Functions of Pelvic Floor Muscle/Pelvic Floor or Pelvic Diaphragm is composed of muscle fibers of the levator ani, the coccygeus muscle, and associated connective tissue which spans the area underneath the pelvis. The pelvic diaphragm is a muscular partition formed by the elevators ani and coccygei, with which may be included the parietal pelvic fascia on their upper and lower aspects. The pelvic floor separates the pelvic cavity above from the perineal region (including perineum) below. Because to accommodate the birth canal, a female’s pelvic cavity is larger than a male’s, the pelvic floor tends to be considered a part of the female anatomy, but males have an equivalent pelvic floor.
The pelvic floor is an anatomical area where the balance of the different pressures, either visceral, muscular or liquid, plays a fundamental role in the physiological pursuit of the functions of all the structures contained therein. The pelvis is considered superiorly as the space between the pubic and sacral promontory through the unnamed line (present on the inner part of the iliac bone), and inferiorly as the plane between the ischiatic tuberosity and the coccyx apex, closed down from the perineum. [rx] [rx][rx] From a descriptive anatomical point of view, the pelvic floor can be divided into 4 compartments:
Anterior or urinary (bladder, bladder neck, urethra)
Medium or genital (vagina and uterus in women, prostate in men)
Posterior or anterior (anus, anal canal, sigmoid, rectum)
Peritoneal (endopelvic fascia, anus muscle lift, perineal membrane)
The pelvic floor consists of the urogenital triangle, the urogenital diaphragm, and the pelvic diaphragm.
The pudendal nerve innervates the urogenital triangle. It is composed of the Bulbospongiosus muscle, the Ischiocavernosus muscles, the superficial transverse perineal, and the external anal sphincter.
Pudendal nerve innervates the urogenital diaphragm. It is composed of the Compressor urethra and the Ureterovaginal sphincter.
It can also be considered from an anatomical, functional point of view, which will be taken into account by the authors to built the present following
Diaphragm or pelvic floor (ischiococcygien muscle and levator ani muscles), closed at the top by the endopelvic fascia
The urogenital diaphragm or triangular ligament or fascia of Carcassonne is placed caudally, externally and horizontally to the pelvic floor, between the ischiatic branches and the pubic symphysis, and crossed by the urethra and the vagina
The perineum or perineal membrane is the continuation of the Carcassonne fascia, connecting the deep layer of the pelvic floor musculature, the coccyx, and the anal sphincter.
Innervation/ Nerve Supply of Pelvic Floor Muscle
- Branches from the sacral plexus contribute to the innervation of the levator ani group of muscles. The pudendal nerve, which originates from the second to fourth sacral segments (S2-S4) directly innervates the pubococcygeus muscle.
- Direct branches arising from the fourth sacral segment form the nerve to levator ani (S4), which also innervates the pubococcygeus. The remaining coccygeus and iliococcygeus are innervated by direct branches from the fourth and fifth segments (S4 and S5) of the sacral plexus.
- The sacral plexus from L4 through S4 supplies the muscles of the pelvis. It includes the sciatic nerve, pudendal nerve, gluteal nerves, and nerves to the obturator internus and piriformis muscles. The coccygeal plexus from S4 and S5 supplies to the coccygeus and levator ani muscles.
Blood Supply and Lymphatics of Pelvic Floor Muscle
- At the pelvic inlet, the common iliac artery divides into internal and external iliac arteries. The internal iliac artery provides oxygenated blood to pelvic viscera including bladder, prostate in males, urethra, uterus in the female, and vagina in females.
- Branches of internal iliac artery include the superior vesical artery, obturator artery, inferior vesical artery, uterine artery, middle rectal artery, internal pudendal artery, and inferior gluteal artery. Venous drainage is achieved primarily by the internal iliac vein.
- The internal iliac vein combines superiorly with the external iliac vein to form the common iliac vein which then drains into the inferior vena cava.
Functions of Pelvic Floor Muscle
The muscles of the pelvic floor are primarily supportive structures.
