Pelvic peritoneum

This forms a smooth covering over the uterus and fallopian tubes. Anteriorly it forms the uterovesical pouch and covers the upper surface of the bladder. Posteriorly it forms the pouch of Douglas. Laterally it covers the fallopian tubes and forms the broad ligaments, which do not act as supports.

Pelvic fascia

This connective tissue fills the space between the pelvic organs lining the pelvic cavity walls. Its function is to provide support for the organs, whilst at the same time allowing them to move within the limits of normal function (Verralls 1993). In areas where extra support is needed, it thickens to form the pelvic ligaments:

• Transverse cervical ligaments:

form the principal direct supports of the uterus

are known as cardinal or Mackenrodt’s ligaments

are attached to the vaginal vault and supravaginal cervix

extend transversely in a fan-like way across the pelvic floor to the white line of fascia on the lateral pelvic walls.

• Uterosacral ligaments:

attach to the vaginal vault and supravaginal cervix

pass backwards and upwards from the cervix to the lateral border of the sacral body,

• Round ligaments:

originate just below the cornua of the uterus

pass through the inguinal canal and anterior abdominal wall to become inserted into each labium majus

assist in keeping the uterus in its normal anteverted (forward-tilted) anteflexed (bent on itself) position.

• Pubocervical ligaments:

attach to the inner part of the pubic bones

run posteriorly to form attachments to the bladder, vault of vagina and supravaginal cervix

provide support for the bladder (Verralls 1993).

Deep muscle layer

This is formed mainly from symmetrically paired muscles, varying in thickness, collectively known as the levator ani. They arise at the inner circumference of the true pelvis from the white line of the obturator fascia and decussate midline between the urethra, vagina, and rectum. The muscle fibres pass downwards and backwards and are inserted medially into the upper vagina, perineal body, anal canal, anococcygeal body, coccyx, and lower borders of the sacrum.

The main function is to provide a strong sling to support the pelvic organs and to counteract any increase in the intra-abdominal pressure during coughing and laughing. When the levator ani is contracted, the pelvic floor and perineum are lifted upwards – an important mechanism to maintain continence.

The deep muscles are named after the corresponding fused bones of the innominate bone (pubis, ilium and ischium) (Fig. 40.1):

• Pubococcygeus muscles:

arise from the inner surface of the pubic bones

pass posteriorly below the bladder on either side of the urethra, upper vagina and anal canal to the anococcygeal body and coccyx

fibres cross medially and join those from the opposite sides to form U-shaped slings around the urethra, vagina, and rectum

the puborectalis muscle forms a loop around the anorectal junction and its posterior fibres communicate with the external anal sphincter

medial part is attached to the vagina – no direct attachment to the urethra

on dissection, are paler in colour, suggesting they are fast-twitch muscle capable of rapid contraction (Benson 1992)

function is to provide support to the urethra, vagina, and rectum to control micturition and defecation.

• Iliococcygeus muscles:

arise from the inner border of the white line of fascia on the inner aspects of the iliac bones and the ischial spines

join midline and are inserted posteriorly into the anococcygeal raphe and coccyx

on dissection, are darker in colour, suggesting they are slow-twitch muscles (Benson 1992).

• Ischiococcygeus muscles:

are triangular sheets of muscle and fibrous tissue

arise from the ischial spines, pass downwards and inwards to be inserted into the coccyx and lower part of the sacrum

are sometimes known as the coccygeus muscles

main function is to stabilize sacroiliac and sacrococcygeal joints.

Figure 40.1 Muscles of the pelvic floor seen in the female perineum.

(From Principles of Anatomy and Physiology, 7th edn, by Tortora, G.J. and Grabowski, S.R.

Superficial perineal muscles

These are less important than the levator ani muscles; but contribute to the overall strength of the pelvic floor and likely to be damaged during vaginal delivery (Fig. 40.1):

• Bulbospongiosus muscles (previously Bulbocavernosus in older texts):

extend from central point in the perineal body, and encircle the vagina and urethra before inserting anteriorly into the corpora cavernosa of the clitoris

posteriorly some fibres merge with the superficial transverse muscle and external anal sphincter

situated beneath bulbocavernosus are the vestibular bulbs anteriorly and Bartholin’s glands posteriorly

main function is to cause erection of the clitoris and contraction of the vagina during sexual activity.

