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Acetabular Fractures Revisited: Part 2, A New CT-Based Classification
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OBJECTIVE. The objective of this investigation was to provide a new CT-based classification of acetabular fractures.
MATERIALS AND METHODS. The axial CT scans of 112 randomly selected acetabular fractures in patients admitted to a level 1 trauma center between January 1998 and December 2000 were analyzed by an experienced orthopedic trauma surgeon and two experienced emergency radiologists. When available, 3D reformatted images were analyzed as well. The fracture pattern for each acetabular fracture, with respect to column walls and extension beyond the acetabulum, when present, was recorded. Fracture comminution was not a defining characteristic.
RESULTS. Analysis of the 112 acetabular fracture patterns showed that each fracture fell into one of four broad categories. Category 0 included wall fractures only. Category I included acetabular fractures limited to a single (anterior or posterior) column. Category II fractures included those involving both the anterior and posterior columns; category II fractures were further subdivided into those with no fracture extension beyond the acetabulum, those with superior or inferior extension, and those with both superior and inferior extensions beyond the acetabulum. Category III fractures included only the “floating” acetabulum, which is defined as an acetabular fracture in which the acetabulum is separated from the axial skeleton both anteriorly and posteriorly.
CONCLUSION. The axial CT display of acetabular fracture patterns provides a basis for a classification of acetabular fractures that is simple, unambiguous, readily understood by both radiologists and orthopedic surgeons and provides clear direction for both diagnosis and surgical treatment planning. Category and subcategory fracture specificity creates a mechanism for intra- and interdepartmental postoperative assessment of any of the individual acetabular fracture types.
| Introduction |   |
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Before the landmark classification of acetabular fractures by Judet and Letournel [1–4], acetabular fractures were poorly understood and frequently inappropriately treated. The magnitude of the work of Judet and Letournel becomes even more apparent with the realization that it is based on the distribution of fracture lines and fragments as recorded on an anteroposterior (AP) radiograph of the pelvis and AP internally (obturator) and externally (iliac) rotated oblique radiographs of the involved acetabulum. The Judet-Letournel classification remains essentially unchallenged even by contemporary high-resolution CT—including 3D—scanning. However, the Judet-Letournel classification, which consists of only five “elementary” and five “associated” fracture types, has clinical limitations, can be difficult to conceptualize, and is subject to wide variation in interpretation.
CT has provided a marked advance in the display of the pathologic anatomy of acetabular fractures, which in turn, provides the basis for a clinically relevant modification of the Letournel fracture types, particularly those involving both columns.
Although acknowledging the work of Judet and Letournel, this report proposes a new CT-based classification of acetabular fractures.
| Materials and Methods | |
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The complete set of axial CT scans of 112 randomly selected patients admitted to a level 1 trauma center from January 1, 1998, to December 14, 2000, with the diagnosis of acetabular column fracture constitutes the data for this study. Wall fractures associated with only hip dislocations were excluded from this study because they do not constitute a primary acetabular fracture. Axial CT scans of the entire pelvis were obtained on either a CTi helical or LightSpeed MDCT scanner (General Electric Medical Systems). Axial images were printed at consecutive 5-mm levels from the iliac crest to the acetabular roof and in consecutive 3-mm increments through the acetabulum to the ischial tuberosity.
Three-dimensional reformatted images of 68 (61%) of the 112 patients were available and useful in developing an understanding of the axial CT scans of complex (type IID and type III) two-column fractures. Sagittal and coronal reformatted images were not obtained in any of these patients.
