Pelvic inlet
Encyclopedia
The pelvic inlet or superior aperture of the pelvis
is a planar surface which is typically used to define the boundary between the pelvic cavity
and the abdominal cavity
(or, according to some authors, between two parts of the pelvic cavity, called lesser pelvis and greater pelvis).
Its position and orientation relative to the skeleton of the pelvis is anatomically defined by its edge, the pelvic brim
. The pelvic brim is an approximately apple-shaped line passing through the prominence of the sacrum
, the arcuate
and pectineal line
s, and the upper margin of the pubic symphysis
.
Occasionally, the terms pelvic inlet and pelvic brim are used interchangeably.
It has three principal diameters: antero-posterior (conjugate), transverse, and oblique.
Pelvis
In human anatomy, the pelvis is the lower part of the trunk, between the abdomen and the lower limbs .The pelvis includes several structures:...
is a planar surface which is typically used to define the boundary between the pelvic cavity
Pelvic cavity
-External links:* * *...
and the abdominal cavity
Abdominal cavity
The abdominal cavity is the body cavity of the human body that holds the bulk of the viscera. It is located below the thoracic cavity, and above the pelvic cavity. Its dome-shaped roof is the thoracic diaphragm , and its oblique floor is the pelvic inlet...
(or, according to some authors, between two parts of the pelvic cavity, called lesser pelvis and greater pelvis).
Its position and orientation relative to the skeleton of the pelvis is anatomically defined by its edge, the pelvic brim
Pelvic brim
The pelvic brim is the edge of the pelvic inlet. It is an approximately apple-shaped line passing through the prominence of the sacrum, the arcuate and pectineal lines, and the upper margin of the pubic symphysis....
. The pelvic brim is an approximately apple-shaped line passing through the prominence of the sacrum
Sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...
, the arcuate
Arcuate line (ilium)
The arcuate line of the ilium is a smooth rounded border on the internal surface of the ilium. It is immediately inferior to the iliac fossa and Iliacus muscle.It forms part of the border of the pelvic inlet....
and pectineal line
Pectineal line (pubis)
The pecten pubis or pectineal line of the pubis is a ridge on the superior ramus of the pubic bone.The pecten pubis forms part of the pelvic brim.Lying across it are fibers of the pectineal ligament and the proximal origin of the pectineus muscle....
s, and the upper margin of the pubic symphysis
Pubic symphysis
The pubic symphysis or symphysis pubis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis...
.
Occasionally, the terms pelvic inlet and pelvic brim are used interchangeably.
Boundaries
The edge of the pelvic inlet (pelvic brim) is formed as follows:| Anteriorly by the pubic crest Pubic crest Medial to the pubic tubercle is the pubic crest, which extends from this process to the medial end of the bone.It affords attachment to the inguinal falx, and to the External Abdominal Oblique and Pyramidalis.... (or pubic symphysis Pubic symphysis The pubic symphysis or symphysis pubis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis... ) |
>- | >- | Posteriorly by the anterior margin of the base of the sacrum Base of the sacrum The base of the sacrum, which is broad and expanded, is directed upward and forward.In the middle is a large oval articular surface, the upper surface of the body of the first sacral vertebra, which is connected with the under surface of the body of the last lumbar vertebra by an intervertebral... (or the ala of sacrum Ala of sacrum On either side of the body of the base of the sacrum is a large triangular surface, which supports the Psoas major and the lumbosacral trunk, and in the articulated pelvis is continuous with the iliac fossa... ) and sacrovertebral angle Sacrovertebral angle The sacrum is curved upon itself and placed very obliquely, its base projecting forward and forming the prominent sacrovertebral angle when articulated with the last lumbar vertebra.It is also known as the "lumbosacral angle".... (or sacral promontory Sacral promontory The sacral promontory is the anatomical term for the superiormost portion of the sacrum. It marks part of the border of the pelvic inlet. The rectosigmoid junction is at the level of the sacral promontory.... ) |
Diameters
It has three principal diameters: antero-posterior (conjugate), transverse, and oblique.
| Name | Description | Average measurement in female >- | anteroposterior or conjugate diameter or conjugata vera |
extends from the sacrovertebral angle (promontorium) to the pubic symphysis Pubic symphysis The pubic symphysis or symphysis pubis is the midline cartilaginous joint uniting the superior rami of the left and right pubic bones. It is located anterior to the urinary bladder and superior to the external genitalia; for females it is above the vulva and for males it is above the penis... ; |
>- | extends across the greatest width of the superior aperture, from the middle of the brim on one side to the same point on the opposite; | >- | extends from the iliopectineal eminence of one side to the sacroiliac articulation of the opposite side; | about 125 mm. |
