The tuning fork test--a useful tool for improving specificity in "Ottawa positive" patients after ankle inversion injury.

The Ottawa ankle rules are a clinical instrument calibrated towards a high sensitivity in order not to miss any fractures of the ankle or mid-foot. This is at the cost of a mean specificity of around only 32%. The aim of this study was to determine the suitability of tuning fork testing in combination with existing Ottawa guidance for increasing the specificity in detecting fractures of the lateral malleolus. A prospective pilot study was carried out, in which a single trained investigator examined all patients with already "Ottawa positive" findings for possible lateral malleolus injury by applying a tuning fork (C(o) 128 Hz). The tuning fork test findings were compared with formal reports of plain ankle radiographs using simple cross-table analysis. The observed prevalence of ankle fractures was 5 of 49 (10%). Sensitivity and specificity were calculated as 100% and 61%, respectively, for tuning fork testing on the tip of the lateral malleolus (TLM), and as 100% and 95%, respectively, for testing on the distal fibula shaft (DFS). The associated positive and negative likelihood ratios were 2.59 and 0 (TLM), and 22 and 0 (DFS), respectively. The data were significant, with p = 0.014 (TLM) and p<0.001 (DFS). This study suggests that additional tuning fork testing of "Ottawa positive" patients may lead to a marked reduction in ankle radiographs, with consequently reduced radiation exposure and journey time. This may be particularly relevant in situations where radiological facilities are not readily available (expedition medicine) or where access to these has to be prioritised (major incidents, natural catastrophes).