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Radiographic Evaluation, Anatomy, and Classification of Pelvic Ring Injuries. Kyle F. Dickson, MD Chief of Orthopaedics, Charity Hospital Director of Orthopaedic Trauma Tulane University Created March 2004 Reviewed April 2007. Palpable Bony Landmarks. Symphysis Pubis

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Radiographic Evaluation, Anatomy, and Classification of Pelvic Ring Injuries

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Radiographic evaluation anatomy and classification of pelvic ring injuries

Radiographic Evaluation, Anatomy, and Classification of Pelvic Ring Injuries

Kyle F. Dickson, MD

Chief of Orthopaedics, Charity Hospital

Director of Orthopaedic Trauma

Tulane UniversityCreated March 2004Reviewed April 2007

Palpable bony landmarks

Palpable Bony Landmarks

  • Symphysis Pubis

  • Anterior Superior Iliac Spine (ASIS)

  • Iliac Wing

  • Posterior Superior Iliac Spine (PSIS)

Pelvic ring

Pelvic Ring

  • 2 innominate bones

  • 1 Sacrum

  • Gap in symphysis < 5 mm

  • SI joint 2-4 mm

Important stabilizing ligaments

Important Stabilizing Ligaments

  • Posterior Iliosacral

  • Anterior Iliosacral

  • Sacrospinous

  • Sacrotuberous

  • Symphyseal

Important muscles

Important Muscles

  • Gluteus Maximus

  • Iliopsoas

  • Rectus Abdominus

Possible arterial bleeders in pelvic injuries

Possible Arterial Bleeders in Pelvic Injuries

  • Iliolumbar artery

  • Superior gluteal artery

  • Lateral sacral artery

  • Internal iliac artery

  • Internal pudendal (active bleeding most commonly found)

Neurologic damage

Neurologic Damage

  • L5 & S1, most common

  • L2 to S4 possible

  • Dependent on location of fracture and amount of displacement

Denis corr 1988

Denis, CORR 1988

  • Sacral Fractures – Neurologic Injury

    • Lateral to foramen – 6% injury

    • Through foramen – 28% injury

    • Medial to foramen – 57% injury

Pohlemann corr 1994

Pohlemann, CORR 1994

  • Amount of displacement move important then location

Potentially damaged visceral anatomy

Potentially Damaged Visceral Anatomy

  • Blunt vs. impaled by bony spike

    • Bladder/urethra

    • Rectum

    • Vagina

Pelvic ring1

Pelvic Ring

  • No inherent stability

  • Ligaments give the pelvis stability

Symphyseal ligaments

Symphyseal Ligaments

  • Resist external rotation in double-leg stance

  • Rami act as struts to resist compressive and internal rotation in single leg stance

  • Sectioning causes little pelvic instability

Ghanayem j trauma 1995

Ghanayem, J Trauma 1995

  • Abdominal wall contributes to pelvic stability (laparotomy increased pelvic displacement in cadaveric model)

Si joint transfers load from appendicular to axial skeleton

SI Joint Transfers Load from Appendicular to Axial Skeleton



  • Inlet View Reverse keystone where compression forces displace sacrum anteriorly

  • Outlet View True keystone compression locks sacrum into pelvic ring

  • Small rotating movements during gait

Posterior ligaments

Posterior Ligaments

  • Ant. SI Joint – resist external rotation

  • Post. SI and Interosseous – posterior stability by tension band (strongest in body)

  • Iliolumbar ligaments augments posterior complex

Radiographic evaluation anatomy and classification of pelvic ring injuries

Sacrotuberous (sacrum behind sacro-spinous into ischial tuberosily vertically)

Resists shear and flexion of SI joint

Sacrospinous – (anterior sacral body to ischial spine horizontally) resists external rotation

Normal si joint motion with gait

Normal SI Joint Motion with Gait

  • < 6 mm of translation

  • < 6° rotation

  • Intact cadaver resist 5,837 N (1,212 lbs)

Nachemson acta orthop scand 1966

Nachemson, Acta Orthop Scand 1966

  • Sitting 710 N (160 lbs) at each Si joint

  • Lying 196 N (44 lbs)

  • Lateral decubitus 686 N (154 lbs)

  • Standing 980 N (220 lbs)

