The Pelvis

1

Imaging assessment

• Radiographic examination

  • AP

  • Oblique views

    • Internal oblique (obturator view)

    • External oblique (iliac view)

  • Inlet view

  • Outlet view

• Computed tomography (CT)

  • Axial

  • Reformatted images

  • Coronal

  • Sagittal

  • 3-D

  • Volume-rendered semitransparent three-dimensional images to simulate radiographic views

    • AP, inlet, outlet, iliac oblique, obturator oblique

    • Lateral view of high quality

      • Not possible to obtain radiographically

2

Anatomic features

• Pelvic ring

  • Composed of two innominate bones and the sacrum

    • Joined posteriorly by the two sacroiliac joints

    • Joined anteriorly by the symphysis pubis

  • Ring consists of two arches

    • The posterior or femorosacral arch extends from one acetabulum to the other.

      • (1)

        The main weight-bearing component of the pelvis

      • (2)

        The stronger of the two arches

    • The tie or anterior arch extends inferiorly and anteriorly from each acetabulum.

      • (1)

        The weaker arch

      • (2)

        Fractures more likely to occur in anterior arch

• Pelvic ligaments

  • Stability of pelvis is dependent on the integrity of strong ligaments.

    • Posterior and anterior sacroiliac ligaments

      • (1)

        Posterior sacroiliac ligaments are strongest ligaments in the body.

    • Sacrotuberous and sacrospinous ligaments

      • (1.)

        Extend from the sacrum to the ischial spine and tuberosity

    • Iliolumbar and iliosacral ligaments

      • (1.)

        Attach fifth lumbar transverse processes to ilium and sacrum

3

Stability of fractures variable

• Stable fractures

  • In general

    • Single fracture limited to either anterior or posterior arch

      • (1.)

        Most common in anterior arch

      • (2.)

        Isolated fxs of posterior arch are rare.

    • Principal pelvic ligaments remain intact.

  • Common stable fractures

    • Pubic rami

    • Body of pubis

    • Iliac – periphery of iliac wing (Duverney fracture)

    • Sacrum – transverse fracture below sciatic notch

    • Coccyx

• Unstable fractures

  • In general

    • Fractures involve both anterior and posterior arches.

    • One or more principal pelvic ligaments disrupted

  • Common types of unstable fractures

    • Ipsilateral displaced fractures of both anterior and posterior arches

    • Pelvic dislocation – disruption of pubic symphysis and SI joint or joints

      • Commonly referred to as an “open book” fracture

    • Unilateral fractures of pubic rami with sacral ala or iliac fracture opposite side of pelvis

      • Commonly referred to as a bucket handle or “diametric” fracture

    • Displaced fracture of medial portion of both pubic rami

      • Known as a “straddle” fracture

4

Specific sites of fracture-disruption in adults

• Pubic bones

  • Inferior ramus

  • Superior ramus

  • Body of pubis

• Iliac bone

  • Stable fracture – periphery of iliac wing (Duverney fracture)

  • Unstable fractures – iliac fracture extending into

    • SI joint

    • Sciatic notch

    • Acetabulum

• Sacrum

  • Stable – transverse fracture below sciatic notch

  • Unstable fractures

    • Sacral ala

    • Sagittal

    • U-shaped

5

Specific patterns of pelvic disruption in adults

• Mechanism of injury

  • Lateral compression – 65%

    • Unilateral sacral alae and bilateral pubic rami

  • Anterior compression – 15%

    • Disruption of symphysis pubis and sacroiliac joints

    • Also known as open book injury or sprung pelvis

  • Vertical shear – 10%

    • Double vertical ipsilateral fractures of pelvic ring

    • Also known as Malgaigne fx

  • Complex – ± 10%

    • Windswept

    • Not readily classified

    • Often include an acetabular component

      • Best classified as complex acetabular fractures

• Classification of pelvic fx

  • Tile Comprehensive

  • Young-Burgess

6

Specific patterns of acetabular fractures in adults

• Acetabular anatomy

  • Anterior and posterior columns of acetabulum

  • Posterior wall of acetabulum

  • Acetabular fossa, labrum, and notch

  • Sciatic buttress

• Judet-Letournel classification of acetabular fractures

• Common patterns of acetabular fracture

  • Transverse

  • T-shaped

  • Both column

  • Transverse with posterior wall

  • Isolated posterior wall

7

Common sites of fractures in the elderly

• Insufficiency fractures

  • Sacrum

  • Body of pubis

  • Pubic rami

  • Supraacetabular iliac

• “Fall, rule-out hip fracture” – look for hip fracture mimics in pelvis

  • Transverse acetabular fracture

  • Pubic rami fracture

  • Iliac wing – Duverney fracture

8

Common sites of fractures in children and adolescents

• Pubic rami

• Iliac wing

• Double arch fractures

• Epiphyseal separation of triradiate cartilage – acetabulum

• Apophyseal avulsion

  • Anterior inferior iliac spine– sartorius

  • Anterior inferior iliac spine – rectus femoris

  • Ischial tuberosity – hamstrings

  • Iliac crest – abdominal obliques

9

Injuries likely to be missed

• Pelvic rami buckle and “ring” fractures

• Posterior wall of acetabulum – undisplaced fracture

• Distortion or nondisplaced fractures of sacral foraminal lines, evidence of sacral ala fracture

• U-shaped fracture of sacrum

10

Where else to look when you see something obvious

11

Where to look when you see nothing at all

• If presented with AP radiograph of pelvis

  • Determine nature of injuring forces.

