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EDUCATION EXHIBIT |
Department of Radiology, Hospital for Joint Diseases and New York University School of Medicine, New York, New York
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Commentary |
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In the preceding article, Robinson and White present an excellent and comprehensive review of the clinical as well as the imaging characteristics of the four most common impingement syndromes in the ankle: anterolateral, anterior, anteromedial, and posterior impingement. Their excellent and cutting-edge review is particularly valuable since up till now there has been only fragmented and somewhat controversial discussion of these entities in the radiology literature. The authors provide us with a beautifully illustrated discussion of the anatomy, mechanism of injury, clinical manifestations, appropriate imaging modalities, and management of the impingement syndromes. In a clearly written and succinct manner, the authors navigate through the often conflicting data available in the radiology literature regarding imaging of these entities.
Of the four entities described, anterolateral impingement syndrome has received the most attention in the radiology literature. Intraarticular synovial hypertrophy and fibrosis may occur in the lateral gutter secondary to capsular or ligamentous tears associated with inversion injuries. This hypertrophy can elicit a locking sensation and difficulty in fully dorsiflexing the ankle. It is commonly noted in ballet dancers and soccer players. The condition is optimally assessed with MR imaging, although reports attesting to the value of both CT arthrography and US in the diagnosis of anterolateral impingement syndrome have been published.
There has been a significant disagreement in the literature as to the accuracy of MR imaging in diagnosing anterolateral impingement syndrome, with sensitivities ranging from 39% to 100% and specificities ranging from 50% to 100%. The authors carefully guide us through this controversy and lead us to the inescapable conclusion, based on the results of a recent prospective study, that MR arthrography correlates most accurately with arthroscopic findings and thus is the optimal modality for assessing anterolateral impingement syndrome.
Anterior impingement syndrome is produced by anterior talar and tibial bone spurs. The exact reason for the formation of the spurs is not definitely known, and various theories ranging from traction at the capsular insertion to traumatic chondral degeneration have been proposed to explain the findings. Repetitive supination injuries, dorsiflexion injuries, and direct trauma to the anterior aspect of the ankle joint are the most common mechanisms associated with anterior impingement syndrome. Since the condition is related to bony changes, it can be easily surmised from plain radiographs. As the authors attest, CT, while potentially useful for assessing the exact location and size of the bone spurs, is nevertheless rarely indicated.
Anteromedial impingement syndrome is the least recognized of the four impingement syndromes discussed in the article. The condition is most likely secondary to inversion injury, although the cause is still not fully understood. Both osseous abnormalities (anteromedial bone spurs) and soft-tissue abnormalities (synovial and capsular thickening in the region of the anterior tibiotalar ligament of the deltoid) contribute to anteromedial pain and tenderness and limitation of dorsiflexion and inversion. Since the pathologic changes affect both the osseous and soft-tissue structures of the ankle, it follows that plain radiography and cross-sectional modalities such as MR imaging will complement each other in the diagnosis of this entity. However, at the present time, there has been scant discussion of anteromedial impingement syndrome in the radiology literature, and more studies are required before the radiologic accuracy can be determined (1).
Posterior impingement syndrome has been discussed at length in the orthopedics literature. This entity, common in ballet dancers, is caused by repetitive plantar flexion, which produces compression of the osseous and soft-tissue structures in the posterior ankle. The presence of osseous and soft-tissue variants such as a prominent os trigonum, a prominent talar lateral tubercle, or the posterior intermalleolar ligament can predispose to the condition and exacerbate the symptoms. Tendinosis of the flexor hallucis longus tendon may also be associated with the entity. Pain and tenderness in the posterior ankle on plantar flexion are common complaints. Since the severity of symptoms is not linearly related to the presence or size of the os trigonum or the lateral talar tubercle, plain radiographs are nonspecific in diagnosis of this entity. Similarly, increased radiotracer uptake in the posterior ankle on nuclear bone scans is suggestive but nonconfirmatory of the diagnosis. CT and MR imaging play complementary roles in assessing the condition (2). While CT allows more accurate assessment of fragmentation of the os trigonum and pressure erosions on the talus, MR imaging with or without gadolinium contrast material is far more accurate in assessing the soft-tissue proliferation associated with this finding. Given a choice, one should study the entity with MR imaging first. CT may be performed if more detailed osseous information is necessary presurgically.
The authors do not emphasize the function of US in diagnosing impingement syndromes in the ankle. However, they mention the role of US in guiding therapeutic injections in these entities. Two excellent US images of impingement syndromes accompany the text.
Another impingement syndrome, which the authors only touch upon, should be kept in mind: posteromedial impingement syndrome (3). Contusion of the deep tibiotalar component of the deltoid ligament following severe inversion injuries can lead to hypertrophic changes at that site. This can produce posteromedial pain and limitation of motion. Coronal and axial MR images are useful for detecting this entity.
In conclusion, the authors provide us with a thorough summary of the relatively uncommon yet important to recognize ankle impingement syndromes. The article, with its easy-to-use approach, serves as an excellent guide to the optimal imaging modality for each of the ankle impingement syndromes.
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