Müller AO Classification of fractures


The Müller AO Classification of fractures is a system for classifying bone fractures initially published in 1987 by the AO Foundation as a method of categorizing injuries according to therognosis of the patient's anatomical and functional outcome. "AO" is an initialism for the German "Arbeitsgemeinschaft für Osteosynthesefragen", the predecessor of the AO Foundation.
It is one of the few complete fracture classification systems to remain in use today after validation.

Comprehensive classification of the long bones

The English language version of the system allows consistent in detail description of a fracture in defined terminology by creating a 5-element alphanumeric code:

Localisation

First, each fracture is given 2 numbers to describe which bone it affects, and where in the bone:
1234
BoneHumerusRadius and UlnaFemurTibia and fibula
SegmentProximal segmentDiaphyseal segmentDistal segmentMalleolar segment (only used with tibia and fibula

Type

Each fracture is next given a letter to describe the joint involvement of the fracture:
SegmentABC
1Extra-articularPartial articularComplete articular
2SimpleWedgeComplex
3Extra-articularPartial articularComplete articular

The exceptions to this step include:
LocalisationABC
11 - Proximal humerusExtra-articular, unifocalExtra-articular, bifocalArticular
31 - Proximal femurExtra-articular, trochantericExtra-articular, neckArticular, head
44 - MalleoliInfrasydesmoticTransyndesmoticSuprasyndesmotic

Groups & Subgroups

Finally, the fracture is given 2 further numbers to denote the fracture pattern and geometry.
For segment 2 fractures:
For segment 1 and 3 fractures:
Subgroups are then used to describe the fractures in terms of displacement, rotation, angulation and shortening.

AO pediatric comprehensive classification of long bone fractures

A pediatric version of the long-bone classification was published in 2006 to further classify fractures of immature bone and so the effects on future growth:

OTA/AO Classification unifying extension

The Orthopaedic Trauma Association Committee for Coding and Classification initially published their classification system covering the whole skeleton in 1996. In 2006 they published a revision, unifying the Muller/AO and OTA systems into a single alphanumeric classification: