There are several classification systems for sacral fractures, but the most commonly employed are the Denis classification and subclassification systems, and the Isler classification system. These classification systems are important to understand as proper classification can impact management.

AO classification of sacral injuries

• type A: lower sacrococcygeal injuries

• type B: posterior pelvic injuries

• type C: spinopelvic injuries

The AO sacral injury classification further subdivides these three injury types and also involves neurological and other modifiers that can be added.

Denis classification

• zone 1: fracture involves the sacral ala lateral to the neural foramina

• zone 2: fracture involves the neural foramina, but does not involve the spinal canal

• zone 3: fracture is medial to the neural foramen, involving the spinal canal; these may be transverse or longitudinal, and can be sub-classified into 4 types:

  • type 1: only kyphotic angulation at the fracture site (no translation)

  • type 2: kyphotic angulation with anterior translation of the distal sacrum

  • type 3: kyphotic angulation with complete offset of the fracture fragments

  • type 4: comminuted S1 segment, usually due to axial compression

Morphologic injury patterns of zone 3 fractures

• “H” shaped fracture

• “U” shaped fracture

• “ʎ” (lambda)  shaped fracture

• “T” shaped fracture

Isler classification

Used for fractures that involve the lumbosacral articulation:

• Isler 1: fracture occurs lateral to the L5/S1 facet

• Isler 2: fractures line involves the L5/S1 facet

• Isler 3: fracture line extends medially to the L5/S1 facet