http://upload.orthobullets.com/topic/1032/images/zone 2.jpg
http://upload.orthobullets.com/topic/1032/images/Xray - AP Pelvis - L sacral fx_moved.jpg
http://upload.orthobullets.com/topic/1032/images/zone 1.jpg
  • Under-diagnosed and often mistreated fractures that may result in neurologic compromise
    • common in pelvic ring injuries (30-45%)
    • 25% are associated with neurologic injury
    • frequently missed
      • 75% in patients who are neurologically intact
      • 50% in patients who have a neurologic deficit
  • Epidemiology 
    • young adults
      • as a result of high energy trauma
    • elderly
      • as a result of low energy falls
  • Prognosis
    • presence of a neurologic deficit is the most important factor in predicting outcome
    • mistreated fractures may result in
      • lower extremity deficits
      • urinary dysfunction
      • rectal dysfunction
      • sexual dysfunction
  • Osteology 
    • formed by fusion of 5 sacral vertebrae
    • articulates with 
      • 5th lumbar vertebra proximally
      • coccyx distally
      • ilium laterally at sacroiliac joints
    • contains 4 foramina which transmit sacral nerves
  • Nerves
    • L5 nerve root runs on top of sacral ala
    • S1-S4 nerve roots are transmitted through the sacral foramina
      • S1 and S2 nerve roots carry higher rate of injury
    • lower sacral nerve roots (S2-S5)
      • function
        • anal sphincter tone / voluntary contracture
        • bulbocavernosus reflex
        • perianal sensation
      • unilateral preservation of nerves is adequate for bowel and bladder control
  • Biomechanics
    • transmission of load distributed by first sacral segment through iliac wings to the acetabulum
  • Denis classification
    • zone 1
      • fracture lateral to foramina
      • characteristics 
        • most common (50%)
        • nerve injury rare (5%)
        • usually occurs to L5 nerve root
    • zone 2
      • fracture through foramina
      • characteristics
        • may be
          • stable
          • unstable
            • zone 2 fracture with shear component highly unstable
            • increased risk of nonunion and poor functional outcome
    • zone 3  
      • fracture medial to foramina into the spinal canal
      • characteristics
        • highest rate of neurologic deficit (60%)
        • bowel, bladder, and sexual dysfunction
  • Transverse sacral fractures
    • higher incidence of nerve dysfunction
  • U-type sacral fractures
    • results from axial loading
    • represent spino-pelvic dissociation
    • high incidence of neurologic complications
  • History 
    • motor vehicle accident or fall from height most common
    • repetitive stress
      • insufficiency fracture in osteoporotic adults
  • Symptoms
    • peripelvic pain
  • Physical exam
    • inspection
      • soft tissue trauma around pelvis should raise concerns for pelvic or sacral fracture
    • palpation
      • test pelvic ring stability by internally and externally rotating iliac wings
      • palpate for subcutaneous fluid mass indicative of lumbosacral fascial degloving (Morel-Lavallee lesion)
      • perform vaginal exam in women to rule-out open injury
    • neurologic exam
      • rectal exam
      • light touch and pinprick sensation along S2-S5 dermatomes
      • perianal wink
      • bulbocavernosus and cremasteric reflexes
    • vascular exam
      • distal pulses
        • if different consider ankle-brachial index or angiogram
  • Radiographs
    • only show 30% of sacral fractures
    • recommended views
      • AP pelvis
      • inlet view
        • best assessment of sacral spinal canal and superior view of S1
      • outlet view
        • provides true AP of sacrum
    • additional views
      • cross-table lateral
        • effective screening tool for sacral fractures
        • often of poor quality
    • findings
      • L4 or L5 transverse process fractures
      • asymmetric foramina
  • CT
    • diagnostic study of choice
    • recommend coronal and sagittal reconstruction views
  • MRI
    • recommended when neural compromise is suspected
  • Nonoperative 
    • progressive weight bearing +/- orthosis
      • indications
        • <1 cm displacement and no neurologic deficit
        • insufficiency fractures
  • Operative
    • surgical fixation
      • indications
        • displaced fractures >1 cm
        • soft tissue compromise
        • persistent pain after non-operative management
        • displacement of fracture after non-operative management
    • surgical fixation with decompression
      • indications
        • any evidence of neurologic injury
Surgical Techniques
  • Percutaneous screw fixation
    • screws may be placed as sacroiliac, trans-sacral or trans-iliac trans-sacral 
    • useful for sagittal plane fractures
    • technique
      • screws placed percutaneously under fluoroscopy
      • beware of L5 nerve root
      • avoid overcompression of fracture
        • may cause iatrogenic nerve dysfunction
    • cons
      • may result in loss of fixation or malreduction
      • does not allow for removal of loose bone fragments
      • do not use in osteoporotic bone
  • Posterior tension band plating 
    • approach
      • posterior two-incision approach
    • technique
      • may use in addition to iliosacral screws
    • pros
      • allows for direct visualization of fracture
    • cons
      • wound healing complications
  • Iliosacral and lumbopelvic fixation
    • approach
      • posterior approach to lower lumbar spine and sacrum
    • technique
      • pedicle screw fixation in lumbar spine
      • iliac screws parallel to the inclination angle of outer table of ilium
      • longitudinal and transverse rods
    • pros
      • shown to have greatest stiffness when used for an unstable sacral fracture 
    • cons
      • invasive
  • Decompression of neural elements
    • technique
      • indirect
        • reduction through axial traction
      • direct
        • posterior approach followed by laminectomy or foraminotomy
  • Venous thromboembolism
    • often as a result of immobility
  • Iatrogenic nerve injury
    • may result from
      • overcompression of fracture
      • improper hardware placement
  • Malreduction
    • more common with vertically displaced fractures