• Ischiocavernosus muscles:

arise from ischial tuberosities

pass upwards and inwards along the pubic arch and are inserted into the corpora cavernosa of the clitoris

some fibres interweave with those forming the membranous sphincter of the urethra.

• Transverse perineal muscles:

arise from ischial tuberosities

pass transversely to converge at central point of the perineum

fibres of each transverse muscle unite and interweave with the superficial tissue of the perineal body and external anal sphincter

provide additional support transversely across the perineal region, helping fix the position of the perineal body.

Sphincters

• Membranous sphincter of the urethra:

arises from one pubic bone

passes above and below the urethra to the opposite pubic bone

not a true sphincter but capable of contracting to occlude the lumen of the urethra.

• External anal sphincter (EAS):

teardrop-shaped circle of muscle

surrounds the anus and is subdivided into three parts (not easily defined during dissection)

– subcutaneous

– superficial

– deep

in females, the EAS is shorter anteriorly and fuses with the bulbocavernosus and transverse perinei in the lower part of the perineum (Sultan et al 1994a)

the deep EAS is inseparable from the puborectalis muscle and posteriorly is attached to the coccyx by some of its fibres

the circular striated (voluntary) muscle of the EAS, when dissected or torn, looks similar to ‘dark red meat’

main function is to close the anal canal lumen and control voluntary passage of faeces and flatus.

• Internal anal sphincter (IAS):

a condensation of the circular smooth muscle of the rectum

approximately 3–4 cm long and 2–3 mm thick in younger women

not easily defined

on dissection, is paler in colour than the external anal sphincter

main function is to close the lumen of the anus and to prevent involuntary passage of faeces and flatus (very important during sleep).

Ischiorectal fossa

is a deep wedge-shaped area, filled with fat, bounded by the gluteus maximus, anal sphincter, transverse perinei and bulbocavernosus muscles. It is a potential area for haematoma formation.

Subcutaneous fat and skin

Neither has any supporting function.

Prevalence

Over 85% of women who have a vaginal birth will sustain some form of perineal trauma (McCandlish et al 1998) and up to 69% of these will require stitches (McCandlish et al 1998, Sleep et al 1984).

Rates will vary considerably according to individual practices and hospital policies throughout the world, illustrated by wide variations in episiotomy rates internationally from 8% in the Netherlands, 13% in England and 43% in the USA, to 99% in the Eastern European countries (Graham & Graham 1997, Graves 1995, Statistical Bulletin 2003, Wagner 1994).

Certain intrapartum interventions or alternative forms of care may also affect the rate and extent of perineal trauma; including continuous support during labour, delivery position, epidural anaesthesia, style of pushing, restricted use of episiotomy and ventouse delivery (Kettle 1999, 2001).

Aetiology and risk factors

Perineal trauma occurs during spontaneous or assisted vaginal delivery and is usually more extensive after the first vaginal birth (Sultan et al 1996). Women who have no visible damage may be subject to transient pudendal or peripheral nerve injury due to prolonged active pushing or pressure exerted by the fetal head on the surrounding structures (Allen et al 1990).

Associated risk factors include:

Other maternal factors are:

Short- and long-term effects

In the UK, approximately 23–42% of women will have perineal pain and discomfort up to 10–12 days following vaginal delivery and 7–10% of these women will continue to have long-term pain up to 18 months post partum (Glazener et al 1995, Gordon et al 1998, Grant et al 2001, McCandlish et al 1998, Mackrodt et al 1998, Sleep et al 1984).

In terms of sexual function, 62–88% of women will resume intercourse by 8–12 weeks postpartum, though 17–23% of women experience superficial dyspareunia at 3 months after delivery and 10–14% will continue to have pain at 12 months (Barrett et al 2000, Glazener 1997, Gordon et al 1998, Grant et al 2001, Kettle et al 2002, Mackrodt et al 1998).

Estimation of the extent of urinary and faecal incontinence is difficult because of under-reporting of these problems due to the sensitive nature of the complaint (Sultan et al 1996). One survey found that 15.2% of participating women (number 1782) reported stress incontinence which started for the first time within 3 months of the baby’s birth, and 75% of these still had problems over a year later (MacArthur et al 1993). Sleep & Grant (1987) and MacArthur et al (1997) found that up to 4% of women reported occasional loss of bowel control.