LG 2

Lecture Information

  • Lecture Number: 2
  • By: Dr. NALI Abdulkader
  • Topic: Pelvis and Perineum

Outline

  • Components of the Bony Pelvis
  • Subdivision of the pelvis (Greater and Lesser pelvis)
  • Structures forming the walls of the pelvis
  • Types of female bony pelvises
  • Pelvic floor under the following headings:
    • Location
    • Parts
    • Gaps
  • Definitions:
    • Perineal body
    • Anococcygeal body
  • Boundaries and contents of the Ischiorectal fossa and anal triangle

Clinical Scenarios

  • Scenario 1:

    • Patient Profile: 27-year-old woman in active labor
    • Observations: Prolonged labor, heart-shaped pelvic inlet, prominent ischial spines, narrow subpubic angle
    • Pelvis Type:
    • A. Gynecoid pelvis
    • B. Anthropoid pelvis
    • C. Android pelvis
    • D. Platypelloid pelvis
    • E. Dolichopelvic pelvis

  • Scenario 2:

    • Patient Observations: Rounded pelvic inlet, wide subpubic angle, short broad sacrum
    • Outcome: Labor progressed smoothly, vaginal delivery without complications
    • Pelvis Type:
    • A. Android
    • B. Gynecoid
    • C. Anthropoid
    • D. Platypelloid
    • E. Mesatipelvic

General Structure of the Pelvis

  • Definition: The pelvis is the lower part of the trunk located between the abdomen and the lower limb. It consists of the bony pelvis and a cavity.
  • Perineum: Anatomical region in the pelvis located between the thighs; contains external genitalia.

Components of the Bony Pelvis

  • Bones Constituting the Pelvis:
    • Two hip bones
    • Sacrum
    • Coccyx
  • Function: Provides a strong and stable connection between the trunk and lower limb.
  • Articulations:
    • The two hip bones articulate:
    • Anteriorly at the symphysis pubis
    • Posteriorly with the sacrum at the sacroiliac joint

Joints of the Pelvis

  • Types of Joints:
    • Symphysis Pubis
    • Sacroiliac Joints
    • Sacrococcygeal Joint

Differences Between Male and Female Pelvis

FeatureMaleFemale
General StructureHeavy and thickLight and thin
Articular SurfacesLargeSmall
False PelvisDeepShallow
Pelvic InletHeart-shapedOval
Pelvic Canal/CavityFunnel-shaped and narrowRoomy and wide
Pelvic OutletSmall (inverted)Large (everted)
SacrumLong, narrow with smooth forward concavityShort, wide, flat, curving forward in the lower part
Subpubic Angle< 90° (angle between the middle and index fingers)90° or more (angle between the thumb and the index finger)
AcetabulumLargeSmall
Ischial TuberositiesInvertedEverted
Obturator ForamenLarger and ovalSmaller and triangular

Division of the Pelvis

  • Pelvic Brim: Divides the pelvis into two parts:
    • False pelvis (greater/major pelvis):
    • Part of the abdominal cavity.
    • True pelvis (lesser/minor pelvis):
    • Lies inferior to the pelvic brim and is the true pelvic cavity.

Boundaries of the False Pelvis

  • Bounded by:
    • Posteriorly: Lumbar vertebrae
    • Laterally: Iliac fossae and iliacus muscle
    • Anteriorly: Lower part of the anterior abdominal wall
    • Function: Supports the abdominal contents.

Pelvic Aperture Definitions

  • Pelvic Inlet:
    • Also called the superior pelvic aperture
  • Pelvic Outlet:
    • Also called inferior pelvic aperture
    • Closed by the pelvic diaphragm

Types of Female Bony Pelvis

  • Importance: Information on the shape and dimensions of the female pelvis is crucial in obstetrics, as it is the bony canal through which the child passes during birth.
  • Types:
    • Gynecoid:
    • Ideal obstetric pelvis; typical female pelvis
    • Found in 80% of Asian women; 50-70% of white women
    • Characteristics: Rounded or slightly oval inlet, large everted outlet, straight sidewalls, wide subpubic arch
    • Android:
    • Least favorable for vaginal delivery
    • Narrow diameters can lead to obstructed labor
    • Anthropoid:
    • Often allows spontaneous vaginal delivery, especially when fetal head engages in an anteroposterior direction
    • Platypelloid:
    • Leads to prolonged labor

