1.5 Fracture classification

Transcription

1 1 AO philosophy and basic principles 1.5 Fracture classification 1 Introduction 69 2 The principles of the Müller AO Classification of fractures long bones Overall structure and attributes Describing the fracture localization: bones and segments Describing the fracture morphology: types, groups, subgroups, qualifiers, and modifiers 74 3 Issue of classification validation Defining the classification process Research pathway to classification 83 4 Conclusion 83 5 Classification terminology 84 6 Bibliography 85 7 Acknowledgments PFxM2_1_5_T14F.indd 68 12/7/06 9:48:49 AM

2 Authors James F Kellam, Laurent Audigé 1.5 Fracture classification 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 1 Introduction Injury localization and severity are important factors influencing the surgeon s choice of treatment and the patient s anatomical and functional outcome. These factors are often catalogued according to the description and subsequent classification of fractures and soft-tissue lesions. In this chapter, we will highlight the significance and practical application of fracture classification systems. The classifications of soft-tissue lesions are presented in chapter 1.6. Fracture classification systems have multiple purposes. They should facilitate communication between physicians and assist documentation and research. For clinical relevance, they should have a prognostic value for the outcome of patients, and assist physicians in their planning of managing fractures. The basis of all clinical activity, be it assessment and treatment, investigation and evaluation, or learning and teaching, must be sound data: properly assembled, clearly expressed, and readily accessible. Numerous fracture classification systems have been proposed in orthopedics [1, 2, 3], but only a small number of them have become widely accepted in practice, one such being the Müller AO Classification of fractures long bones [4], while even fewer have stood the rigorous test of validation [5]. In its early days the AO group sought to document all the fracture cases treated by its members. Quality control was a principal reason for this major effort at the outset of the AO s work. There was a need, during this pioneering phase, to assess the efficacy and the risks of what, at that time, were often viewed as very aggressive methods of fracture management. However, as the volume of information increased it became clear that some means of codification had to be found, so that data could readily be added and extracted. This meant the development of a workable system of fracture classification [6]. Of course, the concept of classifying fractures was not new. On the contrary, almost every kind of fracture had attracted at least one classification of its own, which was often of considerable value in actual management. However, these groupings were usually freestanding and uncoordinated, and proved not very helpful for comparisons between the outcomes of different treatment regimes [3, 7]. What was needed was a classification system that would not only be universally applicable but also universally acceptable. Maurice E Müller and his associates set about this monumental task and developed the Müller AO Classification of fractures long bones. The Müller AO Classification has been variously published and titled. Some of its elements appeared in the first and second AO manuals. Its first complete version was published in French as the AO Classification ( classification AO des fractures ) [8] and shortly afterwards in English [4] as the comprehensive classification of fractures (CCF), both by Müller et al. Various helpful leaflets presenting a summary of the classification as well as the classification in CD format have also been published. The system for long bones has been expanded by the addition of classifications for pelvic [9] and spinal fractures [10]. Other systems, such as for foot fractures [11], are still being developed. The latest comprehensive publication in print was in 1996 in the form of a supplement to volume 10 of the Journal of Orthopaedic Trauma [12], where the numbering of the smaller bones was more complete. The AO Foundation has established a committee to maintain the quality and consistency of the Müller AO/OTA Classification. Work on the classification of fractures of other skeletal areas continues, based on the principles highlighted in this chapter and with 69 PFxM2_1_5_T14F.indd 69 12/7/06 9:48:50 AM

