1.4 Fracture classification: biological significance

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1 Fracture classification: biological significance William M. Murphy & Dieter Leu 1 Introduction 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. Recognizing this, the AO group in its early days sought to document all the fracture cases treated by its members. Obviously, quality control, by whatever name it was then known, 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 were, at that time, often viewed as very aggressive methods of fracture management. However, it became clear, as the volume of information built up, that some means must be found of codifying it, so that data could readily be added and extracted. This meant the development of a workable system of fracture classification [1]. Of course, the concept of classifying fractures was not new. On the contrary, almost every fracture had attracted at least one classification of its own, which was often of considerable value in actual management. However, these groupings were usually free-standing and uncoordinated and proved quite unhelpful for comparisons between the outcomes of different treatment regimes [2, 3]. What was needed was a classification protocol which would be not only universally applicable but also universally acceptable. Maurice Müller and his associates set about this monumental task and it is a measure of its complexity that it was not until 1990 that the third edition of the AO Manual [4] carried an extended account of the AO Classification of Long Bones, based on the achievements of Müller s group as published in 1987 and 1990 [5, 6]. Work on classification of fractures of the axial skeleton as well as of the foot and hand followed and still continues. 1 1 Notes from the editors-in-chief T.P. Rüedi and W.M. Murphy: The AO Classification has been variously published and titled. Elements of it appeared in the first and second AO Manuals. The first complete version of the Long Bone Classification appeared in French as the AO Classification (1987) and shortly afterwards in English (1990) as the Comprehensive Classification, both by Müller et al. This modification, deriving from a SICOT Commission chaired by Professor Müller, was subsequently expanded by the addition of Pelvic and Spinal Classification, with work on the latter, as well as on foot and hand fractures, still developing. Various helpful leaflets presenting the classification in summary form and in CD format have also appeared. The latest comprehensive publication in print came in 1996 in the form of a supplement to Volume 10 of the Journal of the Orthopaedic Trauma Association. The numbering of the smaller bones is more complete in this than in the Comprehensive version and so we have adhered to it in this Volume. We have exercised our editorial discretion also in describing the classification as the AO Müller Classification, in a gesture of respect both to the documentation on which it is based and the remarkable genius who was its instigator. 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 The basis for all clinical activity must be sound data.

2 A fracture classification must be adaptable. The system presents a way not just to document fractures but to understand them in biomechanical and biological terms. The discipline of the alphanumeric notation serves to guide the surgeon s assessment of the fracture. The key which unlocks this fracture classification is accurate description. Within the AO, a decentralized documentation process has been developed, with the additional option of pooling the locally collected data from different centers. The AO clinical investigation and documentation department now provides guidelines and assistance in coordinating such multi-center clinical investigations from the planning phase to the final evaluation and publication. Underpinning this activity is the system on which Müller based his comprehensive fracture classification of the long bones, and on which other groups related to the AO Foundation have built or are building classifications of other skeletal areas. The system presents a way not just to document fractures but to understand them in biomechanical and biological terms. Needless to say, the state of the relevant soft tissues must also be diligently observed for incorporation into the decision-making process and recorded following the systems set out in chapter 1.5. Any classification system should offer competence in the acquisition, storage, and retrieval of data; what distinguishes Müller s system is that it provides a framework within which a surgeon can recognize, identify, and describe the injury to the bone. Thereafter, the other attributes of classification as defined by Müller at the head of this chapter can follow. The discipline of the alpha-numeric notation serves to guide the surgeon s assessment of the fracture to whatever depth the situation requires and afterwards to record and store his observations. However, it is the surgeon s description of the fracture which is central to the exercise. It is needed to permit good decision making in the light of the structured observations required by the classification protocol, and also to generate the code. It follows, given the evolving and progressive nature of our understanding of fractures, and the consequent development of new treatment techniques which may influence outcomes, that a fracture classification, while remaining consistent, must be adaptable. This is of importance in the face of dynamic developments in treatment which, in particular, may influence the prediction and evaluation of outcomes [7]. 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 [8]. 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. 2 The principles of the fracture classification If the surgeon is to make full use of this system, the first aim must be to identify what Müller has called as the essence of the fracture. This is the attribute which gives the fracture its particular identity and enables it to be assigned to one particular type rather than another. After this comes the process of putting into words what the surgeon understands as prime characteristics of the fracture, the challenges it brings, how it is to be managed, and what outcome may be anticipated with proper treatment. The key which unlocks this fracture classification, therefore, is accurate description. Each bone or bone region is numbered and the long bones are each divided into three segments (Fig and Fig ).

