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Pelvic bones
1. Pelvic Bones and Joints
Themba Hospital FCOG(SA) Part 1 Tutorials
By Dr N.E Manana
2. General description of the Pelvis
• The pelvis and the perineum are interrelated regions associated with
the pelvic bones and parts of the vertebral column
• The pelvis is divided into 2 regions
• False pelvis/Greater pelvis: considered part of the abdomen
• True pelvis/Lesser pelvis: has inlet and outlet
• The pelvic cavity consist of inlet, walls and floor, and contains
elements of the urinary, gastrointestinal and reproductive systems
• The perineum is inferior to the floor of the pelvic cavity, its
boundaries form the pelvic outlet
3. Pelvic bones
• Bones of the pelvis consist of the right and left pelvic bone, the
sacrum and the coccyx
• The sacrum articulates with L5 superiorly at the lumbosacral joint
• The pelvic bones articulates posteriorly with the sacrum at the sacro-
iliac joints
• And with each other anteriorly at the pubic symphysis
5. Pelvic bone
• Its irregular in shape, Medial surface has two major parts separated by an
oblique line on its medial surface
• The Linea terminalis is the lower 2/3 of these line and contributes to the
margin of the pelvic inlet
• The lateral surface of the pelvic bone has a large articular socket
(Acetabulum) with together with the head of the femur forms the hip joint
• Inferior to the acetabulum is the large obturator foramen, mostly closed by
the obturator membrane, a small obturator foramen remains
• The posterior part has two notches separated by the ischial spine (Greater
and lesser sciatic notch). Posterior part terminates inferior as the Ischial
tuberosity
• The anterior margin is marked by the ASIP, AIIS and the pubic tubercle
7. Components of the Pelvic bone
• Formed by 3 elements:
• The ilium
• The pubis
• The ischium
• These bones are initially (at birth) connected by cartilage
• They fuse at between 16-18 years of age into a single bone
9. Ilium
• The most superior of the 3 components, it is separated into upper and
lower parts by the ridge on the medial surface
• Posteriorly the ridge lies immediately superior to the surface of the bone
that articulated with the sacrum
• The sacral surface has an L shaped facet and an expanded posterior
roughened area for ligament attachment
• Anterior the ridge is rounded and termed the arcuate line, which is part of
the linea terminalis
11. Ilium
• The upper part of the ilium expands to form a flat-fan shaped “wing” which
provides bony support to the lower abdomen
• It also provides attachment for muscle associated with the lower limb
• The anterior medial surface of the wing is concave and forms the iliac fossa
• The superior part of the wing is thickened forming an iliac crest, terminates
anteriorly as the ASIS and posteriorly as the PSIS, it’s a site of attachment
for muscle and fascia of the abdomen, back and lower limb
• Less prominent AIIS which serves as attachment for rectus fermis muscle
an iliofemoral ligament, the PIIS forms the superior margin of the greater
sciatic notch
12. Pubis
• The anterior and inferior part of the pubic bone is the pubis
• It has a body and two arms (rami), the body is flattened dorsoventrally and
articulates with the body of the pubic bone on the other side at the pubic
symphysis
• The superior surface is rounded and end laterally as the pubic tubercle
• Superior pubic ramus projects posterolateral and joins the ilium and
ischium at its base
• The sharp superior margin is termed the pectineal line (part of the linea
terminalis)
• The inferior rami projects laterally and inferiorly to join with the ramus of
the ischium
13. Ischium
• The posterior and inferior part of the pelvic bone
• Its has a large body that projects superiorly to join the ilium and the
superior ramus of the pubis
• And a ramus that projects anteriorly to join with the inferior ramus of
the pubis
• Posterior margin marked by the ischial spine
• On the posteroinferior aspect is the ischial tuberosity
• This tuberosity is an important site of attachment of lower limb
muscles and supports the body when seating
14. Sacrum
• Has the appearance of an inverted triangle, it is formed by fusion of 5 sacral