3 1 AO philosophy and basic principles 91- an emphasis on providing scientific evidence of validity. Recently, an adaptation of the Müller AO Classification of fractures long bones to pediatric fractures was proposed following initial scientific validation [13] as presented in this chapter. This chapter presents the principles of application of the Müller AO Classification of fractures long bones, and the adaptation recently made for pediatric fractures. For classification systems of other skeletal areas, the readers should consult the references presented in Tab 1.5-1, as well as the corresponding chapters in this book. The coding of bones is that used by the Orthopaedic Trauma Association (OTA) [12], which is shown in Fig Coding 1 Regions/ bones Chapter in this book Other relevant references 1- Humerus 2- Radius/ ulna Spine Craniomaxillofacial bones 15- Clavicula 14- Scapula 6- Pelvis/acetabulum 14 Scapula Clavicle Hand 5 Spine [10] 61 Pelvic ring 6.4 [9] 62 Acetabulum 6.5 [9, 14] 7 Hand [15] 34 Patella Femur/patella Foot [11] 91 Craniomidface 2 [16] Foot Fig AO/OTA system for numbering the anatomical location of a fracture in three bone segments (proximal = 1, diaphyseal = 2, distal = 3). 4- Tibia/fibula 92 Mandible 2 [17] 1 Some differences in the numbering of some bones between the comprehensive and OTA versions [12] of the Müller AO Classification [4, 14] have been resolved according to this consensus in Projects for the development or revision and validation of fracture classifications in these skeletal areas are being conducted as part of the activities of the AO Classification Supervisory Committee. Tab Overall structure of the Müller AO/OTA Classification (long-bone classification excepted). 70 PFxM2_1_5_T14F.indd 70 12/7/06 9:48:50 AM

4 1.5 Fracture classification 2 The principles of the Müller AO Classification of fractures long bones 2.1 Overall structure and attributes Any classification system should offer competence in the acquisition, storage, and retrieval of data; Müller s system provides a framework within which a surgeon can recognize, identify, and describe long-bone injuries. It presents a way not only to document fractures but to understand them in biomechanical and biological terms. The system is based on well defined terminology, which allows the surgeon to consistently describe the fracture in as much detail as required for the clinical situation. This description is the key to classification and forms the basis for the alphanumeric code that allows documentation and research. If the surgeon is to make full use of this system, the first aim must be to identify what Müller has 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 challenge faced by the surgeon is to put into words, and subsequently codes, what is understood as prime characteristics of the fracture, which will determine its management and/or the anticipated outcome. Classification or diagnosis is an ongoing process depending on the information available to the surgeon at any given time. Only when all information concerning the fracture is collected, may the classification be considered concluded and complete. But this is not the end of its usefulness as the clinical information, upon which it is built, helps surgeons to determine treatment. Diagnosis is obtained by combining the anatomical location and the morphological characteristics of the fracture. For each fracture the answers to the questions listed below will provide a detailed description as well as a 5-element alphanumeric code (Fig 1.5-2). This consists of a description of the location (bone segment), followed by the fracture type, and lastly the morphological characteristics of the fracture. Adults Diagnosis = essence of the fracture Localization Morphology Bone Segment - Type Group Subgroup (4) A B C long bones 3 or 4 segments 3 types 3 groups 3 subgroups Fig Alphanumeric structure of the Müller AO Classification of fractures long bones. 71 PFxM2_1_5_T14F.indd 71 12/7/06 9:48:52 AM

