Classification of Common Acetabular Fractures: Radiographic and CT Appearances

Transcription

1 urkee et al. Radiographic and T lassification of cetabular Fractures Musculoskeletal Imaging Pictorial ssay M N U T R Y L I M I G O F I N G N. Jarrod urkee 1,2 Jon Jacobson 1 avid Jamadar 1 Madhav. Karunakar 3 Yoav Morag 1 urtis Hayes 1,4 urkee NJ, Jacobson J, Jamadar, Karunakar M, Morag Y, Hayes Keywords: acetabular fracture, T, musculoskeletal imaging, pelvic imaging, radiography, trauma OI: /JR Received July 21, 2005; accepted after revision September 18, epartment of Radiology, University of Michigan Medical enter, 1500 Medical enter r., T-2910G, nn rbor, MI ddress correspondence to J. Jacobson (jjacobsn@umich.edu). 2 Present address: epartment of Radiology, University of Washington, Seattle, W. 3 epartment of Orthopedic Surgery, University of Michigan Medical enter, nn rbor, MI Present address: epartment of Radiology, Medical ollege of Virginia, Virginia ommonwealth University, Richmond, V. M This article is available for 1 M credit. See for more information. JR 2006; 187: X/06/ merican Roentgen Ray Society lassification of ommon cetabular Fractures: Radiographic and T ppearances OJTIV. ccurate characterization of acetabular fractures can be difficult because of the complex acetabular anatomy and the many fracture patterns. In this article, the five most common acetabular fractures are reviewed: both-column, T-shaped, transverse, transverse with posterior wall, and isolated posterior wall. Fracture patterns on radiography are correlated with T, including multiplanar reconstruction and 3 surface rendering. ONLUSION. In the evaluation of the five most common acetabular fractures, assessment of the obturator ring, followed by the iliopectineal and ilioischial lines and iliac wing, for fracture allows accurate classification. T is helpful in understanding the various fracture patterns. ccurate classification of acetabular fractures is important for determining the proper surgical treatment [1, 2]. ecause of the complex acetabular anatomy, various classification schemes have been suggested [3 5], but the Judet-Letournel classification system remains the most widely accepted [2, 4, 6]. lthough radiographic examination provides essential information for acetabular classification, T, including multiplanar reconstruction, is helpful in the visualization of complex fractures [7]. This article reviews the pelvic bone anatomy and the five most common acetabular fractures: both-column, T-shaped, transverse, transverse with posterior wall, and isolated posterior wall [2]. fracture classification algorithm based on radiography is used, with correlation made to T. Normal natomy: olumns and Walls The acetabulum is formed by anterior and posterior columns of bone, which join in the supraacetabular region [2, 6, 8]. The anterior and posterior walls extend from each respective column and form the cup of the acetabulum. The anterior and posterior columns connect to the axial skeleton through a strut of bone called the sciatic buttress. When looking at the acetabulum en face, the anterior and posterior columns have the appearance of the Greek letter lambda (λ) [2, 6] (Fig. 1). The anterior column represents the longer, larger portion, which extends superiorly from the superior pubic ramus into the iliac wing. The posterior column extends superiorly from the ischiopubic ramus as the ischium toward the ilium. The anterior and posterior columns of bone unite to support the acetabulum. In turn, the sciatic buttress extends posteriorly from the anterior and posterior columns to become the articular surface of the sacroiliac joint, Fig. 1 Normal pelvic bone anatomy., Surface-rendering 3 T of pelvis in lateral view with femur and right hemipelvis removed shows anterior column (green), posterior column (blue), and sciatic buttress (red). (Fig. 1 continues on next page) JR:187, October

2 urkee et al. Fig. 1 (continued) Normal pelvic bone anatomy., xial section through acetabulum shows anterior (arrowhead) and posterior (arrow) walls., nteroposterior radiograph shows iliopectineal line (green), ilioischial line (blue), anterior acetabular wall (yellow), posterior acetabular wall (pink), and obturator foramen (O). Fig. 2 Illustrations of classification of five most common acetabular fractures., oth-column fracture., T-shaped fracture., Transverse fracture. (Fig. 2 continues on next page) which attaches the columns to the axial skeleton. The anterior and posterior walls, which extend from the columns and support the hip joint, are well seen on an axial T (Fig. 1). On radiographs, the iliopectineal (or iliopubic) line represents the border of the anterior column, and the ilioischial line represents the posterior column [9] (Fig. 1). The edges of the anterior and posterior walls are also identified. The obturator rings are composed of the osseous structures that surround the obturator foramen, which include the superior 916 JR:187, October 2006

