Ankle impingement: a review of multimodality imaging approach.

Ankle impingement is defined as entrapment of an anatomic structure that leads to pain and decreased range of motion of the ankle and can be classified as either soft tissue or osseous (Bassett et al. in J Bone Joint Surg Am 72:55-59, 1990). The impingement syndromes of the ankle are a group of painful disorders that limit full range of movement. Symptoms are due to compression of soft-tissues or osseous structures during particular movements (Ogilvie-Harris et al. in Arthroscopy 13:564-574, 1997). Osseous impingement can result from spur formation along the anterior margin of the distal tibia and talus or as a result of a prominent posterolateral talar process, the os trigonum. Soft-tissue impingement usually results from scarring and fibrosis associated with synovial, capsular, or ligamentous injury. Soft-tissue impingement most often occurs in the anterolateral gutter, the medial ankle, or in the region of the syndesmosis (Van den Bekerom and Raven in Knee Surg Sports Traumatol Arthrosc 15:465-471, 2007). The main impingement syndromes are anterolateral, anterior, anteromedial, posterior, and posteromedial impingement. These conditions arise from initial ankle injuries, which, in the subacute or chronic situation, lead to development of abnormal osseous and soft-tissue thickening within the ankle joint. The relative contributions of the osseous and soft-tissue abnormalities are variable, but whatever component is dominant there is physical impingement and painful limitation of ankle movement. Conventional radiography is usually the first imaging technique performer and allows assessment of any potential bone abnormality, particularly in anterior and posterior impingement. Computed tomography (CT) and isotope bone scanning have been largely superseded by magnetic resonance (MR) imaging. MR imaging can demonstrate osseous and soft-tissue edema in anterior or posterior impingement. MR imaging is the most useful imaging modality in evaluating suspected soft-tissue impingement or in excluding other ankle pathology such as an osteochondral lesion of the talus. MR imaging can reveal evidence of previous ligamentous injury and also can demonstrate thickened synovium, fibrosis, or adjacent reactive soft-tissue edema. Studies of conventional MR imaging have produced conflicting sensitivities and specificities in assessment of anterolateral impingement. CT and MR arthrographic techniques allow the most accurate assessment of the capsular recesses, albeit with important limitations in diagnosis of clinical impingement syndromes. In the majority of cases, ankle impingement is treated with conservative measures, with surgical debridement via arthroscopy or an open procedure reserved for patients who have refractory symptoms. In this article, we describe the clinical and potential imaging features, for the four main impingement syndromes of the ankle: anterolateral, anterior, anteromedial, posterior, and posteromedial impingement.