5 1 AO philosophy and basic principles Each major long bone (eg, humerus) and each specific anatomical region (eg, hand) as well as each bone region (segments) are named and numbered. The long bones are each divided into three segments (Fig 1.5-1). The fractures of each bone segment are then divided into three types with a further subdivision into three groups and their subgroups, generating a hierarchical organization in triads. These groups and subgroups are then arranged in an ascending order according to the morphological complexities of the fractures, the assumed difficulties inherent in their treatment, and their perceived prognosis. In this chapter, discussion of the classification is confined largely to bones, segments, types, and groups, as this is what is normally needed for everyday clinical application and communication. 2.2 Describing the fracture localization: bones and segments This fracture description or diagnosis must allow the surgeon to make rational decisions for treatment and allow communicating about the injury with others in a standardized logical fashion. The description and numbering of the bones has been decided by convention and becomes self-evident from Fig The bone is described by its anatomical name, followed by the fracture location within the bone. This description is translated into the first two numbers of an alphanumeric code. It should be noted that the two pairs of bones (radius and ulna, tibia and fibula) are each regarded as one long bone: 1 Humerus 2 Radius/ulna 3 Femur 4 Tibia/fibula The identification of the respective segment needs a little more consideration (Fig 1.5-3). Each long bone has three segments: 1 Proximal end segment 2 Diaphyseal segment 3 Distal end segment The patella and the malleolar segment (4) are exceptions of fractures in adults. In the malleolar segment this is due to the particular anatomical relationship to the tibia and the universal acceptance of the Weber ankle fracture classification, and therefore it is classified as the fourth segment of the tibia/ fibula. Other than in children, where a long bone is divided into a diaphyseal, two metaphyseal, and two epiphyseal parts (Fig 1.5-4) (chapter 4.4:4.2.1), in adults, the epiphysis and the metaphysis are considered one segment. Therefore, each adult long bone has three segments as described above. To determine the limits between the middle and the end segments, the 1 Some differences in the numbering of some of the smaller bones between the comprehensive and OTA versions of the Müller AO Classification have been resolved between the AO Classification Supervisory Committee and the OTA Coding and Classification Committee in PFxM2_1_5_T14F.indd 72 12/7/06 9:48:52 AM

6 1.5 Fracture classification end segments are defined by a square whose sides have the same length as the widest part of the epiphysis (exceptions: proximal femur (31-) and malleolus (44-), see caption of Fig 1.5-3). To assign each fracture to a segment, the center of the fracture must be determined. For a simple fracture, this is apparent as it is the mid point of an oblique or spiral fracture line and for a transverse fracture it is obvious. A wedge fracture has its center at the broadest portion of the wedge or the mid point of a fragmented wedge when reduced. For complex fractures the center may well have to be determined after reduction when the full extent of the fragmentation is determined. This may force the surgeon to classify after treatment but the fact that there is a complex fracture generally guides the treatment decision. A displaced articular fracture will always be classified as that of an end segment regardless of its diaphyseal fracture type, since the articular injury is the most important for treatment and prognosis Fig Anatomical location of the fracture. Anatomical location is designated by two numbers: one for the bone and one for its segment (ulna and radius as well as tibia and fibula are regarded as one bone). The malleolar segment (44-) is an exception. 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 (exceptions 31- and 44-). 73 PFxM2_1_5_T14F.indd 73 12/7/06 9:48:52 AM

7 1 AO philosophy and basic principles Children Diagnosis Localization Morphology Bone long bones Segment / Type E M D Child Severity segments 3 types 4 9 patterns 2 groups Exceptions I IV Fig Overall structure of the AO pediatric comprehensive classification of long-bone fractures. For more details see Slongo et al [13]. E = epiphysis, M = metaphysis, D = diaphysis. The adaptation of this system to pediatric fractures considers child-specific relevant fracture features (Fig 1.5-4). The anatomy is related to the four long bones and their three segments. Fracture localization, however, is classified further as epiphyseal (E), metaphyseal (M), or diaphyseal (D). The morphology of the fracture is documented by a type-specific child code, a severity code, as well as an additional exception code for displacement of specific fractures (chapter 4.4:4.2) [13]. 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. Types The descriptions of the types differ between diaphyseal fractures and proximal or distal end segment fractures (Tab 1.5-2). These descriptions of the fracture types are coded with three letters: A, B, and C. For the proximal humerus, proximal femur, and malleolar segment fractures special definitions are applied (Tab 1.5-3). Groups and subgroups Once a fracture whatever its bone segment has been recognized as one of the three fracture types (A, B, C), it may be further divided into three fracture groups (Tab 1.5-4, 1.5-5). For more specialized requirements these groups are further divided into three subgroups, either based on fracture location or fracture site morphology. The result comprises 27 subgroups for each bone segment and 81 subgroups for each bone. 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. The qualifiers are discussed in the respective chapters of this book. 74 PFxM2_1_5_T14F.indd 74 12/7/06 9:48:53 AM

