Pelvis Anatomy Flashcards
Name the 4 pelvic types according to Caldwell-Moloy (just name them)
- Gynecoid
- Anthropoid
- Android
- Platypelloid
Describe the gynecoid pelvis according to Caldwell-Moloy and its clinical significance
- Classic female shape (bowel shape)
- Most favorable for vaginal birth because nice wide opening at inlet that continues to outlet
Describe the anthropoid pelvis according to Caldwell-Moloy and its clinical significance
- Exaggerated oval shape of inlet (wide ‘U’-shaped pubic arch)
- Largest diameter is AP
- Associated with delivery in OP position (more room in back of pelvis)
- Also more favorable for vaginal birth
- Associated with people of African decent
Describe the android pelvis according to Caldwell-Moloy and its clinical significance
- Classic male shape
- Heart shaped at inlet (‘V’-shaped symphysis pubis), flat sacrum that does not jut out
- Theoretically associated with CPD because ischial spines are closer together and pointing inwards. Ischial tuberosities (outlet) also closer together
- Hard to get 2 fingers into arch of pubic symphysis
Describe the platypelloid pelvis according to Caldwell-Moloy and its clinical significance
- Very narrow pelvis with sacrum close to symphysis
- Theoretically associated with transverse arrest
- Associated with people of Island decent?
What are the 4 main planes of the pelvis?
- Pelvic Inlet
- Upper posterior part of the symphysis, ridge of iliac bones, and sacral promentory
- Measured by diagonal conjugate
- Midpelvis
- Lower border of symphysis to midportion (junction of S4-S5) of sacrum. Interspinous diameter is narrowest point (plane of least dimensions).
- Ischial spines are limiting factor → where most babies get stuck if they are prominent.
- Ischial spines are continuous with ligaments.
- Pelvic outlet
- Two dimensions/triangle. Inferior aspect of symphysis to ischial spines forms one triangle. Ischial tuberosities to sacrococcygeal joint forms the other.
- Plane of greatest dimensions [IGNORE]
Major Blood vessels of pelvis
- Aorta bifurcates → right and left common iliac artery → bifucates into internal and external iliac arteries (right and left) at L5-S1.
- Internal iliac arteries is major artery of pelvis. At the greater sciatic foramen it branches into anterior trunk (Vaginal, Uterine, Internal Pudendal, Middle Rectal, Inferior Gluteal, Obturator, Umbilical and Inferior Vesical arteries) and posterior trunk (Iliolumbar, Lateral Sacral and Superior Gluteal arteries)
- Veins correspond as do many nerves
Major Lymphatics of the Pelvis
Levator ani muscles
- Levator ani - major supporting structure for the pelvic viscera
- 3-part muscle mass:
- Iliococcygeus - broadest and most posterior portion. Extends more laterally from the fascia of obturator internus muscle to the tailbone
- Pubococcygeus - pubic bone (lateral of the origin of the puborectalis muscle) to the tendinous center of the perineum, anococcygeal body and tailbone
- Puborectalis - Lateral from the symphysis on both sides and encircles the rectum (anorectal junction). Partially interwoven with the external anal sphincter
- Innervation of the levator ani is through the third and fourth sacral nerves
Cardinal ligaments
- Located at the base of the broad ligament
- Continuous with the connective tissue of the parametrium
- Attached to the pelvic diaphragm through continuity with the superficial superior fascia of the levator ani
Nerves
- Afferent (sensory) pain fibers for the uterus, tubes, and ovary enter the cord at T10, T11, and T12
- Spinal or epidural anesthesia must extend to these levels.
- Efferent (motor) fibers to the uterus enter above these levels and thus do not interfere with contraction
- Spinal or epidural anesthesia must extend to these levels.
