MR imaging of ankle impingement lesions.

Impingement is defined as a painful limitation of motion. Impingement lesions as identified on MR imaging of the ankle may relate to a range of soft tissue or bony pathologies that can be interpreted as predisposing to painful limitation of motion, accepting that the diagnosis of impingement remains clinical and not radiological. Typically, impingement lesions are classified according to their location and whether the underlying pathology is osseous or soft tissue in nature. Most commonly, impingement lesions relate to posttraumatic synovitis and intra-articular fibrous bands-scar tissue, capsular scarring, or bony prominences, the latter either developmental or acquired. Well-recognized sites of impingement around the ankle include the anterolateral, centroanterior, anteromedial, posteromedial, and posterior sites. This article reviews the anatomy in these regions and focuses on common causes of impingement around the ankle; their pathogenesis, clinical features, and management; the approach to imaging of these lesions with MR imaging and their imaging features; and the relevant imaging differential diagnoses.