Having established the axial CT appearance of the acetabular and iliac skeletal anatomy, including the redefined anterior column (from part 1 of our study), we analyzed axial CT scans of 112 acetabular fractures. Fractures were assigned to the anterior and posterior columns and walls regardless of degree of comminution. The supraacetabular region, including the iliopectineal line, was considered a part of the acetabulum. A fracture extending to the iliac wing above the iliopectineal line was defined as superior extension. Fracture extension to the inferior pubic ramus, the ischium, or both was defined as inferior extension. Therefore, although the direction of fracture extension from the acetabulum (superior or inferior) was a defining fracture characteristic, comminution was not.
| Results | |
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Analysis of the data obtained from the axial CT scans of the 112 acetabular fractures revealed that all the fractures studied fell into one of four general categories, as shown in Table 1. These were category 0, those limited to the wall only; category I, those involving a single column (either anterior or posterior); category II, those involving both the anterior and posterior columns simultaneously, except for the floating acetabulum; and category III, those in which the acetabulum was completely separated from the axial skeleton anteriorly and posteriorly, such as the floating acetabulum.
Wall fractures were designated as category 0 to preserve categories I and II for single- and two-column fractures, respectively.
When a wall fracture (category 0) occurred in conjunction with a single- or a two-column fracture, the injury was described as category I or II with associated anterior or posterior wall component.
Most acetabular column fractures are comminuted, particularly those involving both columns. The column category designations in this classification system are based solely on the number of columns fractured and presence and direction of fracture extension, if any, regardless of the degree of comminution. In category II, the subgroup designations indicate the direction (superior, inferior, or both) of fracture extension because fracture extension is an important feature of surgical planning. The degree of comminution is irrelevant with regard to determination of surgical approach. Therefore, the degree of comminution was purposely excluded with regard to fracture category designation.
The walls, as seen on axial CT scans of the acetabulum, are illustrated in Figure 1. Wall fractures are those limited to the posterior and posterosuperior (common) or anterior (uncommon) wall component of the columns. Wall fractures may occur as isolated injuries (Fig. 2A, 2B, 2C) or in conjunction with any other category of acetabular fracture.
 View larger version (15K) | Fig. 1. —Schematic representation shows mid acetabular CT scan. Line a–a1 establishes anterior (AC) and posterior (PC) columns. Anterior (AW) and posterior (PW) walls lie lateral to line b–b1. |
 View larger version (37K) | Fig. 2A. —Type 0: wall fractures in three patients. Axial CT scan of mid pelvis shows minimally displaced posterior wall fracture (arrow). |
 View larger version (43K) | Fig. 2B. —Type 0: wall fractures in three patients. Axial CT scan shows comminuted displaced posterior wall fracture (arrow). |
 View larger version (77K) | Fig. 2C. —Type 0: wall fractures in three patients. Axial CT scan shows posterior wall fracture with fracture line at wall–column junction (arrow). |
A single-column fracture is limited to only the anterior (Figs. 3A,3B,3C,3D) or the posterior column (Figs. 3E and 3F). Clearly, a single column does not transverse the acetabulum. Single-column fractures may also extend superiorly or inferiorly from the acetabulum.
 View larger version (40K) | Fig. 3A. —Type I: single-column fracture. Axial CT scan of mid pelvis shows minimally displaced left anterior column fracture (arrows). |
 View larger version (43K) | Fig. 3B. —Type I: single-column fracture. Axial CT scan of mid pelvis shows comminuted, minimally displaced left anterior column fracture (arrows). |
 View larger version (46K) | Fig. 3C. —Type I: single-column fracture. Subjacent caudal axial CT scan shows caudal extension of comminuted anterior column fracture (arrows). |
 View larger version (49K) | Fig. 3D. —Type I: single-column fracture. Further subjacent caudal axial CT scan shows extension of anterior column fracture (white arrow) in anterior wall (black arrow). |
 View larger version (61K) | Fig. 3E. —Type I: single-column fracture. Axial CT scan shows posterior column fracture (arrow). |
 View larger version (51K) | Fig. 3F. —Type I: single-column fracture. Axial CT scan obtained more caudad than E of third patient shows comminution of posterior column fracture (arrows). |
The proposed two-column category is a major departure from, and simplification of, the Letournel classification. This broad category includes all fractures that simultaneously involve both the anterior and posterior columns, with the exception of the floating acetabulum, regardless of their pathologic anatomy. This category, therefore, includes the following Letournel fracture types: pure transverse, T-shaped and its varieties, transverse and posterior wall, and anterior column and hemitransverse. None of these is specifically identified in the Letournel system as involving both columns. This category also includes the large variety of unnamed acetabular fractures that involve both columns but are not included in the Letournel classification.
