fractures of the pelvis and acetabulum by marvin tile

3

Marvin Tile, James F Kellam

1 Introduction

This chapter describes the important surgical anatomy nec-essary to understand injuries to the pelvic ring and their treatment, especially operative treatment. A more detailed account of pelvic anatomy is best found in anatomy texts [1].

The pelvis is a ring structure made up of three bones: the sacrum and the two innominate bones. In turn, the in-nominate bones are formed by the fusion of the three sep-arate ossification centers from the ilium, the ischium, and the pubis. They meet at the triradiate cartilage, which fuses by the age of 16 years. The three bone components of the pelvis have no inherent stability; if all soft tissues were re-moved from the pelvis, then it would fall apart (Fig 1.1-1). Yet, in vivo it is able to withstand major forces; therefore, the soft tissues must confer stability to the pelvic girdle while the bone provides structure. Stability and structure to allow weight transference are the essential anatomical features of the pelvis.

2 Structural stability

The pelvic ring is formed by the connection of the sacrum to the innominate bones at the sacroiliac joints and the symphysis pubis. Because the major weight-bearing forces are transmitted from the hip joint through the iliac bone, across the sacroiliac joint into the sacrum and up the spine, it must be assumed that the major stabilizing structures are posterior (Fig 1.1-2). The anterior joint (the symphysis pubis) acts like a strut, preventing collapse of the pelvis, rather than a major weight-bearing, stabilizing structure. Absence of this anterior strut, as in patients with congenital bladder exstrophy (Fig 1.1-3) or trauma victims (Fig 1.1-4), only min-imally affects this weight-bearing function. Many mammals possess a posterior bone strut to provide posterior stability (Fig 1.1-5). In humans this function is accomplished by the strong posterior sacroiliac, sacrospinous, and sacrotuberous ligaments.

2.1 Posterior pelvic stability

2.1.1 Sacroiliac joints The adjacent iliac and sacral surfaces of the sacroiliac joint are divided into two parts: a lower one, the articular sur-faces, and an upper one, the tuberosities (Fig 1.1-6). The articular surface of the sacrum is covered with hyaline car-tilage, and the adjacent surface of the ilium is covered with fibrocartilage; however, the articulation is not truly a syno-vial joint. Embryonically, the sacroiliac joints develop not as other synovial joints do, as clefts in a continuous rod of condensed mesenchyme, but by the direct contact of the ilium and sacrum posteriorly. In the upright position the body weight pushes the sacrum down between the wings of the ilium causing approximately 5° of dorsoventral rotation as the innominate bones move backward and the anterior pubic rami swing upward [2]. This motion is markedly re-stricted by the posterior ligamentous complex, the strongest being the interosseous ligaments [3].

1.1 Anatomy of the pelvic ring MarvinTile,JamesFKellam

Innominate bone Innominate bone

Sacrum

Fig 1.1-1 Anatomy of the pelvis.

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Section 1 Principles of the treatment of pelvic ring injuries

1.1 Anatomy of the pelvic ring

4 Fractures of the Pelvis and Acetabulum—Principles and Methods of Management Marvin Tile, David L Helfet, James F Kellam, Mark Vrahas

Anterior longitudinal ligament

Anterior sacroiliac ligaments

Iliolumbar ligament

Sacrotuberous ligament

Sacrospinous ligament

Inguinal ligament

Fig 1.1-2a–b The major posterior stabilizing structures are ligaments.a Ligaments from anterior aspect of pelvis.b Ligaments from posterior aspect of pelvis.

Fig 1.1-3 X-ray of a 39-year-old woman with congenital bladder ex-strophy. Note the total lack of anterior stability because of excessive widening of the symphysis pubis. Despite this, the sacroiliac joints have remained intact and show no evidence of instability.

Fig 1.1-4 AP x-ray of the pelvis of a 21-year-old woman who had previously lost a portion of the superoinferior pubic rami in an open fracture of the pelvic ring at 12 years old. The superior ramus fracture entered the right acetabulum. No posterior instability is noted despite the pelvic ring gap. The patient has no symptoms referable to the sacroiliac joints or the gap anteriorly. She was seen for an unrelated medical condition.

