SI Dislocation & Crescent Fractures

Author: Derek Moore

Topic updated on 03/28/13 10:06pm

Introduction

Spectrum of injuries that include
- incomplete SI dislocation
  - posterior SI ligaments remain intact
  - only rotationally unstable
- complete SI dislocations
  - posterior SI ligaments injured
  - 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 superior spine (sometimes iliac crest) remain attached to sacrum by posterior SI ligaments
  - lateral ilium dislocates from sacrum as anterior SI ligament rupture
  - when large ilium fragment remains with sacrum and a vertical fracture pattern is seen it is termed a crescent fracture
Mecahnism of injury
- lateral compression force
- usually high energy
Pathoanatomy
- degree of injury to posterior structures determines pelvic stability
- ligamentous structures usually involved
- Iliac wing fractures are more commonly 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 approxiamtely 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 joint injury
- included in LC type injuries as described by Young- Burgess

Presentation

Symptoms
- pelvic pain
Physical Exam
- assess hemodynamic status
- perform detailed neurological exam
- exam pelvis for instabilty (limit number of times pt is examined to avoid further destabilization)
- 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
    - acute complete SI dislocations should be placed in skeletal traction until definitive surgery
- anterior ring ORIF
  - indications
    - incomplete SI dislocations
- anterior and posterior ring ORIF
  - indications
    - complete SI dislocations
      - vertically unstable require anterior and posterior pelvic ring fixation
    - crescent fracture with small fragment of ilium attached to sacrum
- interfragmentary fixation of ilium
  - indications
    - crescent fracture
      - required to restore posterior SI ligaments and pelvic stability

Techniques

Closed Reduction and Percutaneous Fixation
- positioning
  - place patient in traction to aid reduction
- 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
    - tells information regarding anterior curvature of sacral ala and proper starting point on ilium
- complications
  - L5 nerve root at risk with anterior perforation of iliosacral screw as nerve goes inferiorly over sacral ala
ORIF
- approach
  - anterior approach (difficult in obese patients)
  - posterior approach
    - for fixation of crescent fragment to intact ilium
    - for placement of posterior plate
- fixation
  - plates
  - iliosacral lag screws

Complications

DVT
- 35%-50%
Neurological injury
Loss of reduction and failure of fixation

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Qbank (3 Questions)

TAG

(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

PREFERRED RESPONSE ▶

DISCUSSION: The injury shown in Video A reveals a right sided posterior ilium fracture, which is known as a crescent fracture. The presence of a crescent fracture is consistent with a lateral compression type 2 injury; this differentiates this from a type I injury. The ipsilateral anterior sacrum has a small impaction injury anteriorly while the contralateral SI joint has a minor amount of anterior sacral impaction indicative of a lateral compression type I injury.

The reference by Burgess et al is the primary source of the mechanism classification of pelvic ring injuries. Overall blood replacement averaged 5.9 units (lateral compression, 3.6 units; anteroposterior compression, 14.8 units; vertical shear, 9.2 units; combined mechanical, 8.5 units). Overall mortality was 8.6% (lateral compression, 7.0%; anteroposterior, 20.0%, vertical shear, 0%; combined mechanical, 18.0%).

Incorrect answers:
1: The presence of a crescent fracture means this is at least a LC-2 injury. The left-sided fracture pattern is consistent with an LC-1 pattern.
3: A vertical shear fracture pattern would exhibit some vertical displacement and does not typically exhibit the crescent fragment.
4: The fracture pattern does not match an anterior-posterior compression pattern.
5: The fracture pattern does not match an anterior-posterior compression pattern.

REFERENCES:

1. Burgess AR, Eastridge BJ, Young JW, Ellison TS, Ellison PS Jr, Poka A, Bathon GH, Brumback RJ. Pelvic ring disruptions: effective classification system and treatment protocols. J Trauma. 1990 Jul;30(7):848-56. PMID:2381002 (Link to Abstract)

Question Authors:

Ben Taylor MD, Jan Szatkowski MD, John Badylak MD,

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TAG

(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

PREFERRED RESPONSE ▶

DISCUSSION: Penetration of an iliosacral screw through the sacral ala would injure the ipsilateral L5 nerve root (great toe dorsiflexion). This can be avoided with proper understanding of the sacral anatomy as well as iliosacral screw starting points. The three required views for placement of this screw are: lateral sacral, pelvic inlet, and pelvic outlet. The referenced study by Ziran et al is an excellent review of fluoroscopic evaluation of screw placement. They reported that the anterior border of the S1 body is best seen with overlap of the S1 and S2 anterior cortex while the superior aspect of the S1 foramen is best seen with overlap of the S2 foramen on the superior pubic ramus.

The referenced study by Routt et al reviewed 177 patients with pelvic ring injuries treated with these screws and found that quality triplanar imaging decreased intraoperative and postoperative complications. They also recommend supplemental fixation of iliosacral screws with posterior plating in noncompliant patients.

