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orthopaedic plaster cast related content

Sunday 23rd April 2017

 

AO Fracture Classification System 

 

The AO system of fracture classification may be used to describe any type of bony injury to any orthopaedic clinician anywhere in the world. The highly detailed and descriptive nature of the AO fracture classification system serves to identify multiple bony injury types and their severity. It also provides the information upon which to base treatment and to complete an assessment of the injury resolution.

 

The key objective of this alphanumeric coding system of fracture classification is to be able to describe a fracture with sufficient detail for the specific clinical circumstances. What the classification system provides is a code comprising five elements, which are used to convey the essence of the fracture. Each bone class is divided into three segments and the fractures of each segment are divided into three types with subdivisions into groups and subgroups comprising three classes each.

 

The organisation of the resulting fracture codes is a series of hierarchical triads. Groups and subgroups are arranged in ascending order of the morphological complexities of the fracture along with any assumed difficulties in their treatment and the perceived prognosis. The essence of a fracture is discovered by identifying and indicating the bone, the segment, the fracture type and the morphological group/subgroup to which the fracture belongs.

The images which appear on these web pages describing the AO system of fracture classification have been used to demonstrate the concepts under discussion and they are all used with the kind permission of the AO Foundation.  

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

N.B. The AO fracture classification system is under constant review and the reader should be aware that a revision and some changes are currently being finalised for eventual publication in early 2018.

 

There are several long bones which are of great interest to cast technicians because these are the bones which we usually have to enclose in a cast. The long bones are the humerus, radius, ulna, femur, tibia and fibula. Within the AO system of fracture classification both the radius/ulna and the tibia/fibula are regarded as if they are one long bone. Each of these long bones is assigned an index number and the bones are divided into three segments which are also assigned an index number as follows:

 

 

 

 

 

 

 

The anatomical fracture site is designated by the first two numbers; which are used to denote the bone name and the location of the segment which carries the fracture. e.g. 11 would denote a proximal humeral fracture. 23 would denote a distal radial fracture. 32 would denote a diaphyseal femoral fracture. The malleolar segment (44-) and the femoral head (31-) are exceptions. The proximal and the distal segments of long bones are defined by a square whose sides have the same length as the widest part of the epiphysis with the exception of the femoral head and the malleolar area.

 

 

 

 

 

 

 

 

 

note: each character used in a code is a separate part of the classification and in the example case of a fractured distal radius… the first two characters of the derived fracture classification code are not verbally stated as “twenty three”. The classifying numbers are stated, while being very clearly separated, as in this next example. “two-three”. This will ensure that the separate elements of the classification code are understood correctly.

 

The essence of an adult fracture is determined by its localisation and morphology. The table below demonstrates how fractures are characterised by which bone and which segment of the bone is fractured. The type of fracture and the shape and position of the fractured fragments aids the operator with the way that fractures are classified. 

 

 

 

 

 

Fracture Classification Tables

It is first decided upon which bone the fracture is located. That bone may be the humerus (1) the radius and ulna (2) the femur (3) or the tibia and fibula (4).

 

The observer then classifies the fracture type according to its location along the long bone where the injury has occurred. The fracture is assigned a number based upon whether its located position is proximal (1) diaphyseal (2) or distal (3).

 

Proximal injuries are further divided into the following types. These are Extraareticular (A) Partial Articular (B) or Complete Articular (C) Diaphyseal Injuries are divided into groups which are either Simple (A) Wedge (B) or they can be Complex (C). Distal injuries mirror the proximal classifications with Extraareticular (A) Partial Articular (B) or Complete Articular (C).

 

 

 

 

 

 

 

 

 

 

 

There are special definitions applied to proximal humerus, proximal femur and malleolar segment fractures.  The table following this paragraph will illustrate the differences in detail and description for these fracture types.  

 

 

 

 

 

 

 

 

 

 

 

 

Diaphyseal fractures are assigned one of three groups. 

 

 

 

 

 

 

 

 

 

 

 

The end segment fractures are also divided into three groups 

 

 

 

 

 

 

 

 

 

 

The colours are used to denote the progressive severity and/or difficulty in treatment. Therefore, A1 indicates the fracture with the best prognosis and one that is easiest to treat operatively. C3 represents the fracture with the worst prognosis and one that may be very difficult to manage operatively.

 

The value to the cast technician in knowing how this fracture  classification system is used is that we gain an insight into the potential difficulties of treatment and prognosis. We can also transmit accurate knowledge to the orthopaedic clinician who may be taking a phone call from the cast technician in the emergency department. Accuracy of observation and clinical recording are greatly enhanced with the use of a common language that is understood by all.

 

I recommend the use of this system of fracture classification to my cast technician colleagues. It takes a while to learn how to use it well but it becomes second nature as you get used to the terminology and the use of the system. It also promotes clarity when considering the injury which you may find yourself treating; e.g. especially in the absence of skilled and senior orthopaedic clinical input, in a country with limited income and resources.

Copyright by AO Foundation, Switzerland

Source: AO Principles of Fracture Management

T.P. Rüedi R.E. Buckley C.G. Moran

AO/OTA system for numbering the anatomical location of a fracture  

in three bone segments (proximal = 1, diaphyseal = 2, distal = 3)

                                 Bone                                                        Segment

                                 Humerus - 1                                  Proximal - 1

                                 Radius/Ulna - 2                      Diaphyseal - 2

                                 Femur - 3                                               Distal - 3

                                 Tibia/Fibula - 4

Copyright by AO Foundation, Switzerland

Source: AO Principles of Fracture Management

T.P. Rüedi R.E. Buckley C.G. Moran

The anatomical location of a fracture

The essence of a fracture

Copyright by AO Foundation, Switzerland

Source: AO Principles of Fracture Management

T.P. Rüedi R.E. Buckley C.G. Moran

Copyright by AO Foundation, Switzerland

Source: AO Principles of Fracture Management

T.P. Rüedi R.E. Buckley C.G. Moran

Definitions of fracture types for long-bone fractures in adults

Exceptions in the cases of fracture classification

Copyright by AO Foundation, Switzerland

Source: AO Principles of Fracture Management

T.P. Rüedi R.E. Buckley C.G. Moran

Copyright by AO Foundation, Switzerland

Source: AO Principles of Fracture Management

T.P. Rüedi R.E. Buckley C.G. Moran

Copyright by AO Foundation, Switzerland

Source: AO Principles of Fracture Management

T.P. Rüedi R.E. Buckley C.G. Moran