Imaging of Talar Dome Chondral and Osteochondral LesionsJames M. Linklater, MB, BS
Abstract: Talar dome chondral and osteochondral lesions are a com-mon cause of ankle pain and subjective instability. The goal of imagingthese lesions is primarily their detection, demonstration of their positionand extent, including status of the chondral surface, demonstration of anyassociated chondral delamination, assessment of the integrity of thesubchondral plate, and assessment of the cancellous subchondral bonefor bone marrow edema like signal, sclerosis, cystic change, and forthe presence of an unstable osteochondral fragment. Although plainradiography, computerized tomography, and bone scan may be helpful inthe detection and characterization of these lesions, magnetic resonanceimaging is the only imaging modality that will provide a comprehensiveassessment of all these issues. Technical aspects of plain radiography,computerized tomography, and magnetic resonance imaging arediscussed, and imaging findings are presented.
Key Words: ankle, talar dome, chondral, osteochondral, MRI,CT, radiography
(Top Magn Reson Imaging 2010;21: 3Y13)
HISTORICAL PERSPECTIVEChondral and osteochondral lesions in the ankle are a well-
recognized cause of persistent ankle pain and subjective insta-bility after ankle injury.1Y4 Clinically, there may be an overlapbetween a posttraumatic ankle joint synovitis, posttraumaticchondral and osteochondral injury, and extraarticular patholo-gies. Berndt and Harty5 introduced a plain radiographic classi-fication of talar dome osteochondral lesions. In the 1970s and1980s, bone scan became widely used in the workup of sus-pected talar dome lesions. In the late 1980s computerizedtomographic assessment of talar dome lesion became wide-spread6 and magnetic resonance imaging (MRI) began to beapplied to the imaging of the ankle.
The goal of imaging chondral and osteochondral lesions inthe ankle is primarily their detection, demonstration of theirposition and extent, including status of the chondral surface,demonstration of any associated chondral delamination, assess-ment of the integrity of the subchondral plate, and assessmentof the cancellous subchondral bone for bone marrow edemalike signal, sclerosis, cystic change and for the presence of anunstable osteochondral fragment. Although plain radiography,computerized tomography (CT), and bone scan may be helpfulin the detection and characterization of these lesions, MRI isthe only imaging modality that will provide a comprehensiveassessment of all these issues.
Technical AspectsRadiographs should be performed weight bearing in order
to provide a more relevant assessment of alignment. In addition,joint space loss may be more conspicuous or even only bepresent on weight bearing. A routine ankle series should includeantero-posterior (AP), lateral, and mortise views. Computerizedradiography (CR) and digital radiography (DR) are graduallyreplacing film-screen radiography units. Computerized radiog-raphy and DR allow wider latitude in radiographic exposure,resulting in less repeat exposures and providing a better as-sessment of bone and soft tissues. Whereas previously it wascommon to see overexposed radiographs in which the soft tis-sues are blacked out, with CR and DR, this should no longerbe the case. Computerized radiography and DR also offerimprovements in patient throughput, not achievable with film-screen systems. The digital image data from CR and DR is alsoreadily transferred to picture archive and communication system.
Diagnostic FeaturesPlain radiography is of limited sensitivity in the demon-
stration of chondral and osteochondral pathology in the ankle.7
In the setting of acute trauma, plain radiographs may demon-strate an acute osteochondral fracture (Fig. 1). In the chronicsetting, central osteophyte formation may occur at the site of anoverlying chondral defect (Fig. 2). Plain radiographs may alsodemonstrate the development of subchondral cystic change in achronic osteochondral lesion (Fig. 3). In situ, unstable osteo-chondral fragments and displaced osteochondral loose bodiesmay also be demonstrable on plain radiography. Ankle jointosteoarthritis is an uncommon complication of an osteochondrallesion in the ankle. It is indicated at plain radiography by thepresence of joint space loss and osteophyte formation.
