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Lesser (True) Pelvis
Lesser (true) pelvis is the space below the pelvic brim housing the pelvic organs.
RegionPelvis and Perineum
System-
The lesser pelvis, also called the true pelvis, is the portion of the pelvic cavity located below the pelvic brim. It is a funnel-shaped space enclosed entirely by bone and forms the bony walls of the true pelvic cavity, which contains key pelvic viscera such as the urinary bladder, rectum, and reproductive organs. The lesser pelvis is especially important in obstetrics, as it forms the bony birth canal through which the fetus must pass during vaginal delivery.
Structure
The lesser pelvis is bounded superiorly by the pelvic brim and inferiorly by the pelvic outlet. Its walls are formed by the sacrum and coccyx posteriorly, and the ischium and pubis laterally and anteriorly. Unlike the greater pelvis, which is broad and open, the true pelvis is more enclosed and narrow.
Bony Boundaries of the Lesser Pelvis
| Boundary | Structure |
|---|---|
| Superior | Pelvic brim (promontory, arcuate lines, pubic crests) |
| Inferior | Pelvic outlet (bounded by coccyx, ischial tuberosities, and pubic arch) |
| Posterior | Sacrum and coccyx |
| Lateral | Ischial bodies and parts of the ilium |
| Anterior | Pubic symphysis and bodies of pubic bones |
Location
The lesser pelvis lies deep to the pelvic brim and is situated centrally in the lower part of the trunk. It forms the space between the pelvic inlet and outlet and is continuous inferiorly with the perineum. It houses the pelvic cavity proper and is more vertically oriented compared to the tilted greater pelvis above it.
Function
- Supports Pelvic Organs: Encloses and protects internal pelvic structures such as the rectum, bladder, uterus, and ovaries
- Birth Canal: Forms the bony passageway through which the fetus passes during vaginal delivery
- Muscle Attachment: Provides origin and insertion points for pelvic floor muscles that support viscera and control continence
- Neurovascular Passage: Acts as a conduit for pelvic nerves, arteries, veins, and lymphatics
Contents of the Lesser Pelvis
| Structure | Notes |
|---|---|
| Urinary bladder | Occupies anterior part of the cavity when full |
| Rectum | Posterior midline structure descending toward the anal canal |
| Uterus and vagina (female) | Central structures resting above and between bladder and rectum |
| Ovaries and uterine tubes (female) | Located on either side of the uterus within the lateral pelvic walls |
| Prostate and seminal vesicles (male) | Situated posterior to the bladder and anterior to the rectum |
| Pelvic neurovascular bundles | Include internal iliac vessels and sacral plexus branches |
| Pelvic floor musculature | Forms the muscular base supporting all viscera above |
Clinical Significance
- Obstetric Considerations: The dimensions and shape of the lesser pelvis determine ease of vaginal delivery; common assessments include diagonal conjugate and interspinous diameter
- Pelvic Organ Prolapse: Weakness of the pelvic floor may allow descent of organs like the bladder (cystocele), uterus (uterine prolapse), or rectum (rectocele)
- Pelvic Tumors: Masses in the lesser pelvis can compress bladder, rectum, or nerves, leading to urinary retention, constipation, or sciatica
- Surgical Relevance: Accurate knowledge of true pelvis boundaries is essential for pelvic surgeries, hysterectomy, prostatectomy, and pelvic lymph node dissection
Published on May 9, 2025
Last updated on May 9, 2025
Last updated on May 9, 2025