Ankle and Foot 47 - Department of Radiology - University of ...

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2252 VII Imaging of the Musculoskeletal System A B Figure 47-60. Weber injuries. Structures are as identified in Figure 47-59. A, Weber type A. Left, Anteroposterior radiograph of the ankle showing medial displacement of the talus relative to the tibia, a horizontal avulsion fracture through the lateral malleolus, and a vertically oriented compression fracture through the medial malleolus. Right, Schematic showing the mechanism of a Weber type A ankle fracture. As the talus undergoes an inversion rotational injury, it applies avulsive pulling forces on the lateral side of the mortise and compressive pushing forces on the medial side. B, Weber type B. Left, Anteroposterior radiograph of the ankle showing lateral displacement of the talus relative to the tibia, a horizontal avulsion fracture through the medial malleolus, and an obliquely vertically oriented compression fracture through the distal fibular, below the level of the syndesmosis. Right, Schematic showing the mechanism of a Weber type B ankle fracture. As the talus undergoes an eversion rotational injury, it applies avulsive pulling forces on the medial malleolus and compressive pushing forces on the fibula. C, Weber type C. Left, Anteroposterior radiograph of the ankle showing a horizontal avulsion fracture through the medial malleolus and an obliquely vertically oriented compression fracture through the distal fibular, above the level of the syndesmosis. The syndesmosis is disrupted and abnormally widened, with no overlap between the tibia and fibula. Right, Schematic showing the mechanism of a Weber type C ankle fracture. This is the same as a Weber type B, except now the compressive forces extend through the syndesmosis, tearing the tibiofibular ligaments and the distal intraosseous membrane (IOM), with the oblique fracture higher up on the fibula. (If the compressive forces extend proximally up the length of the IOM, fracturing through the proximal fibula up near the knee, this is referred to as a Maisonneuve fracture [not illustrated].) C Ch047-A05375.indd 2252 9/9/2008 5:34:45 PM
47 Ankle and Foot 2253 47 Figure 47-61. CT of Weber type C injury. A, Axial images through both ankles show the abnormally widened left syndesmosis (black arrows) compared with the width of the contralateral normal right syndesmosis (white arrows). B, Mortise coronal image shows widened syndesmosis (black arrows) and the high fibula fracture (white arrow), characteristic of a Weber type C injury. A Right Left B tibial plafond. Radiographically, avulsion fractures can be distinguished from compression fractures by the orientation of the fracture margins. Avulsion fractures are horizontally oriented, in a direction roughly perpendicular to the lines of force. Compression fractures are more obliquely or vertically oriented, in the same direction as the force. This principle is the key to understanding the Weber fractures. Figure 47-60B illustrates a Weber type B injury, radiographically on the left and schematically on the right. Here the talus is undergoing an eversion rotational injury, with the avulsive pulling forces on the medial malleolus and the compressive pushing forces on the lateral side. The medial avulsive forces may cause strain or tearing of the deltoid ligaments, or they may cause a horizontal avulsion fracture through the medial malleolus. The compressive forces on the lateral side cause a vertically oblique fracture through the fibula. If the fibular fracture is distal to the syndesmosis it is characterized as a Weber type B. The syndesmotic ligaments and IOM remain intact. Figure 47-60C illustrates a Weber type C injury, radiographically on the left and schematically on the right. This is the same mechanism as a Weber type B injury, except now the compressive lateral forces extend through the syndesmosis, tearing the tibiofibular ligament as well as the distal IOM. In this case the obliquely oriented fibula fracture will be higher up, above the level of the syndesmosis. Identifying this high fibula fracture is important to recognizing that the syndesmotic ligaments are disrupted, because radiographically the syndesmosis may not appear abnormally widened if not stressed. Indeed, sometimes the fibula fracture is so high that it occurs through the proximal fibula, near the knee joint, and is thus not imaged on ankle radiographs. This is referred to as a Maisonneuve* fracture and can be sus- *Jules Germain François Maisonneuve (1809-1897), a French surgeon and a student of Guillaume Dupuytren, was the first to describe external rotation as a contributing mechanism in the production of ankle fractures. pected when the ankle radiographs demonstrate an avulsion fracture through the medial malleolus without an accompanying fibula fracture. If you cannot tell from ankle radiographs whether you are looking at a Weber type B or C, this is a clue that you may be looking at a Maisonneuve, and radiographs that include the entire length of the fibula should be obtained. Determining the integrity of the syndesmosis is an important surgical consideration because syndesmotic injuries usually require screw fixation. When the integrity of the syndesmosis is unclear based on physical examination and radiographs, a CT scan can be helpful (Fig. 47-61). Scanning in the axial plane through both ankles simultaneously allows for side-by-side comparison of the widths of the injured and uninjured syndesmoses. • Fracture through the Tibial Plafond Intra-articular fractures through the tibial plafond often require surgical open reduction with internal fixation (ORIF) to restore the anatomic alignment of the articular surfaces, and multiplanar reformatted CT scans are often instrumental in such surgical planning. Three fractures in particular that typically come to CT are the pilon 10 fracture in adults, and the juvenile Tillaux 35 and triplane 38 fractures in adolescents. Pilon Fracture Pilon fractures are any tibial fracture that involves the distal articular plafond and are typically the result of an axial loading force. Pilon is French for “pestle,” an instrument used for crushing or pounding, and was first used to describe this fracture in 1911 by Étienne Destot, the father of radiology in France. When they are the result of a highenergy injury, such as a fall from height or a high-speed motor vehicle front-end collision, pilon fractures can produce significant comminution with multiple displaced fracture fragments. Although these comminuted fractures invariably require internal fixation, they are typically not Ch047-A05375.indd 2253 9/9/2008 5:34:46 PM
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