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Human external fixator, use of pelvic angiography,

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Human
pelvis is a very stable structure. It achieves its stability from the surrounding
musculature and ligaments. Hence, pelvic disruption requires high-energy trauma
specifically in young people. It is usually associated with multisystem
injuries due to its close proximity to the vital structures. Mortality in
pelvic injuries is mostly due to the uncontrolled haemorrhage and the late
mortality due to associated multisystem injuries, multiorgan failure, and
sepsis.1

          Pelvic fractures represent approximately 3 –
8% of skeletal injuries with mortality ranges from 5% to 16% while open pelvic
fractures, which comprise 2 – 4% of all pelvic fractures, are associated with high
mortality rates.2, 3 Life threatening haemodynamic
instability occurs in 1 – 4% of all cases of pelvic fractures.4

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          Acute management of the complex
pelvic trauma includes the systemic control of haemorrhage, pelvic
stabilization with external pelvic binder or external fixator, use of pelvic
angiography, and embolization and preperitoneal packing.5

          The complexity of pelvic trauma and
high mortality rates lead to the evolution of multidisciplinary clinical
pathways to deal with the challenge, incorporating the resources of trauma
centres to improve patient’s survival.6 The evolution of such clinical pathways
lead to drop in overall mortality rates and reduced incidence of complications.7

Relevant Anatomy

Osseous Anatomy (Fig; 1.1-1.2)

          The pelvis is the osseous structure that
transfers the weight of the upper axial skeletal structures to the lower
extremity via the hip joint. The pelvic ring is comprised of the sacrum and
three bones on each side that coalesce during adolescence to form the innominate
bone of the adult pelvis. The sacrum connects to the ilium via an irregular
joint, the iliosacral joint, which is technically an apophyseal joint. The
ilium becomes the pubis anteriorly and the ischium inferiorly. Anteriorly, the
two pubic bones connect to one another via the symphysis and thus close the
ring.1 (Fig; 1.1)

(Fig; 1.1) Left
hip bone, outer aspect.8

          The
external iliac fossa is marked with two semicircular lines dividing it into
three zones: posterior (gluteus maximus), middle (gluteus medius), and anterior
(gluteus minimus). The mechanics of bone and load transfer predicate that there
is a strong buttress of bone emanating from the iliosacral joint towards the
acetabulum. This structure is termed the sciatic buttress. (Fig; 1.2)

 

(Fig; 1.2) Left
hip bone, inner aspect.8

 

          

Joints and
ligaments

PUBIC SYMPHYSIS

          The
pubic bones meet in the midline at the pubic symphysis, a secondary cartilaginous
joint. The articulating surfaces are the medial (symphysial) surfaces of the
pubic bones, each covered by a thin layer of tightly adherent hyaline cartilage.
The junction is not ?at but marked by reciprocal crests and papillae. Theoretically,
this would resist shearing. The interpubic disc is strengthened anteriorly by
several interlacing collagenous ?brous layers, passing obliquely from bone to
bone, decussating with ?bres of the external oblique aponeuroses and the medial
tendons of the recti abdominis. These layers constitute the anterior pubic
ligament. There are less well-developed posterior ?bres, sometimes named the
posterior pubic ligament. The main ligaments of the joint are the superior and
arcuate pubic ligaments.8

 

SACROILIAC JOINT8

          The sacroiliac joint is a synovial
articulation between the sacral and iliac auricular surfaces. The ligaments of the sacroiliac joint are the
anterior, interosseous and posterior sacroiliac, iliolumbar, sacrotuberous and
sacrospinus ligaments.

          Anterior sacroiliac ligament:  an anteroinferior capsular thickening,
particularly well- developed near the arcuate line and the posterior inferior
iliac spine, where it connects the third sacral segment to the lateral side of
the preauricular sulcus. It is thin elsewhere.

          Interosseous sacroiliac ligament:  The interosseous sacroiliac ligament is the
major bond between the bones, ?lling the irregular space postero- superior to
the joint.

          The posterior sacroiliac ligament: It consists of
several weak fasciculi connecting the intermediate and lateral sacral crests to
the posterior superior iliac spine and posterior end of the internal lip of the
iliac crest.

          Iliolumbar ligament:  It is attached to the
tip and anteroinferior aspect of the ?fth lumbar transverse process, and sometimes
has a weak attachment to the fourth transverse process. It radiates laterally
and is attached to the pelvis by two main bands. A lower band passes from the
inferior aspect of the ?fth lumbar transverse process and the body of the ?fth
lumbar vertebra across the anterior sacroiliac ligament to reach the posterior
margin of the iliac fossa. An upper band, part of the attachment of quadratus
lumborum, passes to the iliac crest anterior to the sacroiliac joint, and is continuous
above with the anterior layer of the thoracolumbar fascia.

