The pelvis is a basin like structure which connects the spine to lower limbs.
It is skeletal ring formed by 2 innominate (or) hip bone and the sacrum and the coccyx.
- Types of pelvic bones - 4
2 Hip bones (ilium, ischium, pubic)- Innominate
- Pelvic Joints - 4
2 Sacro-iliac joints
1 Pubic symphysis Joints
1 Sacro coccygeal joints
Types - 1. True pelvis (Bony)
2. False pelvis (Soft)
1. True Pelvis (Bony pelvis) :
The true pelvis is the bony canal through which the fetus passes through during birth.
It has 3 Parts - (a) Brim (inlet)
Borders of Brim, Cavity and Outlet - (BCO)
- Posterior- by sacrum
- Lateral - Pectineal lines
- In front - Upper margin of pubic symphysis and pubic crest.
- Anterior - Pelvic surface of the bodies of pubic bone, pubic rami and pubic symphysis.
- Posterior - Sacrum and coccyx
- Lateral - ischium
- Anterior - Lower margin of pubic symphysis.
- Lateral - Ischieal tuberosity
- Posterior - Hip of coccyx.
At inlet (cm) Cavity (cm) At outlet (cm)
Antero-posterior 11 12 13
Oblique 12 12 12
Transverse 13 12 11
2. False Pelvis (Soft pelvis) :
It is formed by Upper flared out portion of the ilium.
- Laterally by - Iliac fossa
- Posteriorly by - 5th lumbar vertebrae
- Anteriorly by - abdominal wall and inguinal ligament.
It protects the abdominal organs, It has no obstetrical importance except that it provide certain landmark for external pelvimetry.
Bones taller,heavier,thicker lighter, less dense
Iliac fossa more cocave Shallow
Asis Inturned Straight forward
Obstructed foramen large,oval Small , traingular
Pelvic inlet Heart shaped Round (longer)
Subpubic angle Narrow, 50-60 degree Wide,80-90degree
Ischial spine Inturned Outturned
Symphysis pubis Elongated Short
Obstetrical Importance :
- Adaptation of the fetal head in the pelvis during parturation.
- Evalution of the adequacy of the pelvis during obstetrical evalution.
- Angled conjugate- evaluated by per vaginal evalution.
- The size of the subpubic arch.
- Pelvis transmits the weight of the trunk to the legs acting as a bridge between femur.
- Affords protection to the pelvic organs to lesser extent to the abdominal context.