Sacral Fractures

Definition

  • Fracture of the Sacrum

Incidence

  • Frequent component of pelvic ring injuries
  • Isolated sacral fractures are less common
  • Bimodal distribution with young high energy and elderly insufficiency fractures
  • Insufficiency fractures are rising with an ageing population

Aetiology

  • High energy trauma such as motor vehicle accidents and falls from height
  • Insufficiency fractures with osteoporosis, pelvic radiotherapy and corticosteroid use
  • Stress fractures in athletes and military recruits
  • Fall from height onto the buttocks causes transverse and U shaped fractures

Anatomy

  • Five fused sacral vertebrae articulating with the ilia at the SI joints
  • Upper sacral bodies accept iliosacral screws within a safe corridor
  • Sacral foramina transmit the ventral rami of the sacral nerves
  • L5 nerve root crosses the anterior sacral ala
  • Upper sacral dysmorphism narrows the safe screw corridor
  • Posterior SI ligaments are the strongest ligaments of the pelvic ring

Classification

  • Vertical, oblique or transverse
    • Vertical
      • Denis classification of Vertical fractures
        • 3 Zones
ZoneDescriptionNerve Injury
1lateral to neural foramen5% rate of nerve injury (L5 usually)
2through neural foramen25% rate of nerve injury
3medial to foramen50% rate of nerve injury – involves central sacral canal
Denis Classification of Vertical Fractures
  • Transverse fractures
    • Usually S12
    • High rate of neurological injury
    • If S23 may lead to loss of bladder and bowel function
    • Pelvic and lower lumbar spine injuries often present

Pathology

  • Vertical fractures form part of a posterior pelvic ring disruption
  • Transverse and U shaped fractures cause spinopelvic dissociation
  • Nerve injury from foraminal or canal compromise
  • Neurological deficit increases from zone I to zone III
  • Bilateral S2 to S4 injury causes bladder, bowel and sexual dysfunction

History

  • Mechanism of Injury
  • Sensory disturbance
  • Bowel | bladder function

Examination

  • Neurological Examination
  • PR
  • Identify associated injuries

Investigations

X-rays

Sacral Fractures, inversion recovery mri of a right sacral alar insufficiency fracture
Inversion recovery MRI of a right sacral alar insufficiency fracture. Image by Mohamed Jarraya, Daichi Hayashi, Frank W. Roemer, Michel D. Crema, Luis Diaz, Jane Conlin, Monica D. Marra, Nabil Jomaah and Ali Guermazi, Wikimedia Commons, CC BY 3.0.
  • often difficult to see

CT Scan

  • bone anatomy

MRI

  • soft tissue anatomy

Treatment

Non-operative

  • Stable fractures, bed rest
  • X-ray monitoring

Operative

  • Unstable or displaced
  • CR & percutaneous SI screws
  • Trans iliac bars
  • Plate and screws
  • +/- laminectomy

Complications

  • Persistent neurological deficit with bladder, bowel and sexual dysfunction
  • Malunion with leg length discrepancy and pelvic obliquity
  • Non union
  • Screw malposition with L5 or S1 root injury
  • Wound breakdown after posterior approaches, especially with Morel Lavallée lesions
  • VTE

Prognosis

  • Stable isolated fractures heal with good function
  • Neurological injury predicts a poorer outcome
  • Displaced vertical fractures and spinopelvic dissociation often leave pain and gait disturbance
  • Most insufficiency fractures heal with mobilisation
  • Elderly insufficiency fractures carry raised mortality

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.