          Sacrotuberous ligament: It is attached
by its broad base to the posterior superior iliac spine, the posterior
sacroiliac ligaments (with which it is partly blended), to the lower transverse
sacral tubercles and the lateral margins of the lower sacrum and upper coccyx.

          Sacrospinous ligament: It extends from
the ischial spine to the lateral margins of the sacrum and coccyx anterior to
the sacrotuberous ligament, with which it blends in part.8(Fig; 1.3)

 

(Fig; 1.3) Joints and ligaments of the pelvis:
anterior aspect. Arrows indicating vascular and muscular spaces.8

Sciatic foramina

          The
sacrotuberous and sacrospinous ligaments convert the sciatic notches into
foramina.

          Greater
sciatic foramen: It is partly ?lled by the emerging piriformis, above
which the superior gluteal vessels and nerve leave the pelvis. Below it, the
inferior gluteal vessels and nerve, internal pudendal vessels and pudendal
nerve, sciatic and posterior femoral cutaneous nerves and the nerves to
obturator internus and quadratus femoris all leave the pelvis.

          Lesser
sciatic foramen: It transmits the tendon of obturator internus,
gemmelli, the nerve to obturator internus, and the internal pudendal vessels
and pudendal nerve.8

 

VASCULAR ANATOMY

          In
the lower peritoneal region, the aorta bifurcates into the common iliac
arteries, with a central ramus that extends in front of the sacrum and becomes
the median sacral artery. The common iliac artery is rather short, beginning at
around L4 and divides at around the L5–S1 junction into the external and
internal arteries. The internal iliac artery branches to form the superior and
inferior gluteal vessels, the obturator, the pudendal, and the coccygeal, as
well as the sacral and vesicular vessels. The internal pudendal artery goes out
from the pelvis underneath the piriformis and re-enters the pelvis through the
minor sciatic notch and terminates as the dorsal artery of penis and clitoris
and cavernous artery.

          The
external iliac branches just proximal to the inguinal ligament into the femoral
artery. The femoral artery has three rami: urethral inferior, epigastric, and
iliac circum?ex. The epigastric travels deep and then anastamoses with
obturator vessels. When this connection is anomalously large, it is called the
corona mortis, or crown of death.1 (Fig; 1.4)

          The posterior venous plexus is a
large collection of veins that join to drain into the internal iliac veins.
Injury to the plexus accounts for most of the bleeding in many pelvic
fractures.9

 

 

(Fig; 1.4) Arteries of the male pelvis.8

NEUROLOGIC
ANATOMY

          The
sacral plexus is made by the union of the lumbosacral trunk (L5 anterior ramus
with an L4 anasamotic ramus) and the anterior rami of the ?rst four sacral
roots. The plexus will ultimately become the major element of the sciatic nerve
(posterior tibial and peroneal). The posterior branches relevant to orthopedic
surgery are the superior gluteal nerve, branches to the external rotators, and
inferior gluteal nerve. As the sciatic nerve exits the greater sciatic notch, it
courses in front of the piriformis nearly 85% of the time (the other variants
include penetration and splitting around the muscle), and then courses behind
the obturator internus, under the gluteal sling to enter the thigh.1

Relevant
Biomechanics

Biomechanics and
Pelvic Stability

          Biomechanical
studies demonstrated that the anterior structures of the pelvis contribute up
to 40% of pelvic stiffness and stability.5 They act as a
strut to prevent anterior collapse of the pelvic ring during weight bearing.
However, their absence has little effect on pelvic stability.10

          Pelvic stability depends on an intact
posterior sacroiliac complex. Its biomechanical structure enables it to
withstand the transference of the weight-bearing forces from the spine to the
lower extremities. The anterior sacroiliac ligaments are flat and
strong, to resist external rotation and shearing forces. The posterior ligamentous
structures form the major tension band effect of the pelvic ring. The
posterior sacroiliac ligamentous complex prevents posterior displacements of
the pelvic ring on the sacrum while the caudally positioned sacrospinous and
sacrotuberous ligaments as well as the pelvic floor augment
stability. Any major degree of vertical instability in the pelvic ring is
associated with disruption of these ligaments and the pelvic floor.5, 10

          Sectioning
studies by Pennal in 1961 showed that cutting the pubic symphyseal ligaments
alone resulted in a diastasis of up to 2.5 cm (Fig; 1.5A). Further pelvic
opening appeared to be prevented by the anterior sacroiliac ligaments, along
with the sacrospinous ligaments. Sectioning of the anterior SI ligaments and
the sacrospinous ligaments allowed the pelvis to completely open, until the posterior superior spines (PSISs) abutted the pelvis. However, even in this situation of complete
rotational instability, the pelvis remained stable to vertical loads, due to
the integrity of the posterior SI ligamentous complex (Fig; 1.5B). Subsequent
to sectioning of the posterior structures, the entire hemi pelvis was noted to
be unstable.5, 10, 11(Fig; 1.5C)

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