3 1.4 Fracture classification W.M. Murphy, D. Leu The plan of the classification The fractures of each bone segment are then divided into three types and with further subdivision into three groups and their subgroups (Fig ) generating a hierarchical organization in triads. The definitive subdivision of each group into subgroups may often be possible only after surgery, when the finer fracture details have been established. These groups and subgroups are then arranged in an ascending order of severity according to the morphological complexities of the fractures, the difficulties inherent in their treatment, and their prognosis Type Group Subgroup A A1 A2 A3 A1.1 A1.2 A1.3 A2.1 A2.2 A2.3 A3.1 A3.2 A Bone segment B C B1 B2 B3 C1 C2 C3 B1.1 B1.2 B1.3 B2.1 B2.2 B2.3 B3.1 B3.2 B3.3 C1.1 C1.2 C1.3 C2.1 C2.2 C2.3 C3.1 C3.2 C3.3 Fig : Numbering, according to the OTA system for the anatomical location of a fracture, in three bone segments (proximal 1, diaphyseal 2, distal 3). Fig : To express the morphological characteristics of the fracture three types are labeled A, B, and C. Each type is then divided into three groups A1, A2, A3, B1, B2, B3, C1, C2, C3.

4 Within this classification, the identity of any fracture emerges from the answers to the following questions: Fig : Which bone? Which bone segment? Which fracture type? Which group? Which subgroup? Within the binary concept, the surgeon asks a question to which the reply must be one of only two possible answers. 2.2 Bones, segments, types, and groups The subgroups represent three characteristic variations within one group. As each group can itself be further subdivided into three subgroups, denoted by number.1,.2,.3, the result is 27 subgroups for each bone segment and 81 subgroups for each bone. Müller and his co-workers have recently [9] refined the process by which, once the bone and the segment have been identified, the surgeon interrogates (for want of a better word) the fracture to establish not just its identity, but its essence. Within this binary concept, the triadbased arrangement remains, but at each hierarchical level the surgeon asks a question to which the reply must be one of only two possible answers. Thus, in a fracture identified as diaphyseal in a long bone, the first binary question relates to severity Is it simple or multifragmentary? (Fig ). If the fracture is identified as simple, type A, the next question relates to mechanism Was it spiral or bending? (Fig ). If the fracture is identified as spiral, it is then classified as A1. A B C simple wedge complex fracture fracture fracture Fig : Type A: simple fractures 30 < 30 A1 A2 A3 spiral oblique transverse

5 1.4 Fracture classification W.M. Murphy, D. Leu 49 Binary questioning has the additional benefit that if a choice from two answers cannot be identified, the imaging is probably inadequate and more information is needed. The process may be continued to whatever depth is appropriate for the particular occasion. Obviously, in certain situations additional refinements, known as modifiers and qualifications, are required to give complete expression to the complexities of the fractures encountered. However, the goal of this chapter is to explain the rationale and process of the classification system, not to provide a detailed guide to implementing it. Therefore, 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. Further division into subgroups is explained and discussed as appropriate elsewhere in the book and in the AO Müller Electronic Classification of Long Bones [10]. In illustrating the classification, the colors green, orange, and red denote progressive severity. Therefore, A1 indicates the fracture with the best prognosis and C3 the fracture with the worst prognosis. Thus, in identifying the information necessary to classify a fracture, one has already gone some way to establishing its mechanism, severity, and prognosis. 3 The coding of the fracture diagnosis The diagnosis of a fracture is obtained by combining its anatomical location with its morphological characteristics. The answers to the questions described above will produce a fiveelement alpha-numeric code for the fracture:. This is made up of the two location numbers (bone and segment) followed by the letter, indicating the fracture type, and two numbers that express the morphological characteristics of the fracture. To use the system one needs to be clear about what these abbreviations mean. The numbering of the bones has been decided simply by convention and is self-evident from Fig It should again be noted that the pairings of radius and ulna, and tibia and fibula are each regarded as one long bone. The identification of the segments needs a little more consideration [11]. 3.1 Bone segments Fig Each long bone has three segments: 1 = the proximal segment 2 = the middle (diaphyseal) segment 3 = the distal segment and for the distal tibia/fibula 4 = malleolar segment The malleolar segment is an exception, related to the complexity of its fractures and is classified as the fourth segment of the tibia/ fibula. A long bone is usually divided into one diaphyseal, two epiphyseal, and two metaphyseal segments. To determine the limits between the middle (diaphyseal) segment and the end segments, the segments are defined by a square whose sides are the same length as the 2 Regrettably, there are differences in the numbering of some of the smaller bones between the Comprehensive and OTA versions of the AO Müller Classification. These will need to be resolved. If a choice from two answers cannot be identified, the imaging is probably inadequate and more information is needed.

