CT produces detailed information on the size, shape, and extent of displacement of the bony injury. It is especially effective for the evaluation of subchondral (cystic) lesions [7]. Because of its effectiveness, a CT-based classification system was established. The stages of this system are I, a cystic lesion in the talar dome with an intact roof; IIA, a cystic lesion with communication to the talar dome surface; IIB, an open articular surface lesion with an overlaying non-displaced fragment; III, a non-displaced lesion with lucency; and IV, a displaced fragment [8]. A common reported disadvantage of CT compared to MRI is the insufficient ability to evaluate the articular cartilage [17]. To overcome this disadvantage, CT techniques which contain a CT arthrography and helical technology with multiplanar reconstructions have been advanced recently. A study on the comparison of MR arthrography and CT arthrography for the evaluation of cartilage lesions in the ankle joint revealed that CT arthrography was superior to MR arthrography with regard to interobserver variability and detecting articular cartilage lesions [20]. It has also been reported that the diagnostic value of MRI did not prove to be better than high-resolution multidetector helical CT for the detection or exclusion of an OCL of the ankle [23]. Furthermore, single-photon emission computed tomography (SPECT)-CT, a combination of a 3-dimensional scintigraphy bone scan and CT, was introduced as a new tool in the orthopedic field recently [12, 14]. SPECT-CT detects scintigraphic osteoblastic activity in the area of interest in combination with the anatomic resolution of a CT scan. The effectiveness of SPECT-CT to diagnose OCL of the ankle has been proven in previous literature [12, 14]. SPECT-CT has been compared to MRI for imaging interpretation and decision making in OCL of the ankle [12]. Ankle OCL was evaluated by MRI, SPECT-CT, or a combination of both. SPECT-CT provided additional information and influenced decision making, and it was recommended in this study to perform both MRI and SPECT-CT for diagnostic evaluation in OCL [12]. Another study on the usefulness of SPECT-CT reported that the advantage was an ability to identify the active lesion, especially in multifocal disease or revision surgeries [14].

MRI has been reported by some as a noninvasive diagnostic imaging of choice for OCL of the ankle [6, 19]. It visualizes the surface of articular cartilage and subchondral bone by means of multiplanar evaluation. There are several classification systems using MRI [11, 15, 21]. One classification system for MRI was based on Berndt and Harty’s 4-stage radiographic classification [11]. Another classification system for MRI was based on arthroscopic findings [15]. T2-weighted MRI provides extra information on articular cartilage status and the subchondral bone. A high-intensity area between a fragment and its attachment to the talar dome can indicate instability of the fragment [4].

Three Tesla (T) MRI has also been applied as a diagnostic tool with the expectation of improved visualization of multiple organ systems. The usefulness of such high-resolution imaging is mostly for the diagnosis of OCL in an ankle with thin cartilage [1, 24]. The imaging quality and ability of 3 T MRI to assess cartilage, ligament, and tendon pathology have been tested in fresh human cadaver specimens and compared to 1.5 T MRI. In this study, the imaging quality was found to be significantly higher (P < 0.05) at 3 T than at 1.5 T [1]. Furthermore, they emphasized the usefulness of 3 T MRI in assessing cartilage pathology. However, because signal patterns in the talus can exaggerate the severity of the bone injury due to its high sensitivity, the decision making of treatment should be decided through a combination of imaging evaluations [7, 17].

Although MRI is useful for detecting articular cartilage injury with morphological abnormality, it cannot detect degenerative cartilage without morphological change. Recently, new techniques which can quantify the structural and composition change of degenerative articular cartilage have been developed and its application to detect OCL in the ankle is expected [2, 16]. Delayed gadolinium-enhanced magnetic resonance imaging of cartilage (dGEMRIC) technique is considered to be specific for assessing the concentration of glycosaminoglycan (GAG) in cartilage which generally reduces in accordance to degeneration of the cartilage [2]. In this technique, negatively charged gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA²⁻) is injected intravenously which distributes inversely to the concentration of negatively charged GAG and alters T1 depending on the amount of GAG [2]. The effectiveness of dGEMRIC has been reported for assessing the thin cartilage layer of the ankle. The technique was used for evaluation of cartilage following matrix-associated autologous chondrocyte implantation [5]. Furthermore, T2 mapping permits evaluation of changes in collagen arrangement and water content in the articular cartilage [16]. Normal articular cartilage contains a close and regular arrangement of collagen with fixed water content. However, as degeneration of the articular cartilage advances, the collagen arrangement becomes irregular and the amount of water content increases, and such changes make T2 intenser than that of normal articular cartilage [16]. This is useful for detection of early-stage degenerative change of articular cartilage and quantitative evaluation of cartilage degeneration [16]. As a clinical evaluation method for OCL of the ankle, T2 mapping has already been used to evaluate cartilage after autologous chondrocyte implantation for OCL of the ankle [10]. Further studies which apply these new techniques for diagnosis of OCL of the ankle are to be expected.