- Support of abdominopelvic viscera – (bladder, intestines, uterus, etc.) through their tonic contraction.
- Resistance to increases in intra-pelvic/abdominal pressure – during activities such as coughing or lifting heavy objects.
- Urinary and fecal continence – The muscle fibers have a sphincter action on the rectum and urethra. They relax to allow urination and defecation.
- Help keep the pelvic viscera in place – and prevent them from being pushed through the pelvis during strain. It achieves this task by being unconsciously contracted at rest and can be consciously contracted during times of raised intra-abdominal pressure (vomiting, sneezing, coughing, lifting a heavy object, or forced expiration).
- Contraction of the levator ani muscles – also provides additional occlusion to the outlet segments of the pelvic viscera. In other words, the muscles aid in maintaining both urinary and fecal continence until it is convenient to void.
- The puborectalis muscle – best demonstrates this function. Recall that it is a muscular sling U-shaped muscle that arches around the anorectal junction. When this part of the muscle is contracted, it pulls the anorectal junction anteriorly, forming a 90 degrees angle between the rectum and anus. Therefore fecal matter cannot flow freely from the rectum. In order for micturition (urination) and defecation to occur, the levator ani muscles must be relaxed.
- The pelvic floor muscles – also provide additional support during childbirth to the presenting fetal part – the part closest to the uterine outlet. It holds the fetus in place while the uterine cervix dilates and contracts. It also keeps the presenting part of the fetus in the anteroposterior plane of the pelvic outlet to further support the process of delivery.
- Histologically – the majority of the pelvic floor muscles are made up of slow-twitch or type I muscle fibers. The prevalence of type I fibers is important given the function of the pelvic floor muscles outlined above. Recall that type I fibers are ideal for long periods of contraction, while type II fibers are needed for quick response to physiological changes.
Muscle Attachment of Pelvic Floor Muscle
The pelvic floor consists of three muscle layers
Superficial perineal layer: innervated by the pudendal nerve
- Superficial transverse perineal
- The external anal sphincter (EAS)
Deep urogenital diaphragm layer: innervated by the pudendal nerve
- Compressor urethra
- Uretrovaginal sphincter
- Deep transverse perineal
Pelvic diaphragm: innervated by sacral nerve roots S3-S5
- Levator ani: pubococcygeus (pubovaginalis, puborectalis), iliococcygeus
- Obturator internus
Trigger Points in the muscles of the PF may refer pain in the distribution of the pudendal nerve
- Bulbocavernosus and Ischiocavernosus refer pain to the perineum and adjoining urogenital structures
- EAS refers to posterior pelvic floor
- Levator ani and coccygeus refer to the sacrococcygeal area
- Levator ani to vagina
- Obturator internus to vagina and anococcygeal area
The perineal body helps strengthen the pelvic floor. It provides attachments to the following muscles[rx]
The bulbospongiosus muscle (striated muscle) adheres anterolaterally to the PB.
Deep transverse perineal muscle (male) adheres laterally to the PB.
Compressor urethra muscle (female) adheres anteriorly to the PB.
The external anal sphincter muscle adheres posterolaterally to the PB.
The internal anal sphincter muscle intermingles with LAM and adheres posteriorly to the PB.
The external urethral sphincter muscle adheres anteriorly to the PB.
Levator anis muscle (the internal fibers of the puborectalis muscle) adheres laterally to the PB along its whole vertical length.
The recto-urethral muscle (perineal smooth muscle) runs from the LAM laterally to the bulbourethral glands adheres anterolaterally to the puborectalis muscle.
The longitudinal anis muscle (LAM) strongly adheres anteriorly and anterolaterally to the PB and puborectalis muscle.
Two fascial structures join to the perineal body[rx]
The superficial perineal fascia, the perineal membrane joins the PB anteriorly.
The rectovaginal septum (female) joins the PB superiorly.
The recto prostatic septum (male) joins the PB superiorly.
The perineal body is critical for maintaining the integrity of the pelvic floor, especially in females.
