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 is formed 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 the lower section, the walls of the small pelvis are not solid; they contain the obturator foramen and sciatic notches, bounded by two pairs of ligaments (sacrospinous and sacrotuberous). The small pelvis has the following sections: inlet, cavity and outlet. In the pelvic cavity there are wide and narrow parts (Table 5). In accordance with this, four planes of the small pelvis are distinguished: 1 - plane of the entrance to the pelvis; 2 - plane of the wide part of the pelvic cavity; 3 - plane of the narrow part of the pelvic cavity; 4 - plane of exit of the pelvis. Table 5
| Pelvic plane | Dimensions, cm | ||
| straight | transverse | oblique | |
| Entrance to the pelvis | 13-13,5 | 12-12,5 | |
| Wide part of the pelvic cavity | 13 (conditional) | ||
| Narrow part of the pelvic cavity | 11-11,5 | - | |
| Pelvic outlet | 9.5-11,5 | - | |
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c) The right and left oblique dimensions are equal to 12-12.5 cm. The right oblique dimension is the distance from the right sacroiliac joint to the left iliopubic tubercle; left oblique dimension - from the left sacroiliac joint to the right iliopubic tubercle. To make it easier to navigate in the direction of oblique pelvic size in a woman in labor, M. S. Malinovsky and M. G. Kushnir suggested next appointment(Fig. 69): 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. |
b) Transverse size - between the middle of the acetabulum; it is equal to 12.5 cm. There are no oblique dimensions in the wide part of the pelvic cavity, since in this place the pelvis does not form a continuous bone ring. Oblique dimensions in the widest part of the pelvis are allowed conditionally (length 13 cm).3. The plane of the narrow part of the pelvic cavity is limited 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. a) The straight dimension goes from the sacrococcygeal joint to the lower edge of the symphysis (apex of the pubic arch); it is equal to 11 - 11.5 cm.
b) The transverse dimension connects the spines of the ischial bones; it is equal to 10.5 cm.4. The plane of exit of the pelvis 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 exit plane of the pelvis consists of two triangular planes, the common base of which is the line connecting the ischial tuberosities. Rice. 70. Dimensions of the pelvic outlet. 1 - straight size 9.5-11.5 cm; 2 - transverse size 11 cm; 3 - coccyx. Thus, at the entrance to the pelvis, the largest dimension is the transverse one. In the wide part of the cavity, the straight and transverse dimensions are equal; The oblique size will be conventionally accepted as the largest. In the narrow part of the cavity and outlet of the pelvis, the straight dimensions are larger than the transverse ones. In addition to the above (classical) pelvic cavities (Fig. 71a), parallel planes are distinguished (Fig. 71b). The first is the upper plane, passes through the terminal line (linca terminalis innominata) and is therefore called the terminal plane. The second is the 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. The third is the spinal plane, parallel to the first and second, intersects the pelvis in the spina ossis ischii region. The fourth is the exit plane, which is the bottom of the pelvis (its diaphragm) and almost coincides with the direction of the coccyx. Wiring axis (line) of the pelvis. All planes (classical) of the pelvis border in front with one or another point of the symphysis, 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 (see Fig. 71a).
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This line connecting the centers of all direct dimensions of the pelvis is called the pelvic axis. At first it is straight, and then 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 tilt. When the woman is in an upright position, the upper edge of the symphysis is below the sacral promontory; true Koyuga-ga forms an angle with the horizontal plane, which is normally 55-60°. The ratio of the pelvis entrance plane to horizontal plane called pelvic tilt (Fig. 72). The degree of pelvic tilt depends on your body type. |
1. Objective examination of a pregnant woman. The height of a pregnant woman. Body type of a pregnant woman. Examination of the skin. Examination of the mammary glands. Abdominal examination.
2. Examination of the internal organs of a pregnant woman.
3. Measuring the pregnant woman's abdomen. Normal size of a pregnant belly. Abdominal circumference.
4. Examination of the pregnant pelvis. Sacral rhombus (Michaelis rhombus).
5. Measuring the size of the pelvis. Transverse dimensions of the pelvis. Distantia spinarum. Distantia cristarum. Distantia trochanterica.
6. Straight pelvic size. Conjugata externa. External conjugate. The dimensions of the external conjugate are normal.
7. True conjugate. Diagonal conjugate (conjugata diagonalis). Calculation of true conjugates. The size of the true conjugate is normal.
