cm. The pubic arch is wide.

The sacrosciatic notch is round. The sacrum is not deviated either anteriorly or posteriorly. Occurs in 50% of women and has best forecast for vaginal birth.

The anthropoid pelvis is distinguished by the fact that the direct diameter of the entrance to the pelvis exceeds the transverse one, therefore the shape of the entrance to the pelvis has the appearance of an oval, narrowed in the anteroposterior direction. The anterior segment is narrow. The sacrosciatic notch is wide, the walls of the pelvis somewhat converge. The sacrum is usually straight and has 6 vertebrae, making the anthropoid pelvis the deepest of all pelvic types. The ischial spines protrude somewhat. The subpubic arch is well defined, but may be somewhat narrowed. This type of pelvis occurs in 25% of white women and about 50% in representatives of other races.

Androidpelvis. The posterior sagittal diameter of the entrance is significantly shorter than the anterior sagittal diameter, which limits the space for the fetal head. The walls of the posterior segment are not round and approach wedge-shaped. The anterior segment is narrow and triangular. The lateral walls of the pelvis tend to move closer together, the ischial spines protrude, and the subpubic arch is narrowed. The sacrosciatic notch is narrow. The sacrum protrudes somewhat into the pelvis and is of course straight, with an unpronounced depression. The posterior sagittal diameter decreases from the inlet to the outlet of the pelvis due to protrusion of the sacrum. May occur in 30% of women. A narrowed android pelvis has a poor prognosis for vaginal delivery.

Platypeloidpelvis- a pelvis that has a flattened gynecoid shape, with a short anteroposterior (straight and wide transverse) diameter. The angle of the anterior segment is very wide, the arcs of the anterior and posterior segments correct form. The sacrum is short, the sacrosciatic notches are wide. This type of pelvis is less common (in 3% of women).

Clinical determination of pelvic capacity

Diagonalconjugate

In many narrowed pelvises, the straight (antero-posterior) diameter of the pelvic inlet is reduced. To predict childbirth, it is important to determine this size, but this is only possible with special instrumental research(X-ray pelvimetry, nuclear magnetic resonance and computer pelvimetry, ultrasound pelvimetry). But the distance between the lower edge of the pubic symphysis and the promontory of the sacrum (diagonal conjugate) can be determined during a gynecological examination.

When determining the diagonal conjugate, the doctor inserts two fingers into the vagina, determines the mobility of the coccyx and the nature of the anterior surface of the sacrum (vertical and lateral arches). In a normal pelvis, only the last three can be palpated sacral vertebrae, whereas in a narrowed pelvis the entire surface of the sacrum is accessible to palpation. If the size of the diagonal conjugate exceeds 11.5 cm, the pelvic capacity is considered sufficient for vaginal delivery, provided normal sizes fetus

Transversenarrowing of the pelvis(this type of pelvic narrowing can be observed with a normal anteroposterior diameter) can only be detected with special research(X-ray pelvimetry, nuclear magnetic resonance and computer pelvimetry, ultrasound pelvimetry). With ultrasonic pelvimetry, it is possible to determine the true conjugate, the dimensions of the pelvic planes, biparietal size fetal head, its location and insertion, expected fetal weight.

The large pelvis is much wider than the small one; it is limited on the sides by the wings of the ilium, behind by the last lumbar vertebrae, and in front by the lower abdominal wall. The volume of the large pelvis can change in accordance with the contraction or relaxation of the abdominal muscles. The large pelvis is available for research; its dimensions are determined quite accurately. The size of the large pelvis is used to judge the size of the small pelvis, which cannot be directly measured. Meanwhile, determining the size of the small pelvis is important, since the newborn fetus passes through the stubborn bony canal of the small pelvis.

Small pelvis

Planes and dimensions of the small pelvis. The pelvis is the bony part of the birth canal. Back wall The small pelvis consists of the sacrum and coccyx, the lateral ones are formed by the ischial bones, the anterior one by the pubic bones and the symphysis. The posterior wall of the pelvis is 3 times longer than the anterior one. Upper section The pelvis is a continuous, inflexible ring of bone. IN lower section the walls of the pelvis are not solid; they contain obturator foramina and sciatic notches, bounded by two pairs of ligaments (sacrospinous and sacrotuberous).

In the small pelvis there are the following sections: inlet, cavity and outlet. In the pelvic cavity there are wide And narrow Part. In accordance with this, four planes of the pelvis are considered: I - the plane of the entrance to the pelvis, II - the plane of the wide part of the pelvic cavity, III - the plane of the narrow part of the pelvic cavity, IV - the plane of the exit of the pelvis.

/. Plane of entry into the pelvis has the following boundaries: in front - the upper edge of the symphysis and the upper inner edge of the pubic bones, on the sides - innominate lines, in the back - the sacral promontory. The entrance plane has the shape of a kidney or a transverse oval with a notch corresponding to the sacral promontory. At the entrance to the pelvis there are three sizes: straight, transverse and two oblique.

