DIAMETER OF PELVIS
- Diameter of the pelvis brim ,cavity and outlet is very important to find out any abnormality.
The brim of the pelvis is the bony rim (edge) that forms the boundary of the pelvic inlet .
Brim of the pelvis formed by these landmarks ‘
THE PELVIS INLET ALSO CALLED BRIM
The pelvic brim is formed by these landmarks from back to front .
1-Sacral promontory
2-Alae of the sacrum
3-Sacroiliac joints
4-Iliopectineal lines
5-Iliopectineal eminencies
6-Upper border of the superior pubic rami
7- Pubic tubercles
8-Pubic crest
9-Upper border of the symphysis pubis
What is brim
the pelvic brim is the bony ring that separates the false pelvis from the true pelvis.
Diameters of pelvic brim – 3 types
1- Antero-Posterior diameter
3 types of diameter present in Anterior posterior diameter of the pelvis brim .
1- True conjugate.– Measured from sacral promontary to upper border of the symphysis pubis – 11 cm
2- Obstetric conjugate – Measured from sacral promontary to middle of the symphysis pubis -10 cm
3- Diagonal conjugate – Measure from the sacral promontary to lower border of symphysis pubis -12 cm ( Largest)
2- Transeverse diameter
Transverse diameter of pelvic brim = 13 cm (approximately)
It is the widest diameter of the pelvic inlet (brim).
Measured between the farthest points of the iliopectineal lines
It is the largest diameter of the pelvic brim
Average length: ≈ 13 cm
3-Oblique diameter – Measure from the sacroiliac joint to iliopubic eminence
Oblique diameter of pelvic brim means the distance from one sacroiliac joint to the opposite iliopubic eminence.
Two oblique diameters: right and left
Measured from:
Right sacroiliac joint to→ Left iliopubic (iliopectineal) eminence
Left sacroiliac joint to → Right iliopubic eminence
Average length: ≈ 12 cm
Sacro- cotyloid diameter -it is the distance from the middle point of sacral promontory to iliopubic eminence which is 9.5 cm (there are two sacrocotyloid diameter)
Diameter of Pelvic cavity
WHAT IS PELVIC CAVITY
Pelvic cavity is is the space within the true pelvis between the pelvic inlet and pelvic outlet that contains pelvic organs .
in the pelvic cavity ,the shape is almost round so anteroposterior ,transverse ,and oblique diameters are nearly equal .12 cm
There are 3 types of pelvic cavity diameters
1-Anteroposterior diameter – It is extends from the centre of the posterior surface of the pubic symphysis which is present anteriorly to the to the junction of the second and third sacral vertebrae .the diameter is 12 cm .
2-Transverse diameter – the transverse diameter of pelvic cavity is the widest side to side distance of the pelvis but we can not measure it exactly because the point we need measure are not on hard bones but on soft tissues that cover the sacrosciatic notches and obturator foramina.
What is Pelvic outlet ?
Pelvic outlet is the inferior opening of the true pelvis through which the fetus passes during delivery.
it appears diamond shaped because of its boundaries:
Anterior: Lower border of symphysis pubis
Lateral: Right & left ischial tuberosities
Posterior: Tip of coccyx
. 1 -Anteroposterior diameter (AP diameter)
It is from the lower border of the symphysis pubis to .
Anatomical – Tip of the coccyx( used for anatomy study)
Obstetrics – Tip of the sacrum(to assess during child birth ) the diameter is 13 cm .
2. Transverse diameter
Transverse diameter of pelvic outlet is the distance between the two ischial tuberosities (about 11 cm).
a- Bituberous diameter
Bituberous diameter is the distance between the two ischial tuberosities at the pelvic outlet (about 11 cm).
The transverse diameter of the pelvic outlet is also called the bituberous (intertuberous) diameter.
b- Bispinous / Interspinous diameter.
It is the narrowest transverse diameter of the pelvis (important in labor).
Key points
Measured between right and left ischial spines
Also called interspinous diameter
Average measurement: ≈ 10.5 cm
Assessed clinically during vaginal examination