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Home , Anal triangle, Bulbospongiosus muscle, Ischiocavernosus muscle, Membranous urethra, Pelvic floor, Perineum

PowerPoint Handout: Lab 1, Musculoskeletal , and Review

Slide Title Slide Number Slide Title Slide Number Osseous Pelvis: Introduction Slide 2 Deep Pouch Slide 14 Osseous Pelvis: Features Slide 3 Superficial Pouch: Man Slide 15 Pelvic and Foramina Slide4 Superficial Pouch: Woman Slide 16 Pelvic Regions Slide 5 Perineal Body Slide 17 Android Versus Gynecoid Pelvis Slide 6 Neurovascular Structures in Superficial Pouch Slide 18 Pelvic Measurements Slide 7 Review: Female Slide 19 Muscles of Slide 8 Review: Male Urethra Slide 20 Muscles Slide 9 Urethral Injury (Goldman Classification Slide 21 Perineum Slide 10 Slide 22 Urogenital and Anal Triangles Slide 11 Pudendal Slide 23 Perineal Membrane: Introduction Slide 12 Spinal, Epidural, and Pudendal Blocks Slide 24 Perineal Membrane: Deep and Superficial Pouches Slide 13 Osseous Pelvis: Introduction

The pelvis is the region of the body surrounded by a ring of that structurally connects the vertebral column to the lower extremity. The axial skeleton and the appendicular skeleton both contribute bones to the pelvis. • The axial skeleton's contribution to the pelvis is the and the . • The appendicular skeleton's contribution to the pelvis is the right and left hip bones (pelvic bones or os coxae), which are joined anteriorly by the fibrocartilaginous . The mature hip bones are formed by the fusion of three bones. • • •

Posterior Anterior Osseous Pelvis: Features

Osteology of the pelvis • Anterior superior iliac spine (ASIS) • Anterior inferior iliac spine • • Sacral promontory • Arcuate line Anterior Inferior Iliac Spine • Sacral ala • • Superior margin pubic symphysis •

• • • Pubic arch • • • Obturator foramen • Pubic symphysis • It is important to note that the pubic tubercles and the anterior superior iliac spines are in the same vertical plane when the pelvis is in its anatomical position, .

Ischiopubic Ramus Pelvic Ligaments and Foramina

Pelvic ligaments • Obturator membrane • Sacrotuberous • • Anterior and posterior sacroiliac ligaments

Pelvic foramina whose boundaries are formed partially by ligaments • Greater sciatic foramen • Lesser sciatic foramen • Obturator canal Pelvic Regions

The pelvic brim divides the into the superiorly and the and the pelvic cavity inferiorly. • The abdominal cavity is the space between the diaphragm and the pelvic brim (). • The pelvic cavity is the space between the pelvic brim (pelvic inlet) and the muscular pelvic floor.

The pelvic brim divides the pelvis into two regions. • The greater pelvis (aka: false pelvis) is the space within the pelvis between the level of the iliac crests and the pelvic brim. The space within the greater pelvis is a component of the abdominal cavity. • The lesser pelvis (aka: true pelvis) is the space between the pelvic brim (pelvic inlet) and the pelvic diaphragm (muscular floor of the pelvis). The space within the lesser pelvis is a component of the pelvic cavity.

Iliac Crest False pelvis

Pelvic Brim (Inlet) True pelvis Android Versus Gynecoid Pelvis

An android (male-like) pelvis can be differentiated from a gynecoid Table 1 (female-like) pelvis by comparing the shape of the pelvic inlet, the size and shape of the , and the subpubic angle (See Table 1).

