Anatomy of the female pelvis

Knowledge of the major features of the female pelvis is essential to the understanding of the processes of reproduction and childbearing and to the effect that various pathological processes may have on the pelvic organs and on the health of woman.

The bony pelvis

The bony pelvis consists of the paired innominate bones (each consisting of an ilium, ischium and pubis) and the sacrum and coccyx. The innominate bones are joined anteriorly at the symphysis pubis, and each articulates posteriorly with the sacrum in the sacroiliac joints. All three joints are fixed in the non-pregnant state, but during pregnancy there is a relaxation of the joints to allow some mobility during labour and birth. The sacrum articulates with the fifth lumbar vertebra superiorly and the coccyx inferiorly.

The pelvis is divided into the false pelvis and the true pelvis by the pelvic brim. The true pelvis is divided into three sections: the pelvic inlet (bounded anteriorly by the superior surface of the pubic bones and posteriorly by the promontory and alae of the sacrum); the mid-pelvis (at the level of the ischial spines); and the pelvic outlet (bounded anteriorly by the lower border of the symphysis, laterally by the ischial tuberosities and posteriorly by the tip of the sacrum).

The external genitalia

The term vulva is generally used to describe the female external genitalia and includes:

• Mons pubis

• Labia majora

• Labia minora

• Clitoris

• External urinary meatus

• Vestibule of the vagina

• Vaginal orifice

• Hymen

The mons pubis, sometimes known as the mons veneris, is composed of a fibrofatty pad of tissue that lies above the pubic symphysis, and in the mature female is covered with dense pubic hair. The upper border of this hair is usually straight or convex upwards and differs from the normal male distribution; pubic hair generally begins to appear between the ages of 11 and 12 years.

The labia majora consists of two longitudinal cutaneous folds that extend downwards and posteriorly from the mons pubis anteriorly to the perineum posteriorly. The labia are composed of an outer surface covered by hair and sweat glands and an inner smooth layer containing sebaceous follicles. The labia majora enclose the pudendal cleft into which the urethra and vagina open. The labia majora are homologus with the male scrotum.

The labia minora are enclosed by the labia majora and are cutaneous folds that enclose the clitoris anteriorly and fuse posteriorly behind the vaginal orifice to form the posterior fourchette or posterior margin of the vaginal introitus. Anteriorly, the labia minora divide to enclose the clitoris, with the anterior fold forming the prepuce and the posterior fold the frenulum. They are richly vascularised and innervated and are erectie. They do not contain hair but are rich in sebaceous glands.

The clitoris is the female homologue of the penis and is situated between the anterior ends of the labia minora. The body of the cilitoris consists of two corpora cavernosa and erectile tissue enclosed in a fibrous sheath. Posteriorly, these two corpora divide to lie along the inferior rami of the pubic bones. The free end of the clitoris contains the glands, composed of erectile tissue covered by skin and richly supplied with sensory nerve endings and hence is very sensitive. The clitoris plays an important role in sexual stimulation and function.