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Questions (3)

(OBQ11.2) A 35 year-old female presents after prolonged extrication from a motor vehicle collision complaining of severe pelvic pain. Physical examination reveals diminished perianal sensation. She is otherwise neurologically intact. Figures A through D are radiographs and representative CT cuts of her injury. Which of the following nerve roots has likely been injured? Review Topic





















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The clinical scenario is consistent with a high-energy sacral fracture. The radiographs in figures A and B demonstrate a sacral fracture with posterior displacement of the right hemipelvis seen on the inlet view. Figures C and D are axial and sagittal CT images which show a displaced fracture of the right hemisacrum along with a transvere fracture component through the S3 body . Diminished perianal sensation is concerning for an S2 nerve root injury.

Mehta et al reviewed the current management of sacral fractures. They note that the S1 and S2 nerve roots are more likely to be injured with sacral fractures as they occupy 1/3 to 1/4 of the neural foramina, as opposed to S3 and S4, which only occupy 1/6 of the neural foramina.

Robles reviewed the current literature to ascertain principles of evaluation and treatment for transverse sacral fractures. The author notes that injury to nerve roots S2 to S5 is manifested by impairment of urinary and anal continence and sexual function.

The first illustration demonstrates the sacral nerve root dermatomal distribution. The second shows a pelvic cadaver dissection demonstrating the sacral nerve roots as they exit the foramina.


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(OBQ11.35) A 20-year-old patient presents after jumping from the window of a burning building with a sacral fracture. Which of the following fracture patterns seen in Figures A through E would give this patient the highest risk of associated nerve injury? Review Topic


Figure A




Figure B




Figure C




Figure D




Figure E



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Answering this question relies on knowledge of the Denis classification of sacral fractures and their associated risks of nerve injury. Figure A represents a Denis Zone 3 (medial to the foramina) sacral fracture, which has the highest associated risk of nerve injury.

Denis et al outlined a novel classification system of sacral fractures based on the position of the fracture line relative to the sacral foramina. The authors found a 56.7% incidence of nerve injury in fractures that extended medial to the sacral foramina (zone 3), compared with 28.4% for fractures through the foramina (zone 2), and 5.9% for fractures lateral to the foramina (zone 1).

Mehta et al reviewed the current principles for management of sacral fractures. They note that bowel, bladder and sexual dysfunction occur in 76% of patients with zone 3 sacral fractures.

Illustration A below demonstrates the Denis classification of sacral fractures.

Incorrect Answers:
2. Figure B shows a zone 1 sacral fracture, which has a 5.9% incidence of nerve injury
3. Figure C shows a zone 2 sacral fracture, which has a 28.4% incidence of nerve injury
4. Figure D shows a sacroiliac joint dislocation, not a sacral fracture
5. Figure E shows a zone 1 sacral fracture with an associated iliac fracture (crescent fracture)


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(OBQ05.32) Which of the following is the most stable construct for fixation of an unstable transforaminal sacral fractures? Review Topic


External fixation




Iliosacral osteosynthesis




Combined iliosacral and lumbopelvic fixation (triangular osteosynthesis)




Anterior pelvic ring plating with bilateral sacroilliac percutaenous screw fixation




Transiliac bars with anterior pelvic ring plating



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Combined iliosacral and lumbopelvic fixation (triangular osteosynthesis) for sacral fractures has the greatest stiffness when used for an unstable sacral fracture.

The referenced article by Schildhauer et al is a cadaveric study that examined the biomechanical properties of different fixation constructs under cyclic loading and demonstrates that triangular osteosynthesis for unstable transforaminal sacral fractures provides significantly greater stability than iliosacral screw fixation under in-vitro cyclical loading.

Illustration below shows the radiographic appearance of lumbopelvic fixation. The addition of iliosacral fixation would complete triangular osteosynthesis.


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