Lecture 1 - Pelvis 1: Pelvic Floor and Perineum Flashcards
What 2 parts of the pelvis are on the same vertical plane in the anatomical position? Why is this important?
ASIS and pubic tubercle =>
- Pelvic outlet: urogenital part with bodies of pubic bones and pubic arch are positioned in a nearly horizontal plane and posterior part of outlet is positioned more vertically
- Pelvic inlet is tilted to face anteriorly
=> pelvic cavity projects posteriorly from the abdominal cavity
What are the 2 diameters that restrict the pelvis? Describe each.
- Conjugal diagonal diameter of the pelvic inlet: distance from sacral promontory to the superior border of pubic symphysis
- Ischial diameter of the pelvic outlet: distance between the 2 ischial spines
Other name for conjugal diameter of the pelvis?
Anteriorposterior (AP) diameter
Why are the 2 diameters that restrict the pelvis important? What to note?
Because they are the 2 narrowest points of the pelvis, so in order for a baby’s head to pass through the conjugal diameter has to be more than 11 cm and the ischial diameter has to be more than 10 cm
Note: hormones like estrogen and relaxin released during labor help to relax the pelvic joints in order to help expand these diameters by about 15%
What is parturition?
Action of giving birth
What is pelvimetry? What to note?
The assessment of the female pelvis in relation to the birth of a baby
Not really used much anymore
What part of the pelvis are the internal genital organs and the lower parts of the intestinal and urinary tracts found in?
Within the true pelvis
3 elements forming each pelvic bone?
- Ilium
- Pubis
- Ischium
5 differences between male and female pelvises?
- The pelvic inlet in women is circular compared with the heart-shaped pelvic inlet in men. The more circular shape is partly caused by the less distinct promontory and broader alae in women
- The angle formed by the two arms of the pubic arch is larger in women (80°–85°) than it is in men (50°–60°)
- The ischial spines generally do not project as far medially into the pelvic cavity in women as they do in men
- Pelvis is thick and heavy in men and thin and light in women
- Pelvic inlet is small in males and large in females
What 3 structures pass below the inguinal ligament?
AVC:
- Femoral artery
- Femoral vein
- Femoral canal
Through what structure does the lymphatic drainage from the external genitalia in males and females pass?
Through the femoral canal
What is the most prominent feature of the ischium? Why is it important?
Large ischial tuberosity on the posteroinferior aspect of the bone
Important site for attachment of lower limb muscles and for supporting the body when sitting
What nerve innervates the perineum (both somatic sensory and motor)?
Pudendal nerve
Spinal cord levels of the pudendal nerve?
S2 to S4
Describe the pathway of the pudendal nerve.
Originate from S2-S4 anterior rami => leaves pelvic cavity through the greater sciatic foramen => passes around the ischial spine (posterolaterally) and medially through the lesser sciatic foramen to enter perineum => travels along the lateral wall of the ischio-anal fossa in the pudendal canal => enters the anal triangle of the perineum
What is the sacrospinous ligament?
Triangular ligament
- Apex: attached to the ischial spine
- Base: attached to the related margins of the sacrum and coccyx
What is a pudendal block? How is it administered? For what purpose?
Anesthesia of the pudendal nerve
Ischial spine can be palpated transvaginally in women and is the landmark to administer the block for vaginal childbirth or for minor surgeries of the vagina and perineum
OR a perineal approach is also possible by injecting through the skin at the points where the ischial spines project (2” above ischial tuberosities), but this is less reliable and is typically only preferred when a baby’s head prevents the transvaginal approach
What is a pudendal nerve entrapment syndrome? Symptom? Treatment?
Pudendal nerve is compressed against the sacrospinous ligament
Symptom: pain in genital area and between upper thighs; worse when sitting and often relieved when standing
Last resort is surgical treatment
What is the sacrotuberous ligament?
Triangular ligament
Base: broad attachment that extends from the posterior superior iliac spine of the pelvic bone, along the dorsal aspect and the lateral margin of the sacrum, and onto the dorsolateral surface of the coccyx
Apex: medial margin of the ischial tuberosity
Where is the greater sciatic foramen? Purpose?
Superior to the sacrospinous ligament and the ischial spine, superior to pelvic floor
Purpose: route of communication between the pelvic cavity and the gluteal region of the lower limb
Where is the lesser sciatic foramen? Purpose?
Inferior to the ischial spine and sacrospinous ligament between the sacrospinous and sacrotuberous ligaments, below the pelvic floor
Purpose: route of communication between the gluteal region of the lower limb and the perineum
Other name for perineal approach to a pudendal block?
Transutaneous approach
Other name for pudendal nerve entrapment syndrome?
Alcock canal syndrome
Is pudendal nerve entrapment syndrome common?
NOPE - rare
What do we call the male pelvis?
Android pelvis
What do we call the female pelvis?
Gynecoid pelvis
What is the cause of much lower back pain? What to note about these?
Sacroiliac ligaments because they’re role is to displace some of the weight associated with vertebral column, head, and neck to the hip (without which the sacrum would move posterosuperiorly)
Some of the strongest ligaments of the body
Why are pelvic fractures common? What to note?
- Anteroposterior compression in auto accidents
- Falls from a height may drive the femoral head through the floor of the acetabulum
In pelvic fractures there is often soft tissue injury
What is the acetabulum? What does it form?
Large articular socket on the lateral surface of the pelvic bone formed by ilium, ischium, and pubis all coming together, which, together with the head of the femur, forms the hip joint
What is the pelvic diaphragm?
Muscular part of the pelvic floor, is shaped like a bowl/funnel, and is attached to pelvic walls
Consists of:
- Levator ani muscles
- Coccygeus muscle
What is the pelvic floor? Purpose?