    • If sustained significant injury, CT examination is required.

  • Re-evaluate radiographic examination looking at the following for evidence of subtle fracture:

    • Sacral neural foraminal (arcuate) lines

    • Pubic rami – iliopectineal and ilioischial lines

    • Width of pubic symphysis and SI joints

    • Fracture transverse processes of L5 = unstable injury posterior arch

    • Are iliac crests level?

    • Posterior rim of acetabulum

    • Margins of obturator ring

  • If any question concerning above, obtain full CT examination of pelvis.

• If presented with CT examination

  • If sustained sacral plexus neurologic injury, obtain MRI.

  • If no visible fracture or dislocation but has significant pain or inability to bear weight

    • Obtain MRI to disclose occult fracture.

1

Imaging assessment

• Radiographic examination

  • AP

  • Oblique views

    • Internal oblique (obturator view)

    • External oblique (iliac view)

    • Inlet view

    • Outlet view

The initial radiograph of those suspected of a pelvic injury is an AP view of the pelvis ( Fig. 8-1 and Fig. 8-2 A ). If severely injured a CT examination (“pan-scan”) of the chest, abdomen, and pelvis follows.

If less severely injured an AP view alone or with additional internal oblique, also known as obturator oblique, and external oblique, also known as iliac oblique, views may be ordered. This 68-year-old man was injured in an MVC. Volume-rendered 3-D transparency images simulating radiographic views were obtained: AP, right internal oblique, and right external oblique ( Figs. 8-2 A , 8-2 B , and 8-2 C , respectively). Transverse right acetabular fracture is clearly shown.

• Computed tomography (CT)

  • Axial

  • Reformatted images

    • Coronal

    • Sagittal

    • 3-D

    • Volume-rendered semitransparent three-dimensional images to simulate radiographic views

      • • (1.)

          AP, inlet, outlet, iliac oblique, obturator oblique

        • (2.)

          Lateral view of high quality

        • Not possible to obtain radiographically

Computed tomography (CT) is now the primary modality to evaluate pelvic fractures. Unfortunately, there are no currently accepted guidelines for clinicians in the ordering of pelvic CT examinations such as the NEXUS and Canadian Rules for the cervical spine. There is a need for a similar set of rules for pelvic CT.

Technique

• Helical CT is performed without intravenous contrast to include entire pelvis and hip joints.

• Scan data are reformatted to 2 mm sections in the axial, sagittal, and coronal planes.

• Surface-rendered 3-D image of the pelvis to allow scrolling of images in both axial and sagittal rotation

• Volume-rendered semitransparent 3-D images using thin overlapping sections to create images that effectively simulate routine radiographic projections (AP, inlet, outlet, iliac and obturator obliques, lateral)

• In those with acetabular fractures, the ipsilateral femoral head and contralateral hemipelvis are removed by region of interest (ROI) subtraction to allow for visualization of the surface of acetabulum.

Thin section axial images are obtained through the entire pelvis, from just above the iliac crest to below the pubic rami. Superiorly the upper sacrum and normal sacroiliac SI joints are shown ( Fig. 8-3 A ). Note the normal smooth cortical surface of the left sacral ala and the cortical disruption or fracture of the outer margin of the right sacral ala. The SI joints are intact and well marginated; the widths of the joints are even throughout. A more inferior image shows the normal lower sacrum and SI joints ( Fig. 8-3 B ).

The third axial image ( Fig. 8-3 C ) shows the domes of the acetabuli. A fracture is present in one hip. Which one? A fine oblique fracture line is present in the right acetabular dome with enlargement of the right obturator internus muscle indicative of edema and hemorrhage within the muscle. Compare with the normal left side. The anatomic features of the dome of the acetabulum and hip joint in the axial plane are designated ( Fig. 8-3 D ). Axial image of the hip joints is shown ( Fig. 8-3 E ).

The next lower axial image ( Fig. 8-3 F ) show the symphysis pubis, femoral heads and necks, and posterior inferior aspect of the hip joint. The lowest axial image ( Fig. 8-3 G ) contains the inferior pubic rami and proximal shaft and lesser trochanters of the femurs.

Two-dimensional (2-D) images are reformatted in the coronal and sagittal images through the entire pelvis. The anterior pubic rami and pubic symphysis are seen in the most anterior image ( Fig. 8-4 A ). The next image contains the hip joints ( Fig. 8-4 B ). The third coronal image shows the quadrilateral surface of the inner wall of the acetabulum and the iliac wings ( Fig. 8-4 C ). The upper sacrum, SI joints, and adjacent iliac bone are seen in the fourth coronal image ( Fig. 8-4 D ).