6 proximal diaphyseal distal widest part of the epiphysis (exceptions: 31- and 44-, see caption of Fig ). In this classification no distinction is made between the epiphysis and the metaphysis. They are considered as one segment because the morphology of the fracture in the metaphysis influences the treatment and the prognosis of the articular fracture. At this point, the important concept of the center of the fracture needs to be addressed. This is relevant because if a fracture is associated with a non-displaced fissure which reaches the joint, it could still be classified as a middle segment fracture (diaphyseal) depending on its center, which must be established before a fracture can definitively attached to any given segment. 4 Center of the fracture In the context of fracture description, the term center means what it says. However, while the center of a simple fracture is apparent, and in a wedge fracture it lies where the wedge is broadest, the center of a complex fracture is usually identifiable only after reduction. When all the features are listed, the fracture can be coded, but while the type and group may be readily identified, clarifying the final details of subgroups and qualifications may, again, only be possible after reduction. Fig : Anatomical location is designated by two numbers: one for the bone and one for its segment (ulna and radius, tibia and fibula are considered 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 are the same length as the widest part of the epiphysis (exceptions 31- and 44-). 5 The long bones Two numbers designate the anatomical location, one for the bone and one for the bone segment.

7 1.4 Fracture classification W.M. Murphy, D. Leu 51 Fig : a) Example of the coding of a fracture without subgroup: 32-B2 3 2 B 2 femur middle wedge bending segment wedge b) Example of the coding of a fracture with subgroup: 33-C C 3.3 femur distal complete multi- metaphyseal complex segment articular fragmentary severity mechanism 5.1 Bones As has been noted, ulna and radius, as well as tibia and fibula are each considered as one bone, making four long bones in all. 1 = humerus 2 = radius/ulna 3 = femur 4 = tibia/fibula Fig : Type A Type B Type C extra-articular fractures, or partial articular fractures, or complete articular 5.2 Types In the proximal (-1) or distal (-3) segments all fractures are either type A, type B, or type C. A B C

8 Exceptions: Fig a: proximal humerus (11-): Type A extra-articular unifocal Type B extra-articular bifocal Type C articular Fig b: proximal femur (31-): Type A trochanteric area Type B neck Type C head A B C A B C Fig c: malleolar segment (44-): Type A infrasyndesmotic level Type B transsyndesmotic level Type C suprasyndesmotic level A fracture at transsyndesmotic level will disrupt the syndesmosis. Fig : All fractures of the middle (2) segment are either simple fractures (type A) or multifragmentary fractures. Thus, multifragmentary fractures are split into wedge (type B) fractures and complex fractures (type C). Type A Type B Type C simple fractures wedge fractures complex fractures A B C A B C

9 1.4 Fracture classification W.M. Murphy, D. Leu 53 Fig : Example of classification of distal femur (33-) fractures into groups (1 3) 33-A extra-articular fracture 33-B partial articular fracture A1 A2 A3 B1 B2 B3 33-A1 simple 33-A2 metaphyseal wedge 33-A3 metaphyseal complex 33-B1 lateral condyle, sagittal 33-B2 medial condyle 33-B3 frontal 33-C complete articular fracture 5.3 Groups, subgroups, and qualifiers or modifiers C1 C2 C3 Once a fracture, whatever its bone segment, has been recognized as one of three fracture types (A, B, C), then each type may be further divided in three fracture groups (1, 2, 3), a process facilitated by binary questioning. For more specialized requirements, these groups are further divisible into three subgroups (.1,.2,.3), and in areas of particular complexity the further sub-categories known as qualifiers may be applied. These must also be known when the fracture has to be fixed and, where relevant, they are discussed in the appropriate sections of the text (Fig ). 33-C1 articular simple, metaphyseal simple 33-C2 articular simple, metaphyseal multifragmentary 33-C3 articular multifragmentary

