Ankle Stress Radiographs Predict Lateral Ankle Instability Better Than MRI
Authors: Danna Natalie R. , Shakked Rachel J. , Sheskier Steven C. 
Published: October 2016

Category: Ankle Introduction/Purpose: Chronic ankle instability is a common entity that may be mechanical or functional in nature. Patients with mechanical instability are thought to have limited rehabilitation potential from non-operative treatment alone. Reliable identification of patients with mechanical instability may be beneficial in their treatment approach. A standardized diagnostic algorithm has not been well established using various modalities including physical examination, stress radiography, and MRI. This study aims to determine the utility of stress radiography and MRI in diagnosing mechanical ankle instability as compared to the gold standard of intra-operative stability. Methods: A retrospective chart review was performed on all patients that had stress radiographs between January 2008 through August 2013. All charts were reviewed for operative reports, progress notes, radiographs, MRI images, and reports. Stress radiographs were performed on those patients presenting with complaints of ankle instability using the Telos Stress Device (Hungen, Germany) and radiographic measurements of talar tilt and anterior drawer distance were performed by a senior resident. One hundred and four patients were identified, and 1 was excluded due to inadequate stress radiographs. The average age was 40 years, and there were 54 males and 49 females. Twenty-nine (28%) patients presented after an automobile accident or work-related injury. Thirty-eight patients (37%) were taken to the operating room, and 20 patients (53%) were found to be unstable requiring lateral ligament repair. An MRI was available for review in 30 (79%) of the patients that were taken to the operating room. Results: Talar tilt measurement of 6 degrees or greater on stress radiographs significantly predicted ligament incompetence (p = 0.0016) using intra-operative stability as the gold standard. Sensitivity of the stress radiograph was found to be 90% with respect to identifying ligament incompetence; specificity was 61%. MRI reports were reviewed and the lateral ligaments were described as intact, thickened, attenuated, or torn. There was no correlation between radiologist description of the anterior talofibular ligament (ATFL) and intra-operative stability (p = 0.31). Of the 29 patients presenting after an automobile accident or work- related injury, 18 (62%) were taken to the operating room; 10 were found to be stable and 8 were unstable requiring lateral ligament repair. Table 1 includes talar tilt measurements and intra-operative findings. Conclusion: The dynamic nature of stress radiographs may be better suited to diagnosing mechanical instability than a static MRI. This study demonstrates that stress radiographs can successfully predict mechanical instability diagnosed intra-operatively. There was no correlation between MRI findings and intra-operative stability. Though physical examination remains an important part of the work-up of a patient complaining of ankle instability, stress radiography may be a more objective tool to utilize in this population of patients.