Uterus: Anatomy, Ligaments, and Clinical Significance

Overview

The uterus is a pear-shaped, hollow muscular organ located in the lesser pelvis between the urinary bladder anteriorly and the rectum posteriorly. In its normal anteverted-anteflexed position, it measures approximately 7.5 × 5 × 2.5 cm in a nulliparous woman and is larger in multiparous women. It is the site of menstruation, implantation, placentation, and parturition.

Gross Anatomy

Parts of the Uterus

1. Fundus: dome-shaped superior portion above the uterine tubes; its position determines uterine lie during pregnancy (used to estimate gestational age — fundal height)
2. Body (corpus): main part; wide, thick-walled; contains the triangular uterine cavity
3. Isthmus: narrow lower segment between body and cervix (~1 cm in non-pregnant uterus); expands dramatically in pregnancy to form the lower uterine segment — site of cesarean section incision
4. Cervix: cylindrical inferior portion (~3 cm), projecting into the vaginal vault; divided into:
   • Supravaginal cervix
   • Vaginal cervix (portio vaginalis)
   • External os (external uterine orifice)
   • Internal os (histological transition from isthmus)

Uterine Cavity

• Triangular in frontal section
• Communicates with uterine tubes at the uterine ostia (cornua)
• Lined by endometrium
• Continuous with the cervical canal below

Wall Layers

1. Perimetrium: outer peritoneal coat; forms the broad ligament laterally
2. Myometrium: thick middle smooth muscle layer; three indistinct layers; responsible for expulsive contractions in labor; hypertrophied uterine fibroids (leiomyomata) arise here
3. Endometrium: inner mucosa; undergoes cyclic changes under estrogen and progesterone influence; shed during menstruation; site of implantation

Position

Normal position: anteverted (uterus tilted forward relative to vaginal axis) + anteflexed (body bent forward at isthmus relative to cervix). This positions the fundus above the bladder.

Variations:

• Retroversion/retroflexion: uterus tilted backward; present in ~20% of women; usually asymptomatic
• Prolapse: herniation of uterus into or through vagina due to pelvic floor weakness

Ligaments of the Uterus

The uterus is supported by a complex of ligaments (fascial condensations) and the pelvic floor:

Ligament	Attachment	Contents	Function
Broad ligament	Uterus to lateral pelvic wall	Uterine tube, round ligament, ovarian vessels	Peritoneal "sail" (not true ligament)
Round ligament	Uterine cornua → inguinal canal → labia majora	—	Maintains anteversion
Cardinal ligament (Mackenrodt)	Cervix → lateral pelvic wall	Uterine artery and vein	Primary support against prolapse
Uterosacral ligaments	Cervix/upper vagina → sacrum (S2–S4)	Nerve plexus	Level I support; maintains position
Pubocervical ligaments	Cervix → pubis	—	Anterior support

The ureter passes under the uterine artery ("water under the bridge") in the cardinal ligament, 1–2 cm lateral to the cervix — surgically critical during hysterectomy.

Blood Supply

• Uterine artery (branch of internal iliac artery): ascends along the lateral uterus, giving helical arteries to myometrium and spiral arteries to endometrium
• Ovarian artery (branch of abdominal aorta): anastomoses with uterine artery in the broad ligament

Uterine blood flow increases 10-fold during pregnancy (from ~50 mL/min to ~500 mL/min at term).

Innervation

• Sensory (pain): uterine body T10–L1 (referred to lower back and thighs); cervix S2–S4 (via hypogastric and pelvic nerves)
• Autonomic: sympathetic (L1–L2) via hypogastric plexus; parasympathetic (S2–S4) via pelvic splanchnic nerves

Lymphatic Drainage

• Fundus and body: para-aortic and iliac nodes (via broad ligament vessels) and inguinal nodes (via round ligament)
• Cervix: internal, external, and common iliac nodes; obturator node

Clinical Relevance

• Fibroids (leiomyomata): benign smooth muscle tumors of the myometrium; most common gynecologic tumor; cause menorrhagia, bulk symptoms, infertility
• Endometriosis: ectopic endometrium; causes dysmenorrhea, dyspareunia, infertility
• Endometrial carcinoma: most common gynecologic cancer; presents with postmenopausal bleeding
• Cervical carcinoma: associated with HPV infection; screened by Pap smear; involves transformation zone at squamocolumnar junction
• Cesarean section: incision in the lower uterine segment (isthmus) — less vascular, heals better

Study Points

• Name the four parts of the uterus and describe the clinical significance of each.
• Explain the surgical importance of the cardinal ligament in relation to the ureter.
• Describe the three layers of the uterine wall and their clinical significance.
• Trace uterine artery blood supply from its origin and describe its anastomoses.
• Explain the lymphatic drainage routes from the uterine fundus and cervix.