Pelvis: Anatomy and Function

Pelvis Overview

• The pelvis is a compartment surrounded by the pelvic girdle
• True pelvis is a bowl-shaped pelvic cavity enclosed by the pelvic inlet, walls, and floor
• This cavity connects with the abdominal cavity and contains the urinary, gastrointestinal, and reproductive systems

Function of the Bony Pelvis

• Weight is transmitted from the vertebral column to the femurs
• Supports and protects the pelvic viscera
• Provides attachment for trunk and lower limb muscles

Composition of the Bony Pelvis

• Formed by a bony ring of two coxal bones, one sacral bone (sacrum), and one coccygeal bone (coccyx)
• Has two sacroiliac synovial joints
• Has two secondary cartilaginous joints, the pubic symphysis and sacro coccygeal joints
• Contains fibro cartilaginous discs and ligaments

Components of the Pelvic Girdle

• The pelvic bone is composed of the ilium, ischium, and pubis
• Before puberty, these bones are separated by triradiate cartilage in the acetabulum

Acetabulum Details

• Serves as the cup for the femoral head, forming the hip joint
• Formed by the ilium (2/5), ischium (2/5), and the superior ramus of the pubic bone (1/5)
• Contains an acetabular fossa
• Contains an acetabular notch
• Joined by a transverse acetabular ligament

Ilium Bone Information

• The ilium is a fan-shaped bone, forming the lateral prominence of the pelvis
• The ilium consists of two main parts, the body and ala
• Has three surfaces and a crest
• The Gluteal (lateral) surface is divided by the posterior, anterior, and inferior gluteal lines
• The Pelvic (medial) surface contains the iliac fossa and the arcuate line

Arcuate Line Definition

• A ridge that forms part of the boundary between the greater and lesser pelvis
• Contains the auricular area for articulating with the sacrum
• The auricular surface articulates with the sacrum at the sacroiliac joint

Iliac Crest Attributes

• The superior free border of the ilium reaches the spinous process of L4
• The outer lip has a posterior 1/3 that serves as the origin of latissimus dorsi and an anterior 1/2 as an insertion for the external oblique
• The inner lip serves as the origin of the transverse abdominis muscle
• The intermediate line is the origin of internal oblique.

Iliac Crest Projections

• Anterior superior iliac spine forms the origin of the sartorius and tensor fascia lata muscles, and the attachment site for the inguinal ligament
• Posterior superior iliac spine is a projection at the posterior end of the iliac crest
• The iliac tuberosity has a rough surface on the iliac crest for the iliolumbar and sacroiliac ligaments

Ilium Projections not Related to the Iliac Crest

• Anterior inferior iliac spine forms the origin of the rectus femoris muscle
• Posterior inferior iliac spine is located above the greater sciatic notch

Ischium Bone Information

• A V-shaped bone forming the postero inferior part of the pelvis
• Consists of a body and a ramus
• The ramus extends medially and joins the inferior ramus of the pubis to form the ischio pubic ramus, completing the obturator foramen

Ischial Spine and Tuberosity

• Ischial spine serves as the site of attachment for the sacrospinous ligament and the origin of the superior gemellus muscle
• The ischial spine separates the greater sciatic notch superiorly from the lesser sciatic notch inferiorly
• The ischial tuberosity is a large roughened bony mass on the dorsal surface of the body
• It is the site of attachment for the sacrotuberous ligament; it is the site of origin of the inferior gemellus muscle, quadratus femoris muscle and the hamstring muscles

Sciatic Notches Details

• Lesser sciatic notch is between the ischial tuberosity and ischial spine
• The lesser sciatic notch is dorsally closed by the sacrotuberous and sacrospinal ligaments to form the lesser sciatic foramen
• The greater sciatic notch is completed posteriorly by the sacrospinal ligament to form the greater sciatic foramen
• The greater sciatic foramen is divided by the piriform muscle into suprapiriform and infrapiriform foramina

Pubis Information

• Angulated bone that forms the anterior part of the pelvis
• Consists of a body & two rami
• Superior and inferior pubic rami forms the obturator foramen
• The superior ramus fuses with the ilium and ischium at the acetabulum
• The inferior ramus joins with the ramus of ischium and together form half of the pubic arch on either side

Pubis Features

• The superior border thickens to form a pubic crest
• Has an anterior projecting prominence at its lateral end, the pubic tubercle, which provides the main pubic attachment point for the inguinal ligament
• The body of the pubis is flattened, joining the opposite pubis to form the pubic symphysis at the median plane

Sacrum Bone Information

• In females, it is wider, shorter, and less curved than in males
• A single triangular bone fused from the 5 sacral vertebrae
• Has a concave pelvic surface and a convex dorsal surface
• Has four pelvic sacral foramina pairs
• Transmits the anterior and posterior primary rami of the sacral spinal nerves 1-4

