Rockwood Adults CH64

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CHAPTER 64 • Ankle Fractures

A, B

C

Figure 64-13.  Anteroposterior ( A ), mortise ( B ), and lateral ( C ) radiographs of the ankle. These constitute a standard ankle trauma series.

Interpretation of the radiographs follows the sequence ABCS, and includes an assessment of technical a dequacy and align- ment (does this radiograph show the joint well enough for you to make a complete assessment?), the cortical outline and tra- becular morphology of each of the b ones, particularly the artic- ular margins where irregularity of the c artilage articular surface,

although not directly visible, can be inferred, and the contour of the overlying s oft tissues. The relationship between the bony components of the ankle is critical, and a number of “normal” features are widely recognized (Table 64-2; Figs. 64-14 and 64-15). These empirical “normal” measurements must, how- ever, be interpreted in the light of some scientific controversy

TABLE 64-2. Radiographic Parameters That Should Be Looked for on Radiographs of Ankle Fractures

Radiographic Feature

Accepted Normal Parameter

Notes

Medial clear space

The joint spaces medial and superior to the talus should be equal. The medial clear space should be < 5 mm, and no more than 2 mm greater than the tibiotalar clear space.

These measurements are influenced by rotation, individual patient morphology, and the presence of ankle arthritis.

> 5 mm

Tibiofibular clear space (syndesmosis A) 10 mm above joint line

Relatively constant with rotation

< 5 mm on AP view and < 1 mm on the mortise view

Tibiofibular overlap (syndesmosis B) 10 mm above joint line

Highly variable dependent on rotation

Fibular length

The articular margins of the distal fibula and the lateral process of the talus on the mortise view should be parallel, and equal to the tibiotalar joint space. The “ball sign” (Fig. 64-15) is a confirmatory visual cue.

Shortening of the fibula results in lateral and valgus subluxation of the talus

Talocrural angle

Approximately 83 degrees, and symmetrical with contralateral ankle.

A further measurement of fibular length

Medial malleolus

Less than 2 mm displacement

Important where this results in talar shift

Lateral malleolus displacement

Less than 2 mm shortening, or displacement posteriorly or proximally

Important where this results in talar shift. Isolated lateral malleolar fractures, although commonly displaced, are not usually an indication for surgery. The size may be underappreciated on plain x-ray.

Posterior malleolus displacement

The fragment must be less than 25% of the ankle joint seen on the lateral radiograph, and less than 2 mm displaced.

Note: A diagrammatic representation of these parameters is shown in Figure 64-14, and the ball sign is explained in Figure 64-15.