8. Measuring the size of the pelvic outlet. Measuring the direct size of the pelvic outlet. Measuring the transverse size of the pelvic outlet.
9. Shape of the pubic angle. Measuring the shape of the pubic angle. Measuring the oblique dimensions of the pelvis.
10. Thickness of the pelvic bones. Solovyov index. Calculation of the true conjugate taking into account the Solovyov index.
Measuring the size of the pelvis. Transverse dimensions of the pelvis. Distantia spinarum. Distantia cristarum. Distantia trochanterica.
Usually measured four pelvis sizes: three transverse and one straight.
Fig.4.11a. Measuring the transverse dimensions of the pelvis. Distantia spinarum.1. Distantia spinarum- the distance between the anterosuperior iliac spines. The buttons of the pelvis are pressed to the outer edges of the feathers and non-upper spines. This size is usually 25-26 cm (Fig. 4.11, a).
Fig.4.11b. Measuring the transverse dimensions of the pelvis. Distantia cristarum.
To make it easier to study pelvic size measurements, we recommend
2. Distantia cristarum- the distance between the most distant points of the iliac crests. After measuring distantia spinarum, the pelvis meter buttons are moved from the spines along the outer edge of the iliac crest until the greatest distance is determined; this distance is distantia cristarum; it averages 28-29 cm (Fig. 4.11, b)
Fig.4.11c. Measuring the transverse dimensions of the pelvis. Distantia trochanterica.3. Distantia trochanterica- distance between greater trochanters femur Find the most prominent points large skewers and press the pelvis gauge buttons to them. This size is 31-32 cm (Fig. 4 11, c)
It also matters relationship between transverse dimensions . For example, normally the difference between them is 3 cm; a difference of less than 3 cm indicates a deviation from the norm in the structure of the pelvis.
1. Transverse diameter, diameter transversa- the distance between the most distant points of both boundary lines.
2. Oblique diameter, diameter obliqua(dextra et sinistra) - measured from the right (left) sacroiliac joint to the left (right) iliopubic eminence.
3. Diagonal conjugate, conjugata diagonalis- the distance from the lower edge of the symphysis to the most prominent point of the sacral promontory. (normally 12.5-13 cm)
The diagonal conjugate is determined when vaginal examination women, which is produced in compliance with all rules of asepsis and antiseptics. The II and III fingers are inserted into the vagina, the IV and V are bent, their back rests against the perineum. The fingers inserted into the vagina are fixed at the top of the promontory, and the edge of the palm rests against the lower edge of the symphysis. After this, the second finger of the other hand marks the place of contact of the examining hand with the lower edge of the symphysis. Without removing the second finger from the intended point, the hand in the vagina is removed, and the assistant measures the distance from the top of the third finger to the point in contact with the lower edge of the symphysis with a pelvis or a centimeter tape. It is not always possible to measure the diagonal conjugate, because when normal sizes the promontory of the pelvis is not reached or can be palpated with difficulty. If the promontory cannot be reached with the end of an extended finger, the volume of this pelvis can be considered normal or close to normal.
3.1. True conjugata, diameter conjugata- the distance from the posterior surface of the pubic symphysis to the most prominent point of the sacral promontory.
To determine the true conjugate, subtract 1.5-2 cm from the size of the diagonal conjugate.
3.2. Anatomical conjugate- the distance from the upper surface of the pubic symphysis to the most prominent point of the sacral promontory.
4. Distantia spinarum- the distance between the superior anterior iliac spines. (normally 25-26 cm)
5. Distantia trochanterica- the distance between the greater trochanters of the femurs. (normally 30-31 cm)
6. Distantia cristarum- the distance between the most distant points of the iliac crest. (normally 28-29 cm)
When determining the size of the pelvis, it is necessary to take into account the thickness of its bones; it is judged by the value of the so-called Solovyov index - circumference wrist joint. The average index value is 14 cm. If the Solovyov index is more than 14 cm, it can be assumed that the pelvic bones are massive and the size of the small pelvis is smaller than expected.
Michaelis rhombus In a standing position, the so-called lumbosacral rhombus, or Michaelis rhombus, is examined. Normally, the vertical size of the rhombus is on average 11 cm, the transverse size is 10 cm. If the structure of the small pelvis is disturbed, the lumbosacral rhombus is not clearly expressed, its shape and size are changed.
