Rockwood Adults CH64

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SECTION FOUR • Lower Extremity

Surgical repair of the medial deltoid injury, although at one time recommended, 43 is unnecessary. 139

In the former, the patient is placed supine on the x-ray table with the leg held in 20 degrees of internal rotation to produce a mortise view. The ankle is held in a plantigrade (neutral) posi- tion and a firm but gently progressive external rotation force is applied to the forefoot and a radiograph is taken. It is important to avoid a plantarflexed position which can result in apparent (but not true) displacement, because the talus narrows poste- riorly. The same effect can be achieved by placing the patient laterally on the x-ray table with the injured limb lowest and the foot hanging free from the end of the table (Fig. 64-19), with gravity thereby exerting the required external rotation force. The two examinations have been shown to produce equivalent results, and the gravity stress examination has the advantages of reducing the exposure of the surgeon to ionizing radiation and reducing discomfort for the patient. 127,335 Although conceptually attractive, evidence for the usefulness of stress views remains elusive. Principally, there is considerable uncertainty as to how much widening is indicative of instability. An absolute medial clear space of either 4 or 5 mm is often quoted as the upper limit of normal. 87,100,141,297 However, the absolute size of the patient, 239 their gender, 174 the degree of magnification of the image and the rotation of the radiograph 304 will all affect this assessment. Alternatively, an increase in the medial clear space from a baseline value (the superior clear space or contralat- eral ankle have been used) of up to 3 mm has been proposed 295 although again this is empirical and can be affected by factors such as ankle arthrosis. Finally, a combination of the two methods with an absolute medial clear space of 4 or 5 mm, which is also an increase on baseline, has been used by some authors. 127,195,239,335 It has been widely assumed that ankles with medial clear space values less than these empirical values on stress examination are stable, while ankles with greater degrees of translation are unsta- ble and should be advised to undergo surgery.

Lateral Malleolar Fracture With Occult Ankle Instability In clinical practice, it is not always straight forward to distin- guish between a stable, isolated, lateral malleolar fracture (most commonly an SER 2 injury, which can be treated nonopera- tively), and a lateral malleolar fracture in combination with a medial deltoid ligament rupture (SER 4 injury, which usually requires surgery) if the mortise is anatomically enlocated on presentation radiographs, and this may result in a diagnostic dilemma (see Fig. 64-18). The anatomical key to stability in this situation is thought to be the integrity of the deltoid, which has both superficial and deep components. It is the deep component, attached to the posterior colliculus of the medial malleolus, that is widely considered to be crucial to talar stability. 250,297 Assessment of the integrity of the deltoid is both clinical and radiographic. Clinical signs should be interpreted with caution: medial swelling, bruis- ing, and tenderness often accompany deltoid ligament rupture and are considered supportive, but not diagnostic, of mechanical instability, 45,94,200,306,325,426 while the absence of these signs is simi- larly indicative (but not diagnostic of) ankle stability. 289 Differentiating between a stable and an unstable ankle frac- ture may require a dynamic test, and the most common tests are stress radiographs (which may be manual or gravity-assisted), and the pragmatic “walking test,” whereby if there is no talar shift on radiographs taken a week after injury, the ankle has “proved” its stability. Alternatively, stability may be inferred from MRI images of the deep deltoid ligament. None of these tests is perfect. The most common practice in North America is to perform a stress radiograph, either manual or gravity-assisted.

A

B Figure 64-18.  A: An anteroposterior radiograph of an SER 4 injury showing no displacement. However the gravity stress views shows displacement ( B ), confirming instability.