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
Lumbosacral Joint:
Facilitates movement of the torso in relation to the pelvis and lower limbs.
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.
Sacrococcygeal Joint:
Facilitates flexion and extension of the coccyx.
Pubic Symphysis:
Has no movement except during pregnancy.
Muscles
Contribute to the lateral walls of the pelvic cavity:
Obturator Internus:
Flat, fan-shaped muscle originating from around the obturator foramen.
Leaves the pelvis through the lesser sciatic foramen.
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
Inlet shape
Arch angle
Sacrum concavity
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:
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).
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.
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.