Page 147 - Clinical Anatomy

ECA2 7/18/06 6:43 PM Page 132

132 The abdomen and pelvis

compression may be followed by dislocation at the symphysis or fractures
through the pubic rami accompanied by dislocation at the sacroiliac joint.
Displacement of part of the pelvic ring must, of course, mean that the
ring has been broken in two places.
Falls upon the leg may force the head of the femur through the acetabu-
lum, the so-called central dislocation of the hip. Isolated fractures may be
produced by local trauma, especially to the iliac wing, sacrum and pubis.
Associated with pelvic fractures one must always consider soft tissue
injuries to bladder, urethra and rectum, which may be penetrated by
spicules of bone or torn by wide displacements of the pelvic fragments.
Occasionally in these pelvic displacements the iliolumbar branch of the
internal iliac artery is ruptured as it crosses above the sacroiliac joint; this
may be followed by a severe or even fatal extraperitoneal haemorrhage.

Sacral (caudal) anaesthesia
The sacral hiatus, between the last piece of sacrum and coccyx, can be
entered by a needle which pierces skin, fascia and the tough posterior
sacrococcygeal ligament to enter the sacral canal. The hiatus can be defined
by palpating the sacral cornua on either side (Fig. 93) immediately above
the natal left.
Anaesthetic solution injected here will travel extradurally to bathe the
spinal roots emerging from the dural sheath, which terminates at the level
of the 2nd sacral segment. The perineal anaesthesia can be used for low
forceps delivery, episiotomy and repair of a perineal tear.

The muscles of the pelvic floor

and perineum

The canal of the bony and ligamentous pelvis is closed by a diaphragm of
muscles and fasciae which the rectum, urethra and, in the female, the
vagina, must pierce to reach the exterior. The muscles are divided into (a)
the pelvic diaphragm, formed by the levator ani and the coccygeus; and (b)
the superficial muscles of the (a) anterior (urogenital) perineum and the (b)
posterior (anal) perineum.
Levator ani (Fig. 97) is the largest and most important muscle of the
pelvic floor. It arises from the posterior aspect of the body of the pubic bone,
the fascia of the side wall of the pelvis (covering obturator internus) and the
spine of the ischium. From this wide origin it sweeps down in a series of
loops:
1◊◊to form a sling around the prostate (levator prostatae) or vagina (sphincter
vaginae), inserting into the perineal body;
2◊◊to form a sling around the rectum and also insert into, and reinforce the
deep part of, the anal sphincter at the anorectal ring (puborectalis);