Anatomy of Pelvis and Pelvic Cavity

Question 1

What are the two main parts of the pelvis?

Answer 1

The bony pelvis (pelvic girdle) and the pelvic cavity (the space).

Question 2

What are the three primary functions of the bony pelvis?

Answer 2

Weight bearing (transfers weight from trunk to lower limbs).

Attachment for soft tissues (muscles of locomotion, pelvic floor, etc.).

Protection and support of pelvic and abdominal viscera.

Question 2

Name the bones that form the bony pelvis.

Answer 2

Hip bones (anterior/lateral walls), sacrum, and coccyx (posterior wall).

Question 2

What is the pelvic brim, and what does it define?

Answer 2

A line joining the sacral promontory, arcuate line, pectineal line, and pubic crest. It defines the pelvic inlet and demarcates the greater (false) and lesser (true) pelvis.

Question 3

What are the key differences between the male and female pelvis?

Answer 3

Male: Narrow/heart-shaped inlet, narrow subpubic angle (<70°), thicker/heavier bones.

Female: Wide/oval inlet, wider subpubic angle (>80°), lighter/thinner bones, cylindrical true pelvis.

Question 4

What are the four types of pelvic inlet shapes?

Answer 4

Gynecoid (rounded).

Android (heart-shaped).

Anthropoid (long, narrow oval).

Platypelloid (transverse oval).

Question 5

What structures form the pelvic floor (pelvic diaphragm)?

Answer 5

Levator ani (pubococcygeus, puborectalis, iliococcygeus) and coccygeus muscles, covered by superior and inferior fasciae.

Question 6

What are the main arteries supplying the pelvis?

Answer 6

Paired internal iliac arteries, median sacral artery, superior rectal artery, and gonadal vessels.

Question 7

How does lymph drain from the pelvis?

Answer 7

Through primary nodes (internal/external/common iliac, sacral) and minor nodes (pararectal, inferior mesenteric), with interconnected pathways.

Question 8

Which nerves contribute to the innervation of the pelvis?

Answer 8

Somatic: Sacral plexus (e.g., sciatic, pudendal nerves), coccygeal plexus.

Autonomic: Pelvic splanchnic nerves (parasympathetic), sacral sympathetic trunks, inferior hypogastric plexus.

Question 9

What are the three groups of pelvic viscera?

Answer 9

Alimentary (rectum).

Urinary (ureters, bladder, urethra).

Reproductive (uterus, ovaries, prostate, etc.).

Question 10

What is the clinical significance of the true (obstetric) conjugate?

Answer 10

The narrowest fixed anteroposterior diameter of the pelvic inlet, critical for assessing fetal head passage during delivery. Measured radiographically.

Question 11

Name the ligaments associated with the sacroiliac joint.

Answer 11

Anterior, posterior, and interosseous sacroiliac ligaments, plus sacrotuberous and sacrospinous ligaments.

Question 12

What is the role of the obturator internus muscle?

Answer 12

Forms part of the lateral pelvic wall; covers the obturator foramen and aids in lateral rotation of the thigh.

Question 13

What structures pass through the greater and lesser sciatic foramina?

Answer 13

Greater sciatic foramen: Piriformis muscle, sciatic nerve, superior/inferior gluteal nerves/vessels, pudendal nerve.

Lesser sciatic foramen: Pudendal nerve, internal pudendal vessels, obturator internus tendon.

Question 14

What is the significance of the sacral promontory in obstetrics?

Answer 14

It marks the posterior boundary of the pelvic inlet; used to measure obstetric conjugate (critical for assessing childbirth feasibility).

Question 15

How does the peritoneum differ in male vs. female pelves?

Answer 15

Male: Rectovesical pouch between bladder and rectum.

Female: Rectouterine pouch (of Douglas) and uterovesical pouch due to uterus presence.

Question 17

Why is the pubic arch wider in females?

Answer 17

To accommodate childbirth; subpubic angle >80° (vs. <70° in males)

Question 18

Name the ligaments stabilizing the pubic symphysis.

Answer 18

Superior pubic ligament and inferior (arcuate) pubic ligament.

Question 19

What is the lumbosacral trunk, and why is it important?

Answer 19

Formed by L4-L5 ventral rami; joins sacral plexus to contribute to sciatic nerve (lower limb innervation).

Question 20

Which veins communicate with the internal vertebral venous plexus, and why is this clinically relevant?

Answer 20

Lateral sacral veins; potential route for pelvic cancer metastasis to the spine (Batson’s plexus).

Question 20

What muscles form the lateral pelvic wall?

Answer 20

Obturator internus (covered by obturator fascia) and piriformis (posterolateral).

Question 20

What is the role of the levator ani muscle group?

Answer 20

Supports pelvic viscera, maintains continence (puborectalis forms rectal sling), and aids in childbirth.

Question 20

What are the branches of the internal iliac artery, and how are they grouped?

Answer 20

Anterior division: Visceral branches (umbilical, uterine, vaginal, inferior vesical) and parietal (obturator, internal pudendal). Posterior division: Parietal branches (iliolumbar, lateral sacral, superior gluteal).

Question 20

What is the clinical significance of the diagonal conjugate?

Answer 20

Measurable during pelvic exam (promontory to pubic symphysis); true conjugate is estimated by subtracting 1.5 cm.

Question 20

How does the pelvic axis influence childbirth?

Answer 20

Curved path (sacral promontory to coccyx); fetal head rotates to follow this axis during delivery.

Question 20

What nerves are at risk during prolonged labor or pelvic surgery?

Answer 20

Pudendal nerve (S2-S4; injury → incontinence) and lumbosacral trunk (L4-L5; injury → foot drop).

Question 20

What are the peritoneal pouches in females, and why are they important?

Answer 20

Rectouterine pouch (site for fluid accumulation) and uterovesical pouch; relevant for ectopic pregnancy or abscess drainage.

Question 20

Name the ligaments converting sciatic notches into foramina.

Answer 20

Sacrospinous ligament (lesser sciatic foramen) and sacrotuberous ligament (greater sciatic foramen).

Question 21

What is the function of the piriformis muscle in the pelvis?

Answer 21

Forms part of the posterolateral wall; laterally rotates the thigh and stabilizes the sacroiliac joint.

Question 22

How does the pelvis transfer weight from the trunk to the lower limbs?

Answer 22

Through the sacroiliac joints to the hip bones (ilium) and then to the femurs via acetabulum.

Question 23

What is the "plane of least pelvic dimension," and what are its boundaries?

Answer 23

Mid-pelvis plane bounded by pubic symphysis, ischial spines, and sacrum; narrowest part of birth canal.

Question 24

Why is the obturator foramen clinically relevant?

Answer 24

Obturator nerve entrapment here can cause medial thigh pain; also a site for hernias.

Question 25

What is the difference between the anatomical and obstetric conjugate?

Answer 25

Anatomical: Promontory to superior pubic symphysis. Obstetric: Promontory to midpoint of symphysis (1 cm below superior margin).