Pelvis and Pelvic Wall

Pelvis and Pelvic Wall

Presented by: Sarah Abutineh, MD
Course: Medical Gross Anatomy
Term: Fall 2025, LMU-CDM


Learning Objectives

  • Identify and describe the major bones of the pelvis:

    • Ilium

    • Ischium

    • Pubis

    • Sacrum

    • Coccyx

  • Differentiate the spaces and contents of the pelvis.

  • Identify the bony features and joints and ligaments of the pelvic girdle.

  • Identify the components of the pelvic diaphragm.


Overview

  • Pelvis:

    • Located inferior to the abdomen.

    • Functions to contain, support, and protect pelvic viscera, lower parts of the intestinal tract, urinary tracts, and internal reproductive organs.

    • Transmits the weight of the body from the vertebral column to the femurs.

    • Provides attachment for trunk and lower limb muscles.

    • Divided into two main regions:

    • False (greater) pelvis

    • True (lesser) pelvis


Terminology

  • Pelvic Inlet:

    • Also known as pelvic brim; boundary between greater pelvis and lesser pelvis.

  • Pelvic Floor:

    • Fibromuscular structure that separates the pelvic cavity above from the perineum below.

  • Perineum:

    • Located inferior to the floor of the pelvic cavity; forms the pelvic outlet.


Pelvic Inlet and Outlet

  • Pelvic Inlet Boundaries:

    • Anterior: Pubic symphysis

    • Lateral: Iliopectineal line

    • Posterior: Sacral promontory and wings

  • Pelvic Outlet Boundaries:

    • Anterior: Pubic arch

    • Lateral: Ischial tuberosities anteriorly and sacrotuberous ligaments posteriorly

    • Posterior: Tip of coccyx


False Pelvis

  • Located superior to the pelvic inlet.

  • Contains distal part of the intestines.

  • Continuous with the inferior part of the anterior abdominal wall.

  • Supports abdominal contents and helps support the gravid uterus after the third month of pregnancy.

  • Has little clinical significance.

  • Short, curved canal with a shallow anterior wall and deeper posterior wall.

  • In females, the pelvis acts as a bony birth canal.


Bony Pelvis

  • Structure of the Bony Pelvis:

    • Composed of pelvic girdle and pelvic spine, forming a strong basin-shaped skeletal framework.

  • Pelvic Girdle:

    • Includes ilium, ischium, pubis, which are fused together to form one hip/pubic bone.

  • Pelvic Spine:

    • Composed of sacrum and coccyx.

  • Pubic Bones Connection:

    • Two pubic bones are connected at the symphysis pubis.

    • Pubic bones articulate with the spine at the sacroiliac joints.


Hip Bone

  • Comprised of ilium, ischium, and pubis.

  • Lateral surface features the acetabulum, which is the principal union point of the three bones.

  • Individual Bones:

    • Ilium: Extends superiorly to the hip joint.

    • Ischium: Posteroinferior portion of the hip bone.

    • Pubis: Anteroinferior part of the hip bone.

  • Obturator Foramen:

    • Located inferior to the acetabulum.


Ilium

  • Arcuate Line:

    • Separates upper and lower parts of the ilium.

  • Positioning:

    • Inferior to arcuate line is the true pelvis.

    • Superior to arcuate line is the fan-shaped wing (ala) that forms the iliac fossa anteriorly, providing attachment for lower limb muscles.

  • Iliac Crest:

    • The thick, superior margin of the ilium.

  • Protrusions of Ilium:

    • Anterior superior iliac spine (ASIS)

    • Posterior superior iliac spine (PSIS)

    • Anterior inferior iliac spine (AIIS)

    • Posterior inferior iliac spine (PIIS)


Greater Sciatic Notch

  • Formed by sacrospinous ligament superiorly and sacrotuberous ligament posteroinferiorly, creating the greater sciatic foramen.

  • Contents:

    • 7 nerves

    • 3 pairs of blood vessels

    • 1 muscle


Ischium

  • Located as the posteroinferior part of the hip bone.

  • Composed of body and ramus.

  • Ischial Spine:

    • Attachment site for the sacrospinous ligament.

  • Lesser Sciatic Notch:

    • Anterior border of the lesser sciatic foramen.

    • Bounded by sacrospinous and sacrotuberous ligaments.