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AOT_PELVAC_1_1_2b_R02

Iliolumbar ligament

Dorsal sacroiliac ligament


Posterior sacroiliac ligament

Superficial dorsalsacrococcygeal ligament


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Fig 1.1-5 The skeleton of an elephant shows the symphysis ischium, a solid bone strut posteriorly.

Iliopectinealeminence

Anterior superioriliac spine

Anterior inferioriliac spine

Superior ramusof pubis

Inferior ramus of pubis

Body of pubis

Body of ischium

Iliac fossa

Articular surface

Posterior superior spine

Posterior inferior spine

Greater sciatic notch

Iliac tuberosity

Iliac crest

Lesser sciatic notch

Ischial tuberosity

Superior articular process

Corona of sacrum and coccyx

BodySacral crest

Articular surface

Transverse process of coccyx

Tip of coccyx

Tuberosity

Fig 1.1-6a–b The adjacent surfaces of the sacroiliac joint, indicating the area of hyaline cartilage on the articular surface and fibrocartilage over the iliac and tuberosity.

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2.1.4 Anterior sacroiliac ligamentsAnterior sacroiliac ligaments are strong, flat bands, comprising transverse and oblique fibers that pass from the anterior surface of the sacrum to the adjacent anterior surface of the ilium (Fig 1.1-9).

2.1.5 Sacrotuberous ligament The sacrotuberous ligament is an extremely strong, broad band extending from the lateral portion of the entire dorsum of the sacrum and the posterior surfaces of the posterior superior and inferior iliac spines to the ischial tuberosity. In some areas it covers, and in others it is contiguous with, the sacrospinous ligaments. The medial border extends as a falciform border to the ischial tuberosity, where it is con-tinuous with the obturator fascia. Laterally, at its superior origin, it gives attachment to the gluteus maximus. The sacrotuberous ligament forms a portion of the pelvic outlet (Fig 1.1-10, Fig 1.1-11).

2.1.2 Interosseous sacroiliac ligamentsThe interosseous sacroiliac ligaments, the strongest in the body, unite the tuberosities of the ilium and sacrum, and confer stability on the posterior sacroiliac complex (Fig 1.1-7).

2.1.3 Posterior sacroiliac ligamentsTwo distinct bands are described: • The short posterior sacroiliac ligament consists of a number

of fibers that pass obliquely from the tubercle or ridge of the sacrum to the posterior superior and posteroinferior spine of the ilium.

• The long posterior sacroiliac ligament comprises longi-tudinal fibers that run from the posterior superior iliac spine to the lateral portion of the sacrum, intermingling with the origin of the sacrotuberous ligament, and covering the short ligament (Fig 1.1-8).

Interosseous sacroiliac ligaments

Posterior superioriliac spine

Fig 1.1-7 Cross-section through the sacroiliac joints shows the direction of the interosseous sacroiliac ligaments.

Dorsal sacroiliac ligament

Posterior sacroiliac ligament

Interosseoussacroiliac ligament

Fig 1.1-8 The posterior sacroiliac ligaments are much stronger and hold the posterior ilium and sacrum together.

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Fig 1.1-9 The anterior sacroiliac ligament is a broad, thin structure crossing the anterior aspect of the joint.

Iliolumbar ligament


Sacrotuberousligament

Posterior sacroiliacligament




Fig 1.1-10a–b a Sacrospinous/sacrotuberous exterior ligaments.b Sacrospinous/sacrotuberous intrapelvic ligaments.

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Superior pubic ligament

Symphysis

Inferior pubic (arcuate) ligament

Fig 1.1-11 Symphysis.

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3 Interior of pelvis

Because visceral injury is so commonly associated with dis-ruption of the pelvic girdle, a description of the proximity of these structures to the skeleton is in order. Pelvis is Latin for basin. The basin is divided into two sections by the pelvic brim: the true pelvis (below) and the false (above). The pelvic brim consists of the promontory of the sacrum, iliopectineal line, pubic crest, and upper portion of the sym-physis pubis. The posterior portion of the pelvic brim is extremely thick in keeping with its weight-bearing function. No muscle crosses the pelvic brim.

3.1 False pelvisThe false pelvis is formed by the ala of the sacrum and the iliac fossa—the fan-shaped inner surface of the ilium covered entirely by the iliacus muscle (Fig 1.1-12).

