Updated: 11/12/2018

SI Dislocation & Crescent Fractures

Topic
Review Topic
0
0
Questions
4
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0
Evidence
4
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https://upload.orthobullets.com/topic/1031/images/Xray - AP - crescent fx (wheeless)_moved.jpg
https://upload.orthobullets.com/topic/1031/images/CT- axial - crescent fx (wheeless)_moved.jpg
https://upload.orthobullets.com/topic/1031/images/inlet.jpg
Introduction
  • Spectrum of injuries that include
    • incomplete (Sacroiliac) SI dislocation
      • posterior SI ligaments remain intact
      • rotationally unstable
    • complete SI dislocations
      • posterior SI ligaments ruptured
      • vertically and rotationally unstable
    • SI fracture-dislocation (crescent fracture)
      • iliac wing fracture that enters the SI joint
      • injury to posterior ligaments vary
      • combination of vertical iliac fx and SI dislocation
      • posterior ilium remains attached to sacrum by posterior SI ligaments
      • anterior ilium dislocates from sacrum with internal rotation deformity
      • when ilium fragment remains with sacrum it is termed a crescent fracture
  • Pathophysiology
    • mechanism of injury
      • lateral compression force 
      • usually high energy
    • pathoanatomy
      • degree of injury to posterior structures determines pelvic stability
      • Iliac wing fractures may be associated with open wounds and may involve bowel entrapment 
  • Prognosis
    • primarily based on accurate and stable reduction of SI joint
Anatomy
  • Ligaments
    • the SI joint is stabilized by the posterior pelvic ligaments 
      • sacrospinous
      • sacrotuberous
      • anterior sacroiliac
      • posterior sacroiliac
  • Nerves
    • the L5 nerve root crosses the sacral ala  approximately 2 cm medial to SI joint
  • Blood supply
    • the superior gluteal artery runs across SI joint
    • exits pelvis via greater sciatic notch
Classification
  • No classification system specifically for SI injury
    • included in Young- Burgess and Tile classification of pelvic fractures 
    • crescent fractures described as LC-2 injury according to Young-Burgess 
Presentation
  • Symptoms
    • pelvic pain
  • Physical Exam
    • assess hemodynamic status
    • perform detailed neurological exam
    • abdominal assessment to look for distention
    • rectal exam
    • examine urethral meatus for blood
Imaging
  • Radiographs 
    • recommended views
      • AP pelvis
      • inlet and outlet views
  • CT scan 
    • evaluation of sacral fractures
    • posterior pelvis better delineated
Treatment
  • Operative
    • immediate skeletal traction
      • indications
        • vertical translation of the hemipelvis
    • anterior ring ORIF
      • indications
        • incomplete SI dislocations with pubic symphyseal diastasis
    • anterior and posterior ring ORIF
      • indications
        • complete SI dislocations
          • vertically unstable require anterior and posterior pelvic ring fixation
    • ORIF of ilium
      • indications
        • crescent fracture
          • required to restore posterior SI ligaments and pelvic stability
Techniques
  • Closed Reduction and Percutaneous Fixation
    • positioning
      • intraoperative traction may aid in reduction
      • small midline bump under sacrum may assist with SI screw placement
    • imaging
      • inlet view
        • shows anterior-posterior position of SI joint(s) for screw placement 
      • outlet view
        • shows cephalad-caudad position of SI joint(s) for screw placement  
      • lateral sacral view
        • ensures safe placement of SI or sacral screws relative to the anterior cortex of the sacral ala and the nerve root tunnel
    • complications
      • L5 nerve root at risk with anterior perforation of iliosacral screw as nerve goes inferiorly over sacral ala  
  • ORIF
    • approach
      • anterior approach 
        • lateral window with elevation iliacus back to SI joint
      • posterior approach
        • for fixation of crescent fragment to intact ilium
    • fixation
      • plates
      • iliosacral lag screws (SI screws)
Complications
  • DVT
    • 35%-50% 
  • Neurological injury
  • Loss of reduction and failure of fixation
 

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Questions (4)

(OBQ07.62) If a percutaneous iliosacral screw is placed too anteriorly, and the screw exits anterior to the sacral ala before re-entering the sacral body, what will be the most likely finding postoperatively? Review Topic

QID: 723
1

Lack of ankle dorsiflexion

7%

(71/973)

2

Lack of ankle plantarflexion

6%

(61/973)

3

Lack of knee extension

2%

(16/973)

4

Loss of bowel and/or bladder control

3%

(30/973)

5

Lack of great toe extension

81%

(789/973)

ML 1

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(OBQ06.13) A 39-year-old male is thrown from his motorcycle into a fast-food restaurant and sustains a closed pelvic ring injury. During placement of percutaneous iliosacral screws, the outlet radiograph in Figure A is obtained. What purpose does this view serve? Review Topic

QID: 24
FIGURES:
1

Evaluation of possible injury to L5 nerve root

10%

(59/605)

2

Evaluation of anterior-posterior position of screw(s)

10%

(62/605)

3

Best visualization of sagittal curvature of sacral ala

4%

(24/605)

4

Best visualization of spinal canal

2%

(13/605)

5

Best visualization of sacral neural foramina

73%

(444/605)

ML 2

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(OBQ10.159) Anterior penetration of an iliosacral screw through the sacral ala would most likely lead to weakness of which of the following movements? Review Topic

QID: 3247
1

Hip flexion

3%

(146/4656)

2

Hip adduction

2%

(76/4656)

3

Knee extension

2%

(102/4656)

4

Ankle plantarflexion

9%

(428/4656)

5

Great toe dorsiflexion

84%

(3888/4656)

ML 1

Select Answer to see Preferred Response

PREFERRED RESPONSE 5

(SBQ06TR.40) A 32-year-old female sustains the injury shown in Video A. The right-sided pelvic injury is best classified as which of the following? Review Topic

QID: 2652
FIGURES:
1

Lateral compression 1

16%

(103/644)

2

Lateral compression 2

73%

(469/644)

3

Vertical shear

4%

(25/644)

4

Anterior-posterior compression 2

4%

(28/644)

5

Anterior-posterior compression 3

2%

(12/644)

ML 2

Select Answer to see Preferred Response

PREFERRED RESPONSE 2
ARTICLES (9)
Topic COMMENTS (5)
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