Female Male Pelvic Measurements The size of the lesser pelvis is important in obstetrics because it determines, to a large extent, the capacity for vaginal . Several measurements, determined radiographically or manually during pelvic examination, are used to assess the size of the lesser pelvis and its suitability for a vaginal delivery. • The interspinous distance is the transverse distance between the ischial spines, which is typically the narrowest diameter of the canal. • The transverse diameter is the distance between the inner edges of the ischial tuberosities. • The true (anatomical) conjugate diameter is the distance between the sacral promontory and the most superior point on the pubic symphysis. This distance can only be measured on radiographs. • The obstetrical conjugate diameter is the shortest distance between the sacral promontory and the pubic symphysis. This distance cannot be measured directly during the pelvic examination, but can be estimated by first determining the diagonal conjugate diameter (see below). • The diagonal conjugate diameter is the distance between the sacral promontory (palpated by the middle finger) and the anterior surface of the pubic symphysis' inferior margin. • This distance can be determined during a pelvic examination, which is then used to calculate the obstetrical conjugate. Once the diagonal conjugate is measured, the examiner subtracts 1.5 to 2 cm from the diagonal conjugate measurement. Muscles of Pelvic Cavity Pelvic muscles contribute to the walls and floor of the pelvic cavity. • Lateral walls • Obturator internus muscle: The obturator internus muscle inserts on the internal surface of the obturator membrane and passes through the lesser sciatic foramen to insert on the greater trochanter of the femur. Within the pelvis, the obturator internus muscle is covered in thick called the obturator fascia. • Posterior walls • Piriformis muscle: The proximal attachment of the piriformis muscle is on the anterior aspects of the S2-4 vertebral segments and passes through the greater sciatic foramen to its distal attachment on the greater trochanter of the femur. • Floor • The pelvic floor (pelvic diaphragm) is a funnel--shaped structure composed of the following muscles: and coccygeus (next slide).

Pelvic Diaphragm Pelvic Floor Muscles

The following muscles form the funnel-shaped pelvic floor (pelvic https://3d4medic.al/8K6xxapi diaphragm). • Levator ani (consisting of 3 muscles) • Puborectalis muscle • Pubococcygeus muscle • Iliococcygeus muscle: (Note that the iliococcygeus muscle has its origin on the tendinous arch, which is continuous with the obturator fascia.) • Coccygeus (ischiococcygeus) muscle • The 's superior border is adjacent to the inferior border of the piriformis muscle. • Its origin is on the ischial spine and the pelvic surface of the sacrospinous ligament. • It inserts onto the lateral margin of coccyx and the most inferior portion of sacrum. Perineum

The funnel-shaped pelvic floor (diaphragm) forms a physical boundary between the pelvic cavity and the perineum.

The perineum is a diamond-shaped region of the body wall inferior to the pelvic diaphragm between the and thighs. Its borders consist of the following structures. • Anterior: inferior border of pubic symphysis • Anteriolateral margin: ischiopubic ramus • Posteriolateral margin: • Posterior: tip of coccyx

The pelvic floor contains openings for important structures to pass between the pelvic cavity and the perineum. • The is an anterior opening in the pelvic floor through which structures pass to enter the in the of the perineum. Note that different structures pass

through this hiatus in males as compared to females rectal hiatus • In males the urethra passes from the lesser pelvis to the (anal aperture) perineum via the urogenital hiatus. • In females the urethra and pass from the lesser pelvis to the perineum via the urogenital hiatus.

• The rectal hiatus (anal aperture) is a posterior opening of the pelvic floor through with the passes to enter the region of the perineum. Urogenital and Anal Triangles The diamond-shaped perineum can be further subdivided into two triangular regions (urogenital triangle and anal triangle) by an imaginary line connecting the two ischial tuberosities. Take note that the two triangles are not in the same plane when the pelvis is in anatomical position.

• The urogenital triangle is the anterior triangular region of the diamond-shaped perineum • In anatomical position, the urogenital triangle is oriented in a horizontal plane. • The urogenital triangle contains the urethra and external genitalia.

• The anal triangle is the posterior triangular region of the diamond-shaped perineum • In anatomical position, the anal triangle is oriented in a plane that is almost vertical. • The anal triangle contains the anal canal, , , inferior rectal nerve (branch of ), and the fat-filled ischioanal fossa.