8 1.5 Fracture classification Segment Type A B C 1 Proximal Extraarticular Partial articular Complete articular No involvement of displaced fractures extending into the articular surface Part of the articular component is involved, leaving the other part attached to the meta-/diaphysis Articular surface involved, metaphyseal fracture completely separates articular component from the diaphysis 2 Diaphyseal Simple Wedge Complex One fracture line, cortical contact between fragments exceeds 90% after reduction Three or more fragments, main fragments have contact after reduction Three or more fragments, main fragments have no contact after reduction 3 Distal Extraarticular Partial articular Complete articular No involvement of displaced fractures extending into the articular surface Part of the articular component is involved, leaving the other part attached to the meta-/diaphysis Articular surface involved, metaphyseal fracture completely separates articular component from the diaphysis Tab Definitions of fracture types for long-bone fractures in adults. For exceptions see Tab PFxM2_1_5_T14F.indd 75 12/7/06 9:48:53 AM

9 1 AO philosophy and basic principles Bone and segment Type A B C 11- Humerus, proximal Extraarticular, unifocal Tuberosity or nonimpacted/impacted metaphyseal Extraarticular, bifocal With or without metaphyseal impaction, or with glenohumeral dislocation Articular Displaced, impacted or dislocated 31- Femur, proximal 32- Femur, shaft, subtrochanteric See chapter Malleoli Extraarticular, trochanteric Pertrochanteric simple or multifragmentary, or intertrochanteric Extraarticular, neck Subcapital with displacement or transcervical Articular, head Split, depression or neck Infrasyndesmotic With or without medial lesion Transsyndesmotic, fibular With or without medial or posterior lesion Suprasyndesmotic With or without medial or posterior lesion Tab Exceptions in the classification of fracture types. 76 PFxM2_1_5_T14F.indd 76 12/7/06 9:48:54 AM

10 1.5 Fracture classification Type Group A Simple Spiral Oblique Transverse B Wedge Spiral Bending Multifragmentary C Complex Spiral Segmental Irregular Tab Classification of fractures of the diaphysis into the three fracture groups. 77 PFxM2_1_5_T14F.indd 77 12/7/06 9:48:56 AM

11 1 AO philosophy and basic principles Type Group A Extraarticular Simple Wedge Complex B Partial articular Split Depression Split-depression C Articular Simple articular, simple metaphyseal Simple articular, complex metaphyseal Complex articular, complex metaphyseal Tab Classification of fractures of the end segment into the three fracture groups. 78 PFxM2_1_5_T14F.indd 78 12/7/06 9:48:57 AM

12 1.5 Fracture classification Identifying a fracture step by step In illustrating the classification, the colors green, orange, and red denote 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. Thus, in identifying the information necessary to classify a fracture, one has already made progress in establishing its mechanism, severity, prognosis and in understanding the potential problems in treatment. Once the fracture has been described, it may be translated into an alphanumeric code. This code is extremely 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 seems logical to use this description for daily communication with colleagues. Müller and his colleagues [18] have refined the process of classification once the bone and the segment have been identified. The surgeon interrogates the fracture to establish not only its identity, but its essence as well. The essence of the fracture is the one feature(s) that makes the fracture different and may help in determining prognosis or treatment. This interrogation of the fracture usually takes a binary, an either/or approach: For most questions there is only one answer out of two possibilities. This binary concept also applies to the triad-based classification (Tab 1.5-6; 1.5-7). For a diaphyseal fracture of a long bone (Tab 1.5-6), the first binary question determines the type of fracture and relates to the severity of fracture: Is it simple or multifragmentary? The second binary question determines the group of fracture and relates to mechanism: Is it spiral or bending? The third binary question establishes the subgroup and will be determined by the specific characteristics of the fracture. In a fracture identified as an end segment long-bone fracture (Tab 1.5-7), the surgeon must determine whether the articular surface is involved. If so, the fracture is articular. The second binary question must tell whether the entire articular surface is separated from the diaphysis or not. A positive response classifies the fracture as complete articular. The next question relates to the number of fracture lines crossing the joint surface (one = simple; more than one = multifragmentary). The final question will ask how the metaphysis is fractured. This outline describes the standard method of using the Müller AO Classification of fractures long bones. However, no classification is all-inclusive and there are some exceptions to this system (Tab 1.5-3). These are based on anatomical variations such as the shoulder and hip or widespread accepted usage, such as for the ankle. 79 PFxM2_1_5_T14F.indd 79 12/7/06 9:48:58 AM

