1.4 Fracture classification
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1 Introduction
“A classification is useful only if it considers the severity of the bone lesion and serves as a basis for treatment and for evaluation of the results.” Maurice E Müller
Fracture localization and severity are important factors influencing the surgeon′s choice of treatment and the patient′s functional outcome. These factors are often catalogued into a classification that should facilitate communication among physicians, assist physicians in their treatment, aid documentation and research and have a prognostic value for patients [1–3]. Almost every kind of fracture has at least one classification. However, these groupings were usually freestanding and uncoordinated and were not helpful for comparisons [3–5]. What was needed was a classification system that would be universally applicable and universally acceptable. Maurice E Müller and associates set about this monumental task and developed the Müller AO/OTA Classification of Fractures—Long Bones [6] first published in French as the AO Classification (“classification AO des fractures”) [6, 7]. The system for long bones has been expanded by the addition of classifications for fractures of the pelvis [8], spine [9], hand [10], and foot [11]. In 1996, the AO Foundation and the Orthopaedic Trauma Association agreed to develop a Fracture Classification Compendium encompassing all appendicular bones, pelvis, and spine based on the principles and definitions of the Müller system [12, 13]. This compendium was updated in 2018 [14]. Children′s fractures have also been incorporated into the compendium following initial scientific validation [15–17].
2 Principles of the AO/OTA Fracture and Dislocation Classification (based on the Müller AO Classification)
2.1 Overall structure and attributes
Diagnosis is an ongoing process of collecting information about the fracture. In many clinical situations, treatment decisions can be made before all information is available.
Classification, however, is completed when all information is collected, including intraoperative observations.
The AO/OTA system is based upon well-defined terminology that allows the surgeon to describe consistently the fracture in as much detail as required for the clinical situation. This description is the key to the classification and aids understanding in biomechanical and biological terms. It forms the basis for an alphanumeric code for documentation and research.
The first aim is to identify what Müller called “the essence of the fracture”. This is the attribute that gives the fracture its particular identity and enables it to be assigned to one particular type rather than another. The defined terminology translates the prime characteristics of the fracture into words and subsequently codes, allowing it to be classified.
The classification′s terminology provides a complete description of the fracture with regard to location (bone segment) and morphology of the fracture ( Fig 1.4-1 ).
2.2 Describing the fracture localization: bones and segments
The bone is described by its anatomical name, followed by the fracture location within the bone. The numbering of the bones has been decided by convention and becomes self-evident from Fig 1.4-1 . This description is translated into the first number of an alphanumeric code Fig 1.4-2 .
The identification of the respective segment needs more consideration. Each long bone has three segments: a middle portion or diaphysis and two end segments or metaphyses. The tibia/fibula is an exception due to the malleolar segment (44). Because of the anatomical relationship to the tibia and the universal acceptance of the Weber ankle fracture classification, the malleolar segment is classified as the fourth segment of the tibia/fibula.
In adults, the epiphysis and the metaphysis are fused and are considered one segment—the metaphysis or end segment. The end segment is defined by a square whose sides have the same length as the widest part of the metaphysis (exception: proximal femur). Therefore, each adult long bone has three segments: one shaft (diaphysis) and two end segments (metaphysis). The proximal end segment is labeled 1, the shaft is 2, and the distal end segment is 3 ( Fig 1.4-3 ).
2.3 Describing the fracture morphology: types, groups, subgroups, qualifiers, and modifiers
The morphology of the fracture is described by precise definitions allowing the surgeon to determine the type, group, and subgroup.
2.3.1 Types
The descriptions of the types differ between diaphyseal and metaphyseal (end-segment) fractures ( Table 1.4-1 ). Fractures can be simple, with a single fracture line that produces two fracture fragments or have additional fracture lines to produce multiple fragments (three or more).
