Classification and imaging of ankle impingement syndromes.

Learning Objectives: To review the classification of ankle impingement syndromes. To describe and illustrate the spectrum of appearance of ankle impingement syndromes using conventional radiography (CR), multidetector computed tomography (MDCT), ultrasonography (US), magnetic resonance imaging (MRI), and MR arthrography (MRA). Background: Ankle impingement syndromes are a spectrum of diseases common in both athletic and general population and depend on many causes that can be distinguished by the type of tissue which determines the conflict (bone, fibrous, synovial). In general, classification of ankle impingement syndromes takes into account the anatomical site relative to the tibio-tarsal joint, and thus they may be classified as anterior, antero-medial, antero-lateral, posterior and postero-medial. Imaging findings: CR alone already suffices to demonstrate a bone impingement in most cases, while there is necessity to use MDCT where the site of impingement is in an anatomical site not clearly demonstrable by CR because of the presence of superimposed structures. US has the ability to recognize the presence of an anterior impingement and it may assess tendon disorders (stenosing tenosynovitis) which may be an associate sign of an impingement syndrome. MRI is the method of choice to assess synovial or fibrous impingement syndromes thanks to its excellent contrast resolution. MRA is used when there is capsular thickening that could not be detected by simple MRI. Conclusion: Diagnostic imaging has a very important role in the recognition of the cause of impingement and of the anatomical site where such a conflict takes place, thus allowing a correct therapeutic management.