SI Dislocation & Crescent Fractures

Topic updated on 12/17/14 4:26pm
  • 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
  • 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
  • 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
  • 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
  • Radiographs 
    • recommended views
      • AP pelvis
      • inlet and outlet views
  • CT scan 
    • evaluation of sacral fractures
    • posterior pelvis better delineated
  • 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
  • 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)
  • DVT
    • 35%-50% 
  • Neurological injury
  • Loss of reduction and failure of fixation


Please Rate Educational Value!
Average 3.0 of 35 Ratings

Qbank (4 Questions)

(SBQ06.40) 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? Topic Review Topic
FIGURES: V          

1. Lateral compression 1
2. Lateral compression 2
3. Vertical shear
4. Anterior-posterior compression 2
5. Anterior-posterior compression 3

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

1. Hip flexion
2. Hip adduction
3. Knee extension
4. Ankle plantarflexion
5. Great toe dorsiflexion

(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? Topic Review Topic

1. Lack of ankle dorsiflexion
2. Lack of ankle plantarflexion
3. Lack of knee extension
4. Loss of bowel and/or bladder control
5. Lack of great toe extension

(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? Topic Review Topic
FIGURES: A          

1. Evaluation of possible injury to L5 nerve root
2. Evaluation of anterior-posterior position of screw(s)
3. Best visualization of sagittal curvature of sacral ala
4. Best visualization of spinal canal
5. Best visualization of sacral neural foramina



Topic Comments