Kegel exercises may help in the early stages by strengthening the muscles. Vaginal pessaries can be used. In symptomatic conditions, surgery is also a helpful solution.
|Bulbospongiosus||Male: median raphe, ventral surface of bulb of penis
Female: perineal body then divides to wrap around vagina
|Male: Corpora spongiosum and cavernosa, fascia of bulb of penis
Female: fascia of corpus cavernosal
|Male: Empties urethra, acts as a sphincter to compress bulb of penis, assists erection, propels semen down the urethra
Female: empties urethra, acts as a sphincter to reduce lumen of vagina and assists erection of clitoris
|Deep branch of the perineal nerve (branch of the pudendal nerve)|
|Ischiocavernosus||Ischial ramus and tuberosity||Crus of penis or clitoris||Maintains erection of penis or clitoris by compression of outflow veins||Deep branch of perineal nerve (branch of pudendal nerve)|
|Superficial transverse perineal||Ischial tuberosity||Perineal body||Reinforces action of deep transverse perineal muscle to stabilize perineal body||Deep branch of perineal nerve (branch of pudendal nerve)|
|External anal sphincter||Perineal body and encircles anal canal||Coccyx||Part of voluntary sphincter of anal canal||Inferior rectal (anal) nerve|
|Sphincter urethrae||Inferior aspect of pubic ramus and ischial tuberosity||Surrounds urethra; in females, some fibres also enclose the vagina||Controls flow of urine through urethra; also compresses vagina in females||Deep branch of perineal nerve (branch of pudendal nerve)|
(only in females)
|Ischiopubic ramus||Vaginal wall||Compresses ventral wall of the urethra|
|Sphincter urethral vaginalis
(only in females)
|Vaginal walls||Ventral surface of urethra||Compresses ventral wall of the urethra|
|Deep transverse perineal||The inner aspect of the ischiopubic ramus||Median raphe (male), perineal body and external anal sphincter||Fixes perineal body, supports the function of the levator ani and sphincter urethra||Deep branch of the perineal nerve (branch of the pudendal nerve)|
|Perineal membrane (fascial thickening, not a muscle)||Physical attachments at the pubic symphysis||Fascial attachments at the ischial spine||The suspensory ligament that provides extra support to prevent the descent of the perineal body|
|Levator Ani (Pubococcygeus)||Dorsal surface of pubis and fascia of obturator internus||The anococcygeal body between tip of the coccyx and the anal canal||Voluntary sphincter of the anal canal||Nerve to levator ani (branches of S4), inferior rectal nerve (from pudendal nerve – S3, S4), coccygeal plexus|
|Levator Ani (Puborectalis)||Dorsal surface of pubis and fascia of obturator internus||Unites with its partner to make a U-shaped sling around the rectum||Controls defecation by pulling anorectal junction forward||Nerve to levator ani (branches of S4), branch of the pudendal nerve (S2-4)|
|Levator Ani (Pubovaginalis)||Nerve to levator ani (branches of S4), branch of the pudendal nerve (S2-4)|
|Levator Ani (Iliococcygeus)||Posterior aspect of arcus tendinous levator ani and the ischial spine||Anococcygeal body and the coccyx||Helps to support pelvic viscera and lateral coccyx||Nerve to levator ani (branches of S4), inferior rectal nerve (from pudendal nerve – S3, S4), coccygeal plexus|
some consider this more of a ligament than a muscle
|Ischial Spine||Lower two sacral and upper two coccygeal spinal segments, blends with sacrospinous ligament on its external surface||Supports pelvic viscera, flexion of the coccyx, stabilizes sacroiliac joint||Anterior rami of S4 and S5|
|Piriformis||The pelvic surface of the sacrum, passes through greater sciatic foramen||The superior border of the greater trochanter of the femur||Hip external rotation, assist with hip abduction if the hip is flexed||Anterior rami of S1 & S2|
|Obturator Internus||The internal or pelvic surface of the obturator foramen||Medial surface of the greater trochanter of the femur||Hip external rotation assists with hip abduction if the hip is flexed||Nerve to obturator internus (L5, S1, S2)|
|Arcus tendinous levator ani (fascial thickening, not a muscle)||Facial attachments at the pubic symphysis||Fascial attachments at the ischial spine||The suspensory ligament that provides extra support to prevent the descent of the perineal body|
|Arcus tendinous fasciae pelvis (fascial thickening, not a muscle)||Facial attachments at pubic symphysis||Fascial attachments at the ischial spine||The suspensory ligament that provides extra support to prevent descent of the perineal body|
Ligaments and Fascia of Pelvic floor
Ligaments of the Pelvis
- Iliolumbar ligament – from the tip of the transverse process of L5 to posterior aspect of the inner lip of iliac crest; strengthens the lumbosacral joint.
