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| The Pelvis back |
The pelvis forms a boney 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:
The top half is the ilium. Also known as the iliac crest.
The middle is the pubis. The front of the pelvis where the two
sides join together and is called the symphysis pubis.
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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Anatomy of the Pelvis
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Symphysis Pubis |
Anterior Sacroiliac Joint |
Posterior Sacroiliac Joint |
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| Symphysis Pubis back |
| "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).
The anterior width of the symphysis pubis is 3-5 mm greater than
its intrapelvic posterior width. This joint is connected by
fibrocartilage and may contain a fluid filled cavity; the center is
avascular; possibly due to the nature of the compressive forces
passing through this joint which may lead to harmful vascular
diseases. The ends of both pubic bones are covered by a thin layer
of hyaline cartilage which is attached to the fibrocartilage.
In the past obstetrical services relied heavily on pelvimetry but
with the increased safety of modern caesarean section and increased
medico legal concerns the need for pelvimetry has diminished. It is
always a valid question to ask your Healthcare Provider to determine
your pelvic shape and use it as an indicator for yourself.
The fibrocartilaginous disk is reinforced by a series of ligaments.
These ligaments cling to the fibrocartilaginous disk to the point
that fibers intermix with it. Two such ligaments are the
superior
and inferior, these being the ligaments that provide the most
stability; the posterior and anterior ligaments are weaker. The
strong and thicker superior ligament is reinforced by the tendons of
the rectus abdominis, obliques externus, gracilis and thigh
adductors muscles. The strong inferior ligament in the pubic arch is
known as the arcuate pubic ligament.
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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| Fibrocartilage back |
| 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 back |
| 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.
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| Sacroiliac Joint back |
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 width and length of the pubic arch depends on the shape of the pelvis.
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| Pelvimetry back |
| 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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| The Hip back |
| 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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