Accuracy of plain radiographs versus 3D analysis of ankle stress test

Radiographic stress testing using both the anterior drawer (AD) and talar tilt (TT) technique is a widely accepted means of assessing ankle instability. The purpose of this study was to investigate the accuracy of plain film radiography in measuring translation of the talus during the AD test and the rotation of the talus during TT stress testing. In addition to determining the true accuracy of radiologic assessment in two planes, our goal was to further define instability in the sagittal, coronal and transverse planes.

Twenty lower extremity specimens were placed in a Telos ankle stress apparatus, and respective lateral and AP radiographs were taken during simulated AD and TT testing. Positional measurements were calculated from the films. Next, a three-dimensional tracking system was used to calculate these displacements. The anterior talofibular ligament and calcaneofibular ligament were sectioned to simulate an unstable ankle, followed by repeat measurement using both methods. Movement calculated using the three dimensional system was compared to that of plain radiographs using a paired t-test.

Mean positional changes determined by plain film radiographs were found to be significantly lower than those calculated by the three-dimensional system in both AD and TT tests in the intact and sectioned states (p < 0.001).

Radiographic stress testing assessment of ankle instability appears to be much less accurate than previously believed.

Compared to values calculated with the 3D system, radiographic measurements may underestimate the true magnitude of TT and AD changes which could influence clinical decision making.