- Straight size - the distance from the sacral promontory to the most prominent point on the inner surface of the symphysis pubis. This size is called the obstetric, or true, conjugate (conjugata vera). There is also an anatomical conjugate - the distance from the promontory to the middle of the upper inner edge of the symphysis; the anatomical conjugate is slightly (0.3-0.5 cm) larger than the obstetric conjugate. Obstetric, or true conjugate is equal to 1 1 cm.

- Transverse size - the distance between the most distant points of unnamed lines. This size is 13-13.5 cm.

Oblique sizes two: right and left, which are equal to 12-12.5 cm. Right oblique size - distance from the right sacroiliac joint to the left iliopubic tubercle, left oblique size- from the left sacroiliac joint to the right iliopubic tubercle. In order to more easily navigate in the direction of the oblique dimensions of the pelvis in a woman in labor, M.S. Malinovsky and M.G. Kushnir suggests the following technique. The hands of both hands are folded at right angles, with the palms facing upward; the ends of the fingers are brought closer to the outlet of the pelvis of the lying woman. The plane of the left hand will coincide with the left oblique size of the pelvis, the plane of the right - with the right.

II. The plane of the wide part of the pelvic cavity has the following boundaries: in front - the middle of the inner surface of the symphysis, on the sides - the middle of the acetabulum, in the back - the junction of the II and III sacral vertebrae. In the wide part of the pelvic cavity, two sizes are distinguished: straight and transverse.

- Straight size - from the junction of the II and III sacral vertebrae to the middle of the inner surface of the symphysis; equals 12.5 cm.

- Transverse size - between the tips of the acetabulum; equals 12.5 cm.

There are no oblique dimensions in the wide part of the pelvic cavity because in this place the pelvis does not form a continuous bone ring. Oblique dimensions in the widest part of the pelvis are conditionally allowed (length 13 cm).

///. The plane of the narrow part of the pelvic cavity bounded in front by the lower edge of the symphysis, on the sides by the spines of the ischial bones, and behind by the sacrococcygeal joint. There are two sizes: straight and transverse.

- Straight size goes from the sacrococcygeal joint to the lower edge of the symphysis (apex of the pubic arch); equals 11-11,5 cm.

- Transverse size connects the spines ischium; equal to 10.5 cm.

IV. Pelvic exit plane has the following boundaries: in front - the lower edge of the symphysis, on the sides - the ischial tuberosities, in the back - the apex of the coccyx. The pelvic exit plane consists of two triangular planes, common ground which is the line connecting the ischial tuberosities. There are two sizes of the pelvic outlet: straight and transverse.

- Straight pelvic outlet size goes from the top of the coccyx to the lower edge of the symphysis; it is equal to 9.5 cm. As the fetus passes through the small pelvis, the tailbone moves away by 1.5-2 cm and the direct size increases to 1 1.5 cm.

- Transverse size of the pelvic outlet connects the inner surfaces of the ischial tuberosities; equal to 11 cm. Thus, at the entrance to the pelvis, the largest dimension is the transverse one. In the widest part of the cavity, straight and transverse dimensions equal; the largest size will be the conventionally accepted oblique size. In the narrow part of the cavity and the pelvic outlet, the straight dimensions are larger than the transverse ones.

In addition to the above (classical) pelvic cavities, there are parallel planes of the pelvis (planes Goji).

The first (upper) plane passes through the terminal line (I. terminalis innominata) and is therefore called terminal plane.

Second - main plane, runs parallel to the first at the level of the lower edge of the symphysis. It is called the main one because the head, having passed this plane, does not encounter significant obstacles, since it has passed a solid bone ring.

Third - spinal plane, parallel to the first and second, crosses the pelvis in the spina oss area. ischii.

Fourth - exit plane, represents the bottom of the pelvis (its diaphragm) and almost coincides with the direction of the coccyx.

Wired axis (line) of the pelvis. All planes (classical) of the pelvis border in front with one or another point of the symphysis, and in the back - with different points of the sacrum or coccyx. The symphysis is much shorter than the sacrum and coccyx, so the planes of the pelvis converge anteriorly and fan out posteriorly. If you connect the middle of the straight dimensions of all the planes of the pelvis, you will get not a straight line, but a concave anterior (towards the symphysis) line. This conventional line connecting the centers of all direct dimensions of the pelvis is called wire axis of the pelvis. The wire axis of the pelvis is initially straight; it bends in the pelvic cavity according to the concavity of the inner surface of the sacrum. In the direction of the wire axis of the pelvis, the born fetus passes through the birth canal.

Pelvic angle(the intersection of the plane of its entrance with the plane of the horizon) when a woman is standing can be different depending on the physique and ranges from 45-55°. It can be reduced by forcing a woman lying on her back to strongly pull her thighs towards her stomach, which leads to elevation of the womb. It can be increased by placing a roll-shaped hard pillow under the lower back, which will lead to a downward deviation of the womb. A decrease in the angle of inclination of the pelvis is also achieved if the woman is given a semi-sitting position, squatting.