Lecture 12

The Core and Pelvic Wall Structure

  • The Core: Defined functionally as the unit comprising the diaphragm (top), the pelvic floor (bottom), the abdominal muscles (front), and the spinal muscles (back).

  • The Pelvic Wall: Described as the sides of the "bowl" structure of the pelvis.

    • It contains the following structures from anterior to posterior: Urethra, Vagina, and Rectum.

    • The wall contains three primary muscles: Obturator Internus, Piriformis, and Iliacus.

Muscles of the Pelvic Wall

  • Obturator Internus:

    • Location: Situated under the fascia of the pelvic wall.

    • Origin (O): Pelvic surface of the obturator membrane and surrounding bones.

    • Insertion (I): Trochanteric fossa (medial surface of the greater trochanter of the femur).

    • Action (A): External rotation (ER) of the thigh; rotation during thigh extension; abduction (ABD) of a flexed thigh; steadies the femoral head within the acetabulum.

    • Clinical Application: This muscle is particularly relevant for hurdler athletes.

    • Innervation (INE): Nerve to obturator internus (L5−S2L_5-S_2).

  • Piriformis:

    • Origin (O): Anterior surface of the sacrum and superior surface; Sacrotuberous ligament.

    • Insertion (I): Greater trochanter of the femur.

    • Action (A): External rotation (ER); abduction (ABD) of the thigh; assists in holding the head of the femur in the acetabulum.

    • Innervation (INE): Anterior rami of S1−S2S_1-S_2.

  • Iliacus:

    • Origin (O): Superior two-thirds (2/32/3) of the iliac fossa; iliac crest; ala of the sacrum; anterior sacroiliac ligaments.

    • Insertion (I): Lesser trochanter of the femur and the shaft of the femur inferior to it; psoas major tendon.

    • Action (A): Flexion (FLX) of the thigh; stabilizes the hip joint; acts in conjunction with the psoas major.

    • Innervation (INE): Femoral nerve (L2−3L_{2-3}).

The Pelvic Floor (Levator Ani Muscles)

  • Overview: The pelvic floor consists of four muscles, collectively referred to as the levator ani muscles. Most are named based on their origin and insertion.

  • The "True" Levator Ani: Strictly speaking, the true levator ani group consists of only three muscles: Puborectalis, Pubococcygeus, and Iliococcygeus.

  • Innervation: All four muscles (including the Coccygeus) are innervated by the nerve to levator ani (S3−S4S_3-S_4).

  • Puborectalis:

    • Origin (O): Body of the pubis.

    • Insertion (I): Loops around the rectum to join the other side of the body of the pubis.

    • Action (A): Crimps off the opening of the rectum to maintain continence.

    • Clinical Note: Continuous straining can weaken this muscle, potentially leading to fecal incontinence.

  • Pubococcygeus:

    • Origin (O): Pubic bone, located lateral to the puborectalis.

    • Insertion (I): Coccyx bone and sacrum.

  • Iliococcygeus:

    • Origin (O): Obturator foramen (arcus tendineus of levator ani).

    • Insertion (I): Sacrum and coccyx.

  • Ischiococcygeus (also known as Coccygeus):

    • Note: While grouped with the floor, it is NOT considered part of the "true" levator ani.

    • Origin (O): Ischial spine.

    • Insertion (I): Inferior sacrum and coccyx.

  • Support and Rehabilitation: These muscles support internal viscera (organs). Strengthening can be achieved through:

    • Electromyography (EMG) or Biofeedback: Used to determine current activation levels.

    • Body positioning exercises (e.g., Kegels).

Female Internal Anatomy and Uterine Positioning

  • Internal Arrangement: The urinary bladder leads down to the urethra. The uterus sits directly on top of the urinary bladder.

  • Uterine Positions: Positions are named based on the location of the fundus (crown) of the uterus.

    • Anteflexed: The fundus is oriented more anteriorly, overtop of the bladder. This is the most common position. During pregnancy, the growing fetus typically pushes down on the bladder.

    • Retroflexed: The fundus lies along the posterior wall of the abdomen. As the uterus enlarges during pregnancy, it pushes against the posterior abdominal wall, typically causing back pain.

