I.
PELVIC ANATOMY
A. The pelvis (bones, ligaments, joints, muscles, internal
organs) and perineum (the structure between the lower portion of
vulva à fourchette and anus à
muscles & external organs) are interrelated regions associated with
the pelvic bones and terminal parts of the vertebral column
(sacrum & coccyx).
B. The pelvis is part of the trunk anteroposterior to the abdomen and
between the trunk and the lower limbs.
C. The pelvis is divided into two regions:
1. The superior region related to the upper parts of the pelvic
bones and lower lumbar vertebrae are the false pelvis (greater pelvis) and are
generally considered part of the abdominal cavity.
2. The true pelvis (lesser pelvis) is related to
the inferior parts of the pelvic bones, sacrum, and coccyx,
and has an inlet (true conjugate) and an outlet
3. The pelvic cavity is the inferior most part of the
abdominopelvic cavity.
4. Anatomically, the pelvis is the part of the body surrounded by the pelvic girdle (bony pelvis), part of the appendicular skeleton of the lower limb (femur, tibia & fibula, knee, tarsals, metatarsals, and phalanges)
The pelvic girdle is a basin-shaped ring of bones that connects the vertebral column to the two femurs.
a.
The primary functions of the pelvic girdle are to:
i.
Bear the weight of the upper body when sitting and
standing.
ii.
Transfer that weight from the axial to the lower appendicular
skeleton for standing and walking.
iii.
Provide attachment for the powerful muscles of
locomotion
iv.
posture and those of the abdominal wall, withstanding the forces
generated by their actions.
b.
The pelvic girdle is strong and rigid, especially compared
to the pectoral (shoulder) girdle. Other functions of the pelvic girdle
are to:
i. Contain and protect the pelvic viscera (inferior parts of the
urinary tracts and the internal reproductive organs) and the inferior abdominal
viscera (intestines), while permitting passage of their terminal parts (and, in
females, a full-term fetus) via the perineum.
i. Provide support for the abdominopelvic viscera and
gravid (pregnant) uterus.
ii. Provide attachment for the erectile bodies of the
external genitalia.
iii.
Provide attachment for the muscles and membranes that assist the
functions listed above by forming the pelvic floor and filling gaps that exist
in or around it.
During pregnancy –
partial gape joints: hormone relaxin
II. Bones and Features of
Pelvic Girdle
A.
The two hip bones
articulate (joint) with each:
1.
Anteriorly - the symphysis
pubis
2.
posteriorly - the sacroiliac joint
B. The pelvis is divided into two parts by the pelvic brim:
1. which is formed by the sacral promontory (anterior
and upper margin of the first sacral vertebra) behind
2. the iliopectineal lines (a line that runs downward
and forward around the inner surface of the ileum) laterally,
3. the symphysis pubis (joint between bodies of pubic
bones) anteriorly.
C. Adult pelvis (pel ́vis; pl., pelves, pel ́vēz;
basin) is composed of four bones:
1. the sacrum = 5 fused 1
2. the coccyx = 5 fused 1
3. the right and left ossa coxae (os ́ă cox ́ē; sing., os coxae; hip bone) 2
D. Each
pelvic bone (hip bone) is formed by three elements: the ilium, pubis,
and ischium.
1. At birth, these bones are connected by cartilage in
the area of the acetabulum;
2. later, at between 16 and 18 years of age, they fuse
into a single bone
E. Ilium à the ilium is the most superior
in position. The ilium is separated into upper and lower parts by a
ridge on the medial surface
F. The ischium is the posterior and inferior part of the
pelvic bone. It has:
1. a large body that projects superiorly to join with the
ilium and the superior ramus of the pubis,
2. a ramus that projects anteriorly to join with the inferior
ramus of the pubis
G. Pubis àThe anterior and the inferior part of the pelvic bone. It has a body and two arms (rami)
Pelvimetry à important measurements in obstetrics
The pelvis is described as having four imaginary planes:
A.
The plane of the pelvic inlet—the
superior strait.
B.
The plane of the mid pelvis—the least pelvic
dimensions.
C.
The plane of the pelvic outlet—the inferior strait.
D.
The plane of greatest
pelvic dimension—of no obstetrical significance.
A.
Pelvic
inlet
1.
Obstetric conjugate: should be > 10 cm
a. The narrowest fixed distance that fetal head passes
through during birth
b. Cannot measure directly
on pelvic exam
*****The obstetrically important anteroposterior
diameter is the shortest distance
between the promontory of the sacrum and the symphysis pubis and is designated
the obstetrical conjugate.
Normally, this measures 10 cm or more. The obstetrical conjugate cannot be measured directly with the examining fingers.
For clinical purposes, the obstetrical conjugate is estimated indirectly by subtracting 1.5 to 2 cm from the diagonal conjugate, which is determined by measuring the distance from the lower margin of the symphysis to the sacral promontory
DCJ = 14cm – 1.5 = 12.5
14cm – 2.0 =
12.0
OCj = 12.0-12.5
2.
Diagonal conjugate
a. Used as a surrogate
measure for above (obstetric conjugate)
b. Distance between the lower
border of the pubis and sacral promontory (at the level of ischial spines)
c. Must be > 11.5 cm to
accommodate the fetal head
3 DIAMETERS IN PELVIC INLET
1. anteroposterior diameter is the shortest distance between the promontory of the sacrum and the symphysis pubis and is designated the obstetrical
conjugate
2. The transverse diameter is constructed
at right angles to the obstetrical conjugate and represents the greatest
distance between the linea terminalis on either side
a. It usually intersects
the obstetrical conjugate at a point approximately 4 cm in front of the
promontory.
3. Two oblique diameters extend from one of the sacroiliac synchondroses to the iliopectineal eminence on the opposite side. They average less than 13 cm.
B.
Midpelvis
1. Interspinous diameter: the distance between
ischial spines
2. Should be > 10 cm
C.
Pelvic
outlet
1. Transverse diameter (distance between 2 ischial tuberosities): > 11 cm
2. Anteroposterior (pubic arch to the tip of the sacrum) 9.5-11 cm