Sitting or double leg stance

Sitting or Double Leg Stance

  • Pubic rami tension and compression posteriorly

  • External rotation injury – displaces in sitting or double leg stance

Single leg stance

Single Leg Stance

  • Tension shear posteriorly and compression of rami

  • Will displace internal rotation injury

Direction of force

Direction of Force

  • Anteroposterior

  • Lateral compression

  • Vertical shear

Stability ability of pelvic ring to withstand physiologic forces without abnormal deformation

Stability – ability of pelvic ring to withstand physiologic forces without abnormal deformation

Translational deformities

Translational Deformities

  • X axis – Diastasis or impaction

  • Y axis – Caudad or cephalad displacement

  • Z axis – Anterior or posterior displacement

Rotational deformities

Rotational Deformities

  • X axis – Flexion or extension

  • Y axis – Internal rotation or external rotation

  • Z axis – Abduction or adduction

Deformity of pelvis

Deformity of Pelvis

  • Defined from an anatomically positioned pelvis in space

  • Deformity a combination of rotational & translational deformities

Deformity of pelvis cont

Deformity of Pelvis (cont.)

  • Does not deform around a single point but can be represented as a vector from a normally positioned pelvis

  • Acute deformity difficult to measure but direction often able to be determined

Pelvic instability

Pelvic Instability

  • These injuries which will have worsening deformity

  • Physical exam and radiographic evaluation

Determining stability

Determining Stability

  • Integrity of posterior bone and ligament, unstable = vertical plane displacement

  • Some partial instability in rotation

Physical exam

Physical Exam

  • Symmetrical palpable ASIS, iliac wing, and symphysis

  • ASIS compression test

  • Iliac wing compression test

Radiographic evaluation

Radiographic Evaluation

  • Anteroposterior view (AP)

  • Inlet view (40° caudad)

  • Outlet view (40 ° cephalad)

  • CT

Good quality radiographs are essential

Good Quality Radiographsare Essential

Inlet caudad view

Inlet (Caudad) View

  • Horizontal Plane Rotation

  • Posterior Displacement

  • Sacral ala

Outlet cephalad view

Outlet (Cephalad) View

  • Sacrum

  • Cephalad Displacement

  • Sacral Foramina

Placement of wires show

Placement of Wires Show

  • Ant. SI joint lateral to post. SI

  • Radiographic brim does not always correlate with anatomical brim

Ct scan

CT Scan

  • Better defines posterior injury

  • Amount of displacement versus impaction

  • Rotation of fragments

  • Amount of comminution

  • Assess neural foramina

Radiographic signs of instability

Radiographic Signs of Instability

  • Sacroiliac displacement of 5 mm in any plane

  • Posterior fracture gap (rather than impaction)

  • Avulsion of fifth lumbar transverse process, lateral border of sacrum (sacrotuberous ligament), or ischial spine (sacrospinous ligament)



  • Aids in predicting hemodynamic instability

  • Aids in predicting visceral and g.u. injuries

  • Aids in predicting pelvic instability

  • Aids in understanding mechanism of injury, force vector of injury, and surgical tactic for reduction

Classification systems

Classification Systems

  • Anatomical (Letournel)

  • Stability & Deformity (Pennal, Bucholz, Tile)

  • Vector force and associated injuries (Young & Burgess)

Anatomical classification letournel

Anatomical Classification(Letournel)

Where The Pelvis Breaks



  • Iliac wing fracture

  • Iliac wing/sacroiliac (SI) joint (crescent fracture)

  • SI joint

  • Sacrum/SI joint

  • Sacrum fracture



  • Rami fractures

  • Symphyseal disruption

Pennal 1961

Pennal, 1961

  • Magnitude and direction of forces

    • Lateral posterior compression (LC)

    • Anterior posterior compression (APC)

    • Vertical shear (VS)

Bucholz 1981 tile 1988

Bucholz, 1981 Tile, 1988

Added stability to the classification

Ota ao pelvic injury classification

OTA/AO – Pelvic Injury Classification

  • 61A – Lesion sparing (or with no displacement of ) posterior arch

  • B – Incomplete disruption at posterior arch; partially stable

  • C – Complete disruption of posterior arch; unstable

A fractures ring intact

A Fractures – Ring Intact

  • A-1 – Fracture of innominate bone; avulsion

  • A-2 – Fracture of innominate bone; direct blow

  • A-3 – Transverse fracture of sacrum and coccyx

B ring injury partially stable

B-Ring Injury – Partially stable

  • B-1 – Unilateral partial disruption of posterior arch, external rotation (“open book” injury)