vertebrae
• The base of the sacrum articulates with the lumber vertebra and its apex with the
coccyx
• It has an L shaped facet on its lateral side that articulates with the ilium
• Posterior to the facet is a large roughened area for ligament attachment to
support the sacro-iliac joint
• Superiorly its is flat (body of S1) with a flat wing like lateral projection termed the
Ala
• The anterior edge projects forward as the promontory, with an anterior surface
that is concave and convex posterior surface
• Due to the fusion of the transverse processes into posterior and anterior foramen
• The sacral canal terminates at the sacral hiatus
16. Coccyx
• It is the small terminal part of the vertebral column, consists of 4
fused vertebrae
• Has the shape of an inverted triangle, with its base directed
superiorly
• It has a facet that articulates with the sacrum and two horns or
cornua, with project upwards to articulate with similar projections
from the sacrum
• Each lateral surface has a rudimentary transverse process
• No bony vertebral canal is present
17. Joints
Lumbosacral joint (LSJ)
• The LS joints are formed between vertebra L5 and the sacrum, it
consist of :
• 2 zygapophysial joints: which occur between adjacent inferior and
superior articular processes and
• An intervertebral disc that joins the bodies of L5 and S1
• The are similar to those of the other vertebrae except that the sacrum
is angled posteriorly, as a result the anterior part of the disc is thicker
than the posterior part
• The LSJ is reinforced by strong iliolumbar and lumbosacral ligaments
19. Joints
Sacro-iliac Joints (SIJ) transmit forces from the lower limbs to the vertebral
column
• They are synovial on the lateral surface of the sacrum and on the iliac parts
of the pelvic bones
• The joint surface has irregular contour and interlock to resist movement
• The joint becomes fibrous with age and may ossify
• Each joint is stabilised by three ligaments:
• 1. The Anterior SI ligament (Thinking of the fibrous membrane of the joint
capsule, runs anteriorly and inferiorly)
• 2. Interosseous SI ligament (Largest and strongest, posterosuperior to the
joint, attaches to the roughened areas of the sacrum and ilium)
• 3. Posterior SI ligament (Covers the interosseous SI ligament posteriorly)
21. Joints
Pubic symphysis joint (PSJ)
• Lies anterior between the adjacent surfaces of the pubic bone
• Each of the surfaces is covered by hyaline cartilage and is linked
across by fibrocartilage
• The joint is surrounded by interwoven collagen layers, and two major
ligaments:
1. Superior pubic ligament
2. Inferior pubic ligament
25. Pelvic wall
• Consists of the sacrum, coccyx, the pelvic bones inferior to the linea
terminalis, 2 Ligaments, 2 Muscles and 3 Apertures
Ligaments (Stabilise the sacrum on the pelvic bone)
1. Sacrospinous ligaments (SSL): Its smaller and triangular in shape, apex
attached to the ischial spine and its base to the sacrum and coccyx
2. Sacrotuberous ligaments (STL): Triangular, superficial to the SSL, it has a
broad base that extends from the PSIS and sacrum into the coccyx surface
• Laterally, the apex of the ligament is attached to the medial margin of the
ischial tuberosity
27. Pelvic wall
Muscles
1. Obturator internus (OI): Is a flat, fan-shaped, originates from the deep
surface of the obturator membrane and the pelvic bone assoc with the
obturator foramen
• The muscle fibers converge to form a tendon that leaves the pelvic cavity
via the lesser sciatic foramen, making a 90 degree turn around the ischium
to insert on the greater trochanter of the femur
2. Puriformis (PF): Is triangular, originating in the bridges of bone btn the 4
anterior sacral foramen, crosses the hip posteriorly to insert on the greater
trochanter of the femur, above the OI insertion
• Forms a large part of the posterolateral pelvic cavity wall, separates the
greater sciatic foramen into two regions
Pelvic inlet
Circular opening between the abdomen and the pelvic cavity
Promontory forms the posterior margin in the midline
On either side of the promontory the margin is formed by the Alae of the sacrum
Then sacro-iliac joint, the linea terminalis, to the pubic symphysis