3.2 True pelvisThe true pelvis is the deep basin below the pelvic brim (Fig 1.1-12). The lateral wall comprises the pubis and ischium, with a small triangular portion of the ilium—the weight-bearing portion. The obturator foramen separating the pubis from the ischium is covered by a membrane, deficient only on top to allow the obturator vessels and nerve to escape from the pelvis. At this point they are vulnerable and may be torn in pelvic trauma or surgical approach (Fig 1.1-13). The obturator internus muscle and fascia, which leave the pelvis through the lesser sciatic foramen, originate from the obturator membrane and cover the lateral wall of the true pelvis (Fig 1.1-14).

The piriformis arises from the lateral mass and anterior portion of the sacrum, leaving the pelvis through the greater sciatic notch. It is the key to the position of the sciatic nerve. In most people, the entire nerve leaves the pelvis below this muscle; although in some the peroneal division either pierces it or, rarely, escapes above it (Fig 1.1-14).

3.2.1 Pelvic diaphragmThe levator ani and the coccygeus form the floor or diaphragm of the true pelvis supporting the pelvic organs and separating them from the perineum. This diaphragm comprises voluntary muscle and is perforated by the urethra, rectum, and vagina (Fig 1.1-15).

2.1.6 Sacrospinous ligamentThe sacrospinous ligament is a strong triangular sheet aris-ing from the lateral margin of the sacrum and the coccyx, deep to the sacrotuberous ligament, and passing to the ischial spine. It divides the ischial area into the greater sciatic notch and the lesser sciatic foramen. Its pelvic surface covers and is adherent to the coccygeus muscle (Fig 1.1-10).

2.1.7 Iliolumbar ligamentsThe pelvis is secured to the axial skeleton at the lumbosacral articulation by the strong L5/S1 intervertebral disc and two ligaments. The iliolumbar ligament is the markedly thickened portion of the fascia covering the quadratus lumborum. Bilaterally, this strong ligament attaches the tip of the fifth lumbar transverse process to the iliac crest. Lying just below the level of the apex of the iliac crest, these transverse pro-cesses are usually large, somewhat conical, and tilt upward.

2.1.8 Lateral lumbosacral ligamentThe lateral lumbosacral ligament spreads downward from the L5 transverse process to the ala of the sacrum. Its sharp medial edge may abut the anterior ramus of the fifth lumbar root.

2.1.9 Posterior tension bandAll the posterior ligaments collectively form the posterior tension band of the pelvis, binding together the skeletal elements to resist deforming forces. The transversely placed ligaments, short posterior sacroiliac, anterior sacroiliac, iliolumbar, and sacrospinous resist transverse rotational forces, whereas those that are vertically placed resist longi-tudinal shearing forces. These ligaments must act together to assure a stable posterior pelvis [3].

2.2 Anterior pelvic stability

2.2.1 Symphysis pubisThe opposed bone surfaces of the symphysis pubis are covered by hyaline cartilage and are united by layers of fibrocartilage and fibrous tissue. In the fibrocartilage, a cleft frequently appears, often as part of the aging process. Su-periorly and anteriorly, dense ligamentous fibers blend with the fibrocartilage; inferiorly, the symphysis is reinforced by a more independent structure, the inferior pubic or arcuate ligament (Fig 1.1-11).

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True pelvis

Lumbosacralnerve plexus

Obturator nerve

Fig 1.1-13a–ba This view shows the true pelvis and the relationship of the lumbosacral plexus and obturator nerve. The pudendal nerve can be seen

superior to the ischial spine.b The obturator fascia covers the obturator internus and has a small aperture in its superior corner where the obturator nerve exits the

pelvis. The pudendal nerve can be seen traversing posterior to the coccygeus and sacrospinous ligament and entering the true pelvis through the lesser sciatic notch.

ba

Iliopectineal line

Obturator nerve

Coccygeus muscle

Bare pubic bone

Deep perineal pouchPudendal canal

Obturator fascia

Falciform edge ofsacrotuberous ligament

Obturator internus muscle

Pudendal nerve

False pelvis

True pelvis

Pelvic brim

Fig 1.1-12a–b a The false pelvis (above the pelvic brim) and the pelvic brim and true pelvis below in orange.b The true pelvis (orange shading) below the pelvic brim.