Urogenital Triangle

rectal hiatus (anal aperture)

Anal Triangle Perineal Membrane: Introduction

The perineal membrane is an important fascial layer within the urogenital triangle. • Its attachments are on the ischial tuberosities and the ischiopubic rami. • The posterior margin of the perineal membrane is NOT attached to , but is anchored at its midline to the perineal body. • The perineal membrane creates an important boundary that separates the perineum into two spaces. (See next slide for details.) • A deep space (pouch) superior to the perineal membrane • A superficial space (pouch) inferior the perineal membrane Perineal Membrane: Deep and Superficial Pouches Figure 2 The perineal membrane separates the urogenital triangle into two pouches (spaces). • By definition, the deep perineal pouch (space) is the space located between the perineal membrane and the fascia covering the inferior side of the pelvic floor (diaphragm) muscles (Figure 1). However, there are many inconsistencies in diagrams as to what constitutes the deep perineal space. I think it is easiest to consider the deep space as consisting of two subregions. • Fibromuscular region: This is the thin region of muscle resting on the superior side of the perineal membrane. In older textbooks, this is a structure that was described as the . (Some present authors call this the “perineal membrane.”) This region of the deep space contains , neurovascular structures, and the bulbourethral glands in males. • The anterior recess of the ischioanal fossa is an anterior continuation of the fat- filled ischioanal fossa. The anterior recess is located between the fibromuscular portion of the deep pouch and the levator ani muscles. The medial region of the anterior recess is smaller in size compared to the lateral region. • The superficial perineal pouch (space) is located between the perineal membrane and membranous superficial fascia (Colles fascia). Figure 1

Pelvic Diaphragm Deep Pouch (A Recess Ischioanal Fossa) Deep Pouch (Fibromuscular Region) “Urogenital Diaphragm” Superficial Pouch

Perineal Membrane Colles Fascia Deep Pouch Male Deep Perineal Space The “fibromuscular” region of the the deep pouch differs by gender.

Male deep Pouch • Deep transverse perineal muscle • Urethra passes through the deep space • External urethral sphincter • Bulbourethral glands • Internal pudendal and branches • Dorsal nerve of

Female Deep Pouch • Deep transverse perineal muscle • Urethra and vagina passes through the deep space • External urethral sphincter Female Deep Perineal Space • Compressor urethrae muscle • Urethrovaginalis sphincter muscle • and branches • Dorsal nerve of

Note on : The perineal membrane is sometimes referred to as the “inferior fascia of the urogenital (UG) diaphragm.” However, the UG diaphragm is a structure now considered to no longer exist. It was described as a single (thin) layer of skeletal muscle “sandwiched” between the of the pelvic diaphragm, which inferiorly is the perineal membrane and superiorly the “superior fascia of the urogenital diaphragm." However, evidence of the superior fascia is lacking. In addition, the external urethral sphincter (sphincter urethrae muscle) was previously thought to be the principle content of the deep pouch. However, the external urethral sphincter is now recognized to be contained within the wall of the urethra and extends superiorly beyond the thin region that was formerly identified as the urogenital diaphragm. External Urethral Sphincter Male Superficial Pouch

The following structures are located within the superficial pouch in a man. • The superficial transverse perineal muscles extend from the ischial tuberosities and the rami to the perineal body medially. They function to stabilize the perineal body. • The root of the penis consists of the bulb and crura, which are the regions of the penis attached to the pubic arch and perineal membrane. • The bulb of the penis is the central portion of the root and is anchored to the perineal membrane. The urethra (proximal ) passes through the bulb. • The bulbospongiosus muscles surrounds the bulb of the penis and the proximal corpus spongiosum. The bulbospongiosus muscles are joined in the midline by a raphe on the inferior surface of the bulb and are anchored to the perineal membrane and the perineal body. • The crura (pleural form of crus) are regions of the corpora cavernosa attached to the ischiopubic rami.. • The ischiocavernosus muscles surround each crura. Female Superficial Pouch

The following structures are located within the superficial pouch in a woman. • The superficial transverse perineal muscles extend from the ischial tuberosities and the rami to the perineal body medially. They function to stabilize the perineal body.

