1. The Pelvic girdle, Floor and Cavity Dr. Rana Al-tae 2011-2012
Anatomy Lecture 5
The Pelvic girdle, Floor and Cavity
Dr. Rana Al-tae

2. Pelvic (Hip)Girdle
The pelvic (hip) girdle consists of the two hip bones, also called coxal bones. The pelvic girdle accepts the bones of the lower limbs, connecting them to the axial skeleton. The hip bones are joined together anteriorly at a joint called the pubic symphysis. Posteriorly they unite with the sacrum at the sacroiliac joints. The complete ring composed of the hip bones, pubic symphysis, and sacrum forms a deep basin like structure called the bony pelvis. Functionally, the bony pelvis provides a strong and stable support for the vertebral column and pelvic organs.

3. Each of the two hip bones of a newborn consists of three bones separated by cartilage: a superior ilium, an inferior and anterior pubis, and an inferior and posterior ischium. By age 23 the three separate bones fuse together. Although the hip bones function as single bone anatomists commonly discuss them as three bones:

4. Ilium: (=flank) is the largest of the three hip bones
Ilium: (=flank) is the largest of the three hip bones. It is divided into a superior ala (=wing) and an inferior body, which enters into the formation of the acetabulum ( the socket for the head of femur). The superior border of the ilium, called the iliac crest, ends anteriorly in a blunt anterior superior iliac spine. Below this spine is the anterior inferior iliac spine.

5. . Posteriorly, the iliac crest ends in a sharp posterior superior iliac spine. Below this spine is the posterior inferior iliac spine. The spines serve as points of attachment for the tendons of the muscles of trunk, hip, and thighs. Below the posterior inferior iliac spine is the greater sciatic notch. The medial surface of the ilium contains the iliac fossa ( a concavity where the tendon of the iliacus muscle attaches).

7. Ishium : is the inferior, posterior portion of the hip bone
Ishium : is the inferior, posterior portion of the hip bone. It is composed of a superior body and an inferior ramus (branch). The ischium contains the prominent ischial spine, a lesser sciatic notch below the spine, and a rough thickened ischial tuberosity. This tuberosity may hurts someones thigh when you sit on their lap.

9. Pubis : is the anterior inferior part of the hip bone, it consists of a superior ramus and an inferior ramus and a pubic body in between. the pubic body contributes in the formation of the pubic symphysis. The superior surface of the superior ramus is called the pubic crest that ends laterally as a projection called the pubic tubercle.

10. The pubic arch (pubic angle) is formed by the convergence of the inferior rami of the two pubic bones. . The ischial ramus unites with the inferior ramus of the pubis bone forming the obturator foramen (obturator= closed up), the largest foramen in the skeleton. It is nearly closed by the obturator membrane.

11. True and False Pelvis
The bony pelvis is divided into superior and inferior portions by a boundary called the pelvic brim which is formed by the following landmarks: beginning posteriorly at the sacral promontory of the sacrum, then laterally and inferiorly around the arcuate lines of the ilium, continuing inferiorly along the iliopectineal lines of the pubis, finally anteriorly at the superior portion of the pubic symphysis. Together these points form an oblique plane that is higher in the back than infront. The circumference of this plane is the pelvic brim.

12. The portion of the bony pelvis inferior to the pelvic brim is the True (lesser) pelvis. It is bordered by the sacrum and coccyx posteriorly,inferior portions of the ilium and ishium laterally, and the pubic bones anteriorly. The true pelvis surrounds the pelvic cavity. The superior border of the true pelvis is the pelvic brim which is also called the pelvic inlet; the inferior opening of the true pelvis is the pelvic outlet.

13. The pelvic axis is the imaginary line that curves through the true pelvis and joins the central points of the planes of the pelvic inlet and outlet. During childbirth the pelvic axis is the route taken by the baby's head as it descends through the pelvis.

14. Comparison of Female and Male pelves
Assuming that the the male and female are near in age and physical stature, generally, the bones of a male are larger and heavier than those of a female and have larger surface markings. Most of the structural differences in the pelves are adaptations to the requirements of pregnancy and childbirth. The female's pelvis is wider and shallower than the male's. consequently, there is more space in the true pelvis of the female, especially in the pelvic inlet and outlet which accommodate the passage of the infant's head at birth.