Segment | Type | ||
A | B | C | |
Proximal 1 |  Extraarticular |  Partial articular |  Complete articular |
Diaphyseal 2 |  Simple |  Wedge |  Multifragmentary |
Distal 3 |  Extraarticular |  Partial articular |  Complete articular |
The types of diaphyseal fractures are:
Simple—type A with a single circumferential fracture.
Wedge—type B fracture with one or more intermediate fragments. After reduction there is some cortical contact between the main proximal and distal fragments.
Multifragmentary—type C with one or more intermediate fragments. After reduction there is no contact between the main proximal and distal fragments.
The types of end-segment fractures are:
Extraarticular—type A, when the fracture does not involve the joint surface.
Partial articular—type B, when the fracture involves one part of the articular surface while the remainder of the joint remains attached to the metaphysis and diaphysis.
Complete articular—type C, when the fracture has disrupted the joint surface, which is completely separated from the diaphysis.
For the proximal humerus, proximal femur, and malleolar segment, special definitions are applied. The description of proximal humerus uses the term “focal” to describe fracture lines. A unifocal fracture represents one fracture line (type A) and bifocal represents two fractures lines (type B) while type C fractures are articular. The proximal femur is defined as the segment of the proximal femur above a transverse line at the inferior border of the lesser trochanter. These are trochanteric fractures (type A), neck and subcapital fractures (type B), and fractures of the articular surface (type C). The malleolar segment is classified by the level of the lateral malleolar (fibula) fracture with respect to the syndesmosis. The fracture line is infrasyndesmotic (type A), transsyndesmotic (type B), and suprasyndesmotic (type C) ( Table 1.4-2 ).
2.3.2 Groups and subgroups
Once a fracture—whichever its bone segment—has been recognized as one of the three fracture types (A, B, or C), it may be described using further fracture groups.
For diaphyseal fractures, the simple fractures are divided into three groups: spiral (A1), oblique (greater than or equal to 30° to a line perpendicular to the long axis of the bone—A2), or transverse (fracture line less than 30° to a line perpendicular to the long axis of the bone—A3). Wedge fractures are divided into two groups: an intact wedge when there is a single wedge fragment (B2) or fragmentary wedge when there is more than one wedge fragment (B3). Multifragmentary (previously termed complex) also has two groups: intact segmental (C2) and fragmentary segmental (C3) ( Table 1.4-3 ) (see section 5 in this chapter). For more specialized requirements these groups may be further divided into three subgroups, either based on fracture location or fracture site morphology. In areas of particular complexity, further subgroups known as qualifiers may be applied. These qualifiers may help in the planning of treatment or may be important in predicting the outcome of a particular fracture.
Type | Group | ||
1 | 2 | 3 | |
Simple A |  Spiral |  Oblique |  Transverse |
Wedge B |  Intact |  Fragmentary | |
Multifragmentary C |  Intact segmental |  Fragmentary segmental | |
For end-segment fractures, the metaphyseal extraarticular fracture types are grouped as avulsion (A1), simple (A2), and multifragmentary (A3) while the partial articular fractures are grouped as simple (B1), B2 is variable and based upon the bone involved, and fragmentary (B3). The complete articular fractures are grouped as a simple fracture into the articular surface and simple metaphyseal fracture (C1), simple articular fracture with multifragmentary metaphyseal fractures (C2), and multifragmentary articular with multifragmentary metaphyseal fracture (C3) ( Table 1.4-4 ). For more information and further subclassifications (for research purposes), see the 2018 Fracture and Dislocation Classification Compendium in the Journal of Orthopaedic Trauma Supplement [14].
When identifying the information necessary to classify a fracture, the surgeon makes progress in establishing its mechanism, severity, prognosis, and begins to understand the potential problems in treatment. The description may be translated into an alphanumeric code that is useful for computer data acquisition. It may also be used as a method of communication with those who are familiar with the code. However, as the surgeon first has to describe the fracture to make an accurate diagnosis, it is logical to use this description for daily communication among colleagues and for research purposes.
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