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Introduction
  • 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
Anatomy
  • 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
Classification
  • 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
Presentation
  • 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
Imaging
  • 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
Treatment
  • 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
Complications
  • 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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