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Pelvic shape | ||||||
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Normal | ||||||
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Transversely tapered | ||||||
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Generally uniformly narrowed | ||||||
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Infantile | ||||||
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Simple flat | ||||||
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Flat-rachitic | ||||||
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Generally tapered flat |
During a vaginal examination, the diagonal conjugate is measured (12.5-13 cm). Obstetric conjugate – c. vera (subtract 2 cm from the size of the diagonal conjugate).
The true conjugate is calculated:
along a diagonal cone;
along the outer conjugate;
according to the vertical dimension of the Michaelis rhombus;
using X-ray pelviometry;
according to ultrasound data.
The capacity of the small pelvis depends on the thickness of its bones, which is indirectly determined by measuring the circumference of the wrist joint and calculating the Solovyov index (13.5-15.5 cm).
Michaelis rhombus (normally 11 x 10 cm).
Direct size of the pelvic outlet (9.5 cm).
Transverse size of the pelvic outlet (11 cm).
Pubic angle (90 0 -100 0).
External oblique dimensions of the pelvis.
Lateral conjugate (the distance between the anterior and posterosuperior iliac spines on one side) – 15 cm.
The distance from the anterior superior spine on one side to the posterosuperior spine on the other side (21-22 cm).
Distance from the middle of the upper edge of the symphysis to the posterosuperior spines on the right and left (17.5 cm); the difference in size indicates pelvic asymmetry.
Distance from the suprasacral fossa to the anterior superior spines on both sides.
Pelvic circumference at the level of the iliac crests (85 cm); the same at the level of the greater trochanters (90 – 95 cm).
Height of the fundus of the uterus; abdominal circumference.
Diameter of the fetal head (12 cm).
Pubosacral size (distance from the middle of the symphysis to the junction of the 2nd and 3rd sacral vertebrae - a point located 1 cm below the intersection of the diagonals of the Michaelis rhombus - 22 cm); a decrease in this size by 2-3 cm is accompanied by a decrease straight size wide part of the pelvic cavity.
X-ray pelviometry allows you to determine all the diameters of the small pelvis, shape, inclination of the pelvic walls, shape of the pubic arch, degree of curvature and inclination of the sacrum. It is recommended to produce at 38-40 weeks. pregnancy or before labor activity.
Ultrasound examination - ultrasound, is used to diagnose an anatomically narrow pelvis and makes it possible to obtain the value of the true conjugate and biparietal size of the fetal head, their ratio.
The course of pregnancy and childbirth with a narrow pelvis
A narrow pelvis as such does not lead to changes in the course of pregnancy.
The adverse effect of a narrowed pelvis on the course of pregnancy is felt in its last months and at the beginning of labor.
Features that an obstetrician should know about:
In primigravidas, due to a discrepancy between the pelvis and the head, the latter does not enter the pelvis and remains mobile above the entrance throughout pregnancy and at the beginning of labor. The height of the uterine fundus on the eve of birth remains at the same level.
In primiparous women with a narrow pelvis, by the end of pregnancy the abdomen has a pointed shape, and in multiparous women it has a drooping shape.
Anomalies of the bony pelvis are common reasons incorrect position of the fetus - oblique, transverse and pelvic presentation of the fetus, as well as unfavorable insertion of the head - extensor.
One of the most common and serious complications pregnancy with a narrow pelvis is premature (prenatal) rupture of water. This is due to the absence of a contact belt - the head stands high, it does not touch the pelvic ring, so the waters are not divided into anterior and posterior - the entire mass is poured out at the beginning of labor under increasing uterine pressure.
When amniotic fluid leaks and the fetal head moves, there is a high risk of prolapse of the umbilical cord and small parts of the fetus. Prolapse of the umbilical cord leads to the development of acute hypoxia of the fetus and its death if the head presses it against the pelvic wall. In these cases, only emergency measures can save the child. C-section(intrapartum mortality among newborns in these cases is 60-70%).
With a narrow pelvis, childbirth is often complicated by weak labor. Firstly, in women with narrow pelvis there is hormonal deficiency, sexual infantilism, secondly, labor is protracted, which leads to fatigue of the woman in labor, depletion of energy resources and the development of secondary weakness of labor.
Maternal trauma. Prolonged compression fetal head Bladder and rectum can lead to the formation of genitourinary and enterogenital fistulas (on days 6-7). Compression of the cervix can lead to swelling, necrosis, and deep ruptures.
The absence of forward movement of the fetus with continued intense labor leads to a gradual thinning of the lower segment and the occurrence of a threatening uterine rupture.
