PB
Pelvic Brim
Pelvic brim is the iliopectineal line dividing the greater (false) pelvis from the lesser (true) pelvis.
RegionPelvis and Perineum
System-
The pelvic brim is a continuous, oval-shaped bony ridge that forms the edge of the pelvic inlet. It marks the anatomical boundary between the greater (false) pelvis above and the lesser (true) pelvis below. Composed of parts of the sacrum, ilium, and pubis, the pelvic brim serves as a critical landmark in obstetrics and radiology. It defines the upper limit of the pelvic cavity and is used to measure pelvic dimensions important for childbirth and surgical planning.
Structure
The pelvic brim is not a separate bone but a compound structure formed by a collection of ridges and lines from the pelvic bones. It outlines the superior aperture of the true pelvis.
Bony Components of the Pelvic Brim
| Component | Bone |
|---|---|
| Promontory | Sacrum |
| Ala (wing) | Sacrum |
| Arcuate Line | Ilium |
| Pectineal Line (Pecten Pubis) | Pubis |
| Pubic Crest | Pubis |
| Upper border of Pubic Symphysis | Pubis (midline junction) |
Location
The pelvic brim forms the circumference of the pelvic inlet. It begins at the sacral promontory, passes along the arcuate lines of the ilium, continues through the pectineal lines and pubic crests, and ends at the superior border of the pubic symphysis. It slants anteriorly and inferiorly due to the natural tilt of the pelvis in anatomical position.
Function
- Divides Pelvic Regions: Separates the greater pelvis (supporting abdominal contents) from the lesser pelvis (containing pelvic viscera)
- Structural Support: Acts as a rim that helps transmit body weight to the lower limbs through the pelvic ring
- Obstetric Landmark: Used to assess the adequacy of the pelvis for vaginal delivery
- Radiological Guide: Provides a consistent anatomic reference in imaging studies of the pelvis and lower abdomen
Clinical Significance
- Pelvic Shape Classification: The contour of the pelvic brim helps define pelvic types (gynecoid, android, anthropoid, platypelloid) in obstetrics
- Pelvimetry: Clinical or radiological measurement of pelvic brim diameter helps determine if the pelvis is adequate for vaginal delivery
- Obstruction Risk: Abnormalities or narrowing of the brim may impede fetal descent during labor
- Surgical Landmark: Used as a reference point during pelvic and lower abdominal surgeries for orientation and access planning
Published on May 9, 2025
Last updated on May 9, 2025
Last updated on May 9, 2025