Fractures in category II fall into subcategories based on fracture extension beyond the acetabulum as follows:
Subcategory IIA includes those two-column acetabular fractures in which the fracture is limited to the acetabulum without extension beyond the acetabulum (Fig. 4A, 4B). This category of acetabular fractures includes the Letournel pure transverse regardless of whether the fracture is horizontal or obliquely horizontal and regardless of its location through the acetabulum, such as supratectal, tectal, infratectal, or through the middle or inferior portions of the acetabulum; transverse and posterior fractures; and fractures of the anterior column or wall associated with a hemitransverse fracture posteriorly.
 View larger version (36K) | Fig. 4A. —Type IIA: two-column fracture without extension but with associated posterior wall fracture. Supraacetabular axial CT scan shows anterior column fracture (white arrow), iliopectineal line (arrowhead), and posterior column fracture (solid black arrow). Open arrow indicates superiorly displaced posterior wall fragment. |
 View larger version (44K) | Fig. 4B. —Type IIA: two-column fracture without extension but with associated posterior wall fracture. Axial CT scan obtained more caudad than A of same patient shows anterior (white arrow) and posterior (solid black arrow) column fractures. Open arrows indicate associated posterior wall fracture. |
Subcategory IIB includes those two-column acetabular fractures in which a fracture component extends superiorly above the iliopectineal line into the iliac wing (Fig. 5A, 5B, 5C, 5D).
 View larger version (69K) | Fig. 5A. —Type IIB: two-column fracture with superior extension to iliac wing. Three-dimensional reformatted CT scan shows anterior (white arrows) and posterior (curved arrow) column fractures. Arrowhead indicates iliopectineal line. Straight black arrow indicates superior extension of acetabular fracture to iliac wing. |
 View larger version (50K) | Fig. 5B. —Type IIB: two-column fracture with superior extension to iliac wing. Axial CT scan of false pelvis shows superior extension of fracture (arrow) above iliopectineal line (arrowhead) into iliac wing. |
 View larger version (42K) | Fig. 5C. —Type IIB: two-column fracture with superior extension to iliac wing. Axial CT scan of false pelvis shows fracture (arrow) at level of iliopectineal line. |
 View larger version (44K) | Fig. 5D. —Type IIB: two-column fracture with superior extension to iliac wing. Axial CT scan shows comminuted anterior column fracture with associated anterior wall component (white arrows) and posterior column fracture (black arrow). |
Subcategory IIC includes those two-column acetabular fractures in which a fracture component extends into either the ischium, to the junction of the ischium and inferior pubic ramus (Letournel T-shaped and variants), or to the inferior pubic ramus (Fig. 6A, 6B, 6C).
 View larger version (52K) | Fig. 6A. —Type IIC: two-column acetabular fracture with inferior extension. Axial CT scan of false pelvis shows each iliac wing intact thereby excluding superior fracture extension. |
 View larger version (91K) | Fig. 6B. —Type IIC: two-column acetabular fracture with inferior extension. Axial CT scan shows comminuted and displaced anterior (white arrow) and posterior (black arrow) column fractures. |
 View larger version (66K) | Fig. 6C. —Type IIC: two-column acetabular fracture with inferior extension. Axial CT scan through level of pelvic outlet shows fracture (arrow) of left ischial tuberosity. |
Subcategory IID includes those acetabular fractures with both superior and inferior extensions beyond the acetabulum (Fig. 7A, 7B, 7C, 7D). The Letournel classification does not include this variety of acetabular fracture.