13 1 AO philosophy and basic principles Diaphyseal fracture Step Question Answer 1 Which bone? Specific bone (X) 2 Is the fracture at the end or in the middle segment of the bone? 3 Type: Is the fracture a simple or multifragmentary one (does it have > 2 parts)? Middle segment (X2) Simple (X2-A) If it is multifragmentary, go to step 3a 3a Is there contact between both fracture ends or not? If there is contact it is a wedge (X2-B) If there is no contact it is complex (X2-C) 4 Group: Is the fracture pattern caused by a twisting (spiral) or bending force? (Tab 1.5-4) Spiral or twisting forces will result in a simple spiral (X2-A1), a spiral wedge (X2-B1), or a spiral fragmented complex fracture (X2-C1) Bending forces produce simple oblique (X2-A2), simple transverse (X2-A3), bending wedge (X2-B2), fragmented wedge (X2- B3), or complex (X2-C3) fractures C2 fractures are segmental by definition 5 The next question will be specific to the fracture, its prognosis or treatment. For example, in the tibia the surgeon s question is aimed at locating the level of the fibular fracture. Tab Steps in identifying diaphyseal fractures. 80 PFxM2_1_5_T14F.indd 80 12/7/06 9:48:59 AM

14 1.5 Fracture classification End segment fracture Step Question Answer 1 Which bone? Specific bone (X) 2 Is the fracture at the end or middle segment of the bone? 3 Is the fracture through the proximal or distal end segment? End segment Proximal (X1) Distal (X3) 4a Type: Does the fracture enter the articular surface? If it does not enter it is extraarticular (XX-A), go to step 6 If it enters it is articular, go to step 4b 4b Type: Is it partial or total articular? If part of the joint is still attached to the meta-/diaphysis it is partial articular (XX-B) If it is not attached to the diaphysis it is complete articular (XX-C) 5 Group: How many fracture lines cross the joint surface? If there is one line it is simple If there are > 2 lines it is multifragmentary 6 Group: How is the metaphysis fractured? Simple: extraarticular (XX-A1), or simple articular (XX-C1) 7 This question determines the subgroups and is fracture specific. Wedge: extraarticular (XX-A2) Complex: extraarticular (XX-A3), or simple articular (XX-C2), or complex articular (XX-C3) Tab Steps in identifying end segment fractures. 81 PFxM2_1_5_T14F.indd 81 12/7/06 9:48:59 AM

