Pelvic Cavity

Pelvis (Latin) = basin

Pelvic brim (330)

Formed in continuity by pubic crest, pectineal line, arcuate line of ilium, ala & promontory of sacrum. 
Plane of brim 60¡ to horizontal (same plane as vagina), cavity projects back from here to buttocks.

In upright individual, ASIS and upper symphysis lie in same vertical plane

-           upper symphysis, ischial spine, tip of coccyx, and head of femur, apex of grt troch = same horizontal plane.

Sex differences

 

Female

Male

Width

Broad

Narrow

Bones

Slender

Sturdy

Sub-pubic angle

Wide

Acute

Pelvic brim

Oval

Heart-shaped

-           female ilium may show a preauricular sulcus below the arcuate line.

Pelvic walls

Pelvic brim divides false pelvis above from true pelvis.

The muscles of the pelvis are: 1. obturator internus, 2.piriformis, (walls) 3. levator ani, 4. coccygeus (floor). (see plate 391 in 3rd edition)

Side wall: hip bone, clad with obturator internus & its fascia, curved posterior wall formed by sacrum with piriformis lateral.
note that obturator lines the wall while levator branches out sideways to form floor for pelvic contents

Piriformis (333-5)

From middle 3 pieces of ipsilateral sacrum + lateral mass ¨ back laterally through gr sciatic foramen (which it almost fills) ¨ apex of gr trochanter.

-           emerging sacral plexus lies on this muscle

-           both are covered by pelvic fascia attached to sacral periosteum at the muscleÕs margins.

Innervation: anterior division of S1, S2. (own nerve off sacral plexus) 

Obturator internus (333-5)

Contains a Ôfelted massÕ of fibrous tissue the obturator membrane, with a defect above that forms the obturator canal (for obturator nerve and vessels Ð see 335).

Muscle arises from this membrane, bony margins of obturator foramen, ischial tuberosity, across ischium to greater sciatic notch (ie a big origin)

Inserts ¨ R-angled turn around lesser sciatic foramen ¨ medial surface of greater trochanter (461)

-           where it runs over bone, there is hyaline cartilage and a bursa.

Innervation: nerve to OI (L5, S1, S2, posterior division of sacral plexus).

Muscle overlain by dense obturator fascia (attached to bone at muscle margins); the tendinous arch of levator ani slopes across this fascia.

Pelvic floor (333-6) (345 in 3rd)

Pelvic diaphragm = gutter of muscle slung around midline structures.  Slopes down and forwards.

Consider muscles as one entity, arising in continuity from ischial spine (above obturator), tendinous arch over obturator fascia, body of pubis -> Insert into coccyx & anococcygeal raphe. 

Levator Ani

2 parts: arise in continuity from body of pubis to ischial spine across obturator fascia and a condensation of that fascia: the tendinous arch.  Slow twitch sphincter muscle.

Iliococcygeus part

From posterior 1/2 of tendinous arch and ischial spine ¨ side of coccyx and anococcygeal raphe.

NB silly name - doesnÕt arise from ilium (does in other mammals)

Pubococcygeus part

From anterior 1/2 of tendinous arch + posterior surface of body of pubis.  Fibres in functional sets:

(1) Pubococcygeus muscle proper: posterior fibres ¨ tip of coccyx and anococcygeal raphe

(2) Puborectalis: More anterior fibres of this part (from body of pubis) form a sling holding anorectal jx forward.

(3) Levator prostatae/pubovaginalis fibres most medial; surround prostate/vagina ¨ perineal body; riase from longitudinal coat of rectum

-           most medial fibres around urethra exert some sphincteric action.

-           gap anteriorly between most medial fibres, filled by puboprostatic (m) or pubovesical (f) ligaments and deep dorsal vein in midline. 

Post-anal Plate

Musculotendinous structure b/n anal canal and caudal vertebral column, terminal rectum sits on it.

-           layers (top down): presacral fascia, tendinous pubococcygeus, muscular raphe of iliococcygeus, posterior puborectalis, and external anal sphincter.

Coccygeus (= Ischiococcygeus)

Tail-wagging muscle.  Gluteal surface = sacrospinous ligament.

From tip of ischial spine ¨ fans out to insert into coccyx and lower sacrum (334).

Lies edge to edge with lower border of piriformis and iliococcygeus.

Nerve supply of pelvic floor

Levator ani:  sacral plexus: perineal branches of S3, S4, (465) entering pelvic (upper) surface of muscle;  travel in / very close to pelvic splanchnic nerves

-           puborectalis also supplied from below by perineal branch of S4 and inferior rectal nerve off the pudendal nerve.

Coccygeus:  perineal branches of S4, S5

-           all posterior divisions of sacral plexus

Actions

(1) ­Abdominal P ¨ muscle contraction (eg sneezing, lifting).

(2) Relaxes to allow evacuation of visceral contents

(3) Pubovaginalis ¨ urethral compression at the end of micturition

(4) Parturition: directs fetal head to pelvic outlet (though liable to tear).

(5) Puborectalis sling ¨ 120¡ angle between rectum and anal canal. 

(6) Active in quiet respiration

Note that in erect position pubic bones and perineal body support most of weight of viscera. 

Pelvic fascia (341)

DoesnÕt extend over bare bone.  Consider in 3 parts (really parietal or visceral):

(1) Of pelvic wall

Covers muscles (OI, piriformis), not bone (exception: WaldeyerÕs fascia).  Spinal nerves & sacral plexus lie superficial to fascia, vessels lie deep to it \ vessels to buttock must pierce it. 

(2) Of pelvic floor

Loose areolar tissue overlying pelvic diaphragm.  Dead space exists between pelvic viscera to allow expansion.  Condensations of tissue surround vessels and nerves (lateral ligament of uterus & bladder); some ligaments exist in their own right independent of vessels & nerves (round ligament of uterus, uterosacral ligament). 

(3)  Of pelvic viscera

Loose (bladder & rectum) or dense (prostate) according to organ distensibility.

-           condensed around neurovascular bundles supplying these viscera to form ligaments eg lateral cervical ligaments of uterus, WaldeyerÕs fascia, pubovesical and puboprostatic ligaments