3 Radiographic and T lassification of cetabular Fractures Fig. 2 (continued) Illustrations of classification of five most common acetabular fractures., Transverse with posterior wall fracture., Isolated posterior wall fracture. Fig. 3 lassification algorithm for five common acetabular fractures [2]. YS OTH-OLUMN FRTUR pubic ramus and a combination of the inferior pubic ramus and ischium (or ischiopubic ramus). nteroposterior and bilateral oblique (or Judet) views of the pelvis are important to adequately assess each of the radiographic lines for fracture. FRTUR LIN XTNSION INTO ILI WING? NO T-SHP FRTUR YS TULR FRTUR INTIFI OTURTOR RING ISRUPTION? NO YS POSTRIOR WLL FRTUR? ILIOISHIL N ILIOPTINL LIN ISRUPTION? POSTRIOR WLL FRTUR? Fracture Patterns The most widely accepted classification scheme for acetabular fractures is that of Judet and Letournel [2, 4, 6]. lthough this classification scheme describes 10 types of acetabular fractures, we have focused NO YS NO YS TRNSVRS + POSTRIOR WLL FRTUR TRNSVRS FRTUR ISOLT POSTRIOR WLL FRTUR on the most common fracture patterns, which represent 90% of acetabular fractures [2, 6] (Fig. 2). The five most common fracture types may be divided into two groups on the basis of presence or absence of obturator ring fracture (Fig. 3). lthough fracture of the obturator ring may be seen in combination with acetabular fractures, it is important to note that obturator ring fractures may be associated with other pelvic injuries outside of the acetabulum, such as lateral pelvic compression injury, where the obturator ring fracture is associated with either an ipsilateral or contralateral sacral fracture [6]. We first discuss the two acetabular fracture types (both-column and T-shaped) associated with obturator ring disruption. Next we discuss the three acetabular fractures types that spare the obturator ring (transverse, transverse with posterior wall, and isolated posterior wall). oth-olumn Fracture both-column acetabular fracture (Figs. 4 and 5) involves both anterior and posterior columns with extension into the obturator ring and iliac wing, and is one of the most common acetabular fractures [4]. On radiographs, fracture involvement of the anterior and posterior columns is characterized by disruption of the iliopectineal line and ilioischial line, respectively. However, disruption of these lines may also be seen with other fracture patterns, such as a transverse fracture. Obturator ring and iliac wing involvement must also be present for classification as a both-column acetabular fracture. Fracture extension into the iliac wing is not always obvious on the anteroposterior radiograph; oblique Judet views or T often reveal this finding. On T, fracture involvement of the anterior and posterior columns is seen, and the fracture may be comminuted. Fracture disruption of the obturator ring has a variable appearance; fracture of the superior pubic ramus may occur at the puboacetabular junction. In addition, fracture of the inferior pubic ramus may be difficult to identify if nondisplaced. The principal fracture line, which extends superiorly from the acetabulum into the iliac wing, is characteristically in the coronal plane. If present, a pathognomonic sign of a both-column fracture is the spur sign [2] (Fig. 5). This sign represents posterior displacement of the sciatic buttress of the iliac wing fracture, which essentially discon- JR:187, October

4 urkee et al. nects the roof of the acetabulum from the axial skeleton. When this occurs, weight from the torso and upper body can no longer be supported by the acetabulum. On radiographs and T, the spur sign appears as a shard of bone extending posteriorly at the level of the superior acetabulum. valuation of sequential T images shows the fracture, which separates the sciatic buttress from the acetabular roof. T-Shaped Fracture T-shaped acetabular fracture (Fig. 6) is a combination of a transverse acetabular fracture with extension inferiorly into the obturator ring. It is similar to a both-column fracture Fig year-old man with both-column acetabular fracture., nteroposterior pelvic radiograph (), bilateral oblique pelvic radiographs (, ), axial T scan (), and sagittal reconstruction T scan () show acetabular fracture (straight arrows, ), with break in obturator ring (arrowheads, ) and extension into iliac wing (curved arrows). Note coronal plane of fracture on T and superior pubic ramus fractured at puboacetabular junction. (Fig. 4 continues on next page) 918 JR:187, October 2006

