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BONY PELVIS

Continuation

Joints of the Pelvis
Recall that a joint as the name suggests is a meeting point or an articulation of two bones. The bony pelvis has four major joints as follows:
Lumbosacral joint
Sacrococcygeal joint
Sacroiliac joint
Pubic symphysis (or symphysis pubis)
Lumbosacral joint
It is a cartilaginous joint between the fifth lumbar vertebrae (L5) and the sacrum. This joint allows flexion, extension and minimal lateral rotation
Sacrococcygeal joint
It is an articulation between the apex of the sacrum and the base of the coccyx. It is slightly mobile allowing limited degree of flexion and extension. It is even more mobile in the female. This mobility increases the anteroposterior diameter of the pelvis during labour and defecation. It is a cartilaginous joint.

Sacroiliac joint
The sacroiliac joint is a synovial joint formed by the auricular surface of the sacrum and the ilium of the hipbones. There are right and left sacroiliac joints. These joints allow very little to no movement. The major function of the joint is to bear the weight of the body and transmit it to the hipbones. From the hipbone, the weight is then distributed to the two femurs in the standing position or the ischial bone in the seating position.


Pubic symphysis
The pubic symphysis or symphysis pubis is a cartilaginous joint between the right and left pubic bones. It is slightly movable and helps in absorbing shock while walking.
During childbirth, the hormone relaxin acts on the pubic symphysis making it more flexible. This flexibility allows the expansion that aids passage of the baby.
Hip joint
The hip joint is a ball and socket type of synovial joint that connects the pelvis to the lower limb. It is formed by the femoral head and the acetabulum of the pelvis. It permits high range of motion such as flexion, extension, abduction, adduction, internal and external rotation, circumduction etc. The entire weight of the upper body is transmitted through this joint to the lower limbs while standing. It is the most stable joint in the human body.
Note: The acetabulum is a suture connecting the ilium, ischium and pubic bones.
Ligaments of the Pelvis
Recall that ligaments are fibrous connective tissues that connect bone to bone.
The bones of the pelvis are connected by five major ligaments
Interpubic ligament found between the pubic bones forming the pubic symphysis
Sacroiliac ligaments (anterior/posterior) that attach the sacrum to the coccyx.
Sacrotuberous ligaments connect the sacrum to the ischial spines.

Pelvic Viscera
The pelvic viscera are the organs located within the pelvis and form its major contents.
They include:
Distal organs of the urinary system
Distal organs of the GIT
Internal genital organs
Urinary Organs
Distal half of the ureters
Urinary bladder
Entire female urethra (except the orifice)
Proximal part of male urethra.
Gastrointestinal organ
Sigmoid colon
Rectum
Male Internal Genital organs
Vas deferens
Seminal Vesicles
Ejaculatory duct
Prostate
Bulbourethral glands
Female internal genital organs
Ovaries
Oviducts
Uterus
Vagina
Diameters of the Pelvis
Recall from basic mathematics that a diameter is a straight line drawn between two points on a circumference of a circle that passes through the centre (origin). It is twice (2x) the radius.
The size of the lesser (true) pelvis is important because it is the bony canal through which the foetus passes during normal childbirth. To determine the capacity of the female pelvis for childbearing, the diameters of the lesser pelvis are noted radiographically or manually during a pelvic examination. The important diameters include:

Anteroposterior diameter
Oblique diameter
Transverse diameter
Anteroposterior diameter
This is the distance from the sacral promontory to the pubic symphysis. It is generally 11cm (true conjugate).
Transverse Diameter
This is th distance between the right and left illiopectineal lines. It measures about 13 cm amd is regarded as the longest diameter in the pelvis.
Oblique Diameter
This is the distance from the sacroiliac joint to the illiopectineal eminence. It has both right and left and measures 12cm.




Classification of the Female Pelvis
Four types of female pelves have been described:
Gynecoid pelvis
Anthropoid pelvis
Android pelvis
Platypelloid pelvis
Gynecoid pelvis
It is the normal female type of pelvis
Has a round inlet
Sidewalls are straight with blunt ischial spines.
It present the least amount of trauma during childbirth.
50% of women have gynecoid pelvis.
Anthropoid pelvis
This type of pelvis is common to apes.
Has an oval inlet with narrow cavity.
All anteroposterior diameters are long.
All transverse diameters are short.
Found in 25% of women.
Android Pelvis
It is the male type of pelvis
Has a heart-shaped inlet.
Has prominent ischial spines.
Women with android pelvis may experience longer labour.
Found in 20% of women.
Platypelloid Pelvis
Has a kidney-shaped inlet.
AP diameter is short
Transverse diameter is long
Found in 5% of women.

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