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CHAPTER 64 • Ankle Fractures

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Figure 64-19.  During the gravity stress view, the patient is made to lie in the lateral decubitus position on the side of the affected ankle with the distal leg, ankle, and foot allowed to hang dependent off the end of the table while a mortise view is obtained. This patient positioning, in effect, acts to impart an external rotational force as in the manual stress view.

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There is increasing evidence, however, that such stress test measurements do not directly equate with clinical stability or outcome. No specific cut-off value for medial clear space has been shown to equate to stability, or definitive deltoid ligament rupture as confirmed by arthroscopy. 337 A key study by Egol et al. 100 reported on 101 patients who had apparently stable isolated lateral malleolar fractures and underwent manual stress views. Sixty-six patients were considered to have had positive stress tests as judged by an absolute medial clear space of more than 4 mm. Thirty-six of these also had clinical signs of medial injury and were empirically judged to have unstable injuries and underwent stabilization; it is not possible to judge how many of these were truly unstable. The most interesting group comprised 30 patients who had a positive stress test but no clinical signs. This group was offered the option of surgery or functional treatment. Twenty chose functional treatment, and 10 chose operative treatment. Their functional results at 7 to 10 months were identical and no patient developed functional or radiographic instability. The fact that 66% of the initial cohort were considered to be radiographically unstable suggests that a cut-off of 4 mm on stress radiographs is likely to be too stringent a criterion, and the clinical outcomes of this cohort appear to confirm this. Tornetta supported these findings with a report of a cohort of 114 patients with a “positive” stress test with 5 mm of medial clear space. Fifty-four of these patients were man- aged nonoperatively and went on to union with an anatomi- cal mortise. 385 Another study, of a cohort of 155 patients with apparent SER 2 fractures undergoing gravity stress testing, and using a medial clear space of 4 mm as the cut-off, found 79% of patients to have positive stress radiographs. As all of these patients were successfully treated nonoperatively with good outcomes, these were deemed to be false-positives. When the cut-off was increased to 6 mm, 19% remained false-positive and even when there was a requirement for the medial clear space to be greater than 6 mm and greater than a baseline value, 15% were false-positives. The role of stress tests remains undefined.

Investigators have also assessed the usefulness of clinical indicators of deltoid injury such as medial bruising and swell- ing. When stress test measurements are taken as the gold stan- dard indicators of instability, these clinical findings appear to add little additional information. The presence of tenderness has been shown to have a positive predictive value of less than 50%, and the absence of tenderness has been shown to have a negative predictive value of just 66%. 87 Moreover, the absence of combined tenderness and bruising has a negative predictive value of 39%. When judged using a stress test as the gold stan- dard, there is a 61% chance of missing instability if the absence of these clinical signs is used as the criterion. 100 However, given that a positive stress test seems not to relate closely to true insta- bility, and seems actually to be a poor “gold standard,” the low negative predictive value of clinical signs of medial injury may have been overstated 87 : That is, it seems likely that the absence of medial tenderness, swelling, or bruising probably is a good indicator of functional ankle stability, as previous outcome studies have long assumed. 45,94,200,306,325,426 To assess the relationship between clinical signs, deltoid injury and outcome further, Koval et al. 195 subsequently reported on a group of 21 patients with lateral malleolar fractures who were clinically suspected of having an associated medial-sided injury. They underwent manual stress views, and all were shown to have between 5 and 8 mm of absolute medial clear space and were therefore deemed to have a positive stress radiograph. All 21 patients underwent MRI scanning and all were found to have superficial deltoid ruptures. Two also had complete deep deltoid ruptures and were advised to undergo surgery. The remaining 19 had only partially ruptured deep deltoid ligaments despite the abnormal clear space and were advised to have conserva- tive management with full weightbearing in a removable boot. Each was kept under review for a year and went on to make a full recovery. Other authors have also reported poor correlation between the stress test and MRI assessment of the deltoid liga- ment. 336 Thus the manual stress test appears to have low positive