L7 Pelvic content: Vessels and Nerves

Question 1

Describe the Sacrum - major joint with pelvis, foramina, canal and hiatus

Answer 1

This is 5 fused vertebrae- at the bodies, spinous processes, lamina, and transverse processes.
It articulates with the iliac bones via wing processes: Ala on the side of S1.

The cauda equina travels down the sacral canal posteriorly.
The spinal nerves have to go out the 8 intervertebral foramina before choosing to go either to the 8 anterior sacral foramina or the 8 posterior sacral foramina - 4 on each side.

Question 2

Where does the dural sac of the spinal cord end and what does that mean for the Sacral hiatus

Answer 2

Ends at S2, this means that the Sacral hiatus, which is after S4 on the post only contains epidural fat. Sacral hiatus good for epidural nerve blocks, with a needle there the anaesthetic will go into this space and anaesthetise terminal nerves.

Question 3

What are the differences between the male and female pelvic shape

Answer 3

Inlet: M= heart- small and sharp ischial spines, F=transverse oval (big)

Outlet: M=skinny vertical oval, F=normal circle

Cavity: M=upside down cone (no nose), F= cylinder
Pub

Pubic arch: M= triangle, subpubic angle <90, F= rainbow,spa >90

Question 4

What is the tilt of the pelvis and the boundaries of the pelvis

Answer 4

There is a 60’ anterior tilt so that ASIS are inline with pubic tubercle. The sacrum is also tilted 40’.
Anterior= pubic bones
Posterior: Sacrum, coccyx and piriformis lateral walls
Lat: pelvic bones.
Floor: pelvic diaphragm

Question 5

What type of joints are fibrous, synovial, 2ndary cartilagenous in the pelvis

Answer 5

Fibrous: Post. sacroiliac joint (+lig.)

Synovial: Ant. Sacroiliac joint +lig.

2ndary cartilagenous; pubic symphysis and lumbosacral joint

Question 6

What are the ligaments of the pelvis

Answer 6

Sacrotuberous= goes from the sacrum to the ischial tuberosity
Sacrospinous= goes from the sacrum to the ischial spine
- Both create the greater sciatic foramen and lesser sciatic foramen

Inguinal lig. ASIS to pubic tubercle

Question 7

What are the muscles of the pelvic wall that go through the sciatic foramina and where do they fit in the pelvis

Answer 7

Piriformis: Goes from the anterior aspect of the sacrum between the ant sacral foramina and passes through the Greater sciatic foramen to the G trochanter of the femur.
Obturator internus: starts from the ischium, filling the obturator foramen on the inner aspect and passing through the lesser sciatic foramen, hooking 90’ around the lesser sciatic notch.

Question 8

List the structures that go through the GSF + LSF (or both)

Answer 8

GSF
-Above piriformis: Sup. gluteal artery and nerve
-Below piriformis:
Inf gluteal artery and nerve
Sciatic nerve
Post. Cut, Nerve of the thigh
-Going through and then back into the LSF
Pudendal nerve and internal pudendal artery
Nerve to obturator internus.

Question 9

What are the nerve root values for pudendal nerve, sciatic nerve, and post cut nerve of the thigh, obturator nerve

Answer 9

Pud: S2-4
Sciatic: L4-S3
PCNT: S1-3
Obt: L2-4

Question 10

Which nerve is at risk during a lateral approach to hip surgery and which for intramuscular injection

Answer 10

Sup. Gluteal nerve for lateral approach to hip

Sciatic for im injection- go anteriolateral

Question 11

What is the variation in supply between male and female for anterior division of the internal iliac artery

Answer 11

M: They have prostate, seminal vesicles and ductus deferens supplied by inf. vesical and middle rectal artery.

F: Have vagina/female arteries supplied by uterine artery.

NB different from the ovary/testis which is L2.

Question 12

What artery is the main one coming from the posterior division of the internal iliac

Answer 12

Sup Gluteal

Question 13

What is the venous drainage of the pelvis and the exception

Answer 13

Rich venous plexuses around the bladder, prostate, rectum (inf+sup), vagina, uterus which drain to Internal iliac veins.
Except: Deep dorsal vein of the penis/clitoris which passes through an ant deficiency in the perineal membrane to join the vesical/ prostatic plexuses in the pelvic cavity.
Rest of the perineum drains back with the internal pudendal vein

Question 14

How does the Sacral plexus form, which nerve root values its from and the nerves in it- values, what its innervating and path if necessary

Answer 14

S1-4 from the anterior sacral foramina is joined by L4/5 lumbosacral trunk to make Sacral plexus

• Sup + inf gluteal nerves -motor to glut medius, minimus + maximus
• Sciatic nerve L4-S3 made from Tibial and Common fibular generally leaves below piriformis. Motor and sensory to hamstrings + leg

Nerve to Levator Ani and Coccygeus (S3-4) runs along the pelvic floor to give motor innervation. Damage to this causes

Pudendal N: S2-4: motor + sensory to perineum muscles, anal canal and ext genitalia.
Inf rectal, perineal nerve, dorsal nerve to clit/penis, scrotal/labia

Post. Cut. Nerve thigh- (S1-3) sensory to post thigh, leg, perineum

Question 15

What are the two ANS plexuses to pelvic viscera and where

Answer 15

Superior Hypogastric: Ant to the body of L5 and sacral promontory

Inferior Hypogastric: inner surface pelvic floor (predominant)

Question 16

What are the fibres and functions of the symp and parasymp supply to the pelvic plexuses

Answer 16

Symp: L1/2
- contract internal urethra and anal sphincters, ejaculation, moving secretions along epididymis
Parasymp: S2-4
-Vasodilation- erection, contraction of the bladder

Question 17

What is the path of the sympathetic and parasymp fibres that go to the pelvic viscera

Answer 17

Symp
-L1/2 fibres Mostly Descend into the pelvis via the Superior hypogastric plexus (from lumbar splanchnic nerves that supplied the terminal hindgut AND directly from the sacral splanchnic nerves exiting symp chain.
The plexus splits to form two big Hypogastric nerves to get to the inferior hypogastric plexus.

Parasympathetic :
Exit directly from S2-4 ant sacral foramina as pelvic splanchnic nerves straight into inferior hypogastric plexus. Otherwise Ascend via hypogastric nerves into the Sup. Hypogastric plexus then into the abdomen to do more plexuses

Question 18

What is a saddle fracture

Answer 18

Large force between the legs that splits the pelvis apart - ring fracture