The mechanism of birth in the plane pelvis

Flat rachitic pelvis. It was noted above that in the structure of flat rachitic pelvis characteristic is the direct reduction of the size of the entrance, while the transverse may even be increased. The cavity size and output may be higher than normal. These features of the structure of the pelvis mainly determine the mechanism of birth, characteristic of this form.
With the onset of labor head as normal birth, is set at the entrance of the pelvis with a slight bend to its arrow-shaped in cross stitch. But meeting obstacle in connection with reduction true conjugates, it is delayed at the entrance. In the future, with the development of labor activity, is its adaptation to the peculiarities of the structure of the pelvis and overcoming obstacles encountered. It consists in the following: when faced with an obstacle, the head makes two adaptive motion. The first is in one of its extension (Fig. 47) and the second in offset arrow-shaped bead wire axis of the pelvis to fold or sacrum (Fig. 48, 49). If swept the seam is deflected backwards (Fig. 49 and 50, 51),in the entrance of the pelvis before entering the front of the parietal bone (right or left, depending on the position of the fetus), and back - delayed at the Cape. This shift swept seam called anterior syncletica (or Nehalevsky decline, by author - Negelle described is the insertion of the head). On the contrary, if swept joint is anteriorly, i.e. to fold, then at the entrance of the pelvis is inserted posterior parietal bone, and the front, have delayed the womb. This shift swept seam is called the back syncletica (or limanowska declination) (Fig. 49,6), on behalf of the author, who described his (Litzmann).


Fig. 47. The direction of the expulsive force leads to the omission of a large fontanel.

Fig. 48. Syncleticea inserting head.

Fig. 49. Syncleticea inserting head.
a - front asinkritos; b - rear asinkritos.


Fig. 50. Inserting head in the plane pelvis - front asinkritos. Swept seam rejected to the Cape, the "front" half of the skull below "back".

Fig. 51. Prednamerennoe inserting head in flat rachitic the pelvis (bottom view).

At that time, under other equal conditions the education front acyclicity is considered as one of the types of fixtures head and under certain conditions can be abrupt ending, childbirth, rear asinkritos, occurring more rarely, is a severe complication.
Let us consider these two adaptive motion of the head, which makes it flat rachitic the pelvis, to overcome met at the entrance of the pelvis obstacles.
Extensor movement. Remember the shape and size of the head of the fruit (Fig. 52). The figure shows that bivariately head size more than bitemporal. If the head enters the entrance of the pelvis in a bent position, its more the transverse size (dist. biparietalis) is set in the middle of a circle of input, i.e. between the Cape and bosom, and the youngest (dist. bitemporalis) - is located away from the direct size.
Therefore, when flat rachitic the pelvis, which reduced the direct size of the input, the head of the state inflections would have to go through the narrowest part of it to its large size. Under the narrowing of the pelvic this is not possible and head for a long time remains fluid, crooked or straight, depending on labour, until then, until, finally, are its smaller cross-sectional dimension (bitemporal) between Cape sacrum and bosom. Larger head size (separately) will be rejected in this case, aside from the direct size of the pelvis. If by this time, the uterus will have sufficient tone, then such a modest extension head locks. When the internal investigation of the woman is the position of the head is characterized by the fact that a large fontanel will be determined on the same level with little or even slightly below it.


Fig. 52. Start inserting head in the plane pelvis. Bivariately size is set in the area of the true conjugates (bottom view).

Fig. 53. The passage head through flattened entrance of the pelvis, the head rotates "the back" half past the Cape.