Clinical Conditions: Prolapsed Viscera and Fistulas

  • Visceral Prolapse: A condition where pelvic organs drop or fall out due to muscle weakness. This is common in female anatomy.

  • Uterine Prolapse: The uterus descends into the vaginal canal due to muscle weakness or multiple pregnancies.

    • Rating System: Measured on a 1-4 scale.

    • 4th Degree: The tip of the uterus is external to the body.

    • Management: Conservative management can typically help reduce the prolapse by one degree before it reaches the 4th degree.

  • Cystocele (Bladder Prolapse): The bladder balloons and pushes into the anterior vaginal wall.

    • Symptoms: Difficulty emptying the bladder; patients often must change positions on the toilet to complete urination.

    • Fistula Risk: Further weakening can cause a fistula, where the bladder breaks into the vaginal canal, allowing urine to enter the vagina. This requires surgical intervention.

  • Rectocele (Rectum Prolapse): The rectum balloons and pushes into the posterior vaginal wall.

    • Symptoms: Difficulty with defecation, requiring harder pushing, which further balloons the rectum.

    • Fistula Risk: Fecal matter can enter the vaginal canal if a fistula develops.

Male Internal Anatomy and Prostate Health

  • Urinary Bladder: Generally not as flattened as the female bladder.

  • Prostate Gland: Located inferior to the bladder.

    • The urethra passes through the center of the prostate.

    • Benign Prostatic Hyperplasia (BPH): In older males, an enlarged prostate can constrict the urethra, making it difficult to initiate or sustain a stream of urination.

    • Location: Situated at the anterior wall of the rectum.

    • Clinical Screening: The Digital Rectal Exam (DRE) is used to palpate the prostate through the rectum wall to check for enlargement.

Anatomy of the Penis and Scrotum

  • Parts of the Penis:

    • Base (Root).

    • Body.

    • Glans (the tip).

  • Erectile Tissues:

    • Corpus Cavernosum: Located on the dorsal aspect. It consists of two sections fused in the median plane, which separate posteriorly to form the crura (plural of crus) of the penis.

    • Corpus Spongiosum: Located on the ventral side. There is only one section, and the urethra travels through it.

  • Scrotal Structures:

    • Testes: The site of sperm production.

    • Epididymis: Located on top of the testes; serves as the site for sperm storage and maturation. It has three parts:

      • Head (most medial).

      • Body.

      • Tail (most lateral).

    • Ductus Vas Deferens: Connects to the tail of the epididymis. It transports semen to the ejaculatory duct to be expelled via the urethra during ejaculation.

The Inguinal Region

  • Inguinal Ligament (Ligament of Poupart):

    • A prominent band of fibrous connective tissue in the groin.

    • Path: Extends from the Anterior Superior Iliac Spine (ASIS) to the pubic tubercle.

    • Composition: Formed by the thickened aponeurosis of the external oblique muscle.

  • Inguinal Triangle: Located just above the ligament; serves as a passageway for the ductus vas deferens as it enters the pelvis.

  • Spermatic Cord:

    • Position: Superior to the inguinal ligament and lateral to the conjoint tendon.

    • Contents: Carries the ductus vas deferens, blood supply, nerves, and tissue into the pelvic cavity.

    • Protective Layers: Derived from abdominal wall layers (External oblique, Internal oblique, Transversus abdominis, and Transversalis fascia). The external spermatic fascia is formed by the external oblique.

  • Testicular Descent: During development, the testes travel through the abdominal fascial layers to reach the outside of the body, creating the spermatic cord and its tunics.

  • Cremaster Muscle: Covers the spermatic cord and testes. It contracts to lift the scrotum and relaxes to lower it, maintaining a viable temperature for sperm.

Classifications of Hernias

  • General Definition: Protrusion of viscera (often intestines) through a space in the abdominal wall, usually caused by increased pressure.

  • Direct Inguinal Hernia:

    • Mechanism: Increased pressure pierces the peritoneum; the viscera protrude through the inguinal triangle, travel down the inguinal canal, and exit via the superficial inguinal ring.