  • B-2 – Unilateral, partial disruption of posterior arch, internal rotation (lateral compression injury)

  • B-3 – Bilateral, partial lesion of posterior arch

C complete disruption posterior arch unstable pelvis

C – Complete Disruption Posterior Arch, Unstable Pelvis

  • C-1 – Unilateral, complete disruption of posterior arch

  • C-2 – Bilateral, ipsilateral complete, contralateral incomplete

  • C –3 – Bilateral, complete disruption

Further classification

Further Classification

  • A.1 – Location of avulsion

  • A.2 – Type of fracture anteriorly

  • A.3 – Amount of displacement sacrum

Further classification cont

Further Classification (cont.)

  • B – Location of fracture

Further classification cont1

Further Classification (cont.)

  • C – Location of fractures – iliac wing, SI joint, and sacrum

Young and burgess rad 1986

Young and Burgess, Rad 1986

  • Increases clinicians diagnosis of frequently missed lesions

  • Predictive index for associated injuries

  • Helps clinicians to select treatment based on probable pathology and hemodynamic status

Lateral compression

Lateral Compression

  • LC-1 – Ant. superior inf. rami or symphysis and compression of sacrum same side

  • LC-2 - LC-1 – anteriorly and posteriorly crescent fracture near anterior border at SI joint  Ileum rotated internally

Lateral compression1

Lateral Compression

LC I: Sacral compression

Patient wh

Patient WH

  • Progressive IR deformity that became fixed

  • Required anterior release & post sacral osteotomy followed by external rotation

  • Pre-& postop, AP and inlet, and 2 year follow-up

Lateral compression2

Lateral Compression

LC II: Iliac wing fracture

Lc cont

LC (cont.)

  • LC-3 – Windswept pelvis – LCI or II on one side of the pelvis and open book (APC) on contralateral side (roll over mechanism by IR on LC side and ER on contralateral side)

Lc iii windswept pelvis

LC III: “Windswept pelvis”

Lc iii


Anteroposterior compression

Anteroposterior Compression

  • Diastasis anteriorly through symphysis pubis or vertical Rami fractures

  • Posteriorly usually through SI joint – amount of displacement defines subset

Anteroposterior cont


  • APC-1 – 1-2 cm symphysis diastasis and minimal SI diastasis anteriorly (external rotation of hemipelvis – stable pelvis).

Radiographic evaluation anatomy and classification of pelvic ring injuries


  • Note that the ligaments are stretched, and not torn

Anteroposterior cont1

Anteroposterior (cont.)

  • APC-2 – Sacrotuberous, sacrospinous, and anterior SI joint ligaments disrupted (post SI ligaments intact)

  • APC-3 – Complete SI joint disruption (usually not vertically displaced)

Ap ii


  • Note: pelvic floor ligaments are violated, as well as anterior SI ligaments

Anteroposterior compression1

Anteroposterior Compression

APC III: Complete Iliosacral Dissociation

Vertical shear

Vertical Shear

  • Always unstable

  • Ant. symphsis or vertical rami fractures-post. Injury variable

  • Vertical displacement

Vertical shear1

Vertical Shear

Patient nj

Patient NJ

  • VS initially attempted to be treated with anterior plate and ex-fix with hardware failure

  • 3 stage pelvic reconstruction ( ant.  post ant. 2 yr follow-up – Auburn football player)



  • Combined vectors occasionally 2 separate injuries (ejection/landing)

  • Often LC/VS, or AP/VS

Combined mechanical injury

Combined Mechanical Injury

Patient lc

Patient LC

  • Combination LC and VS

  • Treated conservatively initially

  • Required 3 stage pelvic reconstruction to restore ischial height

See emergent management of pelvic injuries for application of classification to treatment

See Emergent Management of Pelvic Injuries for Application of Classification to Treatment



Joel Matta, Phil Kregor, and Mark

Vrahas for the use of their slides

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