Walls of the Pelvic Cavity

  • Walls:
    1. Anterior pelvic wall
    2. Lateral pelvic wall
    3. Posterior wall
    4. Pelvic floor

Anterior Pelvic Wall

  • Formed By:
    • Symphysis pubis (secondary cartilaginous joint)
    • Reinforced by two ligaments (superior and inferior pubic ligaments)
    • Pubic rami (superior and inferior)

Posterior Pelvic Wall

  • Formed By:
    • Sacrum and coccyx
    • Piriformis muscle
  • Piriformis Muscles Functions:
    • Origin: Pelvic surface of sacrum
    • Insertion: Greater trochanter of femur
    • Action: Rotates femur laterally

Lateral Pelvic Wall

  • Formed By:
    • Hip bone
    • Obturator muscle and fascia
    • Sacrotuberous and sacrospinous ligaments

Pelvic Floor Components

  • Definition: The pelvic floor is a funnel-shaped structure separating the pelvic cavity from the perineum below.
  • Gaps of the Pelvic Floor:
    • Urogenital hiatus: Anterior gap for urethra (and vagina in females).
    • Rectal hiatus: Central gap for anal canal.

Pelvic Diaphragm

  • Components:
    • Levator ani muscles (largest component)
    • Coccygeus muscle
    • Fascia coverings of the muscles
  • Levator Ani Muscles:
    • A broad sheet composed of three paired muscles:
    1. Puborectalis
    2. Pubococcygeus
    3. Iliococcygeus
    • Innervation: Anterior ramus of S4 and branches of the pudendal nerve (roots S2, S3, S4)

Perineal Body

  • Definition: A pyramidal fibromuscular mass located at the junction of the urogenital triangle and anal triangle.
  • Attachment Points:
    • External anal sphincter
    • Bulbospongiosus muscle
    • Superficial transverse perineal muscle
    • Levator ani (anterior part)

Injury to Pelvic Diaphragm

  • Causes: Tearing of the perineal body during difficult childbirth can lead to pelvic diaphragm injury.
  • Consequences:
    • Weakness in support to pelvic viscera
    • Possible uterine and rectal prolapse

Anococcygeal Body

  • Description: A complex musculotendinous structure situated between the anterior aspect of the coccyx and the posterior wall of the anorectal canal.
  • Function: Receives insertion fibers of the levator ani muscle.

Perineum

  • Definition: The region below the pelvic diaphragm, diamond-shaped area between the thighs.
  • Contents:
    • Lower ends of urethra, vagina, and anal canal
    • External genitalia
    • Perineal body and Anococcygeal body

Boundaries of the Perineum

  • Bony Boundaries:
    • Anterior: Symphysis pubis
    • Posterior: Coccyx
    • Lateral: Ischiopubic rami, ischial tuberosities, sacrotuberous ligament
  • Division: Divided into two triangles by a line passing through the two ischial tuberosities:
    • Urogenital triangle (anteriorly)
    • Anal triangle (posteriorly)

Urogenital Triangle

  • Boundaries:
    • Anteriorly: Symphysis pubis
    • Posteriorly: Transverse line passing through the two ischial tuberosities
    • Laterally: Ischiopubic rami and ischial tuberosities
  • Contents:
    • Lower part of urethra and vagina
    • External genitalia (vulva)

Anal Triangle

  • Boundaries:
    • Anteriorly: Transverse line passing through the two ischial tuberosities
    • Posteriorly: Coccyx
    • Laterally: Ischial tuberosity and sacrotuberous ligaments
  • Contents:
    • Lower part of anal canal
    • Anococcygeal body
    • Ischiorectal fossa on each side

Ischiorectal Fossa

  • Definition: Also called ischiorectal canal, a fascial lined wedge-shaped space on each side of the anal canal.
  • Boundaries:
    • Base: Skin of the perineum
    • Medial wall: Levator ani and anal canal
    • Lateral wall: Obturator internus, covered with fascia
  • Contents:
    • Dense fat
    • Pudendal nerve and internal pudendal vessels within the pudendal canal
    • Inferior rectal nerve and vessels crossing the fossa to reach the anal canal
    • Rectum
    • Levator ani muscle