 View larger version (74K) | Fig. 7A. —Type IID: two-column acetabular fracture with superior and inferior extension. Three-dimensional reformatted CT scan shows anterior (white arrows) and posterior (long black arrow) column fractures, superior extension above iliopectineal line (short black arrow), and inferior extension (arrowhead). |
 View larger version (61K) | Fig. 7B. —Type IID: two-column acetabular fracture with superior and inferior extension. Mid pelvic axial CT scan shows left anterior (white arrow) and posterior (black arrow) column fractures. |
 View larger version (37K) | Fig. 7C. —Type IID: two-column acetabular fracture with superior and inferior extension. Axial CT scan obtained rostral to iliopectineal line (arrowhead) shows superior fracture extension to iliac wing (arrow). |
 View larger version (40K) | Fig. 7D. —Type IID: two-column acetabular fracture with superior and inferior extension. Axial CT scan obtained through inferior pubic rami shows inferior fracture extension to left inferior pubic ramus (arrows). |
The essential feature of the floating acetabulum that distinguishes it from all other two-column fractures is that the articulating surface of the acetabulum is separated from the axial skeleton both anteriorly and posteriorly (Fig. 8A, 8B, 8C, 8D, 8E). The Letournel classification does not include this fracture but does include the “associated both column fracture,” the definition of which is ambiguous. This ambiguity is further extended by the implication contained in its name that the “associated both column fracture” is the only acetabular fracture that involves both columns. Because the acetabular articulating surface is uniquely separated from the axial skeleton, we believe, as does Tile [9], this fracture merits category designation unto itself, which is another departure from the Letournel system.
 View larger version (74K) | Fig. 8A. —Type III: floating acetabulum. Three-dimensional reformatted CT scan shows anterior (long white arrows) and inferior pubic ramus fractures (short white arrow) which, together, separate acetabulum from axial skeleton anteriorly; posterior column fracture (long black arrow), which separates acetabulum from axial skeleton posteriorly; superior fracture extension to right iliac wing (arrowhead); and inferior fracture extension (short black arrow). |
 View larger version (49K) | Fig. 8B. —Type III: floating acetabulum. Axial CT scan obtained through level of iliopectineal line shows right superior fracture extension (arrow). |
 View larger version (62K) | Fig. 8C. —Type III: floating acetabulum. Axial CT scan shows comminuted displaced right posterior column fracture (arrows). Arrowhead indicates iliopectineal line. |
 View larger version (61K) | Fig. 8D. —Type III: floating acetabulum. Mid pelvic axial CT scan shows comminuted, displaced anterior column fracture (arrows). |
 View larger version (46K) | Fig. 8E. —Type III: floating acetabulum. Axial CT scan obtained through level of inferior pubic rami shows comminuted, displaced fracture of right inferior pubic ramus (arrow). |
The floating acetabulum (category III) fracture is characterized by fracture lines that extend transversely through the posterior column and separate the acetabulum from the axial skeleton posteriorly, and fractures of the pubic rami, body, or both that separate the articulating surface from the axial skeleton anteriorly.
The distinction between the category IID (two-column with superior and inferior extensions) and the category III (floating acetabulum) is frequently difficult because of their complexity and similar appearance on axial CT. Although a complete fracture through the posterior column disrupts the osseous continuity between the acetabulum and the axial skeleton, an incomplete posterior column fracture does not, thereby excluding a category III fracture.
The relationship of the Letournel fracture types to the proposed classification is shown in Figure 9 and the frequency of the various fracture types, in Table 1.
 View larger version (16K) | Fig. 9. —Diagram shows relationship of Letournel fracture types to Harris-Coupe categories. |
| Discussion | |
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The Letournel classification of acetabular fractures was a major advance in the recognition and treatment of acetabular fractures and it has stood the test of time. Indeed, the AO (Arbeitsgemeinschaft für Osteosynthesefragen [Association for the Study of Internal Fixation]) acetabular fracture classification [5] has as its basis the Letournel classification. However, even with CT and 3D reformations to augment conventional radiography, application of the Letournel classification to the more complex fracture types remains difficult [6]. In spite of Letournel's statement, “discrete (fracture) groups are artificial for all varieties of fractures and dislocations fit in a continuous spectrum” [3], the Letournel classification consists of only 10 specific fracture types. The Letournel classification, therefore, requires that the “infinite” [7] number of acetabular fracture patterns must fit in one of the 10 Letournel fracture types.
