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The Pelvis back |
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The pelvis forms a bony ring that sits between the vertebral
column and the hip bones, the acetabulum. It is stronger and more
massive than the wall of the cranial or thoracic cavities. The
pelvis gains its strength through the ligaments and muscles.
The pelvis is symmetrical and each side is
actually made up of three separate bones:
1.
The top half is the ilium. Also known as the iliac crest.
2.
The middle is the pubis. The front of the pelvis where the two
sides join together and is called the symphysis pubis.
3.
The bottom is the ischium. The ischium forms the lower and back
part of the hip bone. It is situated below the ilium.
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| Pelvic Shapes
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| The female pelvis comes in four
shapes:
1. Gynecoid: The gynecoid pelvis (sometimes called a "true
female pelvis") is found in about 50% of the women.
2. Android: The android pelvis (sometimes called a "true make
pelvis") is found in about 20% of women.
3. Anthropoid: The anthropoid pelvis is very long and almost
"ovoid" in shape. It is more common in non-white females (it makes
up about 25% of pelvic type in white women and close to 50% in
non-white women).
4. Platypelloid: The platypelloid pelvis is very short (almost
like a "flattened gynecoid shape"). Only about 3% of women have a
true and pure pelvis of this type.
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| Pelvimetry
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| Pelvimetry assesses the size of a
woman's pelvis aiming to predict whether she will be able to deliver
vaginally or not. This assessment can be done by either a clinical
examination, conventional x-rays, computerized tomography scanning,
or magnetic resonance imaging.
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| Symphysis Pubis
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| "Symphysis" is a Greek word that
means "growing together". The symphysis pubis is a non synovial
amphiarthrodial joint, (a joint in which the opposing bony surfaces
are covered with a layer of hyaline cartilage or fibrocartilage and
in which some degree of free movement is possible).
At the time of birth the symphysis pubis is 9-10mm in width,
with thick cartilaginous end-plates. By mid-adolescence the adult
size is achieved. During adulthood the end-plates decrease in width
to a thinner layer. Degeneration of the symphysis pubis accompanies
aging and postpartum. Women have a greater thickness of this pubic
disc which allows more mobility of the pelvic bones, hence providing
a greater diameter of pelvic cavity during parturition. ;
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| Pelvic Ligaments
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| 1. Those connecting the sacrum and ilium.
2. Those passing between the sacrum and ischium.
3. Those uniting the sacrum and coccyx.
4. Those between the two pubic bones.
Pubic Ligaments
The Anterior Pubic Ligament. The anterior pubic
ligament consists of several superimposed layers, which pass across
the front of the articulation. The superficial fibers pass obliquely
from one bone to the other, decussating and forming an interlacement
with the fibers of the aponeuroses of the Obliqui externi and the
medial tendons of origin of the Recti abdominis. The deep fibers
pass transversely across the symphysis, and are blended with the
fibrocartilaginous lamina.
The Posterior Pubic Ligament. The posterior pubic
ligament consists of a few thin, scattered fibers, which unite the
two pubic bones posteriorly.
The Superior Pubic Ligament (ligamentum pubicum
superius). The superior pubic ligament connects together the two
pubic bones superiorly, extending laterally as far as the pubic
tubercles.
The Arcuate Pubic Ligament (ligamentum arcuatum pubis;
inferior pubic or subpubic ligament). The arcuate pubic
ligament is a thick, triangular arch of ligamentous fibers,
connecting together the two pubic bones below, and forming the upper
boundary of the pubic arch. Above, it is blended with the
interpubic fibrocartilaginous lamina; laterally, it is
attached to the inferior rami of the pubic bones; below, it
is free, and is separated from the fascia of the urogenital
diaphragm by an opening through which the deep dorsal vein of the
penis passes into the pelvis.
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| Fibrocartilage
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| Fibrocartilage is composed of small
chained bundles of thick clearly defined type I collagen fibers.
This fibrous connective tissue bundles have cartilage cells between
them and to a certain extent resemble tendon cells. The collagenous
fibers are usually place in an orderly arrangement parallel to
tension on the tissue. It has a low content of glycosaminoglycans
(2% of dry weight).
Glycosaminoglycans are long unbranched polysaccharides
(relatively complex carbohydrates) consisting of a repeating
disaccharide unit. Disaccharide is a sugar (a carbohydrate) composed
of two monosaccharides. The two monosaccharides are bonded via a
dehydration reaction that leads to the loss of a molecule of water.
Fibrocartilage does not have a surrounding perichondrium.
