Obstetrics and Gynecology - A.M. Gromova 2000

Anomalies of the Bony Pelvis
Anatomically Contracted Pelvis
Diagnosis

To diagnose a contracted pelvis in a pregnant woman, it is necessary to evaluate her height, body mass, and body type, identify any shortening of the limbs (short fingers are an indicator of a contracted pelvis), spinal deformities, or signs of past Rickets or Osteomyelitis. It is advisable to check whether forceps delivery or a Cesarean Section was performed during previous labors, and to investigate any history of traumatic Brain injury in the child or stillbirth. During the obstetric examination, attention should be paid to the shape of the abdomen. A pendulous or pointed abdomen indicates a contracted pelvis.

In the absence of engagement of the fetal presenting part, a higher standing of the uterine fundus is observed. Since there is insufficient space for the Uterus within the Abdominal cavity (especially in short-stature women), it deviates toward the path of least resistance, which is forward.

As a result, in primigravidas with firm abdominal walls, the upper part of the abdomen becomes significantly elongated, forming a so-called pointed abdomen. In multiparous women, due to laxity of the abdominal wall, the uterus bends sharply forward, protruding the middle and lower PARTS OF THE abdomen, which results in a so-called pendulous abdomen.

Signs of pelvic contraction may include pronounced lumbar lordosis and an incomplete thigh-closing line.

Of great importance in diagnosing a contracted pelvis is the shape of the Michaelis rhombus, which appears vertically elongated in a generally evenly contracted pelvis, flattened in a flat pelvis, and asymmetric (with sides of different dimensions) in a generally unequally contracted pelvis.

The primary method for examining the pelvis is its external measurement using a pelvimeter.

External pelvimetry makes it possible to detect deviations from normal pelvic dimensions and assess their severity:

✵ dist. spinarum - 25-26 cm;

✵ dist. cristarum - 28-29 cm;

✵ dist. trochanterica - 30-31 cm;

✵ conjg. externa - 20-21 cm;

✵ conjg. diagonalis - 12.5-13 cm;

✵ Michaelis rhombus: vertical diameter - 11 cm, transverse diameter - 10 cm;

✵ Solovjev index - 1.4-1.6 (the circumference of the pregnant woman's wrist divided by 10);

✵ direct diameter of the pelvic outlet - 9.5 cm;

✵ transverse diameter of the pelvic outlet - 11 cm;

✵ pubic angle - 90-100°;

✵ pubosacral diameter (the distance from the midpoint of the anterior surface of the symphysis to the Articulation of the S_II and S_III vertebrae) - 21.8 cm (a value of 20.5 cm indicates a contracted pelvis, while 19.3 cm indicates a marked reduction in the anteroposterior diameter of the pelvic cavity's wide part);

✵ height of the Pubic Symphysis - 4-5 cm (in cases of a high pubic symphysis, 0.5 cm must be subtracted from the true conjugate).

External oblique pelvic diameters:

✵ distance from the anterior-superior iliac spine of one side to the posterior-superior iliac spine of the other side and vice versa — 21 cm;

✵ distance from the upper margin of the symphysis to the right and left posterior-superior iliac spines - 17.5 cm;

✵ distance from the supra-sacral fossa to the right and left anterior-superior iliac spines - 18 cm;

✵ Baudelocque's conjugate - 15 cm;

✵ pelvic inclination angle in the supine position - 30°, in the standing position - 55-60°;

✵ pelvic circumference at the level of the upper vertex of Michaelis rhombus, the sacrum, iliac bones, and the upper margin of the symphysis is 85 cm (a value close to 75 cm strongly indicates significant pelvic narrowing);

✵ pelvic circumference along the trochanteric line (lin. trochanterica) is 90–95 cm;

The estimated dimensions of the fetus are determined by measuring:

✵ abdominal circumference at the umbilical level (90–95 cm at term Pregnancy);

✵ height of the uterine fundus (32–34 cm at term pregnancy);

✵ fetal HEAD diameter (12 cm at term pregnancy).

More reliable data regarding the dimensions and capacity of the pelvis are obtained through vaginal examination by measuring the diagonal conjugate, assessing the sacral cavity, ischial spines and tuberosities, and detecting any exostoses, false promontories, or other deformities within the lesser pelvis.

The true conjugate can be determined from the diagonal conjugate by subtracting 1.5 or 2 cm, depending on the thickness of the woman's bones.

The thickness of the parturient woman's bones (and consequently the thickness of the pelvic bones) is indicated by the wrist index (Solovyov's index), as well as the height of the pubic symphysis, which is determined by grasping the upper and lower margins of the pubic symphysis with the thumb and index finger. Normally, it is 4–5 cm.

If necessary, X-ray pelvimetry (performed after 37 weeks of gestation) or pelvic Ultrasonography is utilized.