Composed of:
- Pelvic diaphragm
- Perineal membrane
- Muscles in the deep perineal pouch
Separates the pelvic cavity from the perineum
Levator ani muscles:
- Origin
- Insertion
- Innervation
- Function
- In a line around the pelvic wall: from the posterior aspect of the pubic bone => tendinous arch of obturator internus muscle (thickening of the obturator internus fascia) => ischial spine
- Anterior part: superior surface of the perineal membrane
- Posterior part: meets its partner on the other side at the perineal body, around the anal canal, and along the anococcygeal ligament
- Branches direct from the anterior ramus of S4, and by the inferior rectal branch of the pudendal nerve (S2 to S4)
- Contributes to the formation of the pelvic floor, which supports the pelvic viscera
- Maintains a 90 degree angle between the rectum and anal canal
- Reinforces the external anal sphincter
- In women: functions as a vaginal sphincter (sphincter vaginae) during orgasm
- In men: principal support for the prostate (levator prostatae)
Coccygeus:
- Origin
- Insertion
- Innervation
- Function
- Ischial spine and pelvic surface of the sacrospinous ligament
- Lateral margin of coccyx and related border of sacrum
- Branches from the anterior rami of S3 and S4
- Contributes to the formation of the pelvic floor, which supports the pelvic viscera; pulls coccyx forward after defecation
Why is it important the the levator ani muscles maintain an angle between the rectum and anal canal?
Major factor in anal canal continence
Shape of true pelvis?
Cylindrical
4 parts of bony pelvis?
2 pelvic bones
1 sacrum
1 coccyx
Borders of the pelvic inlet?
- Posteriorly: body of vertebra SI, which projects into the inlet as the sacral promontory + on each side of this vertebra, wing-like transverse processes called the alae (wings) which connect with each other
- Laterally: linea terminalis = arcuate line + pectineal line + pubic crest
- Anteriorly: pubic symphysis, where the two pelvic bones are joined in the midline
Passage of baby during childbirth?
Abdomen => pelvic inlet => pelvic outlet
Borders of the pelvic outlet?
- Posteriorly/laterally: sacrotuberous ligament
- Antero/laterally: pubic arch = inferior margin of the body of pubis + inferior ramus of pubis + ramus of ischium + ischial tuberosity
- Anteriorly: pubic symphysis
- Laterally: ischial tuberosities
- Posteriorly: coccyx and sacrum
4 main purposes of pelvic diaphragm?
- Supports the pelvic viscera
- In conjunction with the thoraco-abdominal diaphragm, increases intra-abdominal pressure
- Resists downwards thrust, e.g., in forced expiration and coughing.
- Assists the anterior abdominal wall muscles in compressing the abdominal contents and even helps to fix the trunk during weight lifting
When does injury to pelvic floor muscles most often occurs? Explain. Recovery?
During parturition:
- The most common complaint of women after delivering a baby is that “my bottom is falling out” => in essence, the pelvic contents are now supported mostly by skin and fascia since the muscle was completely spread apart during the delivery => as the muscles slowly “recover” and adopt their normal position and integrity, they can once again assume their role of supporting the pelvic viscera
- Weakness of the muscles (stretching or tearing) may alter the position of the neck of the bladder or the urethra causing urinary stress incontinence => there may be dribbling of urine when intra-abdominal pressure is increased (coughing, lifting)
What are the Kegel muscles? What is their purpose?
Include the pelvic floor muscles as well as other muscles in the perineum
Purpose: women patients who have just given birth and leak urine should exercise them
Connection between main diaphragm and pelvic diaphragm?
They often act synergistically
What is located below the pelvic diaphragm?
Perineum
What 3 parts of the pelvic outlet can be palpated?
- Pubic symphysis
- Ischial tuberosities
- Coccyx (*not technically part of pelvic outlet)
What are the 3 levator ani muscles?
- Iliococcygeus muscle
- Pubococcygeus muscle
- Puborectalis muscle
What surrounds the true pelvis?
Pelvic inlet and outlet
What is cyclists’ syndrome?
Condition caused by sitting on a bike seat for too long causing person to lose sensation in the perineum because the pudendal nerve gets pressed against the pelvic bone in the ischium region
Is cyclists’ syndrome common?
YUP
What is the pudendal canal? Other name? What does it contain?
Tubular compartment formed in the fascia that covers the obturator internus muscle
= Alcock canal
Contains the internal pudendal artery and accompanying vein and the pudendal nerve
Describe the pathway of the inferior rectal nerve and its function.
Penetrates through the fascia of the pudendal canal, and courses medially across the ischio-anal fossa
- Innervates the external anal sphincter and related regions of the levator ani muscles
- Provides general sensory for the skin of the anal triangle
Describe the pathway of the perineal nerve and its function.
Passes into the urogenital triangle and gives rise to motor and cutaneous branches
- The motor branches supply skeletal muscles in the superficial and deep perineal pouches
- The largest of the sensory branches is the posterior scrotal nerve in men and the posterior labial nerve in women
Describe the pathway of the dorsal nerve of the penis/clitoris and its function.
Enters the deep perineal pouch => passes along the lateral margin of the pouch => exits by passing inferiorly through the perineal membrane in a position just inferior to the pubic symphysis where it meets the body of the clitoris or the penis => courses along the dorsal surface of the body to reach the glans
Sensory to the penis and clitoris, particularly to the glans
3 branches of the pudendal nerve?
- Inferior rectal nerve
- Perineal nerve
- Dorsal nerve of the penis/clitoris
What are the sacroiliac ligaments?
- Sacrospinous ligament
2. Sacrotuberous ligament
What is the lithotomy position?
A supine position of the body with the legs separated, flexed, and supported in raised stirrups