The AO/OTA classification is one of the systems for classifying pelvic ring fractures. Like other fractures, they are divided into three groups subject to the severity and complexity of the respective injury 1:
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type A: intact posterior arch
- A1: a pelvic or innominate bone avulsion fracture
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A2: pelvic or innominate bone fracture
- A2.1 iliac wing fracture
- A2.2 unilateral anterior arch fracture
- A2.3 bilateral anterior arch fracture
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A3: transverse sacral fracture
- A3.1 simple oblique fracture
- A3.2 simple transverse fracture
- A3.3 wedge fracture or multifragmentary fracture
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type B: incomplete posterior arch disruption*
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B1: incomplete posterior arch disruption with no rotational instability
- B1.1 pelvic lateral compression fracture
- B1.2 open book fracture
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B2: unilateral posterior injury with rotational instability
- B2.1 lateral sacral compression fracture with internal rotational instability
- B2.2 lateral iliac crescent compression fracture with internal rotational instability
- B2.3 unilateral injury with an open book or external rotational instability
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B3: bilateral posterior injury with rotational instability
- B2.1 internal rotational instability on one side and external rotational instability on the other
- B2.2 bilateral sacral compression fracture
- B2.3 bilateral injury with an open book or external rotational instability
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B1: incomplete posterior arch disruption with no rotational instability
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type C: pelvic ring fracture with complete posterior arch disruption*
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C1: unilateral posterior arch disruption or vertical shear injury
- C1.1 iliac bone fracture
- C1.2 sacroiliac joint disruption
- C1.3 sacral fracture
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C2: bilateral posterior arch injury with complete disruption of one side and incomplete disruption of the other**
- C2.1 complete disruption of the iliac bone
- C2.2 complete disruption of the sacroiliac joint
- C2.3 complete disruption of the sacral bone joint
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C3: complete bilateral posterior arch disruption
- C3.1 bilateral posterior arch disruption outside the sacrum (iliac bone or sacroiliac joint)
- C3.2 sacral disruption on one side, outside the sacral bone on the other
- C3.3 bilateral sacral bone disruption
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C1: unilateral posterior arch disruption or vertical shear injury
*qualifications of type B and type C fractures include the following:
- unilateral (ipsilateral or contralateral) pubic ramus fractures
- bilateral pubic ramus fractures
- symphyseal disruption
- parasymphyseal fracture
- tilt fracture
- locked symphysis
** qualifications include the following
- contralateral posterior compression injuries of the sacrum or iliac crescent
- contralateral sacroiliac joint injury or fracture-dislocation with external rotation of the pelvic wing