    • Acts as a passageway for:

    • Pudendal nerve

    • Internal pudendal vessels

    • Nerve to obturator internus

    • Tendon of obturator internus


Ligaments

  • Sacrotuberous and Sacrospinous Ligaments:

    • Stabilize the sacrum on the pelvic bones, preventing upward tilting of the inferior sacrum.

    • Convert the greater and lesser sciatic notches into foramina.


Pubis

  • Consists of a small body and two rami (superior and inferior).

  • Medially, the two bones articulate at the symphysis pubis joint.

  • Pubic Tubercle:

    • Approximately 2.5 cm lateral to symphysis pubis; serves as an attachment point for the inguinal ligament.

  • Pubic Arch:

    • Located inferior to the pubic symphysis; sexually dimorphic features.


Sacrum

  • Composed of five fused sacral bones.

  • Features differences between pelvic and gluteal surfaces.

  • Base:

    • Features a midline projection known as the sacral promontory.

  • Ala of Sacrum:

    • Comprised of fused transverse processes of S1/S2.

  • Contains the sacroiliac joint on the lateral surface of each ala.


Joints

  1. Lumbosacral Joint:

    • Facilitates movement of the torso in relation to the pelvis and lower limbs.

  2. Sacroiliac Joint:

    • Ligaments soften during pregnancy, enabling an increase in pelvic diameter; otherwise limited mobility due to interlocking surfaces.

    • Stabilized by three ligaments: anterior, posterior, and interosseous sacroiliac ligaments.

  3. Sacrococcygeal Joint:

    • Facilitates flexion and extension of the coccyx.

  4. Pubic Symphysis:

    • Has no movement except during pregnancy.


Muscles

  • Contribute to the lateral walls of the pelvic cavity:

    1. Obturator Internus:

    • Flat, fan-shaped muscle originating from around the obturator foramen.

    • Leaves the pelvis through the lesser sciatic foramen.

    1. Piriformis:

    • Originates between four anterior sacral foramina and leaves the pelvis through the greater sciatic foramen.

  • Both muscles attach to the greater trochanter of the femur.


Male vs Female Pelvis

  • Shape Differences:

    • Pelvic inlet in women is circular compared to the heart-shaped inlet in men.

  • Sub-Pubic Angle:

    • Larger in women (80°–85°) than men (50°–60°).

  • Ischial Spines:

    • Generally do not project as far medially into the pelvic cavity in women compared to men.

  • Curvature of Sacrum:

    • More curved in men.


Male vs Female Pelvis Differences

  1. Inlet shape

  2. Arch angle

  3. Sacrum concavity

  4. Ischial spine projection


Pelvic Floor

  • Division between the main pelvic cavity above and perineum below.

  • Formed mainly by the pelvic diaphragm.

  • Additional Elements:

    • Perineal membrane and muscles of the deep perineal pouch in the anterior midline.

  • Composition of Pelvic Diaphragm:

    • Formed by levator ani and coccygeus muscles along with their fascial coverings.

  • Significant Gaps:

    • Urogenital hiatus

    • Rectal hiatus

  • Perineal Body:

    • Fibrous node connecting the pelvic floor to the perineum.


Levator Ani Muscles

  • Composition:

    • Broad sheet consisting of three separate paired muscles:

    1. Pubococcygeus:

      • The most important for maintaining fecal continence.

      • Originates from one side of the pubis and attaches to the other side, forming a sling around the rectal hiatus.

      • Some pre-rectal fibers form a sling around the urogenital hiatus (known as pubovaginalis or sphincter urethrae/vaginae).

    2. Pubococcygeus:

      • Forms the bulk of the complex; originates from the posterior surface of the pubis and blends with the contralateral muscle in the midline of the pelvic floor.

    3. Iliococcygeus:

      • Originates from the ischial spines and inserts onto the coccyx, perineal body, and anococcygeal ligament.

  • All three muscles are innervated by the nerve to levator ani and branches of the pudendal nerve.


Coccygeus Muscle

  • A small triangular muscle located posterior to the levator ani muscle group.

  • Origin:

    • From the ischial spines.

  • Insertion:

    • Onto the inferior end of the sacrum and coccyx.

  • Function:

    • Supports the pelvic viscera and flexes the coccyx.

  • Innervation:

    • Anterior rami of S4 and S5.