10 Classification of softtissue injuries Many different variables must be included when grading an open or closed fracture including the skin injury (IC, IO), the underlying muscle and tendon injury (MT), and the neurovascular injury (NV). This soft-tissue classification is fully discussed in chapter Classification of spinal injuries Compressive force, which causes compression and burst injuries, type A; Tensile force, which causes injuries with transverse disruption, type B; Axial torque, which causes rotational injuries, type C. The exception to this is the lower cervical spine to 51.05, where injury caused by distraction is more severe than that from rotation and is, therefore, assigned to type C, with rotation injuries falling into type B. The application of the AO Classification to the principles of managing spinal fractures is discussed in chapter (see chapter 4.11) Within this classification the spine injuries are hierarchically ranked according to severity and anatomical location corresponding to the AO Müller Classification of long bones (Fig ). Severity progresses from type A to type C and similarly within each type, group, and further subdivision. Ranking of the spine injuries was primarily determined by the degree of instability. Prognostic aspects were taken into consideration as far as possible. This classification needs to cater for the varying anatomical characteristics prevailing at different levels of the spine. There are four main segments of the spine (to which the number 5 had been assigned) with each vertebra having its own identity as a subsegment, except in the sacrum which is regarded as a single entity. Within this arrangement, the three main categories, the types, have their typical fundamental injury pattern, which is defined by (usually) recognizable radiological criteria. Three different mechanisms can be identified as common dominators of the types: Fig : The four spine levels. The vertebral subsegments are numbered according to their levels within the segment, for example, T6 is and so on. 5 Spine 51 Cervical 52 Thoracic 53 Lumbar

11 1.4 Fracture classification W.M. Murphy, D. Leu 55 8 Classification of pelvic ring and acetabular injuries 8.1 Pelvic ring (see chapter 4.4) This classification of pelvis injuries is based on and is adapted to the universal AO Classification nomenclature suggested by M.E. Müller et al. and the classification nomenclature suggested by M. Tile et al. This classification is also divided into bone (6), segments (1,2), types (A, B, C), and groups (1, 2, 3). For a scientific classification for specialized surgeons or clinical investigators each of the three groups can be further subdivided into three subgroups (.1,.2,.3) and qualifications. Anatomically, pelvic ring injuries can be described as anterior lesions or posterior lesions and as a combination of both types [12]. Anterior lesions or lesions of the anterior arch may be a disruption of the symphysis pubis, or a fracture of one or both pubic rami, may be in combination with a disruption of the symphysis, or avulsion of the insertion of the rectus abdominis muscle, or combined lesions. Posterior lesions or lesions of the posterior arch may be unilateral or bilateral injuries and may involve the Ilium: An iliac fracture usually extends from the greater sciatic notch to the iliac crest, but it can also extend into the posterior column of the acetabulum. Sacroiliac joint: A sacroiliac lesion may be a pure dislocation, but more commonly it includes a portion of the ilium or the sacrum. Sacrum: Fractures of the sacrum may be vertical or transverse below the sacrogluteal line. Vertical fractures are common in pelvic ring injuries. Transverse fractures are really spinal injuries. Displacement of the posterior complex is most important in estimating the stability of the pelvic ring injuries. All the pelvic ring injuries, depending on the degree of posterior bony or ligamentous damage, can be classified as stable, rotationally unstable but vertically stable, or unstable both rotationally and vertically. Any break in the continuity of the sacrogluteal line represents displacement of the posterior complex. The following terms are particularly relevant to pelvic injuries: bilateral: both sides are involved. contralateral: the other side, secondary lesion. high variety: upper end of the fracture reaches the iliac crest. ipsilateral: injury of the same side as the more severe lesion. low variety: upper end of the fracture reaches the anterior boarder of the iliac crest. partial unstable: (pelvic fractures) rotationally unstable but vertically and posteriorly stable. Posterior displacement less than 1 cm. stable: able to withstand normal physiological stresses without displacement. unilateral: only one side is involved. unstable: (pelvic fractures) complete disruption of the posterior complex with a three-dimensional translational and rotational instability.