The Letournel classification is simultaneously complex and oversimplified: complex, because the descriptive terminology is difficult to mentally conceptualize and the corresponding schematic illustrations are difficult to apply to either conventional radiographs or CT scans. The classification is overly simplistic because it contends that acetabular fracture patterns occur in only the 10 types specified by Letournel. These characteristics of the Letournel classification result in remarkable variation in the diagnosis of acetabular fractures with similar axial CT appearance by different observers [8, 9].
The more recent AO acetabular fracture classification [5] illustrated and described by Tile [7], based entirely on the Letournel classification, limits the number of fracture types to nine (compared with 10 in the Letournel scheme) in three groups. These groups are type A, partial acetabular one-column fracture; type B, partial acetabular transverse oriented fracture; and type C, complete acetabular, both-column fractures (floating acetabulum). Furthermore, the AO classification also includes 13 Greek-letter modifiers indicating the position of the femoral head, the condition of the acetabular surface and femoral head, and the presence of intraarticular fragments and nondisplaced fractures of the acetabulum. As was intended by its formulators, the AO classification provides a method for more definitive analysis of acetabular fracture types than the Letournel classification and is therefore an excellent research tool. However, its complexity has diminished its clinical acceptance.
During the past 15 years, several authors have emphasized the value of multiplanar CT [10–13] and 3D CT [14–18] in the assessment of, and surgical planning for, acetabular fractures. Potok et al. [19] selected axial CT and 3D reformatted images to match, as closely as possible, the fracture types as illustrated by Letournel. These works [8, 20, 21], although intending to explain the Letournel classification, perpetuate its inherent limitations. Today, 2D CT and 3D CT reformations are the definitive imaging techniques for the assessment of acetabular fractures. Therefore, an attempt to devise a classification of acetabular fractures based on axial CT scans, although retaining the anterior and posterior column and wall concepts of Judet and Letournel, seemed reasonable.
To be useful, a fracture classification must have clinical relevance, be inclusive, provide fracture-type specificity, and be easily understood by all physicians involved in the diagnosis and treatment of the fracture being classified.
The proposed classification is practical, being based on readily available axial CT scans routinely obtained for acetabular fracture assessment.
The axial CT scans clearly identify not only the walls and columns involved but the direction of fracture extension beyond the acetabulum, thereby making both diagnosis and surgical planning unambiguous.
The categories of this classification, which are based on the axial CT depiction of wall or column fracture location and fracture extension, are sufficiently broad to include the “infinite” [7] number of fracture patterns. At the same time, the category and subcategory definitions retain fracture-type specificity. These features, unique to the proposed classification, are not present in the Letournel classification.
Correct classification of acetabular fractures precedes the choice of the surgical approach and serves as the basis for preoperative planning [13, 19]. By using the anatomic display of the anterior and posterior columns as shown on axial CT scans, the proposed classification unambiguously identifies which columns are fractured, thereby guiding the surgeon in selecting the appropriate surgical approach, whether anterior, posterior, or combined anterior and posterior.
Because the proposed classification is based on axial CT scans, it should be easily understandable by radiologists and orthopedic trauma surgeons.
The category and subcategory descriptions of acetabular fractures are sufficiently detailed that each fracture category and subcategory is specific for that particular fracture type. This feature provides a basis for postoperative treatment assessment not available with the Letournel classification because of its imaging ambiguity and limited number of fracture types.
Although based on the axial CT appearance of acetabular fractures, the proposed classification has direct application to 3D reformatted images as well.
Address correspondence to J. H. Harris, Jr. ([email protected])
We gratefully acknowledge the contribution of William H. Harris, Alan Gerry Clinical Professor of Orthopedic Surgery, Harvard, whose challenging questions and rigorous editing greatly enhanced the accuracy and clarity of this manuscript.
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