5 Radiographic and T lassification of cetabular Fractures Fig. 4 (continued) 45-year-old man with both-column acetabular fracture., nteroposterior pelvic radiograph (), bilateral oblique pelvic radiographs (, ), axial T scan (), and sagittal reconstruction T scan () show acetabular fracture (straight arrows, ), with break in obturator ring (arrowheads, ) and extension into iliac wing (curved arrows). Note coronal plane of fracture on T and superior pubic ramus fractured at puboacetabular junction. Fig year-old man with both-column acetabular fracture and spur sign. and, Oblique pelvic radiograph () and axial T image () show spur sign (arrow), which represents displacement of fracture involving sciatic buttress (arrowheads). Note that sciatic buttress (arrowheads, ) no longer connects to weight-bearing portion of acetabulum. in that it disrupts the obturator ring (Figs. 6 6). nother similarity is disruption of both the iliopectineal and ilioischial lines (Figs. 6 6). However, the superior extension of the fracture does not involve the iliac wing, which allows differentiation from the both-column fracture. One area of potential confusion with the T- shaped fracture is in regard to the transverse component. The transverse fracture line is not actually in the anatomic transverse plane, but rather it is transverse relative to the acetabulum. ecause the cup shape of the acetabulum is normally tilted inferiorly and anteriorly, the transverse fracture plane assumes a similar JR:187, October

6 urkee et al. orientation. Therefore, on radiographs, the fracture lines that disrupt the iliopectineal and ilioischial lines course superiorly and medially in an oblique plane from the acetabulum. This is best appreciated by looking at the acetabulum en face (Fig. 6). On T, this transverse fracture component is seen as a sagittally oriented fracture coursing medially and superiorly from the acetabulum. Transverse Fracture The transverse fracture of the acetabulum (Fig. 7) is limited to the acetabulum, without involvement of the obturator ring. transverse fracture must involve both the anterior and posterior aspects of the acetabulum, so the iliopectineal and ilioischial lines are disrupted on radiography. Similar to the transverse component of the T-shaped Fig year-old man with T-shaped acetabular fracture., nteroposterior pelvic radiograph (), bilateral oblique pelvic radiographs (, ), axial T scan (), and surface-rendering 3 T scan viewed laterally (), with right hemipelvis and femur removed, show obturator ring fractures (arrowheads) and transverse component (arrows) through acetabulum. Note characteristic oblique sagittal orientation of transverse acetabular fracture component on T scans that is transverse relative to acetabulum on radiographs. (Fig. 6 continues on next page) fracture described previously, this fracture line extends superiorly and medially from the acetabulum. On T, the characteristic sagittally oriented fracture line can be seen moving laterally to medially on subsequent T images when scrolling from inferior to superior. lthough not anatomically transverse, the fracture plane is transverse relative to the acetabulum, which is relatively 920 JR:187, October 2006

7 Radiographic and T lassification of cetabular Fractures Fig. 6 (continued) 40-year-old man with T-shaped acetabular fracture., nteroposterior pelvic radiograph (), bilateral oblique pelvic radiographs (, ), axial T scan (), and surfacerendering 3 T scan viewed laterally (), with right hemipelvis and femur removed, show obturator ring fractures (arrowheads) and transverse component (arrows) through acetabulum. Note characteristic oblique sagittal orientation of transverse acetabular fracture component on T scans that is transverse relative to acetabulum on radiographs. Fig year-old woman with transverse acetabular fracture., nteroposterior pelvic radiograph (), bilateral oblique pelvic radiographs (, ), axial T scan (), and surface-rendering 3 T scan viewed laterally (), with right hemipelvis and femur removed, show fracture (arrows) orientation transverse to acetabulum, disrupting iliopectineal and ilioischial lines (arrowheads). Note characteristic sagittal oblique fracture plane on T scan (). (Fig. 7 continues on next page) tilted inferiorly and anteriorly. This fracture plane orientation is best seen on T reconstruction images of the acetabulum en face (Fig. 7). Transverse with Posterior Wall The transverse with posterior wall fracture (Fig. 8) is a transverse fracture, described previously, with the addition of a comminuted posterior wall fracture that is often displaced. s with an isolated transverse fracture, the key is recognizing that the obturator ring is not disrupted, as this excludes both-column JR:187, October

