The structure of the female pelvis. obstetric research. Pelvis measurement and conjugates Determination of the true conjugate by the Michaelis diamond

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Pelvis dimensions are of key importance in obstetrics: they determine the possibility and the proposed mechanism of childbirth, are necessary for choosing the tactics of childbirth, indications for a caesarean section.

wire axle= midpoints of straight dimensions

Anatomical conjugate- from the middle of the upper edge of the pubic arch to the most protruding point of the cape = true conjugate+ 0.2-0.3 cm

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Pelvic plane	Landmarks	Dimensions (cm)
Pelvic plane	Landmarks	Straight (cm)		Transverse (cm)		oblique (cm)
Login	Upper inner edge of the pubic arch, nameless lines, summit of the sacrum		the middle of the upper inner edge of the pubic arch is the most protruding point of the cape = true conjugate	13,5	between the most distant points of the nameless lines		right - from the right sacroiliac joint to the left iliac-pubic tubercle, the left - vice versa)
wide part	The middle of the inner surface of the pubic arch, the middle of the smooth plates, the articulation between II and III sacral vertebrae	12,5	the middle of the inner surface of the pubic arch - the articulation between II and III sacral vertebrae	12,5	between the most distant points of the acetabulum
bottleneck	The lower edge of the pubic joint, ischial bones, sacrococcygeal joint	11,5	lower edge of the pubic arch - sacrococcygeal joint	10,5	between the inner surfaces of the ischial spines
Exit	The lower edge of the pubic arch, the inner surfaces of the ischial tuberosities, the tip of the coccyx (two planes converging at an angle along the line connecting the ischial tuberosities)	9,5 (11,5)	the middle of the lower edge of the pubic joint - the tip of the coccyx		between the most distant points of the inner surfaces of the ischial tuberosities

true conjugate.

True, or obstetric, conjugate(conjugata vera, s. obstetrica) is called the shortest distance between the cape and the most prominent point in the pelvic cavity on the inner surface of the symphysis. Normally, this distance is 11 cm.

Exists four main ways to determine the size of conjugata vera.

By the size of the outer conjugates. For example, with an external conjugate of 20 cm and a Solovyov index of 1.2, 8 cm must be subtracted from 20 cm, we get a true conjugate equal to 12 cm; with a Solovyov index of 1.4, subtract 9 cm from 20 cm; with a Solovyov index of 1.6, 10 cm must be subtracted, the true conjugate will be equal to 10 cm, etc.

By the size of the diagonal conjugate. To do this, the Solovyov index is subtracted from the length of the diagonal conjugate. For example, subtracting from the value of the diagonal conjugate (10.5 cm) Solovyov's index 1.4, we obtain a true conjugate of 9.1 cm (I degree of narrowing of the pelvis), and subtracting 1.6 - 8.9 cm (II degree of narrowing of the pelvis).

According to the size of the vertical size of the Michaelis rhombus (distantia Tridondani). The vertical size of the rhombus corresponds to the size of the true conjugate.

By the value of the Frank index (distance from the incisura jugularis to the spinous process of the VII cervical vertebra). This size corresponds to the size of the true conjugate.

External conjugate. To determine the true conjugate, 9 cm is subtracted from the length of the outer conjugate. For example, if the outer conjugate is 20 cm, then the true conjugate is 11 cm; if the outer conjugate is 18 cm long, then the true conjugate is 9 cm, and so on.

The difference between the external and true conjugate depends on the thickness of the sacrum, symphysis and soft tissues. The thickness of the bones and soft tissues in women is different, so the difference between the size of the outer and true conjugate is not always exactly 9 cm. The true conjugate can be more accurately determined by the diagonal conjugate.

Diagonal conjugate(conjugata diagonalis) is the distance from the lower edge of the symphysis to the most prominent point of the promontory of the sacrum. The diagonal conjugate is determined during a vaginal examination of a woman, which is performed in compliance with all the rules of asepsis and antisepsis. II and III fingers are inserted into the vagina, IV and V are bent, their rear rests against the perineum. The fingers inserted into the vagina are fixed at the top of the promontory, and with the edge of the palm rest against the lower edge of the symphysis. After that, 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 tazometer or centimeter tape.

Distantia spinarum - the distance between the anterior-superior iliac spines is 25-26 cm.
Distantia cristarum - the distance between the distant points of the iliac crests is 28-29 cm.
Distantia trochanterica - the distance between the large trochanters of the femur, normally 30-31 cm.
Conjugata externa (external conjugate, direct size of the pelvis) - the distance from the middle of the upper outer edge of the symphysis to the supra-sacral fossa, located between the spinous process of the V lumbar vertebra and the beginning of the middle sacral crest (coincides with the upper corner of the Michaelis rhombus), is 20-21 cm.

