The puborectalis arises from the posterior inferior pubic rami and passes posteriorly forming a U‐shaped sling around the vagina, rectum, and perineal body to form the anorectal angle. Some of the fibres of the muscle intermingle with the anal sphincter muscle and contribute to faecal continence. The pubococcygeus has a similar origin, but it inserts in the midline onto the anococcygeal raphe and the anterolateral borders of the coccyx. The openings between the levatorani muscles through which the urethra, vagina, and rectum pass are known as the urogenital hiatus (Figure 2.1).
The pelvic floor muscle fibres maintain resting tone (type I or slow‐twitch fibres) to support the pelvic viscera, and voluntarily contract (type II or fast‐twitch fibres) when required. It is the skeletal component that contracts to help maintain continence in acute stress states such as cough, laugh, or sneeze. Contraction of the levator ani can be assessed and felt as a U‐shaped sling on rectovaginal examination.
The levator ani muscle may get thinner and attenuated with ageing and POP. Neuromuscular injury to the levator, as occurs during childbirth, can lead to widening of the urogenital hiatus, which leads to vertical inclination of the levator plate with resulting pelvic organ dysfunction or POP. Levator avulsion, a documented injury of childbirth, involves the detachment of the puborectalis portion from the pelvic sidewalls. It occurs in about 36% of women after vaginal delivery and about 50–60% after forceps delivery. Avulsion can be diagnosed digitally by palpating the inferior pubic ramus and feeling for the insertion of the puborectalis portion. In the presence of levator avulsion, 2–3 cm lateral to the urethra, the bony surface of the pubic ramus can be palpated devoid of the muscle.
Figure 2.1 Levator ani muscle –pubococcygeus, puborectalis, and iliococcygeus.
The perineal body is an important structure that supports the distal vagina and maintains normal rectal function. Lying between the distal vagina and anus, it provides insertion of bulbospongiosus, superficial, and deep transverse perineal muscles, external anal sphincter, perineal membrane, distal part of rectovaginal fascia (RVF), pubococcygeus and puborectalis portions of the levator ani. Surgical reconstruction of perineum (perineorrhaphy) requires proper approximation of these muscles in order to restore the normal function of perineal body (Figure 2.2).
The perineal membrane (formerly known as the urogenital diaphragm) is a thick fibromuscular sheet that stretches across the anterior urogenital triangle. It attaches laterally to the ischiopubic rami and has a free posterior margin with anchorage at the perineal body. The urethra and vagina pass through the hiatus in the perineal membrane. The perineal membrane therefore fixes the distal urethra, distal vagina, and the perineal body to the bony pelvis at the ischiopubic rami. The superficial perineal space lies external to the perineal membrane and contains the superficial perineal muscles, ischiocavernosus muscle, bulbospongiosus muscle, and superficial transverse perineal muscles.
Figure 2.2 Perineal body with its muscular attachments.
The deep perineal pouch lies between the perineal membrane and levator ani and contains the external urethral sphincter, the compressor urethra, urethrovaginalis, and the deep transverse perineal muscles (Figure 2.3).
Fascial Support
The parietal and visceral (endopelvic) fascia constitute the fascial components. Parietal fascia covers the pelvic skeletal muscles and provides attachment of muscles to the bony pelvis extending from the lateral pelvic wall to the superior surface of pelvic diaphragm, and it is characterised histologically by regular arrangements of collagen. The obturator fascia covering the obturator muscle has two parts: ATLA and arcus tendineus fascia pelvis (ATFP), extending from IS to posterior pubis. Visceral endopelvic fascia is less discrete and not a true fascia but is endopelvic connective tissue. It contains a meshwork of loosely arranged collagen, elastin, and adipose tissue through which the blood vessels, lymphatics, and nerves travel to reach the pelvic organs. By surgical convention, condensations of this fascia have been described as discrete ‘ligaments’, such as the cardinal, uterosacral, pubovisceral, and pubourethral ligaments. The endopelvic tissue is a continuous layer extending from the uterosacral ligaments proximally to the pelvic portion of levator ani muscle distally, up to the level of urethra. The fascia also extends from the lateral wall of the cervix and vagina to the pelvic sidewall along the ATFP. This attachment stretches the vagina horizontally between the bladder and rectum thereby dividing the pelvis into an anterior and posterior compartment. The bladder and urethra occupy the anterior compartment; the rectum and anal canal, the posterior compartment; and the uterus and cervix, the middle or apical compartment.
Figure 2.3 Muscles of the deep perineal pouch.
DeLancey (1994) described the three integrated levels of pelvic support defined by the endopelvic connective tissue attachments to explain POP (see Table 2.1). All are connected through a continuation of the endopelvic fascia (Figure 2.4).
Table 2.1 Level of supports, with diagnosis and co‐relation to symptoms.
| Level of pelvic organ support | Organ affected | Type of Prolapse | Symptoms |
|---|---|---|---|
| Level I – uterosacral ligaments/ Cardinal ligaments | Uterus and cervix/vaginal vault | Uterocervical/ vault prolapse/ enterocele | Vaginal pressure, sacral backache, ‘something coming down’, dyspareunia, vaginal discharge |
| Level II – arcus tendineus fascia pelvis (ATFP) | Anterior ‐ Urinary bladder Posterior – Rectum | Cystocele Rectocele | ‘Something coming down’, double voiding, occult stress incontinence, recurrent urinary tract infections ‘Something coming down’, difficult defecation, manual digitation |
| Level III – anterior (pubourethral ligaments) | Urethra | Urethrocele | ‘Something coming down’, stress incontinence |
| Level III – posterior (perineal body) |
Lower third of the
|