- Lateral lumbosacral ligament
- Sacrotuberous ligament– from sacrum to tuberosity of the ischium
- Sacrospinous ligament – from the ischial spine to lateral margins of the sacrum
- Ventral/Anterior sacroiliac ligament– from the anterolateral aspect of the sacrum to auricular surface of the ilium
- Dorsal/Posterior sacroiliac ligament
- The upper portion (short posterior sacroiliac ligament) – from 1st and 2nd transverse tubercles of the sacrum to the tuberosity of ilium
- The lower portion (long posterior sacroiliac ligament) – from 3rd transverse tubercle of the sacrum to the posterior superior iliac spine (PSIS)
- Interosseous sacroiliac ligament– lies deep to posterior SI ligament and runs between the tuberosities of the sacrum and ilium
- Ventral/Anterior sacrococcygeal ligament – from the anterior surface of sacrum to the front of the coccyx; continuation of the anterior longitudinal ligament of the spine
- Dorsal sacrococcygeal ligament
- Deep portion – from the inside sacral canal at the 5th sacral segment to the dorsal surface of the coccyx; continuation of the posterior longitudinal ligament of the spine
- Superficial portion – from free margin of sacral hiatus to dorsal surface of the coccyx; corresponds with the ligamentum flavum of the spine
- Lateral sacrococcygeal ligament – from the inferior lateral angle of the sacrum to the transverse process of the 1st coccygeal vertebra
Pubic Symphysis Ligaments
- Superior pubic ligament – runs between pubic tubercles
- Inferior pubic ligament (aka arcuate pubic ligament) – runs between inferior pubic rami and blends with a fibrocartilaginous disc of the pubic symphysis
- Anterior pubic ligament
- Posterior pubic ligament – a membranous structure which blends with periosteum
Endopelvic Fascia – Ligaments
- Female: Pubovesical ligaments – attach bladder to the pubic symphysis
- Male: Puboprostatic ligaments – attach bladder to the pubic symphysis
- Sacrogenital – these are thickenings of the fascia, not specific ligaments
- Uterosacral ligaments – attach upper vagina, the upper portion of cervix and uterus to the 3rd sacral vertebra
- Cardinal ligaments (aka Mackenrodt’s) – attach upper vagina, cervix, and uterus to the sidewalls of the pelvis
- Round ligaments – attach the uterus to the mons pubis
- Broad ligaments – attach the uterus to the medial aspect of the ilium
- Uranus ligament – attaches bladder to the umbilicus (formed from the remnants of the umbilical vein)
Penile Suspensory Ligaments
- Penile Suspensory ligament – attaches to the anterior aspect of the interpubic disc and divides in two to sling around the penis
- Fundiform ligament – extends from inferior linea alba and divides to wrap around the penis
- Parietal pelvic fascia – lines the internal surface of the muscles of the pelvic floor and walls
- Visceral pelvic fascia – invests each pelvic organ. The parietal and visceral fascia is continuous where organs penetrate the pelvic floor. They thicken to form the arcus tendinous, arches of fascia running adjacent to the viscera from the pubis to the sacrum.
- Endopelvic fascia – a meshwork of smooth muscle, ligaments, blood vessels and connective tissue lying between the parietal and visceral fascia, sometimes condensing to form fibrous fascial septa which separate and suspend the organs.