During prolonged labor with a long anhydrous interval significantly increases the risk of developing endometritis, chorioamnionitis, and ascending infection of the fetus.
Complications from the fetus. The fetal head changes slowly, lingers for a long time in various planes of the small pelvis, which causes cerebral circulation disturbance, edema, an increase in the volume of the head, the formation of cephalohematomas, subdural and subarachnoid hemorrhages. At further development child, a scar-adhesive process forms in these areas, leading to the occurrence of abnormalities in the neuropsychic sphere and physical development, up to the development of hydrocephalus, hyperkinesis, epilepsy and dementia. Moreover, with deep, irreversible disorders of brain function, cerebral palsy can form.
2. Dimensions of the plane of the wide part of the small pelvis. Dimensions of the plane of the narrow part of the small pelvis.
3. Wired pelvic axis. Pelvic inclination angle.
4. Physiology of the female reproductive system. Menstrual cycle. Menses.
5. Ovaries. Cyclic changes in the ovaries. Primordial, preantral, antral, dominant follicle.
6. Ovulation. Yellow body. Female hormones synthesized in the ovaries (estradiol, progesterone, androgens).
7. Cyclic changes in the uterine mucosa (endometrium). Proliferation phase. Secretion phase. Menstruation.
8. The role of the central nervous system in the regulation of menstruation. Neurohormones (luteinizing hormone (LH), follicle-stimulating hormone (FSH).
9. Types of feedback. The role of the feedback system in the regulation of menstrual function.
10. Basal temperature. Pupil symptom. Karyopyknotic index.
Big pelvis for the birth of a child is not significant. The bony basis of the birth canal, which represents an obstacle to the fetus being born, is the small pelvis. However, by the size of the large pelvis one can indirectly judge the shape and size of the small pelvis. The inner surface of the large and small pelvis is lined with muscles.
Rice. 2.7. Female pelvis(sagittal section).1 - anatomical conjugate;
2 - true conjugate;
3 - direct dimension of the plane of the wide part of the pelvic cavity;
4 - direct dimension of the plane of the narrow part of the pelvic cavity;
5 - direct size of the pelvic outlet with the normal position of the coccyx;
6 - direct size of the pelvic outlet with the tailbone bent posteriorly;
7 - wire axis pelvis
Pelvic cavity is the space enclosed between the walls of the pelvis, limited above and below by the planes of inlet and outlet of the pelvis. It has the appearance of a cylinder, truncated from front to back, with the front part facing the womb almost 3 times lower than the back part facing the sacrum. Due to this shape of the pelvic cavity, its various parts have different shapes and sizes. These sections are imaginary planes passing through identification points of the inner surface of the pelvis. In the small pelvis, the following planes are distinguished: the entrance plane, the wide part plane, the narrow part plane and the exit plane (Table 2.1; Fig. 2.7).
Plane of entry into the pelvis passes through the upper inner edge of the pubic arch, the innominate lines and the apex of the promontory. In the entrance plane, the following dimensions are distinguished (Fig. 2.8).
Straight size- the shortest distance between the middle of the upper inner edge of the pubic arch and the most prominent point of the cape. This distance is called true conjugata (conjugata vera); it is equal to 11 cm. It is also customary to distinguish the anatomical conjugate - the distance from the middle of the upper edge of the pubic arch to the same point of the promontory; it is 0.2-0.3 cm longer than the true conjugate (see Fig. 2.7).
Transverse size- the distance between the most distant points of the nameless lines of opposite sides. It is equal to 13.5 cm. This size intersects the true conjugate at a right angle eccentrically, closer to the cape.
Rice. 2.8. Dimensions of the plane of entry into the small pelvis.
1 - direct size (true conjugate);
2 - transverse size;
3 - oblique dimensions.
Oblique dimensions - right and left. The right oblique dimension goes from the right sacroiliac joint to the left iliopubic tubercle, and the left oblique dimension goes from the left sacroiliac joint to the right iliopubic tubercle. Each of these sizes is 12 cm.
As can be seen from the given dimensions, the entrance plane has a transverse oval shape.
The plane of the wide part of the pelvic cavity passes in front through the middle of the inner surface of the pubic arch, on the sides - through the middle of the smooth plates located under the fossae of the acetabulum (lamina acetabuli), and behind - through the articulation between the II and III sacral vertebrae.
Table 2.1 Planes and dimensions of the small pelvis
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