15 1 AO philosophy and basic principles 3 Issue of classification validation 3.1 Defining the classification process While a fracture classification system represents the important diagnoses to be made for treatment decisions, it says nothing about how surgeons should proceed to make a reliable and accurate diagnosis. This is similar to a situation in which a clinician is asked to diagnose infectious diseases without knowing which tests to use for which disease and how reliable these tests are. In the context of fracture classification systems, it is now a requirement that classification processes be defined and evaluated before a classification system may be used with confidence. These are the diagnostic procedures surgeons should follow to allocate fractures to respective classification categories. A classification process is complex and may be described in terms of several components such as history and physical examination; diagnostic imaging: image modalities used, such as specific x-ray projections or CT scans, or direct observation of the fractured bones during open reduction; timing of classification: before treatment, after fracture manipulation or reposition, or after fracture fixation; type and training of the observer(s): expert surgeon, trainee, research assistant, or radiologist; use of recording tool(s): a measurement made on the diagnostic images using a ruler, a set of square patterns on a transparency, or the use of specific classification software; method of obtaining and selecting clinical information: a systematic and standardized approach for multiple coding such as the binary questioning of the Müller AO Classification of fractures long bones; the diagnostic rule: a single diagnosis or a consensus diagnosis between two or more observers. The process of classifying pediatric long-bone fractures has recently been evaluated [13]. It involved the examination of standard AP and lateral x-rays taken before treatment. The initial results demonstrated that the determination of the specific definition of fractures and their location needed to be standardized. Templates were created to allow the surgeon to accurately determine the end segment and fracture angle. These two simple additions improved the reliability of the classification process. More detailed diagnostic procedures or the development of specific classification software may be required for complex fractures or difficult anatomical locations. With classification systems including multiple diagnostic decisions, a systematic approach in reading diagnostic images may provide valuable guidance to surgeons and lead to more accurate classification. For instance, the binary questioning introduced for the Müller AO Classification has the additional benefit of leading surgeons through important diagnostic items. If a choice cannot be made from the two answers, the imaging is probably inadequate and more information is needed. The use of invasive, expensive or complex diagnostic procedures might be necessary for definite and accurate classification. Such classification processes should be considered as the reference standard and should be applied whenever possible. However, timing, cost, ethics, and other factors may be prohibitive and compromises must be made by using other methods that probably are less reliable and accurate. Surgeons should ensure that the compromises are still acceptable for the treatment of their patients. 82 PFxM2_1_5_T14F.indd 82 12/7/06 9:48:59 AM

16 1.5 Fracture classification 3.2 Research pathway to classification Fracture classification systems should have a prognostic value for patients, and assist physicians in planning the fracture management. However, the key to the understanding of a fracture classification is a reliable and accurate description. Reliability evaluates how well repeated applications of the classification process on the same fracture agree with each other. Accuracy measures how well classification diagnoses agree with the true fracture status. This true status may not be known or observable, but can be best recorded by an acceptable reference standard classification process (an excellent reference standard is often referred to as a gold standard). It is important to estimate these parameters before a classification system is applied in clinical practice [5, 6, 19 21]. There are many factors influencing classification reliability and accuracy which may be difficult to address. Available diagnostic imaging techniques may be inherently imperfect [22]. In addition, classification systems often transform continuous variables into categorical ones; for instance the obliquity of diaphyseal fractures is reduced to a dichotomous variable (< 30 versus > 30 ) in the Müller AO Classification of fractures long bones [4]. Following the steps of Müller and his colleagues and a long history of fracture classification at the AO Foundation, the AO Classification Supervisory Committee and AO Clinical Investigation and Documentation are implementing projects aimed at the development and validation of fracture classification systems. Cooperation with the Orthopaedic Trauma Association was initiated to achieve wide consensus in this endeavor. Each project follows a sequential path of research and development with three phases, so that classification systems can be regarded as validated [23]. The first phase of development is conducted by surgeons with expertise in the management of the type of fracture being investigated. Its objective is to provide a clear definition of the proposed classification system as well as the process used to allow reliable and accurate diagnosis. This is a long and difficult exercise that often requires a series of pilot agreement studies to test the understanding and adequacy of the definitions, whereby experts are asked to classify large series of representative cases. For instance, the pediatric long-bone fracture classification mentioned in this chapter required four pilot agreement studies over two years, with five surgeons and up to 270 cases to complete this phase [13, 24]. Once pilot agreement studies have provided acceptable results among clinical experts, the classification process is then tested in a second phase among a larger group of surgeons with different levels of training and from multiple centers. This is a critical step since reliability and accuracy results should be duplicated in clinical settings. In addition, this phase allows consultation among surgeons worldwide as well as initial use in clinical settings. The last phase of validation is conducted via a prospective clinical study where patients are followed to assess their treatment and outcomes, so that the prognostic value of tested classification systems can be documented. After completion of this third phase a classification may be officially validated. It is, however, recommended that its value is monitored over time and that the classification is adapted to any significant clinical changes (eg, new options in diagnostic imaging or treatment). 4 Conclusion Given the evolving and progressive nature of our understanding of fractures, and the consequent development of new treatment techniques that may influence outcomes, a fracture 83 PFxM2_1_5_T14F.indd 83 12/7/06 9:49:00 AM