Technical AspectsModern multislice helical CT involves acquisition of a thin
slice volume data set in the transverse plane that can be recon-structed in any plane and also reconstructed into 3-D images.Computerized tomography arthrography will provide detailedassessment of the chondral surfaces and may be used as analternative means of assessment when MRI is contraindicated.8
The disadvantage of CT arthrography compared with MRI liesin its invasive nature and its use of ionizing radiation. Com-puterized tomography single proton emission computerisedtomography bone scans will demonstrate areas of increasedosteoblastic activity associated with an osteochondral lesion.The greater anatomical detail provided by fusing the bone scandata with CT scan data allows more accurate localization ofthe hot spot.
Diagnostic FeaturesIn the acute setting, CT can provide an assessment for
fractures in cases where plain radiographs are equivocal ordemonstrate a complex fracture. In the setting of chronicosteochondral lesions, CT will demonstrate the presence of
Top Magn Reson Imaging & Volume 21, Number 1, February 2010 www.topicsinmri.com 3
From the Castlereagh Sports Imaging, North Sydney Orthopaedic and SportsMedicine Centre, Crows Nest, New South Wales, Australia.
Reprints: James M. Linklater, MB, BS, Castlereagh Sports Imaging, NorthSydney Orthopaedic and Sports Medicine Centre, 286 Pacific Hwy,Crows Nest, New South Wales 2065, Australia (e-mail: email@example.com).
This article was previously published: Linklater, JM. Imaging of talardome chondral and osteochondral lesions. Tech Foot Ankle Surg.2008;7:140Y151.
Copyright * 2011 by Lippincott Williams & Wilkins
Copyright 2011 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.
subchondral sclerosis and cystic change, central osteophytesand in situ and displaced ossific loose bodies. Computerizedtomography is superior to MRI in demonstrating small cracks inthe subchondral plate associated with cystic change which mayallow propulsion of synovial fluid into the cyst. Computerizedtomography will not demonstrate the chondral surfaces and willnot demonstrate bone marrow edema. Therefore, in general,MRI is preferred over CT in the assessment of talar domechondral and osteochondral lesions.
MAGNETIC RESONANCE IMAGINGMagnetic resonance imaging provides a noninvasive
assessment of the chondral surfaces, subchondral plate, sub-chondral bone, joint fluid, capsule, and ligaments. Magneticresonance imaging is at present the best single imagingmodality for assessment of ankle joint chondral and osteo-chondral lesions.
Field StrengthMagnetic resonance imaging units in clinical practice range
in field strength from 0.3 to 3.0 Tesla. In general, low fieldstrength MRI units (G0.5 Tesla) do not provide detailed articularcartilage assessment.
Pulse SequencesThe pulse sequences typically used in ankle MRI consist
of proton density (PD) and fat-suppressed proton densitysequences (PD-FS).9,10 The pulse sequences should have suffi-cient spatial and contrast resolution to provide detailed assess-ment of articular cartilage. Spatial resolution is a function ofthe slice thickness (usually 2.5Y4 mm), field of view (usually10Y16 cm) image matrix (the number of data points in the imagegrid, expressed numerically in 2 axes) typically between 512 384 and 256 192.
The nonfat-suppressed PD sequence renders joint fluidbright and provides high-resolution images of articular cartilage,enabling assessment of the chondral surface, demonstratingchondral fissure/fracture and basal chondral delamination.9,11
Chondral fibrillation, commonly seen in patellar articular carti-lage, is uncommon in the ankle.12 Proton density sequencingalso provides some assessment of the subchondral bone, inthat low signal intensity change in the subchondral bone isindicative of subchondral sclerosis or fibrosis. Bone marrowedema is not demonstrable on a nonfat-suppressed PD sequence.
Fat suppression is achieved by the use of a radio frequencypulse that reduces the amount of signal derived from fat,rescaling the contrast characteristics of the pulse sequence towhich it is applied. If applied to a PD sequence, areas ofincreased water content within bone marrow will be of higher
FIGURE 4. Minimally displaced chondral flap midlateral talar dome, with a small crack in the chondral surface at the medial andposterior margins