• The bulbospongiosus muscles, which are anchored to the anteriorly, the perineal membrane along its lateral sides, and posteriorly to the perineal body, cover two other structures located in the superficial pouch. • The bulbs of the vestibule are a pair of erectile structures firmly anchored to the perineal membrane located on each side of the vaginal orifice. Their anterior ends connect to the glans clitoris by small bands of erectile tissue. The bulbs of the vestibule are the structural homolog of the bulb of the penis. • The greater vestibular (Bartholin's) glands are located posterior to the bulb of the vestibule. During , the vestibular glands secrete mucus into the vestibule via ducts to moisten the and vestibule.

• The ischiocavernosus muscles are located along the ischiopubic rami and surround the root of the clitoris. The root of the clitoris consists of two erectile tissue structures called crura. • The crura of clitoris are attached to the ischiopubic rami. They meet at the midline and detach from bone to become the corpora cavernosum of the clitoris. The unattached corpora cavernosa constitute the body of the clitoris and terminate as the glans clitoris. • Upon contraction, the crura force blood into the body of the clitoris. Perineal Body The perineal body is an important fibromuscular structure maintaining the integrity of the pelvic floor. It is located in the midline of the body along the posterior border of the perineal membrane where the urogenital and anal triangles meet. It is a central attachment point for the following structures/muscles. • Perineal membrane • Anterior muscle fibers of levator ani • External anal sphincter • • External urethral sphincter • Superficial and deep transverse perineal muscles • Sphincter urethrovaginalis (females)

CLINICAL : The perineal body is especially important in women because it is the final support of the pelvic viscera. Disruption of the perineal body can result in loss of support and of pelvic viscera.

Coccygeus Obturator Internus

Levator Ani Neurovascular Structures in Superficial Pouch

The following neurovascular structures are located within the superficial pouch. • Perineal branches of internal pudendal artery • Perineal branches of pudendal nerve Review: Female Urethra Anterior Posterior

• Urine enters the urethra by passing through the bladder’s internal urethral orifice. • The proximal urethra passes through the of the bladder. The smooth muscle within the wall of the bladder neck intermingles with fibers, but lacks a well-defined sphincter arrangement as is present in a man’s bladder neck. Technically speaking, women lack an internal urethral sphincter. However, physiological descriptions of micturition will describe an the internal urethral sphincter needing to relax for urination to occur. Details of micturition are on an upcoming slide. • The urethra courses in an inferior direction along a path that is parallel and anterior to the vagina. • The external urethral sphincter, consisting of skeletal muscle, surrounds the urethra as it passes through the deep perineal pouch. The external urethral sphincter is innervated by the pudendal nerve (S2-4). • The urethra opens into the vestibule (space surrounded by ) at the urethra’s external urethral orifice. • Ducts of the paraurethral (Skene’s) glands are located on either side of the external urethra orifice. These glands are the homologues of the and are thought to secrete fluid to lubricate the urethral opening. Review: Male Urethra

• Urine enters the urethra by passing through the bladder’s internal urethral orifice. The urethra in men consists of 4 named regions and is surrounded by two sphincters. • The intramural (preprostatic) urethra is the short, proximal portion of the male urethra within the neck of the bladder. • The preprostatic urethra is surrounded by the internal urethral sphincter, which is innervated by pelvic splanchnic .

• The portion of the urethra within the prostate gland, is called the . The ejaculatory ducts (right and left) connect to the urethra within the prostate gland. • The mass of skeletal muscle fibers located immediately inferior to the prostate gland form the external urethral sphincter located within the deep perineal space/pouch (space superior to the perineal membrane in the region formerly known as the urogenital diaphragm ).

• The is the short section of the urethra surrounded by the external urethral sphincter as it courses through the “fibromuscular” region of the deep pouch (former urogenital diaphragm). • The spongy (penile) urethra is the section of urethra coursing through the penis. • The external urethral orifice is the opening of the urethra at its termination point. Urethral Injury (Goldman Classification)

CLINICAL ANATOMY: Damage to the urethra can cause urine to leak into different spaces. One method of classify urethral injuries is by the Goldman Classification.

