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2276 VII Imaging of the Musculoskeletal System A B C Figure 47-84. Anterior process of the calcaneus (APC) fracture in a 34-year-old who presented to the urgent care clinic 1 day after a minor motor vehicle collision, complaining of pain along the lateral midfoot. A, Lateral radiograph shows the small APC fracture resembling an os calcaneus secondarius (arrowheads in magnified dashed box). CT scans were obtained the next day. B, Sagittal scan through the APC demonstrating sharp, noncorticated, margins (arrowheads in dotted magnified box) on the vertically oriented fracture. C, The axial source scan confirms that this is an acute fracture with sharp but nonsclerotic margins (arrowheads in dashed magnified box). Ch047-A05375.indd 2276 9/9/2008 5:35:23 PM
47 Ankle and Foot 2277 47 Figure 47-85. Example of a Lisfranc amputation in a 53-year-old who has had chronic peripheral neuropathy of unknown cause since 16 years of age. Lateral (A), anteroposterior (B), and (C) oblique radiographs. Cu, cuboid; 1, 2, and 3 indicate the first, second, and third cuneiforms. A B C bears his name, he did describe an amputation along the tarsometatarsal joint, an example of which is shown in Figure 47-85. In a Lisfranc dislocation, the second to fifth metatarsals are dislocated laterally, or dorsolaterally, relative to the tarsal bones. The Lisfranc dislocations are subdivided into two categories based on what happens to the first metatarsal relative to the other four. If the first metatarsal dislocates laterally along with the second to fifth metatarsals, it is called homolateral (Fig. 47-86). If the first metatarsal diverges from the other four metatarsals, remaining aligned with the medial cuneiform (Fig. 47-87), or if the first metatarsal dislocates medially (Fig. 47-88), it is called divergent. When a Lisfranc fracture is grossly displaced, a CT scan is not needed to confirm the diagnosis. However, because the exact location of dislocated metatarsals may be difficult to discern based solely on radiographs, a threedimensionally reformatted CT scan may prove useful in presurgical planning (see Figs. 47-86H and 47-87F and G). The three-dimensional nature of these dislocations can best be appreciated by creating a series of three-dimensional images rotated along longitudinal and transverse axes and played as a movie loop on the PACS. We find that a series of 36 images, each 10 degrees apart, works well. When only minimally displaced, Lisfranc dislocations can be difficult to discern radiographically, and close attention should be paid to the Lisfranc joint on all views of the foot. Normally there is perfect alignment between the first metatarsal base and first (or medial) cuneiform, between the second metatarsal and the second (or middle) cuneiform, and between the third metatarsal and the third (or lateral) cuneiform. Also, the bases of the fourth and fifth metatarsals should be perfectly aligned with their individual facets on the cuboid (see Fig. 47-86A and B). One clue that a nondisplaced Lisfranc dislocation may be present is fracture fragments off the base of the second metatarsal. As shown on the three-dimensional CT in Figure 47-5, the base of the second metatarsal extends more proximally across the Lisfranc joint than do the other metatarsals. Thus, when dislocations occur along the Lisfranc joint, it Text continued on p. 2282 Ch047-A05375.indd 2277 9/9/2008 5:35:24 PM
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Ankle and Foot 47 - Department of Radiology - University of ...

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