AP - Posterior Abdominal Wall and Pelvic Osteology

11/18/25

what are the muscles of the posterior abdominal wall?

psoas major, iliacus, quadratus lumborum, and respiratory diaphragm

what are the muscles of the posterior abdominal wall enveloped by?

endoabdominal fascia

is continuous laterally with the tranversalis fascia

what is the transversalis fascia?

connective tissue lining most of the abdominal cavity between posterior surface of transversus abdominis (medially arcuate line dependent) and superficial to extraperitineal fat and peritoneum

what are the retroperitoneal structures at the L2 level (transverse section)?

psoas muscle

quadratus lumborum

iliacus muscle

kidney

where is the origin of the psoas muscle?

vertebral bodies T12-L5

where is the insertion of the psoas muscle?

the lesser trochanter of femur

where is the origin of the iliacus muscle?

superior 2/3 of ilaic fossa, ala of sacrum, and anterior sacroiliac ligaments

where is the insertion of the iliacus muscle?

lesser trochanter of femur and shaft inferior to it and to psoas major tendon

where is the origin of the quadratus lumborum?

medial half of inferior border of 12th rib and tips of lumbar transverse processes

where is the insertion of the quadratus lumborum?

iliolumbar ligament and internal lip of iliac crest

where is the origin of the respiratory diaphragm?

thoracic outlet: xiphoid, lower six costal cartilages, L1-L3 vertebrae

where is the insertion of the respiratory diaphragm?

converges into central tendon

what is the diaphragm?

dome shaped muscular sheath that separates the thorax from the abdomen

what are the 3 openings of the diaphragm?

inferior vena cava T8

esophageal t10

and aortic t12

what is the function of psoas major?

acting superiorly with iliacus, flexes hip

what is the iliacus?

flexes thigh at hip and stabilizes hip joint

what is the function of the quadratus lumborum?

extends and laterally flexes vertebral column; fixes 12th rib during inspiration

where does the quadratus lumborum lie in front of?

erector spinae muscles and fascia

what is the pelvis?

the bony weight bearing structure made up of the innominate bone and the sacrum. the fusion of these structures creates the pelvic cavity, or the bowl like space that runs distal to the formal abdominal cavity

what is the innominate bone the fusion of?

ilium, pubis, and ischium

what is the pelvic cavity?

It gets narrower as you go farther down, and the whole thing is covered by peritoneum. That peritoneum is continuous with the lining of the abdominal cavity.

what is the pelvic brim?

demarcation point separating the “abdominal cavity” from the “pelvic cavity”

where does the pelvic brim extend from?

the sacral promontory, past the ala of the sacrum, curving along the medial border of the iliac wing and the superior border of the pubis (AKA iliopectineal line) and eventually to the pubic tubercle where it joins pubic symphysis

what is the ala?

whole bony (flat) portion of ilium bone that looks like an elephant ear

what is the iliac fossa?

medial surface of the ala that is slightly concave

what is the iliac crest?

the superior edge of the ilium

what is the sacroiliac joint?

the articulation point between the ilium and the sacrum

what is the ischial tubercle/tuberosity?

the rounded region of the ischium

boney structure you sit on (AKA sit bone)

what is the ilium have?

it has a body, ala (wing), and iliac fossa

the large auricular surface joins with sacrum to become what?

the sacroiliac joint

what is the iliac crest?

the edge of the ala

what is the SI joint?

where the weight of our body is transferred to pelvis?

where does the iliac crest extend from?

the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS)

what is the pubis made up of?

• superior pubic ramus

• body of the pubis

• inferior pubic ramus (It connects with the innominate bone on the other side at the pubic symphysis, using the pubic tubercle as the joining point)

what are the 4 portions of the ischium?

• superior ischial ramus

• ischial body

• ischial tuberosity

• inferior ischial ramus

what is the ischial ramus?

connection point between pubis bone and ischial bone

what creates the ischiopubic ramus?

inferior ischial ramus and inferior pubic ramus

what becomes an important attachment point for the sacrospinous point?

ischial spine

what is the greater sciatic notch?

allows passage of sciatic nerve and piriformis muscle

what are teh differences between the male and female pelvis?

female cavity is wider and deeper. pubic arch is broader. the inferior aperture is wider

what are the main nerves of abdominal region?

1. iliohypogastric nerve

2. ilioinguinal nerve

3. genitofermoral nerve

4. lateral femoral cutaneous nerve/lateral cutaneous nerve of the thigh

5. femoral nerve

6. obturator nerve

where are the somatic nerve of the posterior abdominal wall derived from?

lumbar plexus

what composes of the lumbar plexus?

anterior rami L1-L4 (with small contribution of T12)

where do the branches of the lumbar plexus innervate?

posterior abdominal wall muscles, pelvic, and thigh muscles

what does the lumbar plexus lie behind and within?

psoas major muscle

what is the function of the ilihypogastric (L1 and sometimes T12) nerve?

motor and sensory

where is the iliohypogastric nerve?

above pubis and posterolateral buttocks

runs along iliac crest

what is the function of the ilioinguinal nerve (L1)?

motor and sensory (sensory to inguinal region)

sensory to scrotum and labia major

where does the ilioinguinal nerve (L1) travel through?

inguinal canal

what are the 2 branches of the genitofermoral nerve (L1-L2)?

2 branches: genital branch to cremaster muscle and femoral branch to femoral triangle

(medial in leg)

what is the function of the genitofemoral (L1-L2) nerve?

sensory to anteromedial thigh

what is the function of cutaneous nerve of thigh (L2-L3)?

sensory to anterolateral thigh (lateral)

what is the innervation of the lateral cutaneous nerve of thigh? (L2-L3)

runs anterior to iliacus to ASIS

what is the function of the of the femoral (L2-L4) nerve?

motor in pelvis and anterior thigh muscles for hip flexion and knee extension

sensory to thigh and medial leg

what happens if the obturator nerve is blocked?

cause difficulties with adduction (if it were to get hit in surgery)

what is the function of the obturator nerve (L2-L4)?

motor to adductor muscles in thigh

sensory to medial thigh

what are the 2 major nerves of the lower extremity?

femoral and obturator nerve

where is the femoral nerve?

runs along the psoas major muscle

is underneath the inguinal ligament, is lateral to femoral artery and psoas major muscle

what nerve is within the psoas muscle?

genitofemoral nerve

what nerves are above the psoas muscle/higher in the pelvis?

lateral cutaneous nerve of the R thigh, ilioinguinal and iliohypogastric

what are the paired arteries?

middle suprarenals → adrenal glands

renals → kidneys

gonadals

what divisions does internal iliac has?

posterior and anterior division

what is in the anterior division of the internal iliac arter?

inferior vesical artery (male)

uterine artery (female)

internal putendal branches

what does the internal pudendal give rise to?

male and female genitalia AND perineal region

what is the common iliac vein is formed by?

internal and external iliac veins

begins at the level of the pelvic brim

what does the IVC receive venous drainage from?

the gonads, kidneys, posterior abdominal wall (lumbar veins), hepatic portal system, and diaphragm