    • Note: It never passes through the deep inguinal ring.

    • Characteristics: Often viscera can be pushed back in. If not, it can cause swelling in the scrotum (males) or labia (females).

    • Prevalence: Accounts for 25−33%25-33\% of all inguinal hernias.

    • Type: Acquired (due to repetitive pressure, aging, and wear and tear); most common in older males.

  • Indirect Inguinal Hernia:

    • Mechanism: Protrusion through the deep inguinal ring, down the inguinal canal, and through the superficial inguinal ring.

    • Characteristics: Intestines travel within the spermatic cord near the lateral umbilical fold, making it highly likely to end up in the scrotum or labia.

    • Prevalence: Accounts for 66−75%66-75\% of all inguinal hernias.

    • Type: Often congenital (present at birth).

    • Demographics: 20×20\times more common in males than females due to differences in spermatic cord development.

  • Other Hernia Types:

    • Femoral Hernia: Occurs lateral to the inguinal hernia where the femoral artery (a.a.) and vein (v.v.) exit the abdominal wall into the thigh.

    • Hiatal Hernia: Occurs where the esophagus passes through the diaphragm; the stomach travels up through the diaphragmatic opening.

    • Strangulated Hernia: An intestinal loop becomes trapped and does not return through the superficial inguinal ring, potentially losing its blood supply.

    • Non-strangulated Hernia: An intestinal loop goes through the opening and returns.

  • Clinical Testing: Inguinal hernias are assessed using the "cough test" to differentiate them from adductor muscle strains. Note that a cough test cannot distinguish between direct and indirect hernias.

  • Remnant Structure: The round ligament of the uterus in females is the remnant of the structure that would have been the spermatic cord in males.

Embryologic Development of Genitalia

  • 4 Months (Unisex Phase): Structures are identical regardless of sex. Components include the Genital tubercle, Urethral groove, Urethral fold, and Labioscrotal swelling.

  • 5 Months (Differentiation Phase):

    • Male: Urethral fold closes to become the shaft of the penis; glans becomes larger; labioscrotal swelling becomes the scrotum.

    • Female: Urethral folds stay open to serve as the urethral opening; labioscrotal swelling becomes the labia majora; glans becomes smaller.

  • At Birth:

    • Male: Fully developed scrotum and glans.

    • Female: Glans of the clitoris, labia majora, and labia minora are developed.

Muscles of the External Genitalia

  • Overview: Three muscles form the perineal triangle. They are all innervated by the pudendal nerve (S2−S4S_2-S_4).

  • Bulbospongiosus (Center):

    • In Males: Located at the shaft of the penis. Compresses the bulb of the penis and corpus spongiosum to empty the urethra of residual urine/semen; assists with erection by compressing the deep dorsal vein (v.v.) of the penis to prevent venous drainage.

    • In Females: Assists with the erection of the clitoris; split by the vaginal opening.

  • Ischiocavernosus (Lateral Border):

    • In Males: Surrounds the crura (fascia) at the root of the penis. Forces blood from cavernous spaces into the distal corpora cavernosa during erection; compresses the deep dorsal vein (v.v.).

    • In Females: Surrounds the crura of the clitoris; forces blood into the clitoris while preventing venous drainage.

  • Superficial Transverse Perineal (Base):

    • Function: Joins the external anal sphincter to the perineal body. It supports the perineal body to assist the pelvic floor in supporting pelvic viscera.

    • In Males: Provides a firmer base for the penis during erection.

External Surface Anatomy

  • Female Surface Anatomy:

    • Labia Majora: Indirectly protect the clitoris, urethral orifice, and vaginal orifice.

    • Labia Minora: Contain erectile tissue.

    • Clitoris: An erectile organ with a body and a glans (similar to the penis); has a covering called the prepuce (foreskin).

    • External Urethral Orifice: Where urine exits.

    • Vaginal Orifice: Opening leading to the vaginal canal.

  • Male Surface Anatomy:

    • Prepuce of Glans of Penis: The skin covering the glans.

    • Scrotum: Homologous to the labia majora in females.