Pelvis Anatomy

The Pelvis

• Continuous with the abdomen superiorly and bounded by the perineum inferiorly, which is located between the proximal thighs.
• Bones of the pelvic girdle demarcate two regions

Greater (False) Pelvis

• Lower portion of the abdomen lying between the flared iliac crests

Lesser (True) Pelvis

• Demarcated by the pelvic brim, sacrum, and coccyx
• Contains the pelvic viscera

Key Surface Anatomy Landmarks

• Umbilicus

• Iliac crest

• Inguinal ligament

• Anterior superior iliac spine

• Pubic tubercle

• Posterior superior iliac spine

• The upper border of the true pelvis (pelvic brim) is the pelvic inlet and the lower border is the pelvic outlet

• The pelvis contains the terminal gastrointestinal tract, the urinary system, and the internal reproductive organs

Functions of the Pelvis

• Protects the pelvic viscera
• Supports the weight of the body
• Aids in ambulation by swinging side to side in a rotary movement at the lumbosacral articulation
• Provides for muscle attachments
• Provides a bony support for the lower birth canal
• The perineum lies below the “pelvic diaphragm" and contains the external genitalia

Pelvic Girdle

• The attachment point of the lower limb to the body's trunk
• Pelvic bones: right and left coxal (hip) bones, sacrum, and coccyx

Pelvic Girdle-Joints

• Joints and ligaments of the pelvis include the iliolumbar, interosseous sacroiliac, anterior sacroiliac, posterior sacroiliac, sacrospinous, sacrotuberous, pubic symphysis and sacrococcygeal joints.

Anatomical Differences Between Male and Female Pelvises

• The bones of the female pelvis usually are smaller, lighter, and thinner
• The pelvic inlet is oval in females, versus heart-shaped in males
• The female pelvic outlet is larger because of everted ischial tuberosities
• The female pelvic cavity is wider and shallower
• The female pubic arch is larger and wider
• The greater sciatic notch is wider in females
• The female sacrum is shorter and wider
• The obturator foramen is oval or triangular in females, round in males

Female Pelvis Shapes

• Gynecoid: normal, most suitable for childbirth
• Android: masculine, heart-shaped inlet, prominent ischial spines, narrower pelvic outlet
• Platypelloid: foreshortened anteroposteriorly, wider transversely
• Anthropoid: oval-shaped inlet, elongated anteroposteriorly, shortened transversely, larger outlet

Muscles of the Pelvis

• The muscles of the true pelvis line its lateral wall and form a floor over the pelvic outlet
• Obturator internus and piriformis muscles line the lateral wall and attach to the femur
• Levator ani and coccygeus muscles form the floor, or pelvic diaphragm
• Levator ani muscles support structure for the pelvic viscera in bipeds and helps maintain closure of the vagina and rectum
• Levator ani muscle consists of: iliococcygeus, pubococcygeus, and puborectalis muscles which form a single sheet of muscle

Distal Gastrointestinal Tract

• The distal gastrointestinal tract enters the pelvis via the rectum and anal canal
• Rectosigmoid junction is located superiorly around the S3 vertebra
• The rectum extends inferiorly to form the anal canal right below the coccyx
• The rectum is covered by peritoneum on its anterolateral surface, but the distal section drops below the peritoneal cavity to form the anorectal flexure
• The pelvic fascia is a layer of connective tissue

Types of Pelvic Fascia

• Membranous
• Endopelvic

Distal Urinary Tract

• Lies within the pelvis
  • Includes the distal ureters, urinary bladder, and urethra

Peritoneal Relationships of the Female Pelvic Viscera

• The peritoneum on the lower internal portion of the anterior abdominal wall reflects the midline from the urinary bladder, known as the median umbilical ligament in both sexes.

Female Pelvic Reproductive Viscera

• Includes the midline uterus, vagina, and adnexa (paired ovaries and uterine tubes)

Male Pelvic Reproductive Viscera

• Include the prostate gland and paired seminal vesicles
• These structures lie in a subperitoneal position and are in close association with the urethra
• The testes are paired gonads and are connected to the seminal vesicles by the ductus (vas) deferens which passes in the spermatic cord and scrotom
• Then ascend throught the inguinal canal and joins the duct of the seminal vesicles (ejaculatory ducts)

Pelvic Peritoneum

• Found on the lower internal portion of the anterior abdominal wall that reflects the midline from the urinary bladder
• Referred to as the median umbilical ligament in both sexes

Arterial Supply

• The arterial supply to the pelvis arises from the paired internal iliac arteries
• Branches into the perineum, the gluteal region, and the medial thigh.
• Male arteries differ from female arteries that they replace the uterine, vaginal, and ovarian branches with arteries to the ductus deferens, prostatic artery, and testicular arteries.
• Aorta bifurcates at L4 into the common iliac artery, which then bifurcates at L5-S1 into the internal and external iliac artery

Lymphatic Drainage

• The lymphatic drainage of the pelvis parallels the venous drainage enters into the lymph nodes of the iliac vessels
• Exception is the drainage from the ovaries and the adjacent uterine tubes/upper uterus, testes, and scrotal structures, which flows into the aortic nodes of the midabdomen

Veins of the Pelvis and Perineum

• Run alongside the arteries and have similar names
• Mostly drain into the internal iliac vein, common iliac vein, inferior vena cava and ultimately to the heart
• The superior rectal vein is connected to the middle (internal iliac vein) and inferior rectal veins of the caval system via portosystemic anastomoses

Innervation of the Pelvis

• Skin and skeletal muscle of the pelvis are innervated by the somatic division of the peripheral nervous system
• Muscle innervation arises via the sacral and coccygeal plexuses' anterior rami
• Somatic afferent fibers send pain, touch, and temperature signals from the skin, skeletal muscle, and joints to the same levels of the spinal cord
• The pelvic splanchnics are innervated by the smooth muscles and glands of the pelvis

Pelvic Fractures

• Fractures of the pelvic ring, do not include acetabular fractures

Urinary Tract Infection (UTI)

• A common condition in females associated with a short urethra
• Results in pathogens and exposure to the urinary tract
• Can lead to urethritis, cystitis (bladder inflammation), and pyelonephritis

Symptoms Include

• Dysuria
• Frequency of urination
• Urgency of urination
• Suprapubic discomfort and tenderness
• Hematuria