- Afferent innervation of the vagina and external genitalia enter at S2, S3, and S4
Piriformis muscle
- Posterior hip muscle
- Origin: pelvic surface of sacrum
- Insertion: Greater trochanter
- Innervation: Sacral plexus (L5 -S1)
- Functions: stabilizes pelvis (with other posterior hio muscles) and hip joint. Externally rotates and aducts: thigh
Bulbocavernosus (aka bulbospongiosus) muscle
- Superficial muscle of the perineum
- Divided into halves that extend from just behind the clitoris to the central tendon of the perineum and serves to constrict the vagina
- One of the muscles that contracts during kegel
- Innervated by pudendal nerve
Ischiocavernosus muscle
- Connects ischium to pubic symphysis
- Contracts during orgasm and kegels? (per wikipedia)
- Innervated by pudendal nerve
Superficial and deep transverse perineal muscles
- Both innervated by pudendal nerve
Central tendinous point of the perineum
(perineal body)
- Ill-defined, fibromuscular mass is located in the middle of the interischial line, between the two triangles of the perineum.
- Many muscles attach at the perineal body.
- Posterior with the external anal sphincter and anterior with bulbospongiosus and the deep and superficial transverse perinei.
- Extends superiorly into the rectovaginal septum of the pelvis.
Obturator internus muscle
- Originates from obturator membrane (covers the foramen created by the ischium)
- Inserts: trochanter and trochanteric fossa
- Function: externally rotates thigh
- Innervation: sacral plexus
External and internal anal sphincter (contains muscle)
- External: made of 3 muscles
- Subcutaneous
- Superficial
- Deep
- Arise from coccyx and converge into central tendon
- Voluntary control
- Internal:
- Muscular ring
- Involuntary control
Describe the function and location of pelvic fascia
Sacrotuberous and Sacrospinous Ligaments
Connect the sacrum and
- Sacrotuberous - ischial tuberosities
- Sacrospinous - ischial spines
Broad, Round, Ovarian, and Suspensatory ligaments
Peritoneal Ligaments
(Uterosacral, Cardinal, Pubocervical)
- Cardinal ligament
- Located at the base of the broad ligament
- Continuous with the connective tissue of the parametrium
- Attached to the pelvic diaphragm through continuity with the superficial superior fascia of the levator ani
- Pubocervical - connects cervix to pubic symphysis (not pictured)
Identify the significant pelvic diameters and the range of their measurements, how they are obtained, their significance and variations according to pelvic type:
Diagonal conjugate
- Measured clinically
- AP diameter of the pelvic inlet - sacral promontory to the inferior (lower) margin of the symphysis pubis
- Normal ≥ 11.5cm
- Fetus may not engage if too narrow
- Platypelloid pelvis
- Android pelvis
- Fetus may not engage if too narrow
Identify the significant pelvic diameters and the range of their measurements, how they are obtained, their significance and variations according to pelvic type:
Obstetric conjugate
- Measures pelvic inlet
- Middle of the sacral promontory to the middle of the posterior symphysis pubis.
- Normal ≥ 10 cm
- Cannot measure clinically, only estimate from diagnonal conjugate
- Obstetrical conjugate = Diagonal conjugate - 1.5cm
Identify the significant pelvic diameters and the range of their measurements, how they are obtained, their significance and variations according to pelvic type:
Transverse diameter of the inlet
- Distance between iliopectineal lines.
- Normal = ~13.5 cm
- May be shorter in an anthropoid pelvis, and wider in a platypelloid pelvis
Identify the significant pelvic diameters and the range of their measurements, how they are obtained, their significance and variations according to pelvic type:
Interspinous diameter
- Distance between the ischial spines.
- Normally approximately 10 cm.
- Smallest diameter of the pelvis that the fetal presenting part must accommodate during labor and birth
Identify the significant pelvic diameters and the range of their measurements, how they are obtained, their significance and variations according to pelvic type:
Bituberous diameter
(intertuberous, biiscial)
- Transverse diameter of the outlet
- Distance between the inner aspect of the lowermost part of ischial tuberosities.
- Measured by placing the fist at the perineum in pelvimetry
- Normally ~ 10 cm
- Platypelloid pelvis - wider
- Android pelvis - more narrow → significant molding