The principal features of the sagittal 2-D images are the midline section of the sacrum ( Fig. 8-5 A ) and sagittal section through the mid-acetabulum ( Fig. 8-5 B ). Fractures of the sacrum are easily overlooked on both plain radiographs and the axial images of a CT examination. It is critical that 2-D sagittal images be reformatted in the CT of every case of significant pelvic trauma to avoid such unfortunate errors and oversights.

Three-dimensional imaging is now immediately available on most CT equipment. There are a variety of potential imaging sequences available, but the most common and most useful for the evaluation of the bony pelvis are surface-rendering and volume-rendering transparencies that mimic radiographic images.

This 54-year-old woman sustained an open book injury of the pelvis in a high-speed MVC. Surface- ( Fig. 8-6 A , AP projection) and volume- ( Fig. 8-6 B , inlet view) rendered CT images of the entire pelvis clearly depict fractures of the right pubic rami and dislocations of the symphysis pubis and bilateral SI joints. The full extent of the injuries is readily apparent.

Surface-rendered 3-D images of two complex injuries of the pelvis are shown. The first ( Fig. 8-6 C ) is a bilateral posterior dislocation of the sacroiliac joints with fractures of the right superior and inferior rami. Note also the bilateral avulsions of the transverse processes of the fifth lumbar vertebra. All injuries are readily identified. The second ( Fig. 8-6 D ) is an inlet projection of a both-column fracture of the left acetabulum. Fractures of the left ilium and disruption of the left obturator ring and acetabulum are obvious.

Three-dimensional imaging should be obtained in every pelvic CT examination for pelvic trauma. Surface-rendered images for scrolling in the axial and sagittal planes allow one to appreciate the full extent of pelvic injuries and are most helpful for treatment planning. Volume-rendered transparencies should be obtained routinely as a substitute for the additional radiographs (inlet, outlet, and obturator and iliac obliques) that are often obtained. Such radiographs take time and effort that the patient’s condition may not allow. Processing the CT database to make 3-D images can be accomplished in a short time and requires no additional examination of the patient.

2

Anatomic features

• Pelvic ring

  • Composed of two innominate bones and the sacrum

    • Joined posteriorly by the two sacroiliac joints

    • Joined anteriorly by the symphysis pubis

  • Ring consists of two arches.

    • The posterior or femorosacral arch extends from one acetabulum to the other.

      • The main weight-bearing component of the pelvis

      • The stronger of the two arches

    • The tie or anterior arch extends inferiorly and anteriorly from each acetabulum.

      • The weaker arch

      • Fractures more likely to occur in anterior arch

• Pelvic ligaments

  • Stability of pelvis is dependent on the integrity of strong ligaments.

    • Posterior and anterior sacroiliac ligaments

      • Posterior sacroiliac ligaments are strongest ligaments in the body.

    • Sacrotuberous and sacrospinous ligaments

      • Extend from the sacrum to the ischial spine and tuberosity

    • Iliolumbar and iliosacral ligaments

      • Attach fifth lumbar transverse processes to ilium and sacrum

Volume-rendered posterior projection of the pelvis ( Fig. 8-8 A ): pelvic floor ligaments (1), posterior sacroiliac ligaments (2), iliolumbar ligaments (3), lumbosacral ligaments (4), and posterior superior iliac spine (5). Volume-rendered lateral projection of the left hemipelvis ( Fig. 8-8 B ): pelvic floor ligaments (1) run from the inferolateral sacrum to the ischial spine and ischial tuberosity.

Coronal CT image shows iliolumbar (top arrow) and lumbosacral (bottom arrow) ligaments ( Fig. 8-8 C ).

Axial CT image through the sacroiliac joints shows the sacroiliac ligaments: anterior SI ligament (1), interosseous ligament (2), and posterior SI ligament (3) ( Fig. 8-8 D ).

3

Stability of fractures variable

• Stable fractures

  • In general

    • Single fracture limited to either anterior or posterior arch

      • Most common in anterior arch

      • Isolated fxs of posterior arch are rare.

    • Principal pelvic ligaments remain intact.

  • Common stable fractures ( Fig. 8-9 )

    • Pubic rami

    • Body of pubis

    • Iliac – periphery of iliac wing (Duverney fracture)

    • Sacrum – transverse fracture below sciatic notch

    • Coccyx

    

• Unstable fractures

  • In general

    • Fractures involve both anterior and posterior arches.

    • One or more principal pelvic ligaments disrupted

  • Common types of unstable fractures ( Fig. 8-10 )

    • Ipsilateral displaced fractures of both anterior and posterior arches

    • Pelvic dislocation – disruption of pubic symphysis and SI joint or joints

      • Commonly referred to as an “open book” fracture

    • Unilateral fractures of pubic rami with sacral ala or iliac fracture opposite side of pelvis

      • Commonly referred to as a bucket handle or “diametric” fracture

    • Displaced fracture of medial portion of both pubic rami

      • Known as a “straddle” fracture