Small pelvis dimensions

1. The plane of entry into the pelvis is limited by the upper edge of the symphysis, the upper-inner edge of the pubic bones (in front), the arcuate lines of the ilium (from the sides), and the sacral promontory (behind). This border between the large and small pelvis is called the boundary (nameless) line.

Conjugata vera (true conjugate, direct size of the entrance to the small pelvis) - the distance from the inner surface of the symphysis to the cape of the sacrum; to determine the true conjugate, subtract 9 cm from the dimensions of the outer conjugate. Normally, the true conjugate is 11 cm.
Anatomical conjugate - the distance from the cape to the middle of the upper inner edge of the symphysis (11.5 cm).
Transverse size - the distance between the most distant points of the arcuate lines (13-13.5 cm).
The oblique dimensions are 12-12.5 cm. The right oblique dimension is the distance from the right sacroiliac joint to the left iliopubic eminence (eminentia iliopubica). Left oblique size - the distance from the left sacroiliac joint to the right iliopubic eminence (eminentia iliopubica).

2. The plane of the wide part of the pelvic cavity is limited by the middle of the inner surface of the symphysis (in front), the middle of the acetabulum (from the sides) and the junction of the II and III sacral vertebrae (behind).

Direct size - the distance from the junction of the II and III sacral vertebrae to the middle of the inner surface of the symphysis is 12.5 cm.
Transverse size - the distance between the middle of the acetabulum (12.5 cm).

3. The plane of the narrow part of the pelvic cavity is limited by the lower edge of the symphysis (in front), the spines of the ischial bones (from the sides) and the sacrococcygeal junction (behind),

Direct size - the distance from the sacrococcygeal junction to the lower edge of the symphysis (11-11.5 cm).
Transverse size - the distance between the spines of the ischial bones (10.5 cm).

4. The plane of the exit of the pelvis is limited by the lower edge of the symphysis (in front), ischial tubercles (from the sides) and the tip of the coccyx (behind).

Direct size - from the top of the coccyx to the lower edge of the symphysis (9.5 cm). When the coccyx moves backward during childbirth - 11.5 cm.
Transverse size - the distance between the inner surfaces of the ischial tubercles (11 cm).

sacral rhombus

When examining the pelvis, pay attention to the sacral rhombus (Michaelis rhombus) - a platform on the back surface of the sacrum. Borders: upper corner - a depression between the spinous process of the V lumbar vertebra and the beginning of the middle sacral crest; lateral angles - posterior superior iliac spines; lower - the top of the sacrum. From above and outside, the rhombus is limited by protrusions of the large dorsal muscles, from below and outside - by protrusions of the gluteal muscles.

Conjugate external (c. externa) distance from the fossa between the spinous processes of the V lumbar and I sacral vertebrae to the middle of the outer (anterior) surface of the pubic symphysis.

Big Medical Dictionary. 2000 .

See what "external conjugate" is in other dictionaries:

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In the pelvis, a large and a small pelvis are distinguished.
The large and small pelvis are separated by an unnamed line. The differences between the female and male pelvis are as follows: in women, the wings of the ilium are more deployed, a more voluminous small pelvis, which in women has the shape of a cylinder, and in men the shape of a cone. The height of the female pelvis is less, the bones are thinner.

Measuring the dimensions of the pelvis:

To assess the capacity of the pelvis, 3 external dimensions of the pelvis and the distance between the femurs are measured. The measurement of the pelvis is called pelvimetry and is carried out using a pelvisometer.

External dimensions of the pelvis:
1. Distancia spinarum - interspinous distance - the distance between the anterior superior iliac spines (spine - spina), in a normal pelvis is 25-26 cm.
2. Distancia cristarum - intercrest distance - the distance between the most distant points of the iliac crests (comb - crista), normally equals 28-29 cm.
3. Distancia trochanterica - intertuberous distance - the distance between the large tubercles of the trochanters of the femur (large tubercle - trochanter major), normally equals 31 cm.
4.
Conjugata externa - external conjugate - the distance between the middle of the upper edge of the symphysis and the supra-sacral fossa (depression between the spinous process of the V lumbar and I sacral vertebrae). Normally it is 20-21 cm.

When measuring the first three parameters, the woman lies in a horizontal position on her back with outstretched legs, the buttons of the tazomer are set on the edges of the size. When measuring the direct size of the wide part of the pelvic cavity To better identify the large trochanters, the woman is asked to bring the toes of her feet together. When measuring the external conjugates, the woman is asked to turn her back to the midwife and bend her lower leg.

