AJR 2004; 182:1367-1375
© American Roentgen Ray Society
Acetabular Fractures Revisited: Part 2, A New CT-Based Classification
John H. Harris, Jr.1,2,
Kevin J. Coupe3,
Jody S. Lee1,4 and
Thea Trotscher3
1 Department of Radiology, University of Texas-Houston Medical School, 6431
Fannin, Houston, TX 77030.
2 Present address: 200 Alta Vista Dr., Sedona, AZ 86351.
3 Department of Orthopaedic Surgery, University of Texas-Houston Medical School,
Houston, TX.
4 Present address: 2019 Red Magnolia Ct., Kingwood, TX 77339.
Received September 25, 2003;
accepted after revision November 25, 2003.
Address correspondence to J. H. Harris, Jr.
(jharris{at}myexcel.com)
Abstract
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
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
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
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.
Category 0: Wall Fracture
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.
Category I: Single-Column Fracture
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.
Category II: Two-Column Fracture
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.
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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.
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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.
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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).
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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.
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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.
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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).
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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).
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.
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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).
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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.
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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).
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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).
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Category III: Floating Acetabulum (Letournel "Associated Both Column Fracture")
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.
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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).
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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.
Discussion
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.
Acknowledgments
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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Abstract
Introduction