Anatomists use the name subserous fascia whereas surgeons refer to this layer of retroperitoneal fascia as endopelvic fascia.
- Hypogastric sheath – separates retropubic space from presacral space; a conduit for vessels and nerves
- Transverse cervical (cardinal) ligaments – part of the hypogastric sheath; runs from lateral pelvic wall to uterine cervix and vagina; transmits uterine artery and provides passive support for the uterus
- Vesicovaginal septum
- Rectovesical septum
- Rectovaginal septum
Pelvic floor dysfunction and muscle weakness may lead to the following disorders
Cystocele, anterior vaginal wall prolapse
Urethrocele, prolapse of the urethra
Cystourethrocele, prolapse of the urethra and bladder
Rectocele, prolapse of the rectum into the vagina
Enterocele, prolapse of the small intestine into the vagina
Uterine prolapse, prolapse of the uterus into the vagina
The pelvic floor is subject to clinically relevant changes that can result in
Anterior vaginal wall prolapse
- Cystocele (bladder into vagina)
- Urethrocele (urethra into the vagina)
- Cystourethrocele (both bladder and urethra)
Posterior vaginal wall prolapse
- Enterocele (small intestine into the vagina)
- Rectocele (rectum into the vagina)
Apical vaginal prolapse
- Uterine prolapse (uterus into the vagina)
- Vaginal vault prolapse (roof of the vagina) – after hysterectomy
Clinical Significance of Pelvic floor
Clinical correlates related to female pelvic anatomy can be summarized as follows:
The standard position of the uterus is anteverted and anteflexed. Abnormal positioning of the uterus is associated with pathology. Retroversion, for example, is a cause of dyspareunia. Additionally, retroversion of a gravid uterus is associated with higher rates of spontaneous abortion.
The posterior cul-de-sac, located between the uterus and the rectum, is a potential space prone to fluid collection. Physiologic fluid accumulates during menses and ovulation. If fluid collection is pathologic, this space can undergo drainage via culdocentesis.
The posterior cul-de-sac communicates with the abdomen via the left and right epiploic gutters, which allows the spread of pelvic pathogens into the abdominal cavity. Due to the leftward position of the rectum, infections usual take the path of the right epiploic gutter. The right epiploic gutter leads to potential spaces surrounding the liver. These include the hepatorenal space, also known as Morrison’s pouch, and the subphrenic space. The infection of the subphrenic space secondary to a gonococcal pelvic infection is termed Fitz-Curtis-Hugh syndrome or gonococcal perihepatitis.
The increased length of the left ovarian vein makes it more susceptible to compression, especially during pregnancy. The compression of this vessel sometimes leads to pelvic venous compression syndrome and is a cause of chronic pelvic pain in both pregnant and non-pregnant patients.
Venous thromboembolism in pregnancy is most commonly left-sided and occur in the iliofemoral vessels, which is thought to be because of pelvic vessel engorgement in combination with the increased path the left iliac vein takes across the pelvis. These factors make this vessel more susceptible to compression by a gravid uterus.
Understanding the lymphatic drainage of the female reproductive tract is important when tracking the spread of gynecologic malignancies. Generally, the female reproductive organs drain to the internal and external iliac lymph nodes. A notable exception is the ovaries, which drain to the paraaortic lymph nodes.
The pudendal nerve receives sensory innervation to the lower vagina. Historically, pudendal nerve blocks were used to alleviate labor pains. However, pudendal nerve blocks are no longer commonly practiced due to the wide-spread use of epidural anesthesia.
The muscles of the pelvic floor are susceptible to injury during vaginal deliveries. The most commonly injured muscles are the pubococcygeus and puborectalis muscles due to their proximity to the vagina.
The pelvic vasculature contains many physiologic variants that are important for surgeons to know. Interventional radiologists should also be knowledgeable of variants, particularly during uterine artery embolization to treat fibroids. The uterine artery most commonly arises from the anterior branch of the internal iliac and shares a trunk with the obliterated umbilical artery. The most common variation is direct branching from the internal iliac.
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