12 Acetabulum (see chapter 4.5) Our understanding of acetabular fractures and their classification derives mainly from the pioneering work of Judet and Letournel [13]. The particular scheme of classification employed by Letournel [14] is extensively used in the day-to-day management of these complex injuries. Anatomically, acetabular injuries may be divided, on the one hand, into partial articular and complete articular fractures and, on the other hand, into fractures of one column or both columns (the anterior and posterior), and into transversely oriented fractures. 9 Classification of foot fractures The AO Foot & Ankle Expert Group is close to completing its work on establishing a classification for fractures of the foot. 10 Classification terminology The main glossary is to be found in the last section of the book. The following list of terms used in classification may be helpful in understanding this chapter. articular: fractures which involve the articular surface. They are subdivided into partial articular and complete articular fractures. articular-partial: these fractures involve only part of the articular surface, while the rest of that surface remains attached to the diaphysis. articular-complete: fractures in which the articular surface is disrupted and completely separated from the diaphysis. The severity of these fractures depends on whether their articular and metaphyseal components are simple or multifragmentary. complex: a fracture with one or more intermediate fragment(s) in which, after reduction, there is no contact between the main proximal and the distal fragments. The complex fractures are spiral, segmental, or irregular. extra-articular: these fractures do not involve the articular surface, also they may be intracapsular. They include apophyseal and metaphyseal fractures. impacted: a stable and usually simple fracture of the metaphysis or epiphysis in which the fragments are driven one into the other. multifragmentary: a term used to characterize any fracture with one or more completely separated intermediate fragment(s) in the diaphyseal segment and the metaphysis. It includes the wedge and the 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 pure depression of the articular surface without a spilt. The depression may be central or peripheral.

13 1.4 Fracture classification W.M. Murphy, D. Leu 57 pure split: a fracture, resulting from a shearing force, in which the direction of the spilt is usually longitudinal. simple: a term used to characterize a single circumferential fracture of a diaphysis or metaphysis, or a single disruption of an articular surface. Simple fractures of the diaphysis or metaphysis are spiral, oblique, or transverse and have only two fragments. wedge: a fracture with one or more intermediate fragment(s) in which, after reduction, there is some contact between the main fragments. The spiral or bending wedge may be intact or fragmented. 11 Bibliography 1. Colton CL (1991) Telling the bones [editorial]. J Bone Joint Surg [Br]; 73(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): ; discussion Colton CL (1997) Fracture classification. J Bone Joint Surg [Br]; 79(5): ; discussion Müller ME, Allgöwer M, Schneider R, et al. (1991) Manual of Internal Fixation. 3rd ed. Berlin Heidelberg New York: Springer-Verlag. 5. Müller ME, Nazarian S, Koch P (1987) Classification AO des fractures: les os longs. Berlin Heidelberg New York: Springer- Verlag. 6. Müller ME, Nazarian S, Koch P, et al. (1990) The Comprehensive Classification of Fractures of Long Bones. Berlin Heidelberg New York: Springer-Verlag. 7. Burstein AH (1993) Fracture classification systems: do they work and are they useful? [editorial]. J Bone Joint Surg [Am]; 75(12): Orozco R, Sales JM, Videla M (2000) Atlas of Internal Fixation. Fractures of Long Bones. Berlin Heidelberg New York: Springer-Verlag. 9. Müller ME (1994) CCF Comprehensive Classification of Fractures. Pamphlet I and II. Bern: M. E. Müller Foundation. 10. AO Müller Electronic Long Bone Fracture Classification. (2000) AO Publishing/ Thieme. (in preparation). 11. Spiegel PG, et al. (1996) Fracture and Dislocation Compendium. Journal of Orthopaedic Trauma. Official Journal of the Orthopaedic Trauma Association and the International Society for Fracture Repair; 10 (Suppl 1). Philadelphia: Lippincott Raven. 12. Tile M (1995) Fractures of the Pelvis and Acetabulum. Baltimore: Williams & Wilkins. 13. Judet R, Judet J, Letournel E (1964) Fractures of the acetabulum: classification and surgical approaches for open reduction. J Bone Joint Surg; 46: Letournel E, Judet R (1993) Fractures of the Acetabulum. 2nd ed. Berlin Heidelberg New York: Springer-Verlag. 12 Updates Updates and additional references for this chapter are available online at: