The Pelvis

The Pelvis Lectured by Bien Eli Nillos, MD

No. of bones composing the bony pelvis 2. What divides the true pelvis from false pelvis 3 – 5. What comprises the answer to No. 2? (anterior, lateral and posterior) 6. What is the floor of the pelvis? 7 – 8. What comprises answer to No. 8 1.

For no. 9 – 10, answer whether it is a male of female pelvis being described.

9. Pelvic inlet is heart shaped 10. False pelvis is shallower.

The Pelvis  The

region of the trunk that lies below the abdomen. The abdominal and pelvic cavities are continuous.

Surface Landmarks  Iliac

Crest  Anterior Superior Iliac Spine – upper lateral end of the fold of the groin  Posterior Superior Iliac Spine – posterior end of the iliac crest, lies at the bottom of a small skin dimple and on a level with the second sacral spine.

 Pubic

Tubercle – upper border of the

pubis  Symphysis Pubis – cartilaginous joint that lies in the midline between the bodies of the pubic bones.  Pubic Crest – ridge of bone on the superior surface of the pubic bone, medial to the pubic tubercle

 Spinous

Process of the Sacrum – fused in the midline to form the median sacral crest  Sacral Hiatus – posterior aspect of the lower end of the sacrum  Coccyx – inferior surface and tip can be palpated in the natal cleft about 1 inch behind the anus

Pelvis  Composed

of four bones: 2 innominate bones, sacrum and coccyx

 Pelvic

brim: sacral promontory behind, iliopectineal lines laterally, symphysis pubis anteriorly.

 Above

the brim is the FALSE PELVIS (greater pelvis).  Below the brim is the TRUE PELVIS (lesser pelvis)



The Lesser or True Pelvis (pelvis minor). —The lesser pelvis is that part of the pelvic cavity which is situated below and behind the pelvic brim. Its bony walls are more complete than those of the greater pelvis. For convenience of description, it is divided into an inlet bounded by the superior circumference, and outlet bounded by the inferior circumference, and a cavity.

 The

Superior Circumference.—The superior circumference forms the brim of the pelvis, the included space being called the superior aperture or inlet  The superior aperture is somewhat heartshaped, obtusely pointed in front, diverging on either side, and encroached upon behind by the projection forward of the promontory of the sacrum.

 It

has three principal diameters: antero-posterior, transverse, and oblique.  The anteroposterior or conjugate diameter extends from the sacrovertebral angle to the symphysis pubis; its average measurement is about 110 mm. in the female.

 The

transverse diameter extends across the greatest width of the superior aperture, from the middle of the brim on one side to the same point on the opposite; its average measurement is about 135 mm. in the female.

 The

oblique diameter extends from the iliopectineal eminence of one side to the sacroiliac articulation of the opposite side; its average measurement is about 125 mm. in the female.

 The

Lower Circumference—The lower circumference of the pelvis is very irregular; the space enclosed by it is named the inferior aperture or outlet, is bounded behind by the point of the coccyx, and laterally by the ischial tuberosities.

 The

diameters of the outlet of the pelvis are two: antero-posterior and transverse.  The antero-posterior diameter extends from the tip of the coccyx to the lower part of the pubic symphysis; its measurement is from 90 to 115 mm. in the female.

 The

transverse diameter, measured between the posterior parts of the ischial tuberosities, is about 115 mm. in the female.

 In

the erect posture, the pelvis is placed obliquely with regard to the trunk: the plane of the superior aperture forms an angle of from 50° to 60°, and that of the inferior aperture one of about 15° with the horizontal plane.

 The

pelvic surface of the symphysis pubis looks upward and backward, the concavity of the sacrum and coccyx downward and forward.  The position of the pelvis in the erect posture may be indicated by holding it so that the anterior superior iliac spines and the front of the top of the symphysis pubis are in the same vertical plane.

Muscles of the Pelvis  Piriformis

– Origin: front of sacrum – Insertion: greater trochanter of femur – Action: lateral rotator of femur at hip joint

 Obturator

Internus:

– Origin: obturator membrane and adjoining part of hip bone – Insertion: greater trochanter of femur – Action: lateral rotator of femur at hip joint

 Levator

ani:

– Origin: body of pubis, fascia of obturator internus, spine of ischium – Insertion: perinela body, anococcygeal body, walls of prostate, vagina, rectum and anal canal – Action: supports pelvic organs

 Anterior

fibers – levator prostatae/sphincter vaginae  Intermediate fibers – puborectalis, pubococcygeus, anococcygeal body  Posterior fibers - iliococcygeus

 Coccygeus:

– – –

Origin: spine of ischium Insertion: lower end of sacrum; coccyx Action: assists levator ani to support pelvic organs

Male and Female Pelvis

Urinary Bladder  Receptacle

for storage of urine



Ureter

Crosses the pelvic inlet in front of the bifurcation of the common iliac artery

Vas Deferens



Conveys mature sperm from epididymis to the ejaculatory duct and the urethra

Prostate  Inverted

pyramid, fibromuscular glandular organ.

Ovary  Almond-shaped

organ

4

Uterine (Fallopian) Tubes

inches long, four parts: infundibulum, ampulla, isthmus, intramural

Uterus

Cervix

Vagina