False pelvis

True pelvis

Pelvic brim

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Fig 1.1-14 This posterior view of the pelvis demonstrating the relationship of the sciatic nerve to the piriformis muscle and external hip rotators (the gemelli and internal obturator muscle). Also, the course of the internal obturator from its origin inside the true pelvis to the insertion on the greater trochanter is seen.

Piriformis muscle

Superior gemellus muscle

Internal obturator muscle

Sacrotuberous ligamentInferior gemellus muscle

Sciatic nerve

Acetabulum

Iliococcygeus muscle

Pubococcygeus muscle

Rectum

Coccygeus muscle

AIISASIS

External anal sphincter

Transverseperineal muscle

Fig 1.1-15a−ba The pelvic floor from the true pelvis. b Views of the pelvic floor from below.

a

b

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and inferior gluteal nerves. The branches of the sacral plexus may be grouped as follows: • Branches from the roots of the plexus: rami from the

roots of the plexus include muscular branches to the piriformis, levator ani, and coccygeus and the pelvic splanchnic nerve.

• Branches that pass through the greater sciatic notch: the sciatic nerve forms the largest branch of the sacral plexus. It leaves the pelvis between the lower border of the pir-iformis and the ischial border of the greater sciatic notch. Its two divisions, the tibial and perineal, are loosely held together. This nerve is commonly injured in pelvic trauma, especially in posterior dislocation of the hip with or with-out an acetabular fracture. The perineal division is most prone to injury in this location, and the least likely to recover.

Because the major supply of the peroneal division of the sciatic nerve is the L5 root, it may be difficult to determine clinically whether the injury is to the nerve as it passes through the greater sciatic notch behind the hip joint or to the root.

The pudendal nerve (S2−4) escapes between the piriformis and coccygeus just medial to the sciatic nerve. The collat-eral nerves arising from the plexus include the superior gluteal, inferior gluteal, the nerve to the obturator internus (L5, S1, S2), the nerve to the quadratus femoris (L4, L5), and the posterior cutaneous nerve of the thigh (S1, S2, S3). The superior gluteal nerve (L4, L5, S1) and its artery and vein escape from the pelvis by winding around the greater sciatic notch. Injury to the nerve is uncommon, although the artery may be injured by trauma. This nerve is in jeop-ardy in posterior approaches to the hip joint for acetabular fractures because application along the posterior plate may require excessive retraction, and resultant stretching of the nerve. The inferior gluteal nerve (L5, S1, S2) escapes from the pelvis beneath the piriformis and behind the sciatic nerve to supply the gluteus maximus.

Three branches that emulate the coccygeal plexus terminal branches are the perforating cutaneous branch of S2 and S3, and the perineal branch of S4. These descend anterior to the coccygeus, where they become cutaneous and supply the skin of the buttock and perineum.

3.3.3 Anterior coccygeal plexusThe anterior coccygeal plexus is formed by the anterior rami of S5 and C1, ending in the anterior caudal nerve, a sensory nerve supplying the coccygeal area.

3.3 Structures at risk

3.3.1 Lumbosacral and coccygeal nerve plexusThe lumbosacral and coccygeal nerve plexuses are derived from the anterior rami of the T12–S4 spinal nerves. The L4–S1 segments are of surgical significance. Injury to all these segments has been reported, including occasional in-jury to the femoral nerve. The pelvic splanchnic nerves—the nervi erigentes—arise from the anterior rami of S2, S3, and S4. These nerves are responsible for bladder and sexual func-tion, particularly in men (see also Fig 1.1-16).

3.3.2 Lumbosacral plexus The lumbosacral plexus is formed by a branch of the L4 root crossing the L5 transverse process and the L5 root which crosses and grooves the ala of the sacrum where it joins with L4 to form the lumbosacral trunk. The upper four anterior sacral rami leave the sacral foramina, grooving the lateral mass of the sacrum. The lumbosacral trunk and the first sacral root unite anterior to the sacroiliac joint, and they in turn unite with S2, S3, and S4 anterior to the piriformis, ending in two terminal branches, the sciatic and pudendal nerves, and many collateral branches, including the superior

L5

S1

S2

S3

S4

S5

L4

L3

L2

L1

Lumbar plexus

Sacral plexus

Coccygeus plexus

Fig 1.1-16 The development of the lumbosacral plexus is seen as the L4 and L5 roots merge with the sacroillac joint at the sacral ala and then with S2 and S3 anterior to the sacroillac joint.