17 1 AO philosophy and basic principles classification, while remaining consistent, must be adaptable. This is important in face of the dynamic developments in treatment which, in particular, may influence the prediction and evaluation of outcomes [20]. The founding generation of AO surgeons has bequeathed, in the AO Comprehensive Classification, a very potent means to maintain the quality of our fracture management [25]. The present generation must rise to the challenge of maintaining its unique value while keeping it sufficiently flexible to accommodate new techniques and instruments and widening perceptions. 5 Classification terminology The main glossary is to be at the end of the book. The following list of terms used in classification may be helpful in order to understand this chapter. accuracy Validation parameter that measures how well classification diagnoses fit with the truth. articular Fractures which involve the joint surface. They are subdivided into partial articular and complete articular fractures. articular, partial Only part of the joint is involved while the remainder remains attached to the diaphysis. articular, complete The joint surface is fractured and the entire joint surface is separated from the diaphysis. The severity of these fractures depends on whether their articular and metaphyseal components are simple or multifragmentary. classification system The set of fracture categories and its structure that defines the important fracture diagnoses to be made. The Müller AO Classification of fractures long bones is a classification system. classification process The method by which surgeons allocate fractures to respective classification categories. Such a process can be understood as a diagnostic test. complex Fracture with one or more intermediate fragment(s) in which there is no contact between the main fragments after reduction. The complex fractures are spiral, segmental, or irregular. extraarticular Fracture does not involve the articular surface but may be within the capsule of the joint. They include apophyseal and metaphyseal fractures. impacted A fracture in which the opposing bone surfaces are driven into each other and behave as a single unit. This is a combined clinical and radiological diagnosis. multifragmentary A fracture with more than one fracture line so that there are three or more pieces. It includes wedge and complex fractures. multifragmentary depression A fracture in which part of the joint is depressed and the fragments are completely separated. pure depression An articular fracture in which there is only a depression of the articular surface without a split. The depression may be central or peripheral. pure split An articular fracture in which there is a longitudinal metaphyseal and articular split, without any additional osteochondral lesion. reference standard classification process An accepted prac-tical classification process that is most likely to record the truth, or the essence of the fracture. An excellent (perfect or almost perfect) reference standard is referred to as a gold standard. 84 PFxM2_1_5_T14F.indd 84 12/7/06 9:49:00 AM

