Sacral Fractures¶

Definition¶

Sacral fractures involve the fused vertebral segments of the sacrum (S1–S5) and range from low-energy insufficiency fractures in the elderly to high-energy complex fractures associated with pelvic ring disruption. The sacrum houses the sacral nerve roots (including the cauda equina), and fractures that extend into the sacral foramina or central canal can cause significant neurological injury.

Classification — Denis Sacral Fracture Zones¶

Zone I — Alar (Lateral to the Foramina) Fractures lateral to the sacral foramina, through the sacral ala. These are the most common sacral fractures (approximately 50%). Neurological injury is uncommon (<5%) because the fracture does not involve the neural foramina.

Zone II — Foraminal (Through the Foramina) Fractures extending through one or more sacral foramina. Neurological injury occurs in approximately 25–30% of cases, typically manifesting as unilateral sacral radiculopathy (L5 or S1 distribution).

Zone III — Central (Medial to the Foramina) Fractures involving the sacral canal, medial to the foramina. Neurological injury is common (50–75%), and may include bowel, bladder, and sexual dysfunction due to injury to the sacral nerve roots S2–S4.

Fracture Types¶

High-Energy Fractures¶

Associated with pelvic ring injuries (Young-Burgess or Tile classification):

Vertical shear fractures — Vertical fracture through the sacral ala or foramina, typically associated with vertical displacement of the hemipelvis. These are part of unstable pelvic ring injuries.
Transverse fractures — Horizontal fracture through the sacral body, which may cause kyphotic angulation of the distal sacral segment. Associated with falls from height (landing on the buttocks).
H-shaped and U-shaped fractures — Complex fracture patterns combining vertical and transverse components. U-shaped fractures (bilateral vertical fractures connected by a transverse fracture) are highly unstable and carry a high rate of neurological injury.

Insufficiency Fractures¶

Low-energy fractures occurring in osteoporotic or irradiated bone. Typically present as vertical fractures parallel to the sacroiliac joints through the sacral ala. These are discussed in detail in the Insufficiency Fractures article.

Imaging Findings¶

CT¶

CT is the primary modality for characterizing sacral fractures:

Fracture lines through the sacral ala, foramina, or central canal
Displacement and angulation
Associated pelvic ring fractures (pubic rami, iliac wing, SI joint disruption)
Foraminal extension indicating risk of nerve root injury

MRI¶

Evaluates the sacral nerve roots and cauda equina
Bone marrow edema on STIR sequences (essential for detecting occult insufficiency fractures)
Epidural hematoma within the sacral canal
Disc herniation at L5–S1

Radiography¶

Sacral fractures are notoriously difficult to detect on plain radiographs due to overlying bowel gas and the complex sacral anatomy. CT is far more sensitive.

Clinical Pearl

Sacral fractures are frequently missed on initial imaging — reported miss rates of up to 30% on CT and higher on radiographs. In the polytrauma patient, attention is often directed to the more obvious pelvic fractures. A systematic evaluation of the sacrum on every trauma CT — specifically tracing the sacral foramina and anterior sacral cortex on sagittal and axial images — reduces the miss rate.

Management¶

Stable Zone I fractures — Conservative treatment with pain management and progressive mobilization
Zone II and III fractures with neurological deficit — Surgical decompression may be considered, though evidence is limited
Unstable fractures associated with pelvic ring disruption — Surgical fixation (iliosacral screws, lumbopelvic fixation, or spinopelvic fixation)

Key Points¶

Denis classification divides sacral fractures into Zone I (alar), Zone II (foraminal), and Zone III (central), with increasing neurological risk
High-energy fractures are frequently associated with pelvic ring injuries
Sacral fractures are commonly missed — systematic CT evaluation is essential
Zone III fractures have the highest rate of neurological injury, including bowel/bladder dysfunction
MRI and STIR sequences are essential for detecting occult insufficiency fractures
Treatment depends on fracture stability, neurological status, and associated pelvic injuries

References¶

Rizkalla JM, Lines T, Nimmons S. Classifications in Brief: The Denis Classification of Sacral Fractures. Clin Orthop Relat Res. 2019;477(9):2178–2181. https://pmc.ncbi.nlm.nih.gov/articles/PMC7000068/
Dreizin D, Smith EB. CT of Sacral Fractures: Classification Systems and Management. RadioGraphics. 2022;42(7):1975–1993. doi:10.1148/rg.220075. https://pubs.rsna.org/doi/full/10.1148/rg.220075
Yi C, Hak DJ. Traumatic spinopelvic dissociation or U-shaped sacral fracture: a review of the literature. Injury. 2012;43(4):402–408. https://pubmed.ncbi.nlm.nih.gov/21236426/
Lyders EM, Whitlow CT, Baker MD, Morris PP. Imaging and Treatment of Sacral Insufficiency Fractures. AJNR Am J Neuroradiol. 2010;31(2):201–210. https://pmc.ncbi.nlm.nih.gov/articles/PMC7964142/
Classification of sacral fractures. Radiopaedia.org. https://radiopaedia.org/articles/classification-of-sacral-fractures