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obturator nerve during its course. The ureter lies anteriorly, and its vein posteriorly. Severe trauma to the pelvis may disrupt the internal iliac artery or even the common iliac artery; survival is unlikely in those cases. Usually, the su-perior gluteal, iliolumbar, and lateral sacral arteries arise from the posterior division; all others, including the obturator artery, arise from the anterior division.

Posterior division: Because of their location on the skeletal plane and because severe trauma to the pelvic ring usually causes posterior displacement, vessels in the posterior division are most prone to damage. The superior gluteal artery is the largest branch of the internal iliac artery. It courses across the sacroiliac joint to the greater sciatic notch, where it lies against the ilium, making a U-turn around the notch into the gluteal region, accompanied by its nerve and vein (Fig 1.1-16, Fig 1.1-17). Damage to this large artery is a common cause of massive hemorrhage in pelvic disruption because its course on the ilium crosses the common area of pelvic trauma. Also, traumatic aneurysm of the artery has been reported. The illiolumbar artery is the somatic artery of the fifth lumbar segment; therefore, it must ascend to that level. As it crosses the ala of the sacrum, it too is com-monly injured. The lateral sacral artery descends lateral to the anterior sacral foramina and in front of the sacral plexus.

3.3.4 Blood vesselsMassive hemorrhage is the major complication of a pelvic disruption. Precise knowledge of the anatomy of the pelvic vasculature is essential because embolization of the bleeding vessel has emerged as one of the treatment options. The arteries of the pelvis are the median sacral, superior rectal, and internal iliac—the last being the most surgically sig-nificant (Fig 1.1-17).

3.3.5 Median sacral arteryThe median sacral artery is the continuation of the aorta; therefore, it hugs the vertebral column and may be injured in a sacral disruption. However, it is a small vessel and there-fore not of major surgical significance.

3.3.6 Superior rectal (hemorrhoidal) arteryThe superior rectal artery—the continuation of the superior mesenteric—is rarely involved in pelvic trauma.

3.3.7 Internal iliac arteryThe internal iliac is the vessel of major importance in pelvic trauma. It arises from the common iliac artery in the false pelvis and extends to the pelvic brim, where it splits into anterior and posterior divisions (see Fig 1.1-17a). It crosses medial to the external iliac vein, the psoas muscle, and the

Aorta

Superior gluteal arteryExternal iliac artery

Common iliac artery

Internal iliac artery

Obturator artery

Fig 1.1-17a−ba Arteries of the pelvis.b Veins of the pelvis.

ba

Common iliac vein

Inferior vena carva

Internal iliac vein

External iliac vein

Obturator vein

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systems is not in order; however, genitourinary injuries are so common and so potentially devastating that some descrip-tion is needed. The female perineum (Fig 1.1-18) consists of the pelvic diaphragm with the urethra (Fig 1.1-18b), vagina, and rectum. These structures are relatively pliable and are not commonly injured. However, the vagina may be perfo-rated by bone spicules from pubic rami fractures in particular when the injury is due to a lateral compression force.

Controversy has arisen over the conventional anatomical description of the male urethra and newer anatomical and urological information. The urogenital diaphragm is de-picted in most texts as in Fig 1.1-19, as two separate fascial layers spanning the pubic arch with skeletal muscle between. Normally, the prostate is believed to sit on the superior layer of fascia but separate from the urogenital diaphragm, the only connection being the membranous urethra that perforates the diaphragm at its midpoint. Obviously, if the prostate is displaced or the urogenital diaphragm suddenly shifts, the membranous urethra ruptures at this natural plane between the apex of the prostate and the superior layer of the diaphragmatic fascia. Colapinto [4] offered a different explanation from clinical studies and found that most ure-thral ruptures were not of this “classic” variety but occurred below the urogenital diaphragm. These anatomical studies show that the junction between the prostate and urogenital diaphragm is not a natural weak spot but the prostate and urogenital diaphragm tend to be a single unit. The mem-branous urethra is strong in this region, surrounded by smooth muscle that extends into the prostatic urethra. The muscle ends abruptly at the inferior surface of the diaphragm where the bulbous urethra begins; thus, this is the truly weak area of the urethra, and the location of the rupture of the bulbous urethra confirms a clinical finding. Based on these studies, Colapinto [4] has classified urethral tears as described in Fig 1.1-20.

