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

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2294 VII Imaging of the Musculoskeletal System A B C Figure 47-97. Anterior process of the calcaneus (APC) fracture in a 51-year-old who was playing a jumping game. The patient, who was wearing sandals, landed awkwardly and felt a large “pop” after forcefully inverting the foot. A, Lateral radiograph obtained when the patient came into the emergency department the next day revealed the previously asymptomatic elongated APC (arrows). Careful scrutiny also reveals disruption of the cortex (arrowhead), indicating a nondisplaced APC fracture. B and C, CT scans were obtained the same day. Sagittal (B) and axial (C) scans revealed the APC fracture (black arrowheads) as well as the incidental finding of a calcaneonavicular nonosseous coalition (white arrowhead; N, navicular). The patient was treated nonoperatively with a non–weight-bearing cast. When no healing was seen radiographically 9 weeks later, an ultrasonic bone stimulator was used. Five weeks after that, healing was evident radiographically. Twenty-three weeks later, the injury was essentially asymptomatic. 47-100), small nerve sheath tumors, focal synovitis, or rarely even varicose veins, can potentially impinge on the posterior tibial nerve. 22,30 • Stress Injuries When the foot is subjected to new or excessive forces, such as a change in physical activity or an increased level of workout, certain bones may be subjected to a disproportionate amount of the increased stress and exhibit a stress response. The pattern of stress response depends on which bone is involved and how long it has been untreated. Figure 47-98. Bilateral nonosseous coalitions of the middle facet of the subtalar joint in an 8-year-old. Coronal CT scan reveals an abnormal vertical orientation of the right middle facet (white arrow). On the left, the talar-side middle facet has an abnormal rounded cortical surface (black arrow). • Navicular Stress Fractures 34 Navicular stress fractures begin at the dorsal, central, proximal navicular where it articulates with the head of the talus Ch047-A05375.indd 2294 9/9/2008 5:35:51 PM
47 Ankle and Foot 2295 47 Tarsal tunnel Flexor retinaculum B A Figure 47-99. Location of the tarsal tunnel. A, Illustration of the location of the tarsal tunnel (arrow), deep to the flexor retinaculum. (Artist, M. Schenk, MS, CMI.) B, Axial high-resolution T1-weighted image shows the medial neurovascular bundle (dotted ellipse) deep to the flexor retinaculum (arrows). Figure 47-100. Tarsal tunnel containing a synovial cyst (arrow): axial (A) and sagittal (B) T2-weighted fatsuppressed images. A B (Fig. 47-101A). These fractures tend to be the result of repetitive injuries rather than a specific traumatic event. In our practice, such fatigue injuries are commonly seen in college athletes. Often the athlete’s prognosis and the length of time needed to rest the fatigue injury depend on whether the cortex is broken. When MRI demonstrates just bone marrow edema without a breach in the cortex, these will be radiographically occult, and our sports medicine physicians prefer we use the term stress reaction. We use stress fracture to refer to bones that exhibit a discrete line extending through the cortex by MRI, CT, or plain radiography (Figs. 47-102 and 47-103). Although navicular fatigue fractures may be suspected clinically, initial radiographs are often negative, and MRI is the next imaging study ordered to confirm the diagnosis. As with most stress fractures, MRI is more sensitive than CT for the detection of the bone marrow edema that develops before the cortex breaks (see Fig. 47-101). But MRI, owing to its exquisite sensitivity to marrow edema, may be too sensitive to assess fracture healing. At the UW we have Ch047-A05375.indd 2295 9/9/2008 5:35:53 PM
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