Obstetrics and Gynecology - A.M. Hromova 2000

Pelvic Bone Anomalies
Anatomically Contracted Pelvis
Characteristics of Contracted Pelvises

The generally uniformly contracted pelvis is characterized by a proportional reduction (by 1.5-2 cm or more) in all pelvic dimensions. This pelvic type is typically observed in short women of asthenic or well-proportioned build.

The following varieties of generally uniformly contracted pelvis are distinguished:

1. Infantile pelvis. It occurs in women exhibiting morphological and functional signs of infantilism, such as underdeveloped secondary sexual characteristics, Menstrual disorders, etc. Along with reduced dimensions, the pelvis retains certain childhood features: the sacrum is narrow and poorly convex, the sacral promontory is high, and the pubic angle is acute.

2. Male-type pelvis. It is found in tall women with signs of intersexuality:

massive bones and male-pattern Hair distribution. Structurally, the pelvis resembles a male pelvis, featuring a high funnel-shaped pelvic cavity and an acute pubic angle.

3. Dwarf pelvis. It occurs in short women (120-145 cm) with a well-proportioned body build.

The Diagnosis of a contracted pelvis is based on external pelvimetry and vaginal examination data. The diagnosis can be confirmed using X-ray pelvimetry and ultrasound.

The transversely contracted pelvis is characterized by a reduction in all transverse pelvic dimensions by 0.5-1 cm or more compared to normal, without an increase in the true conjugate. The shape of the pelvic inlet is round or longitudinally oval (normally transversely oval). Flattening of the sacrum, insufficiently flared iliac wings, and a narrow pubic arch are frequently observed.

There are 3 degrees of narrowing for this type of pelvis (R.I. Kolganova, 1978) based on the reduction of the transverse diameter of the pelvic inlet plane (normally 13-13.5 cm):

Grade I: 12.4-11.5 cm

Grade II: 11.4-10.5 cm

Grade III: less than 10.5 cm.

Diagnosing a transversely contracted pelvis using conventional clinical Methods is somewhat challenging. The results of external measurements of the main pelvic dimensions in transverse contraction are of low diagnostic value. The greatest diagnostic significance lies in determining the transverse diameter of Michaelis' rhombus (less than 10 cm) and the transverse diameter of the pelvic outlet (less than 10.5 cm).

A definitive diagnosis of this pelvic shape is possible only through X-ray pelvimetry.

The flat pelvis is characterized by a reduction in the anteroposterior (straight) dimensions of the lesser pelvis with normal transverse dimensions.

1. The simple flat pelvis is characterized by a reduction in all anteroposterior dimensions due to the Displacement of the entire sacrum closer to the pubic arch. The pubic arch is wide, and the transverse diameter of the pelvic inlet is usually increased. Women with this pelvic type have a normal body build with no bone deformities.

Diagnosing this pelvic shape presents certain difficulties. During external pelvimetry, the transverse pelvic dimensions are normal, while the external conjugate is reduced. Vaginal examination reveals a shortened diagonal conjugate and anteroposterior dimension of the pelvic inlet plane. A definitive diagnosis can be established via X-ray pelvimetry.

2. The rachitic flat pelvis is characterized by a reduction in the anteroposterior dimension of the pelvic inlet plane (the true conjugate) and an increase in the anteroposterior dimensions of the lower planes. The sacrum is typically flattened, shortened, and rotated around a horizontal axis such that its base approaches the symphysis, while its apex and coccyx are directed backward, causing the sacral promontory to project sharply forward. The pelvic inlet is Kidney-shaped, and the pubic arch is wide. Consequently, the pelvic inlet plane appears flattened, while the underlying planes are relatively enlarged.

When diagnosing this pelvic shape, attention should be paid to signs of childhood Rickets ("square HEAD", bowed legs, etc.), a reduction in the vertical dimension of Michaelis' rhombus and A change in its shape (the suprasacral fossa is located lower, and the upper angle of Michaelis' rhombus becomes obtuse). The iliac wings are flared, making the distance between the anterior superior iliac spines (d. spinarum) and iliac crests (d. cristarum) almost equal (normally, the difference between them is about 3 cm), and the external conjugate is reduced. On vaginal examination, the sacral promontory is reachable, the coccyx is flattened, and a false promontory is sometimes identified, formed due to the Ossification of the Cartilage between the 1st and 2nd sacral vertebrae. A definitive diagnosis can be established using X-ray pelvimetry.

3. The pelvis with a reduced anteroposterior dimension of the broad part of the pelvic cavity is characterized by flattening of the sacrum up to the loss of its curvature, an increase in its length, a reduction in the anteroposterior dimension (less than 12.5 cm) of the broad pelvic cavity, and the absence of a difference between the anteroposterior dimensions of the pelvic inlet, the broad part, and the narrow part of the pelvic cavity. Other dimensions are usually normal or increased. Depending on the value of the anteroposterior dimension of the broad part of the pelvic cavity, two degrees of narrowing are distinguished:

Grade I: 12.4-11.5 cm;

Grade II: less than 11.5 cm.

Some authors consider this pelvic shape to be a mild or latent form of the rachitic flat pelvis.

The most informative diagnostic parameter for this pelvic shape is the pubococcygeal or pubosacral diameter, which is the distance from the middle of the Pubic Symphysis to the articulation point between the 2nd and 3rd sacral vertebrae. With normal dimensions of the broad part of the pelvic cavity, it is 21.8 cm. A value of less than 20.5 cm indicates the presence of a contracted pelvis, while a value below 19.3 cm suggests a pronounced reduction in the anteroposterior dimension of the broad part of the pelvic cavity (less than 11.5 cm). The definitive diagnosis is based on X-ray pelvimetry data.

The generally contracted flat pelvis. In this type, all dimensions are reduced, but the anteroposterior dimensions are shortened to a greater extent than the transverse ones. It occurs when infantilism is combined with childhood rickets.

The obliquely displaced (asymmetric) pelvis is more commonly observed in women following hip dislocations or malunited femoral fractures, where the primary load during walking falls on the healthy leg, shifting the center of support toward the healthy joint. The pelvic area corresponding to the healthy joint is pressed inward, and the hemipelvis on the side of the healthy leg becomes narrower. This type of pelvic deformity also occurs in rickets, gonitis, and Scoliosis.

The kyphotic pelvis is characterized by a reduction in dimensions toward the pelvic outlet, giving the pelvis a funnel-like shape. It results from childhood Tuberculous Spondylitis.

The spondylolisthetic pelvis is formed when the fifth lumbar vertebra slips off the Base of the sacrum, causing it to protrude over The surface of the first sacral vertebra and obstruct the descent of the fetal presenting part.

The osteomalacic pelvis develops As a result of bone softening and demineralization of the osseous tissue. The pelvis may acquire various shapes in this condition. It is extremely rare.

The assimilative (long) pelvis occurs when the sacrum is enlarged due to fusion with the fifth lumbar vertebra. It is characterized by a reduction in the anteroposterior dimensions of the pelvic cavity.

The funnel-shaped pelvis is characterized by a narrowing of the pelvic outlet cavity resulting from bone development disorders associated with endocrine dysfunctions. The sacrum is elongated, the pubic arch is narrow, and the transverse diameter of the outlet may be significantly reduced.