Anterior division: The visceral branches supply the blad-der, genitalia, and a portion of the rectum. They are: (1) the obliterated obturator artery, which clings to the peritoneum on the side wall of the pelvis above the level of the bladder and ends in the superior vesical arteries that supply the upper surface of the bladder; and (2) the inferior vesical and middle rectal arteries, which run in the retropubic leash of veins and supply the bladder and genitalia.

The limb and perineal branches include the internal pudendal artery and inferior gluteal artery, which descend anterior to the sacral plexus and pass between the borders of the piriformis and coccygeus into the gluteal region. The inferior gluteal artery passes between the first, second, or third sacral nerves and leaves the pelvis inferior to the piriformis to supply the gluteus maximus. The internal pu-dendal artery crosses the ischial spine and returns to the pelvis through the lesser sciatic foramen in the company of its own nerve. Both may be torn by trauma to this area. The obturator artery runs along the side wall of the pelvis to the obturator foramen, lying between its nerve and vein. As it leaves the pelvis through the superior defect in the obturator membrane, it may be disrupted in common injuries to the pubic rami.

3.3.8 Pelvic veinsThe pelvic viscera lie upon a massive thin-walled venous plexus through which the arteries thread their way. Most drain into the internal iliac vein but some drain into the superior rectal, then into the inferior mesenteric, and on to the portal vein (Fig 1.1-17b). Massive bleeding may occur from this venous plexus following pelvic trauma.

3.3.9 Perineum and genitourinary anatomy Because this chapter deals mainly with skeletal injury, a detailed description of the gastrointestinal and genitourinary

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Bulbospongiosus muscle

Ischiocavernosus muscle

Superficial transverse perineal muscle

Bulbospongiosus muscleUrethral opening

Vaginal openingDeep transverse perineal muscle

Ischiocavernosus muscle

Superficial transverse perineal muscle

Fig 1.1-18a−ba Female perineum.b Female urogenital diaphragm.

a

b

Prostatic urethra

Corpus spongiosum

Prostate

Fibers of internalurethral sphincter

Puboprostatic ligament

External urethral sphincter

Bulbospongiosus

BladderPubic symphysis

Corpus cavernosum

Posterior urethra

Anterior urethra

Membranous urethra

Bulbar urethraPenile urethraFossa navicularis

Glans penis

Fig 1.1-19 The male perineum.

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ProstrateUrethra

Urogenital diaphragm

Prostrate


Prostrate

Urethra


Prostrate


Fig 1.1-20a−d Colapinto's [4] classification of urethral tears. a Normal: prostate and urogenital diaphragm blend together as one unit. b Type I: clinical findings may suggest a complete rupture but in fact the urethra is intact although attenuated.c Type II: classic supradiaphragmatic injury.d Type III: supradiaphragmatic rupture. A complete rupture is shown but partial type III rupture also occurs. Type III injuries are common.

A retrograde urethrogram in these patients shows perineal extravasation.

a

c

b

d

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4 References

1. Grant JCB. An Atlas of Anatomy. 6th ed. Baltimore, MD: Williams & Wilkins. 1972.

2. Oonishi, H, Isha, H Hasegawa T. Mechanical analysis of the human pelvis and its application to the artificial hip joint by means of the three dimensional finite element method. J Biomech. 1983;16(6):427–444.

3. Vukicevic S, Marusic A, Stavljenic A, et al. Holographic analysis of the human pelvis. Spine. 1991 Feb;16(2):209–214.

4. Colapinto V. Trauma to the pelvis: urethral injury. Clin Orthop Relat Res. 1980;Sep;(151):46–55.

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fractures of the pelvis and acetabulum by marvin tile

Health & Medicine

posterior pelvic stability

posterior fig

posterior stability

posterior bone strut

sacroiliac joints

innominate bones

ring structure

pelvic ring marvin tile