Perichondrium surrounds the cartilage of developing bone, it has a
layer of dense irregular connective tissue and functions in the
growth and repair of cartilage.
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| Hyaline Cartilage
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| Hyaline cartilage is the white shiny
gristle at the end of long bones. This cartilage has very poor
healing potential, and efforts to get it to repair itself frequently
end up with a similar, but poorer fibrocartilage. |
| Sacroiliac Joint
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| The sacroiliac joints are a C-shaped
amphiarthrodial joints (joint permitting only slight motion) formed
between the articular surfaces of the sacrum and ilium. The
sacroiliac joint is a "viscoelastic joint", meaning that its major
movement comes from giving or stretching. The joints are covered by
two different kinds cartilage; the sacral anterior edge has a
hyaline cartilage and the ilium anterior edge a fibrocartilage. The
stability of the SIJ's are maintained by various muscles and
ligaments. As we age the characteristics of the sacroiliac joint
change. The joint's surface remains flat until sometime after
puberty. In our thirties and forties there is an increase in the
size and number of elevations and depressions on the sacral and
iliac surfaces.
The SI joint's main function appears to be providing shock
absorption for the spine through stretching in various directions.
The SI joint may also provide a "self-locking" mechanism that helps
you to walk. The joint locks on one side as weight is transferred
from one leg to the other and through the pelvis the body weight is
transmitted from the sacrum to the hip bone. These joints bear the
weight of the twists and turns of the trunk of the body. It is
common for the SI joint to become stiff and actually "lock" as we
age. During pregnancy micro tears and small gas pocket can appear
within the joint. Traumatic incidents, biomechanical mal-alignments
and hormonal changes can all lead to SIJ dysfunction. The
self-braced position of the SIJ can be altered by these factors and
the joint can lose its stability. SIJ dysfunction puts abnormal
pressures on the joint surfaces, ligaments and surrounding muscles.
In some situations, pain can be felt at the front of the pelvis,
down near the pubic bone.
The Motions of the Sacroiliac Joint's
The motions of the sacroiliac joint's are:
Sacral flexion
Sacral extension
Sacral forward torsion
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| Pubic Bone
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| The pubic bone consists of the body and two ramus
bones, the superior and inferior pubic rami. This surface generally
is oval. The inferior pubic rami pass posterior and inferior to join
the ramus of ischium to form half of the pubic arch. The and length
of the pubic arch depends on the shape of the pelvis.
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| The Hip
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| Walking takes place from the pelvis
to the foot, not the other way around and occurs in a closed kinetic
chain. When people walk, their pelvises don't drop dramatically on
a non-stance side because gravity's adductor is balanced by an equal
and opposite abductor movement. A major factor of the hip abductor
is in a closed-chain motion to maintain a level pelvis in unilateral
stance. Hip joint reaction force depends on the ratio of lever arm
of abductor muscle force and gravity. Because the centre of gravity
lies posterior to the joint axis, body weight also creates a bending
moment, increased with hip flexion. Because hip abductor activity is
necessary to stabilize the hip in the frontal plane during
unilateral stance, people with weakness have a problem. One might
see the pelvis drop on the unsupported side if we ask a person to
stand briefly on the weakened limb.
The inability to maintain a level pelvis in unilateral stance is
called a "Positive Trendelenburg Sign". The most
direct way to orientate the line of application of the gravity
vector is to shorten the arm movement with respect to the hip joint,
leaning the trunk towards the side of the hip whose abductor muscles
are weak. This movement and type of stance is called
"Trendelenburg Gait Pattern". (Go to
treatments to view Trendelenburg Test).
Hip adductor strength can be recommended to measure, disease and
severity in pelvic instability. Decreased hip adduction strength
appears to be caused by the inability to use the hip muscles rather
than by weakness of the muscles. By using an aid to assist in stance
and movement is to create an additional force that keeps the pelvis
level. Additionally, the person needs adequate strength in the
muscles of the wrist, elbow, shoulder girdle and trunk to transfer
sufficient weight to the aid. (Go to
treatments to view Hip Add / Abduction test).
Hip Anatomy The hip joint is a ball and socket joint between the head of
femur and the acetabulum of the pelvis. The articular capsule
encloses the head and the greater part of the neck of the femur.
Anteriorly the capsule is thickened as the iliofemoral ligament.
This prevents over-extension. Medially the capsule is thickened to
form the pubofemoral ligament. The head of femur is connected with
the hip bone by the ligament of head of femur which connects the pit
on the head and the margins of the acetabular notch. |
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