18 1.5 Fracture classification reliability Validation parameter that measures to what extent codings from repeated applications of the classification process on the same fractures agree. simple There is a single fracture line producing two fracture fragments. Simple fractures of the diaphysis or metaphysis are spiral, oblique, or transverse. wedge Fracture complex with a third fragment in which, after reduction, there is some direct contact between the two main fragments. 6 Bibliography [1] Rockwood CA, Green DP, Bucholz RW, et al (1996) Rockwood and Green s Fractures in Adults. 4th ed. Philadelphia, New York: Lippincott-Raven. [2] Browner BD, Jupiter JB, Levine AM, et al (1998) Skeletal Trauma Fractures, Dislocations, Ligamentous Injuries. 2nd ed. Philadelphia, London, Toronto, Montreal, Sydney, Tokyo: W.B. Saunders. [3] Bernstein J, Monaghan BA, Silber JS, et al (1997) Taxonomy and treatment a classification of fracture classifications. J Bone Joint Surg Br; 79(5): [4] Müller ME, Nazarian S, Koch P, et al (1990) The Comprehensive Classifi cation of Fractures of Long Bones. 1st ed. Berlin, Heidelberg, New York: Springer-Verlag. [5] Audigé L, Bhandari M, Kellam J (2004) How reliable are reliability studies of fracture classifications? A systematic review of their methodologies. Acta Orthop Scand; 75(2): [6] Colton CL (1991) Telling the bones. J Bone Joint Surg Br; 73(3): [7] Colton CL (1997) Fracture classification A response to Bernstein et al. J Bone Joint Surg Br; 79 (5): [8] Müller ME, Nazarian S, Koch P (1987) Classifi cation AO des fractures. Tome I. Les os longs. 1st ed. Berlin: Springer-Verlag. [9] Tile M (2003) Fractures of the Pelvis and Acetabulum. 3rd ed. Philadelphia: Williams & Wilkins. [10] Magerl F, Aebi M, Gertzbein SD, et al (1994) A comprehensive classification of thoracic and lumbar injuries. Eur Spine J; 3(4): [11] Zwipp H, Baumgart F, Cronier P, et al (2004) Integral classification of injuries (ICI) to the bones, joints, and ligaments application to injuries of the foot. Injury; 35 (Suppl 2):SB3 9. [12] Orthopaedic Trauma Association Committee for Coding and Classification (1996) Fracture and dislocation compendium. J Orthop Trauma; 10 (Suppl 1): V IX, [13] Slongo T, Audigé L, Schlickewei W, et al (2006) Development and validation of the AO pediatric comprehensive classification of longbone fractures by the Pediatric Expert Group of the AO Foundation in collaboration with AO Clinical Investigation and Documentation and the International Association for Pediatric Traumatology. J Paediatr Orthop; 26(1): [14] Judet R, Judet J, Letournel E (1964) Fractures of the acetabulum: classification and surgical approaches for open reduction. Preliminary report. J Bone Joint Surg Am; 46: [15] Petracic B, Siebert H (1998) AO Classification of fractures of the hand bones. Handchir Mikrochir Plast Chir; 30(1): [16] Buitrago-Tellez CH, Schilli W, Bohnert M, et al (2002) A comprehensive classification of craniofacial fractures: postmortem and clinical studies with two- and three-dimensional computed tomography. Injury; 33(8): [17] Spiessl B (1989) AO Classification of Mandibular Fractures. Spiessl B (ed), Internal Fixation of the Mandible: A Manual of AO/ASIF Principles with a Contribution by B. Rahn. 1st ed. Berlin, Heidelberg, New York: Springer-Verlag. [18] Müller ME (1996) CCF Comprehensive Classifi cation of Fractures I & II. M.E.Müller Foundation. Bern: MAO/ASIF Documentation Center. [19] Garbuz DS, Masri BA, Esdaile J, et al (2002) Classification systems in orthopaedics. J Am Acad Orthop Surg; 10(4): [20] Burstein AH (1993) Fracture classification systems: do they work and are they useful? J Bone Joint Surg Am; 75(12): [21] Martin JS, Marsh JL (1997) Current classification of fractures. Rationale and utility. Radiol Clin North Am; 35(3): [22] Martin JS, Marsh JL, Nepola JV, et al (2000) Radiographic fracture assessments: which ones can we reliably make? J Orthop Trauma; 14(6): [23] Audigé L, Bhandari M, Hanson B, et al (2005) A concept for the validation of fracture classifications. J Orthop Trauma; 19(6): [24] Audigé L, Hunter J, Weinberg A, Magidson J, et al (2004) Development and evaluation process of a paediatric long-bone fracture classification proposal. Europ J Trauma; 30(4): [25] Orozco R, Sales JM, Videla M (2000) Atlas of Internal Fixation. Fractures of Long Bones. 1st ed. Berlin, Heidelberg, New York: Springer-Verlag. 7 Acknowledgments We wish to thank William M Murphy and Dieter Leu for their contribution to this chapter in the first edition of the AO Principles of Fracture Management. 85 PFxM2_1_5_T14F.indd 85 12/7/06 9:49:00 AM