Details about Sacral Features

• Has superior articular processes that articulate with the fifth lumbar vertebra
• The dorsal surface has five crests
• The Median Sacral Crest is formed from fused spinous processes
• Intermediate Sacral Crests are fused articular processes
• Lateral Sacral Crests are fused transverse processes
• Lateral Sacral Crests attach to lower back and hip muscles
• Auricular Surface articulates with the pelvic girdle (sacroiliac joint) and the fifth lumbar vertebra
• Sacral Tuberosity attaches ligaments of the sacroiliac joint

More about Sacrum

• Sacral canal has replaced the vertebral canal and transmits dorsal/ventral roots of sacral/coccygeal nerves
• Sacral cornua is horn-shaped, formed by the 5th sacral vertebra's laminae
• Sacral hiatus opens at the inferior end, formed by failure of the 5th sacral vertebra to meet at the midline. Covered by connective tissue and used for caudal anesthesia

Coccyx Information

• Inferior portion of the vertebral column
• Formed from 3-5 vertebrae, decreasing caudally
• The first vertebrae contain a body, transverse process and proximally extending cornua
• 1st to 3rd coccygeal vertebrae are separated up until middle age by intervertebral discs
• In higher ages, intervertebral discs are fused by synostosis and form a small triangular bone (coccyx)
• Characterized by a lack of pedicles, laminae or spines

Joints and Ligaments :

• Includes lumbo sacral, sacro coccygeal, sacroiliac & pubic symphysis
• L5 and S1 articulate at 3 points; anterior intervertebral, two posterior synovial joints

Sacro coccygeal Joint :

• Secondary joint composed of cartilage, fibrocartilage and ligaments
• Ossified and obliterated for older persons
• Allows considerable movement during parturition

Vertebro Pelvic Ligaments Information

• Includes iliolumbar, sacrotuberous, sacrospinous & sacroiliac ligaments
• Iliolumbar Ligaments Strong triangular ligament; connects L5, limits rotation and anterior motion
• Sacrotuberous Extends from sacrum to tuberosity, and secures dorsal surfaces
• Sacro spinous From sacrum to spine, and divides sciatic foramen

Sacro iliac Joints

• Strong weight bearing synovial joint that connects L-shaped articulated facets
• Provides stability to transmit the body weight hip bones
• Supplied by branches from superior gluteal, iliolumbar, & lateral sacral arteries and innervated by different nerves
• Contains anterior, posterior, and interosseous ligaments for securing pelvic bones

Pubic Symphysis Joint Features

• The pubic symphysis sits anteriorly between adjacent bone surfaces
• Each surface is lined with cartilage and connects with hyaline in the midline
• Contains a superior and inferior ligament
• Note the superior is located above joint and inferior ligament located below

Bony Pelvis Divisions

• Pelvis is divided in two using the pelvic brim, pelvis can be minor (true/obstretric) or major (false)
• Pelvic brim is a curved bony rim that descends inferiorly to sacral promontory
• Brims passes down to top border of the pubic symphysis on AP axis

Pelvic Brim :

• Formed superior margin of pubic symphysis,
• Formed Pubic crest, Pectineal line, Arcuate line of ilium, Anterior border of ala (sacrum), Promontory of sacrum

Details on Greater and Lesser Pelvis:

• Greater Pelvis (False) which is higher along a narrow bony rim on the Pelvic Brim which makes abdominal viscera like sigmoid colon
• Greater parts bounded anteriorly/laterally/posteriorly by abdominal wall, iliac fossa, L5, L1 Verebra

Lesser Pelvis Details:

• Located just inferior to the pelvic brim with a cavity
• Cavity made from the ilium, pubis. and ischium
• Region is key for both gynecology and obstetrics

Minor Cavity Walls:

• Posterior wall concave, with sacrum & coccyx
• Anterior Wall has pubis symphysis and rami
• Lateral Walls are attached to ilium/ischium
• Contains an inferior boundary/aperture (outlets) which is closed by a diaphragm

Superior Aperture/Pelvic Cavity (Inlet):

• Cylindrical in shape with inlet, wall, outlets
• Shaped variably according to race and nutritional considerations
• Wider in females vs males, and ringed by bones & joints

Relations of Linea Terminalis

• S1 is the vertebral body at the boundary
• Has winged transverse processes
• Sacro illiac joints continues long from iliac terminalis
• Arcuate line and pectineal bound to pubic symphysis

Pelvic Inlets pass birth material and abdominal organs. Birth requires the inlet for expanded pregnancy.

