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AO Classification of Fractures

The AO group has developed a comprehensive classification of fractures. The classification is arranged in order of increasing severity according to the complexities of the fracture, difficulty of treatment and worsening prognosis. The full AO classification is available, with some example X-rays, in the Trauma Imagebank

The classification is generally arranged as:


Femur,
Pertrochanteric, multifragmentary,
One intermediate fragment
The first number represents the long bone:
  1. Humerus
  2. Radius & ulna
  3. Femur
  4. Tibia & fibula
The next defines the bone segment.
  1. Proximal
  2. Middle
  3. Distal
  4. (Malleolar)
The proximal and distal segments are defined as a square whose sides are equal to the maximum widge of the epiphysis (except for proximal femur 31- and malleolar area 44-).

The next letter, A,B or C, designates the fracture type. For diaphyseal fractures these are simple (A), wedge (B) or complex (C). For proximal and distal segments these are extra-articular (A), partial articular (B) and complete articular (C).

The next number defines the fracture group, with that after the decimal it's subgroup. So in the example above the full diagnosis is given as:

3 - Femur
1 - Proximal
A - Trochanteric
2 - Pertrochanteric, multifragmentary
.
1 - One intermediate fragment

View the full AO classification of long bone fractures in the Trauma Imagebank