Pelvic planes:

In the cavity of the small pelvis, conditionally, four classical planes are distinguished.
The 1st plane is called the entry plane. It is bounded in front by the upper edge of the symphysis, behind - by the cape, from the sides - by the nameless line. The direct size of the entrance (between the middle of the upper inner edge of the symphysis and the promontory) coincides with the true conjugate (conjugata vera).
In a normal pelvis, the true conjugate is 11 cm. The transverse dimension of the first plane - the distance between the most distant points of the boundary lines - is 13 cm. Two oblique dimensions, each of which is 12 or 12.5 cm, go from the sacroiliac joint to the opposite iliac - pubic tubercle. The plane of the entrance to the small pelvis has a transverse-oval shape.

The 2nd plane of the small pelvis is called the plane of the wide part. It passes through the middle of the inner surface of the womb, sacrum and projection of the acetabulum. This plane has a rounded shape. The direct size, equal to 12.5 cm, goes from the middle of the inner surface of the pubic articulation to the articulation of the II and III sacral vertebrae. The transverse dimension connects the middle of the plates of the acetabulum and is also 12.5 cm.

The 3rd plane is called the plane of the narrow part of the small pelvis. It is bounded in front by the lower edge of the symphysis, behind by the sacrococcygeal joint, and laterally by the ischial spines. The direct size of this plane between the lower edge of the symphysis and the sacrococcygeal joint is 11 cm.
The transverse dimension - between the inner surfaces of the ischial spines - is 10 cm. This plane has the shape of a longitudinal oval.

The 4th plane is called the exit plane and consists of two planes converging at an angle. In front, it is limited by the lower edge of the symphysis (as well as the 3rd plane), from the sides by the ischial tuberosities, and behind by the edge of the coccyx. The direct size of the exit plane goes from the lower edge of the symphysis to the tip of the coccyx and is equal to 9.5 cm, and in the case of the departure of the coccyx it increases by 2 cm. The transverse size of the exit is limited by the internal surfaces of the ischial tuberosities and is 10.5 cm. longitudinal oval shape. The wire line, or the axis of the pelvis, passes through the intersection of the direct and transverse dimensions of all planes.

Internal dimensions of the pelvis:

The internal dimensions of the pelvis can be measured with ultrasonic pelvimetry, which is not yet widely used. With a vaginal examination, the correct development of the pelvis can be assessed. If the cape is not reached during the study, this is a sign of a capacious pelvis. If the cape is reached, the diagonal conjugate is measured (the distance between the lower outer edge of the symphysis and the cape), which should normally be at least 12.5-13 cm. in a normal pelvis - at least 11 cm.

The true conjugate is calculated using two formulas:
The true conjugate is equal to the outer conjugate minus 9-10 cm.
The true conjugate is equal to the diagonal conjugate minus 1.5-2 cm.

With thick bones, the maximum figure is subtracted, with thin bones, the minimum. To assess the thickness of the bones, the Solovyov index (wrist circumference) was proposed. If the index is less than 14-15 cm - the bones are considered thin, if more than 15 cm - thick. The size and shape of the pelvis can also be judged by the shape and size of the Michaelis rhombus, which corresponds to the projection of the sacrum. Its upper angle corresponds to the supra-sacral fossa, the lateral ones to the posterior superior iliac spines, and the lower one to the apex of the sacrum.

The dimensions of the exit plane, as well as the external dimensions of the pelvis, can also be measured using a pelvis.
The angle of the pelvis is the angle between the plane of its entrance and the horizontal plane. In the vertical position of a woman, it is equal to 45-55 degrees. It decreases if the woman squats or lies in a gynecological position with legs bent and brought to the stomach (possible position in childbirth).

The same positions allow you to increase the direct size of the exit plane. The angle of inclination of the pelvis increases if the woman lies on her back with a roller under her back, or if she bends back when she is upright. The same happens if a woman lies on a gynecological chair with her legs down (Walcher's position). The same provisions allow you to increase the direct size of the entrance.

Pelvis dimensions

Usually four sizes of the pelvis are measured: three transverse and one straight.

Distantia spinarum- the distance between the anterior superior iliac spines. The buttons of the tazomer are pressed against the outer edges of the anterior superior spines. This size is usually 25 - 26 cm.

Distantia cristarum- the distance between the most distant points of the iliac crests. After measuring distantia spinarum, the buttons of the tazomer are moved from the spines along the outer edge of the iliac crest until the greatest distance is determined, this distance will be distantia cristarum, it averages 28 - 29 cm.