Offset swept seam to sacrum (front asinkritos). Experience shows that the head and placed on the line of true conjugates even their smaller cross-sectional dimension, other favorable conditions to overcome the obstacle without additional adaptive movement (lateral declination) cannot.
The mechanism of flexion of the head of the sagittal axis consists in the following:
We know that the flat pelvis and, in particular, flat rachitic is formed as a result of moving to the front of the Cape (promontorium), while the pubic area of articulation is not broken. Therefore, Cape put forward in the lumen of the entrance of the pelvis, represents a major obstacle causing the delay promote head. This leads to the fact that during the battle the head under the influence of the expulsive force snuggles down, but at the same time adapting, makes and lateral flexion. At that the half of it (the parietal bone), which is addressed to the Cape, is delayed, and turned to fold down, - swept seam, thus, rejected the sacrum (Fig. 53).
Further parietal bone turned to a bosom, as development of labor activity falls lower and lateral decline head can be so pronounced that when vaginal examination near the womb can be achieved even in the ear of the fetus.
As soon as the front of the parietal bone pass the pubic joint, starts to fall, slipping from Cape, posterior parietal bone turned to the sacrum. Front asinkritos thus aligned - swept seam newly installed close to the middle of the pelvis (Fig. 54, a, b, C). While upstream parietal bone (delayed) always comes under the child and predlagayu (Fig. 55, a, b).


Fig. 54. The sequential stages of the mechanism of birth in the plane pelvis.
a - prednamerennoe inserting; - promotion of the "back" half head past the Cape; in the back of his head, breaking the bottleneck, falling, turns to the front.



Fig. 55.
and - in passing head through the narrow place the back of his head lowered and rotated toward the front; b - burying the bones of the skull in Suzanna the pelvis. Parietal bone above, comes under the child parietal. Front asinkritos.

In the further course of the mechanism of labor is no different from the mechanism under normal pelvis. If the head was the entrance of the pelvis, childbirth can end very quickly, as in the cavity and the output of the head of the obstacles are not met. The possibility of such a quick end childbirth, after overcoming head obstacles, should always be considered an obstetrician, so as not receive timely assistance can cause tearing of the perineum and adversely affect the condition of the child.
The emergence of the front acyclicity in the plane pelvis can contribute to the deviation of the uterus to the front, as it is observed in the prune belly; pelvic end of fruit together with the fundus of the uterus is rejected anteriorly, and the cylinder is shifted from the wire axis backwards.
This mechanism of births observed in flat rachitic the pelvis (front asinkritos), should be distinguished from the other alternative, characterized by the formation saddetelinara the inducement or rear acyclicity.
In contrast to the front at the rear singletime inclined parietal bone located at the Cape, and turned to fold - delayed and behind.
Swept seam in this case moves forward, that is to fold. In rare cases it is possible to see very marked flexion of the head, which swept the seam so deviates to the bosom that the Cape is determined ear of the fetus.
This feature is observed more often in nulliparous women with elastic abdominal wall, the so-called "acute abdomen". This buttocks fruit together with the fundus of the uterus pressed to the spine of the woman, and the head moves forward, to fold (Fig. 56, 57).


Fig. 56. Inserting head in the plane pelvis - back asinkritos.

Fig. 57. The burying the bones of the skull in Suzanna the pelvis. Parietal bone above, always comes child under the parietal bone. Rear asinkritos.

This option fixtures head of the fruit should be seen as less favourable, and if the position of the head is not corrected, on spontaneous delivery cannot be settled. If the monitoring process is established that the situation does not change and shift the crown is not possible, then at the back singletime childbirth should
to be completed quickly. In the presence of a living fetus, as a rule, through caesarean section.
Why rear asinkritos is less favourable in comparison with the front? The fact that these two provisions head is in various conditions. When the front singletime point, around which delayed the progress of the head is only a Cape which is by the length of a narrow strip, which the head overcomes through configuration. At that the head as it is in parts: first, the front half (addressed to fold), and then with a narrow ledge (Cape) is sliding back.
In the back of singletime delay the promotion of heads of two points: the bosom of that obstacle the head, and the promontory on which rests against the shoulder of a fetus. In contrast to Cape pubic joint represents an obstacle in the form of a narrow band, and much more in length, often reaching up to 3-4 see In this situation the head of the lower will fall back parietal bone (if the location of plocica fruit permits), the more will be above the fold of the front. Therefore, the longer without changing position continues childbirth, the worse the prognosis for the child and the mother.