Narrow Pelvis

Currently, in obstetrics it is advisable to use a classification that allows to take into account such anatomical structures of the female pelvis as the shape of the entrance and the wide part of the cavity, the diameter of the pelvis, the shape and size of the anterior and posterior segments of the pelvis, the degree of curvature and incidence of the sacrum, and etc.

In 1865 A. Ya. Klassovsky published the "Course of Practical Obstetrics", which included a description of the abnormalities of the female pelvis. To the third edition of the manual (1885) A. Ya. Klassovsky wrote anew the chapter on narrow basins. This work presents an unsurpassed description of the most typical, as well as the most rare forms of narrow basins. GG Genter points out that "it is not as easy to give an accurate definition of a narrow pelvis as it seems at first glance." In most cases, the narrow pelvis refers to those in which one of the sizes is reduced by 1.5-2 cm compared with average or normal sizes. MS Malinovsky distinguishes:

1. anatomically narrow pelvis
2. functionally narrow pelvis.

The term "narrow pelvis" remains the main one, it is given this or that refinement depending on the clinical course of labor. Inconsistency can depend not only on the pelvis, but also on the size of the head, its ability to configure and insert.

In the 20th century, a number of obstetricians (Martin, Skrobansky KK) proposed the term "narrow pelvis" to apply only to those pelvis that gave birth to some signs of a discrepancy between the head and the pelvis; Tazes, having a reduced size, regardless of whether they gave one or other signs of incompatibility in childbirth or not, are suggested to be designated by "narrowed" pelvises. Thus, the concept of a narrow pelvis was given purely clinical significance. The term "clinically narrow pelvis" was used in relation to pelvises having normal external dimensions, in which the birth was complicated by some signs of discrepancy between the head and the pelvis.

Rational management of labor in the narrow pelvis is still one of the most difficult areas of practical obstetrics, since the narrow pelvis is one of the causes of maternal and child injuries, as well as the cause of maternal and perinatal mortality. There is also no single classification of the narrow pelvis. In the classification below, four basic "pure" forms of the pelvis are distinguished:

• gynecoid;
• android;
• anthropoid;
• platipelloid;
• "Mixed" forms.

In view of this classification, it must be emphasized that the plane passing through the largest transverse diameter of the pelvis and the posterior edge of the sciatic lobes divides the pelvis into the anterior and posterior segments. Mixed forms of the pelvis are formed from a combination of the posterior segment of one form with the anterior segment of the other.

When determining the shape of the pelvis, consider:

• form of entry;
• cavity shape;
• the value of the transverse and straight diameters;
• position of the pelvic wall;
• shape and size of the anterior and posterior segments of the pelvis;
• the size and shape of the large sciatic recess;
• the degree of curvature and incline of the sacrum and the shape of the lumbar arch.

The pelvic cavity can be compared with an obliquely truncated cylinder.

From the front, this cylinder has a height of 4 cm (height of the pubis), and at the back - 10 cm (height of the sacrum). On the sides, the height is 8 cm.

Anatomical characteristics of the main forms of the female pelvis.

Gynecoid maz. the shape of the entrance is round or cross-oval; well rounded anterior and posterior segments of the pelvis, a large sciatic recess of medium size, lateral walls of the pelvis are straight, broad interoast and intertuberous diameters, average inclination and curvature of the sacrum, wide pubic arch.

The android pelvis. the shape of the entrance approaches the triangular, the trailing angle is narrow, since the anterior segment is narrow; flat wide posterior segment, large sciatic recess narrow, converging pelvic walls, short interostic and bituberous diameters, anterior incline and small curvature of the sacrum, narrow lobar arch.

The anthropoid form of the entry is longitudinal-oval, long narrow segments of the pelvis, the straight diameters of the pelvis are elongated, the transverse diameters are shortened, the pelvic walls are straight, the median slope and curvature of the sacrum, a large sciatic recess of medium size, the pubic arch is somewhat narrowed.

Platipelloidal mas. The entry form is transversely oval, a wide well rounded posterior angle, a wide flat posterior segment, a large sciatic recess narrow, pelvic walls straight, long transverse and shortened straight pelvic diameters, median slope and curvature of the sacrum.

In addition to dividing the female pelvis according to the form, it is subdivided by its size into small, medium, large.

Taz of small size. Transverse diameters: the largest transverse diameter of the entrance is 11.5-12.5 cm, interostic - 10 cm, bituberous - 9.5 cm.

Straight diameters: the entrance is 10.5-11 cm, the wide part is 12-12.5 cm, the narrow part is 11 cm.