• A type I injury is a stretching of the urethra without rupture. • A type II urethral injury is when the urethra is damaged proximally to the muscles within the deep perineal space (formerly known as urogenital diaphragm). Extravasated urine in this situation results in its accumulation within the . • A type III urethral injury is when the urethra is damaged distally to, and within, the region where it passes through the muscles of the deep perineal space (urogenital diaphragm). Extravasated urine flowing with gravity results in its accumulation within the superficial perineal space. Urine can accumulate within the , penis, and anterior . This is the most common type of urethral injury and is often called a straddle injury because of the common mechanism by which it occurs. For example, a boy slides off a bicycle seat and hits the support bar below the seat with his perineal region. • A type IV urethral injury is when the neck of the bladder and the proximal prostatic urethra are damaged. Extravasated urine in this situation results in its accumulation within the retropubic space. • A type V urethral injury is when the penile urethra is torn. Extravasated urine in this situation results in its accumulation deep to the deep fascia of the penis (Buck's fascia). Sacral Plexus

The sacral plexus is located anterior to the piriformis muscle in the pelvic cavity. • It is composed of the S1-S4 ventral rami that enter the pelvic cavity by passing through the anterior sacral foramina. • The sacral plexus receives nerve fiber contributions from the lumbar plexus via the lumbosacral trunk to form the lumbosacral plexus. • The lumbosacral consists of portion of the L4 ventral ramus and the entire L5 ventral ramus. • The lumbosacral trunks enter the pelvic cavity by passing inferiorly across the sacral alae. Pudendal Nerve Lumbosacral plexus branches • See MSI Labs 4 and 5 to review the branches of the lumbosacral plexus that supply the lower extremity. • The pudendal nerve branches from the S2-S4 ventral rami of the sacral plexus. • It exits the pelvic cavity inferior to the piriformis muscle via the greater sciatic foramen. • It passes around the sacrospinous ligament to enter the lesser sciatic foramen. • It then courses through the ischioanal fossa along its lateral wall within the fascia of the obturator internus muscle called the pudendal (Alcock’s) canal. • Branches • The inferior rectal nerves supply the external anal sphincter and of perianal region inferior to pectinate line. • The divides into two branches • Superficial branch becomes the posterior scrotal nerve (male) or labial nerves (female) • Deep (muscular) branch supplies muscle of the urogenital triangle and the bulb. • The pudendal continues as the dorsal nerve of the penis or clitoris by penetrating the perineal membrane to reach its destination. Spinal, Epidural, and Pudendal Blocks CLINICAL ANATOMY: Spinal Block vs Epidural Block

• A spinal block is the delivery of anesthesia into the CSF of the subarachnoid space by a single injection. The anesthesia usually begins to take effect within 1 minute and results in anaesthetizing the body below, and sometimes above, the site of injection. After administration, the patient may not be able to move his or her lower extremities until the anesthetic wears off. A headache may follow the procedure, which is most likely a result of CSF leakage at the injection site.

• An epidural block is the administration of an anesthetic and analgesic into the epidural space through a catheter. This method provides greater control of prolonged pain relief because of continuous, controlled infusion. To anesthetize the lower extremity and pelvis, this procedure can be done in the same location as a lumbar puncture. If the anesthesia is introduced into the sacral canal via the sacral hiatus (caudal epidural block), only the S2-S4 nerve roots are anesthetized (birth canal, pelvic floor, and external genitalia). This procedure spares the lower extremity, which is why it is a popular choice for participatory child birth. However, it must be administered in advance of the actual delivery.

CLINICAL ANATOMY: A pudendal nerve block is a common anesthesia technique for perineal anesthesia during obstetric procedures, including vaginal birth during the second stage of labor, vaginal repairs, and anorectal surgeries such as hemorrhoidectomies. The pudendal nerve is anesthetized where it enters the lesser sciatic foramen, 1 cm inferior and medial relative to the attachment of the sacrospinous ligament to the ischial spine. This procedure can be accomplished by the following approaches: transvaginal (figure), transperineal, or perirectal.