Characteristics of Pelvic Walls :

• Composed of the sacrum, coccyx, pelvic bones inferior to the lineage terminalis, and two ligaments/muscles
• Walls carry blood vessels, lymph nodes and peritoneum
• Walls divided into anterior/posterior/lateral configuration

Key Muscles :

• Obtainator internus and Piriformis are two major regions and can affect rotation
• Nerves reach out to the Sacrum (anterior) at anterior sacral foramina for movement

Pelvic Anterior/Lateral/Posterior Walls:

• Obturator nerves fascia to pubes and internal muscles
• Hip Bone creates below pelvic
• Piriformis then leads laterally to allow gr. sciatic flow

Notes on Apertures of the Pelvic Wall:

• Features an obturator, greater sciatic, and lesser sciatic canals
• The membrane pass all material cavity
• Great sciatic pass ligament to ischial spine for connection to pelvic side

Pelvic Wall Structure

• Lesser Sciatic foremen is near spine and joins sacr spinous ligament
• All material pass to the hindquarters
• All above attach from glute
• Vessels include pudendal artery/nerve.

Diameters

• Form two parts
• First one by pyriform, and vessel
• Followed by n inferior area

Male /Femal Pelvis

• Superior and inferior
• Anterior spine
• Femurs
• And internals

Bony and Ligament Arrangement :

• Bones for hip, sacr spin, sacr tuber
• Prevent tilting
• Lesser Foramen : Allows outlet for muscle and tendons

Angular Dimensions

• Bones and ligaments affect angular aspects

Pudendal nerve Innervation:

• Supplies nerve endings
• Has obturation for nerves
• Obstructed is near sciatic
• Vessels pass in this area too

Pubic Details

• Diameter affected by ligament shape through bone

Diamond Configuration:

• Pelvis shape makes from sacrum, and pubic region

Pelvic Organs:

• Transit via gastro area via outlets

Pelvic Diaphragm:

• Floor support viscera by area

Differences (Male vs Female):

• Hipe apart for females
• Wider wider bones
• Femur farther for the arch

Female Considerations

• Increase inlet size from size
• Wider and short

Key Types of Configurations

• Android : Common with males, narrow heart inlets and cavities
• Anthropoid : More normal with inlets
• Broad types : Uncommon
• Gynecoid Normal : 42 % has larger spacing

Pelvicometry Data :

• Size diameter (measure) and processes
• • Pelvic diameters allow measurement for gyne/obstetrics

Anatomical Considerations:

• Conjugate is key
• Diameter varies
• 13 is usual

Oblique and Inlet Diameter :

• Sacroiliac joint and iliopectine are keys
• Diameter measure 12

Outlet Structure

• Diameters reach for symphysis (13) with shortest distance in pelvis

True Conjugate Diameter:

Obstructed is small. So pelvis has issues passing objects

Key Components :

• 11cm indicates a small
• Under 5 is an obstruction
• Width affects joints

Pelvic Shapes

• Android with two shapes for normal
• Gynecoid
• Other shape occur that affect position

Pelvic Cavity Contents :

• sigmoid colon
• Rectum
• Urinary bladder

Sigmoid Colon Data

• “S" shape for large intestine
• 25 to 38 cm in width from sacral and iliac junction
• Ending is a tenia Mesocol joins

Colon Areas:

• Urinary structures -Rectum to sacrim

Intestine Arrangement :

• Vein supply all
• Lymph drains follow vessels
• Mesenteric transfers
• Connects trunk

Nerves:

• Colon has both nerves
• Lumbar plexus
• Inferior plexus at the pelvic region

Pelvic Rectum :

• Terminus of digestive system ending near vertebra
• Fixed at large intestine parts
• Follows curve to coccyx

Inferior and Superior :

• Outer structure makes muscles with inner lining Angular are important
• Anal features follow anal

Rectal Structure :

• The third surface is key point
• Vesical pouch then forms
• Sexed based system follow

Superior Rectum :

• Secrete separate to the vesicles
• Pelvis shape can affect vessel wall or diameter measure

Supplies :

• Superior mesenteric area
• Descends with right branching

Anastomoses

• Vessels pass each other

Rectal Area:

• Middle rectal connects
• Anal and anal canal follows
• Both provide circulation

Rectum Vessels:

• Tributary flows then inferior with middle to supply area
• union and portal connects the intestine section

Lymph Node:

• Follows rectum
• Half the system runs lumbar

Muscle Innervation

• Follow S2-S4
• Pass vessel. Is part of pelvic area
• Sphinter

Bladder Structure

• Store urine at the pelvic section
• Protected by bone
• Connect near to surface with some surface area

Internal Bladder:

• Trigone and uvula area form together
• Forms a urethral orifice
• The system provides for different structure and muscles

Uretal Shape :

• Shaped with collapsing walls
• Can accumulate as the bladder expands
• The shape stores more volume while maintaining low pressure

Uretal Structure (Apex)

• Is the same with vesicle

Structure

• Vessels near medial Vas connect A Apex then allows urethra system to the area
• The muscle is the main portion Muscle contraction pushes area out

Full Structure :

-12cm max volume of 500ML Palpated and may rupture with overfilling Protected due to pressure and release