The pelvis is of medium size. Transverse diameters: the largest transverse diameter of the entrance is 12.5-14 cm, the interstitial diameter is 10-11 cm, the bituminous diameter is 9.5-10 cm.

Straight diameters: the entrance is 11-11.5 cm, the wide part is 12.5-13 cm, the narrow part is 11-11.5 cm.

A large basin. Transverse diameters: the largest transverse diameter of the entrance is 14 cm or more, interstitial - 11-11.5 cm, bituberous - 10 cm and more.

Straight diameters: the entrance is 11.5 cm or more, the wide part is 13 cm or more, the narrow part is 11.5 cm or more.

Of greatest interest is the management of labor in parturient women with a small pelvis - anatomically narrow. However, the narrow pelvis is now rarely seen, the erased forms of the narrow pelvis are more often observed. Especially important is the evaluation of the pelvis depending on the shape and size of it and the weight of the fetus. It was found that the shape of the pelvis affects the mechanism of birth, and, knowing the shape of the pelvis, it is possible to predict with greater or lesser degree the mechanism and outcome of births. Whether there will be any signs of discrepancy between the pelvis and the fetal head, in the vast majority of cases, it is impossible to predict; in most cases, the final diagnosis is established in childbirth.

The classification of A. Ya. Klassovsky (1885)

A. Extensive Pellets.

B. Narrow basins.

1. Uniformly compressed pelvis:
   1. uniformly compressed pelvis;
   2. dagger of dwarfs;
   3. children's pelvis.
2. Unevenly-concentrated pelvis:
   1. Flat Basins:
      1. simple flat pelvis;
      2. rachitic flat pelvis;
      3. flat luxational pelvis with bilateral hip dislocation;
      4. common flat pelvis.
   2. Skewers:
      1. ankylotic pelvic convoluted pelvis;
      2. coxalgic, coagulated pelvis;
      3. scoliosis-related coagulated pelvis;
      4. kyphoscoliosorrhagic coagulated pelvis;
      5. basins with a unilateral hip dislocation.
   3. Transversely tended pelvis:
      1. ankylotic pelvic arched pelvis;
      2. kyphotic transversal pelvis;
      3. spondylolystic transversal pelvis;
      4. funnel-shaped transversal pelvis.
   4. Collapsed basins:
      1. osteomalacic jointed pelvis;
      2. ricketed sleeping pelvis.
   5. Split or open the front of the pelvis.
   6. Awnless pelvis.
   7. Tazes with neoplasm.
   8. Tazes are closed.

In this classification A. Ya. Klassovsky included both frequently occurring and rare forms of narrow basins.

For the diagnosis of a narrow pelvis a woman must be thoroughly examined. For example, with an anthropoid form of the pelvis with elongated straight and shortened transverse diameters, the insertion of the head occurs with a sagittal suture in the forward or in one of the oblique pelvic diameters, i.e. The largest diameter of the head is set in the largest diameter of the pelvis. The biparietal diameter of the head, as its narrowest size, passes through the narrowest diameter of the pelvis in any plane. The pelvic value less influences the delivery mechanism than its shape. In women with small pelvic size, spontaneous labor is observed when there is no disproportion between the size of the fetal head and the pelvic size. With large pelvic size and large fruit, spontaneous delivery may not be possible due to a disproportion between the size of the pelvis of the mother and the size of the fetal head. According to the research, the following forms of the pelvis were revealed by the method of studying direct and lateral radiographs: gynecoid - in 49.9% of women, android-gynecoid - in 18.9%, flat-scabies - in 11.7%, anthropoid in 10.6%, platipelloid - 0.6%. In addition to the above forms, the authors in 8.3% of women identified a new form of pelvis, which is characterized by a shortening of the direct diameter of a wide part of the cavity due to straightening of the curvature of the sacrum and its flattening. In connection with the flattening of the sacrum, in some cases, the direct entry diameter may be larger than the direct diameter of the wide part of the cavity. With such a structure of the pelvis, the inlet capacity will be larger than the capacity of the wide part of the cavity, and moving the head along the birth canal may encounter an obstacle in the wide part of the pelvic cavity. In addition, a small pelvis was detected in 39.6% of women, middle - in 53.62% and pelvis of large sizes - in 6.78%.

When the gynecoid form prevails, the average size of the pelvis is 81.4%, and a small pelvis with this form is observed in 13.92%. With the shape of the pelvis with a shortening of the straight diameter of the wide part of the cavity, the small pelvis met in 80.4%, and with a flat pelvis - in all 100% of cases. In the case of flat-brachial and android-gynecoid forms, a small pelvis was detected in half of the cases.

[1], [2], [3], [4]