15. Other structural differences between pelves of females and males are listed as follows: Point of comparison Female Male General structure light and thin heavy and thick False (Greater pelvis) shallow Deep Acetabulum small and faces anteriorly large and faces laterally

16. Point of comparison Female Male Pelvic brim (inlet) larger and more oval Smaller and heart-shaped

17. Point of comparison Female Male Pelvic outlet Wider Narrower

18. Point of comparison Female Male Obturator foramen Oval Round Pubic arch Greater than 90°angle Less than 90°angle

19. Point of comparison Female Male Iliac crest less curved More curved Ilium less vertical More vertical

20. Point of comparison Female Male Greater sciatic notch Wide Narrow Coccyx More movable and curved less movable and less curved anteriorly anteriorly Sacrum Short, wide and more Long, narrow and curved anterior less curved Ischial tuberosity Female Shorter, more laterally projecting Male Larger, more medially projecting

22. Pelvic Floor :
Pelvic floor is formed by the pelvic diaphragm which consists of two muscles : Levator ani and coccygeus. These two muscles with the corresponding muscles of the opposite side form the pelvic diaphragm. It resembles a hammock, or a gutter because it slopes from either side towards the median plane where it is pierced by the urethra and anal canal and also by the vagina in females. Pelvic diaphragm separates the perineum below from the pelvis above.

23. The levator ani and coccygeus may be regarded as one morphological entity, divisible into pubococcygeus, iliococcygeus and ischiococcygeus (coccygeus)from before backwards. They have a continuous linear origin from the pelvic surface of the body of pubis, obturator fascia ( white line or tendinous arch ) and the ishial spine. The muscle fibers slope downwards and backwards to the midline, making the gutter shaped pelvic floor.

24. Muscles and their Origins, insertions and nerve supply :
Levator ani
Pubococcygeus
Anterior fibers form levator prostate in males and pubovaginalis (sphincter vaginae) in females. ORIGIN from the pelvic surface of body of pelvis. INSERTION in males they closly surround the prostate (levator prostatae) and are inserted into the perineal body. In females they surround the vagina (sphincter vaginae) and are inserted to the perineal body.

25. Middle fibers form puborectalis ORIGIN from the pelvic surface of body of pubis INSERTION they form a loop (sling) around the anorectal junction and partly continuous with the outer longitudinal muscle coat of the rectum.

26. Posterior fibers may be called pubococcygeus proper ORIGIN from the anterior half of the white line on the obturator fascia. INSERTION to anococcygeal ligament and tip of coccyx

27. Iliococcygeus ORIGIN from the posterior half of the white line on the obturator fascia and from the pelvic surface of the ischal spine. INSERTION to anococcygeal ligament and tip of coccyx and the sides of last two pieces of coccyx.
The above two muscles are supplied by a branch from S4 nerve and another branch from the inferior rectal nerve or from the perineal branch of the pudendal nerve.
Coccygeus (Ishiococcygeus) triangular in shape partly muscular and partly tendinous. ORIGIN from the pelvic surface of the ischial spine and the sacrospinous ligament. INSERTION to the side of coccyx and S5 vertebra. N.SUPPLY from a branch from S4,5 nerves.

28. NOTE the perineal body is a fibromuscular node that nine muscles are attached. It acts as a anchor for the pelvic diaphragm and thus maintains the integrity of the pelvic floor.

29. Additional features of the pelvic muscles:
The levator ani and coccygeus mm. close the posterior part of the pelvic outlet.
The levator ani m. fix the perineal body and support the pelvic viscera.
During coughing, sneezing, lifting and other muscular efforts, the levator ani and coccygeus mm. resist increased intra-abdominal pressure and maintain continence of bladder and rectum. In micturation, defaecation and parturition, they resist the pressure and prevents any prolapse through the pelvic floor.

30. Pelvic Cavity
The pelvic cavity is continuous above with the abdominal cavity at the pelvic brim and is limited below by the pelvic diaphragm. It is curved in such a way that first it is directed downwards and backwards, and then downwards and forwards (J-shaped). It has unequal walls, measuring about 2 inches anteriorly and 6 inches posteriorly. The cavity is more roomy (larger) in females than in males.

31. Contents :
Sigmoid colon and rectum occupy the posterior part of the pelvis.
Urinary bladder lies anteriorly, with the prostate below the neck of bladder.

32. In between the bladder and the rectum there is a transverse connective tissue septum (genital septum). In males, the septum is small being thin in the middle and thick on each side; it contains ductus deferens, seminal vesicle and ureter on each side. In females, the septum is large and contains the uterus, uterine tubes, round ligament of uterus, ligaments of ovaries, the ovaries, vagina and ureters.