REFERENCES:

1. Routt ML Jr, Simonian PT, Mills WJ. Iliosacral screw fixation: early complications of the percutaneous technique. J Orthop Trauma. 1997 Nov;11(8):584-9. PMID:9415865 (Link to Abstract)

2. Ziran BH, Wasan AD, Marks DM, Olson SA, Chapman MW. Fluoroscopic imaging guides of the posterior pelvis pertaining to iliosacral screw placement. J Trauma. 2007 Feb;62(2):347-56; discussion 356. PMID:17297324 (Link to Abstract)

Question Authors:

Ben Taylor MD,

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TAG

(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

PREFERRED RESPONSE ▶

DISCUSSION: This question is a simple review of anatomy and nerve innervation. The L5 root is at risk with an "in-out-in" screw, as described in the question, as the nerve root is just anterior to the sacral ala as it enters the true pelvis. L5 is primarily evaluated by extensor hallucis longus function. L4 is tested with tibialis anterior function and S1 by gastroc-soleus function (ankle plantarflexion).

REFERENCES:

1. Browner BD, Jupiter JB, Levine AM (eds): Skeletal Trauma. Philadelphia, PA, WB Saunders, 1992, pp 849-885

Question Authors:

Ben Taylor MD, Patrick McCulloch MD,

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TAG

(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

PREFERRED RESPONSE ▶

DISCUSSION: Figure A shows an intraoperative outlet view, which provides the best visualization of the neural foramina (and possible screw placement into these foramina). This view provides information regarding cephalad-caudad placement of the screw, whereas the inlet view provides information regarding the anterior-posterior position of the screw. The lateral sacral view provides information regarding the sagittal curvature of the sacral ala and gives information regarding possible iatrogenic L5 nerve injury as it goes over the sacral ala.

The referenced article by Routt et al is a review article regarding the safety and techniques of percutaneous pelvic ring fixation.

REFERENCES:

1. Routt ML Jr, Nork SE, Mills WJ. Percutaneous fixation of pelvic ring disruptions. Clin Orthop Relat Res. 2000 Jun;(375):15-29. PMID:10853150 (Link to Abstract)

Question Authors:

Ben Taylor MD, Jan Szatkowski MD,

Please Rate Educational Value!

4.0

Average 4.0 of 11 Ratings

Groups

ABOS II: SI Dislocation & Cresant Fractures

General - Oral Boards Review

7/29/2011

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Evidence & References Show References

Level of Evidence 2 (Prospective Cohort Study)

Routt ML Jr, Simonian PT, Mills WJ. Iliosacral screw fixation: early complications of the percutaneous technique. J Orthop Trauma. 1997 Nov;11(8):584-9. PMID:9415865 (Link to Abstract)

Level of Evidence 4 (Case Series)

Burgess AR, Eastridge BJ, Young JW, Ellison TS, Ellison PS Jr, Poka A, Bathon GH, Brumback RJ. Pelvic ring disruptions: effective classification system and treatment protocols. J Trauma. 1990 Jul;30(7):848-56. PMID:2381002 (Link to Abstract)

Level of Evidence 5 and Other Journal Articles (includes Case Reports, Expert Opinions, Personal Observations, and Biomechanic Studies)

Ziran BH, Wasan AD, Marks DM, Olson SA, Chapman MW. Fluoroscopic imaging guides of the posterior pelvis pertaining to iliosacral screw placement. J Trauma. 2007 Feb;62(2):347-56; discussion 356. PMID:17297324 (Link to Abstract)

Textbooks

Review of Orthopaedics, 6th Edition, Mark D. Miller MD, Stephen R. Thompson MBBS MEd FRCSC, Jennifer Hart MPAS PA-C ATC, an imprint of Elsevier, Philadelphia, Copyright 2012
AAOS Comprehensive Orthopaedic Review, Jay R. Leiberman. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2009
Orthopaedic Knowledge Update 10, John M Flyn. Published by American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2011
Hoppenfeld SP. Surgical Exposures in Orthopaedics: The Anatomic Approach. Lipponcott, Williams, and Wilkins, Philadelphia, PA, Copyright 2009
Orthopaedic In-training Examination (OITE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012
Self-Assessment Examination (SAE) Questions 2004-2012, American Academy of Orthopaedic Surgeons, Rosemont IL. Copyright 2004-2012

Undefined

Browner BD, Jupiter JB, Levine AM (eds): Skeletal Trauma. Philadelphia, PA, WB Saunders, 1992, pp 849-885
Routt ML Jr, Nork SE, Mills WJ. Percutaneous fixation of pelvic ring disruptions. Clin Orthop Relat Res. 2000 Jun;(375):15-29. PMID:10853150 (Link to Abstract)

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SI Dislocation & Crescent Fractures

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