Distantia trochanterica- the distance between the greater trochanters of the femur. They look for the most prominent points of the large skewers and press the buttons of the tazomer to them. This size is 30 - 31 cm. The size of the outer dimensions can be used with some caution to judge the size of the small pelvis. The ratio between the transverse dimensions is also important. For example, normally the difference between distantia spinarum and distantia cristarum is 3 cm, if the difference is less, this indicates a deviation from the norm in the structure of the pelvis.

Conjugata externa- external conjugate, i.e., the direct size of the pelvis. The woman is laid on her side, the underlying leg is bent at the hip and knee joints, the overlying one is pulled out. The button of one branch of the tazomer is set in the middle of the upper outer edge of the symphysis, the other end is pressed against the supra-sacral fossa, which is located between the spinous process of the V lumbar vertebra and the beginning of the middle sacral crest (the supra-sacral fossa coincides with the upper corner of the sacral rhombus).

The external conjugate is normally 20–21 cm. The upper outer edge of the symphysis is easily determined, to clarify the location of the supracacral fossa, slide your fingers along the spinous processes of the lumbar vertebrae towards the sacrum, the fossa is easily determined by touch under the protrusion of the spinous process of the last lumbar vertebra.

The outer conjugate is important; its value can be used to judge the size of the true conjugate. To determine the true conjugate, 9 cm is subtracted from the length of the outer conjugate. For example, with an outer conjugate equal to 20 cm, the true conjugate is 11 cm, with an outer conjugate 18 cm long, the true conjugate is 9 cm, etc. The difference between the outer and true conjugate depends on the thickness of the sacrum, symphysis and soft tissues. The thickness of the bones and soft tissues in women is different, so the difference between the size of the outer and true conjugate is not always exactly 9 cm. The true conjugate can be more accurately determined by the diagonal conjugate.

Diagonal conjugate (conjugata diagonalis) called the distance from the lower edge of the symphysis to the most prominent point of the promontory of the sacrum. The diagonal conjugate is determined during a vaginal examination of a woman, which is performed in compliance with all the rules of asepsis and antisepsis. II and III fingers are inserted into the vagina, IV and V are bent, their rear rests against the perineum. The fingers inserted into the vagina are fixed at the top of the cape, and the edge of the palm rests against the lower edge of the symphysis.

After that, 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 located in the vagina is removed and measured with a pelvis or centimeter tape using another person, the distance from the top of the third finger to the point in contact with the lower edge of the symphysis. The diagonal conjugate with a normal pelvis is on average 12.5-13 cm. To determine the true conjugate, 1.5-2 cm is subtracted from the size of the diagonal conjugate.

It is not always possible to measure the diagonal conjugate, because with normal dimensions of the pelvis, the promontory is not reached or can be felt with difficulty. If the cape cannot be reached with the end of the extended finger, the volume of this pelvis can be considered normal or close to normal. The transverse dimensions of the pelvis and the external conjugate are measured in all pregnant women and women in labor without exception. If during the examination of a woman there is a suspicion of a narrowing of the pelvic outlet, the size of this cavity is determined.

The dimensions of the outlet of the pelvis are determined as follows. The woman lies on her back, her legs are bent at the hip and knee joints, spread apart and pulled up to her stomach. The direct size of the exit of the pelvis is measured with a conventional pelvis meter. One button of the tazomer is pressed to the middle of the lower edge of the symphysis, the other to the top of the coccyx. The resulting size (11 cm) is larger than the true one.

To determine the direct size of the exit of the pelvis, subtract 1.5 cm from this value (taking into account the thickness of the tissues). The transverse size of the outlet of the pelvis is measured with a centimeter tape or a pelvis with crossed branches. Feel the inner surfaces of the ischial tuberosities and measure the distance between them. To the obtained value, you need to add 1 - 1.5 cm, taking into account the thickness of the soft tissues located between the buttons of the tazomer and the ischial tubercles. Known clinical significance is the definition of the shape of the pubic angle.

With normal pelvic dimensions, it is 90 - 100 °. The shape of the pubic angle is determined by the following method. The woman lies on her back, her legs are bent and pulled up to her stomach. With the palmar side, the thumbs are applied close to the lower branches of the pubic and ischial bones, the touching ends of the fingers are pressed against the lower edge of the symphysis. The location of the fingers allows you to judge the magnitude of the angle of the pubic arch. The oblique dimensions of the pelvis have to be measured with an oblique pelvis.