OBJECTIVES:
We hypothesized that the method of stress external rotation more accurately reproduces the mechanism of injury, and therefore this diagnostic method more likely detects ankle instability than the fibular stress examination.

DESIGN:
Prospective cohort comparison study.

SETTING:
Level 1 trauma center.

PATIENTS:
Twenty-eight consecutive patients with unstable ankle fractures presenting within 7 days from the time of injury. Previous ankle surgical history or age younger than 18 years was excluded.

INTERVENTION:
Stress external rotation and lateral fibular stress examination was performed intraoperatively.

MAIN OUTCOME MEASURE:
Radiographic measurement of the tibiofibular clear space, tibiofibular overlap, and medial clear space were recorded.

RESULTS:
After normalization of the fluoroscopic measurements, there was no difference in detecting changes in tibiofibular clear space or tibiofibular overlap. However, there was a significant difference in detecting medial clear space widening with stress external rotation. Compared with lateral fibular stress, stress external rotation demonstrated a 35% increase (P < 0.05) in medial clear space widening. This difference correlates with the 1-2-mm difference of additional widening with stress external rotation.

CONCLUSIONS:
Untreated instability impacts patient outcomes. The difference in widening with stress external rotation was significantly greater than lateral fibular stress and appreciable on standard fluoroscopic views. Stress external rotation radiographs are a more reliable indicator of mortise instability than traditional lateral fibular stress.

LEVEL OF EVIDENCE:
Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.





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