What is pelvic floor and why talk about it?
The term perineum or pelvic floor is used to define the set of soft tissues, mainly muscle-tendon structures, that enclose the abdominal cavity inferiorly.
By virtue of its position, as well as acting as a support for the abdominal organs, the pelvic floor plays a key role in coordinating various visceral andreproductivephysiologicalfunctions such as sexual function, childbirth, urination, and defecation: the rectum, urethra, and vagina, in women, are partially encompassed within this region.
Pelvic floor dysfunction, caused by mechanical stress or pathological processes here, is often the basis for the onset of symptoms such as urinary, fecal or stress incontinence, dyspareunia, or surgical issues such as prolapse of the uterus, cystocele and rectocele.
- About 1 in 10 women suffer from urinary incontinence, which occurs most frequently during physical activity (stress incontinence)[1];
- fecal incontinence, more prevalent with advancing age, is also an issue in younger, non-menopausal women and has a significant impact on quality of life[2];
- Dyspareunia, or painful perception during sexual intercourse, is present in 10-20% of American women [3].
The pathophysiology of pelvic floor dysfunction is complex and is based on the complex interplay between the effects of physiological hormonal changes throughout the life span and the mechanical forces acting on the perineum.
- From the point of view hormone, estrogen affects the trophism and elasticity of the myotendinous component of the pelvic floor: the physiological changes that occur both during the pregnancy than in menopause alter both the strength and elasticity of muscles and tendon components, which tend to be more extensible in pregnancy and less trophic in menopause.
- Mechanically, both thephysical activity that pregnancy induces a increase in the load the perineum has to bear: the first due to the contraction of the abdomen, which then no longer absorbs intra-abdominal pressure but directs it inferiorly toward the pelvic diaphragm; the second due to the increased volume and weight of the uterus and the unborn child. Obesity also causes mechanical overload of the perineum, thus constitutes a risk factor for various perineal pathologies.
Some anatomical aspects
The pelvic floor can be divided into several regions, including:
- an anterior one: anterior to the transverse muscle of the perineum; also referred to as the genito-urinary diaphragm. Functionally relevant to urination, sexual function, and childbirth.
- A posterior one: posterior to the transverse muscle of the perineum. Functionally relevant to defecation.
- a superficial one: represented by the muscles immediately deeper than the skin and subcutis (bulbocavernosis, ischiocavernosis, transverse perineum and external anal sphincter).
- a deep one: represented by the muscle layer that is more internal than the superficial layer, consisting of the puborectal, pubococcygeal, ischiococcygeal and ileococcygeal muscles.
Pelvic floor muscle structures take insertion on the bony component of the small pelvis, namely the ilium, ischium, pubis, and coccyx. At the apex of the coccyx is a fibrous cord, the perineal raphe, which connects it to the posterior region of the anal sphincter.
The main anatomical structures are:
- Puborectal muscle. It takes insertion on the ascending branch of the pubis and then heads posteriorly until it wraps posteriorly around the rectum and inserts on the perineal raphe. When contracted, the m. puborectal increases fecal continence by reducing the size of the rectum so that stool flows back into the rectal ampulla: functionally assists the anus sphincter.
- Iliococcygeal muscle. It takes insertion on the medial portion of the ileum at the arcuate line and then converges posteriorly to insert on the coccyx. In its course it laterally encircles the vagina in the woman.
- Pudendal nerve . Originates from the sacral plexus within the small pelvis and consists of the nerve roots of S2, S3, S4. It has a tortuous course: first exiting the small pelvis through the large ischial foramen and then re-entering it through the small ischial foramen. In this way, the nerve decays inferiorly to the pelvic floor, within Alcock’s canal (about 3 to 5 cm deep relative to the skin), and provides sensory nerve branches for the external genitalia and anal canal, and motor branches for the muscles of the pelvic diaphragm. Because of these functions, the pudendal nerve is responsible for the coordination of most sexual and visceral functions (e.g., erection and coordination of defecation).
Some aspects of biomechanics
The sacrum moves, oscillating, on a transverse axis passing through the sacroiliac joints. These movements are called nutation and contronutation, representing the anterior swing and posterior swing of the sacrum. Anterior oscillation of the sacrum corresponds to postero-superior rotation of the pelvis, and vice versa. These movements cause the size of the narrows of the pelvis to widen by up to 2-3 cm, as a result the pelvic floor is subjected to different stresses depending on the position of the different bone segments.
By virtue of its position and structure, the pelvic floor supports the abdominal organs and coordinates visceral physiological activities: sexual functions, urination, defecation, and childbirth. Functionally, it can be considered a diaphragm, which is a membrane stretched to close the abdominal cavity inferiorly.
The pelvic diaphragm and the respiratory diaphragm, acting reflexively on the pressures of the abdominal cavity, are coordinated in their action to ensure maximum efficiency of respiration: as the respiratory diaphragm contracts, the abdominal pressure increases, which must be absorbed by the other walls, i.e., the muscles of the abdomen or the pelvic floor. Therefore, it is easy to imagine how, during physical exertion such as running, as the abdominal wall contracts, both intra-abdominal pressure is further increased and the perineum, bladder and end of the intestines are stressed by the increased mechanical load. If sphincter structures are not intact due to trauma, even misrecognized trauma-often microinjuries develop during childbirth without immediate functional relapse-it is easier to go into incontinence, especially urinary incontinence.