8 urkee et al. Fig. 7 (continued) 23-year-old woman with transverse acetabular fracture., nteroposterior pelvic radiograph (), bilateral oblique pelvic radiographs (, ), axial T scan (), and surface-rendering 3 T scan viewed laterally (), with right hemipelvis and femur removed, show fracture (arrows) orientation transverse to acetabulum, disrupting iliopectineal and ilioischial lines (arrowheads). Note characteristic sagittal oblique fracture plane on T scan (). and T-shaped fractures. s with the simple transverse fracture, this fracture type does not extend into the iliac wing. On radiographs, disruption of both iliopectineal and ilioischial lines is seen as with the isolated transverse fracture. Unlike an isolated transverse fracture, however, additional comminution of the posterior wall is seen. In the absence of displacement, comminution of the posterior wall may be difficult to identify on anteroposterior radiographs because the fragments are superimposed on the femoral head. Oblique Judet radiographs and T are helpful in showing the comminuted posterior wall component. Isolated Posterior Wall The isolated posterior wall fracture (Fig. 9) is one of the most common types of acetabular fracture, with a prevalence of 27% [8]. n isolated posterior wall fracture does not have a complete transverse acetabular component. Therefore, the iliopectineal line is not disrupted, which excludes classification of the transverse with posterior wall fracture. However, disruption of the ilioischial line may or may not be present as an extension of the comminuted posterior wall component. Oblique (Judet) radiographs and T are helpful in showing the isolated posterior wall fracture. onclusion ommon acetabular fractures can easily be classified using disruption of the obturator ring as the basis of a decision tree (Fig. 3). Fracture of the obturator ring indicates both-column or T-shaped fracture, with additional iliac wing involvement differentiating the both-column from the T-shaped fracture. Sparing of the obturator ring commonly indicates transverse, transverse with posterior wall, or isolated posterior wall fracture. isruption of both the iliopectineal and ilioischial lines indicates a transverse fracture, and comminution of the posterior wall indicates a posterior wall fracture. bothcolumn fracture is in the coronal plane, whereas 922 JR:187, October 2006

9 Radiographic and T lassification of cetabular Fractures Fig year-old man showing transverse with posterior wall acetabular fracture., nteroposterior pelvic radiograph (), bilateral oblique pelvic radiographs (, ), axial T scan (), and surface-rendering 3 T scan viewed laterally (), with right hemipelvis and femur removed, show transverse fracture (straight arrows) disrupting iliopectineal and ilioischial lines (arrowheads) with displaced and comminuted posterior wall fracture fragment (curved arrows). JR:187, October

10 urkee et al. Fig year-old man with isolated posterior wall acetabular fracture. F, nteroposterior pelvic radiograph (), bilateral oblique pelvic radiographs (, ), axial T images (, ), and parasagittal reconstruction T image (F) show displaced fracture fragments (curved arrows) from isolated posterior wall fracture (straight arrow, ). (Fig. 9 continues on next page) 924 JR:187, October 2006

11 Radiographic and T lassification of cetabular Fractures Fig. 9 (continued) 18-year-old man with isolated posterior wall acetabular fracture. F, nteroposterior pelvic radiograph (), bilateral oblique pelvic radiographs (, ), axial T images (, ), and parasagittal reconstruction T image (F) show displaced fracture fragments (curved arrows) from isolated posterior wall fracture (straight arrow, ). a transverse or T-shaped fracture is in the sagittal oblique plane on T. The addition of T with multiplanar reconstruction and 3 surface rendering is helpful in understanding and classifying acetabular fractures. FOR YOUR INFORMTION cknowledgment We thank Robert W. Jacobson for the illustrations. This article is available for 1 M credit. See for more information. F References 1. Goulet J, ray TJ. omplex acetabular fractures. lin Orthop Relat Res 1989; 240: randser, Marsh JL. cetabular fractures: easier classification with a systematic approach. JR 1998; 171: Judet R, Judet J, Letournel. Fractures of the acetabulum: classification and surgical approaches for open reduction preliminary report. J one Joint Surg m 1964; 46: Letournel, Judet R. Fractures of the acetabulum, 2nd ed. Heidelberg, Germany: Springer-Verlag, Harris JH Jr, oupe KJ, Lee JS, Trotscher T. cetabular fractures revisited. Part 2. new T-based classification. JR 2004; 182: Hunter J, randser, Tran K. Pelvic and acetabular trauma. Radiol lin North m 1997; 35: Falchi M, Rollandi G. T of pelvic fractures. ur J Radiol 2004; 50: Martinez R, i Pasquale TG, Helfet L, Graham W, Sanders RW, Ray L. valuation of acetabular fractures with two- and three-dimensional T. RadioGraphics 1992; 12: Saks J. Normal acetabular anatomy for acetabular fracture assessment: T and plain film correlation. Radiology 1986; 159: JR:187, October