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1
Department of Radiology, University Hospital Utrecht and Central Military
Hospital, Heidelberglaan 100, 3509 AA Utrecht, The Netherlands.
2
Department of Orthopedics, University Hospital Utrecht and Central Military
Hospital, 3509 AA Utrecht, The Netherlands.
3
Department of Radiology, University of Virginia Health Sciences Center, 100
Lee St., Charlottesville, VA 22902.
Received March 31, 2000;
accepted after revision May 31, 2000.
Address correspondence to E. S. Sijbrandij.
Abstract
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MATERIALS AND METHODS. We retrospectively reviewed the images of all consecutive patients who underwent MR imaging of the ankle after acute or recurrent sprain occurring between January and December 1997. The number and location of subchondral contusions or fractures revealed on MR imaging were recorded, and a comparison was made with the radiographs obtained for each patient.
RESULTS. Of the 146 ankles, 42 osteochondral lesions were revealed on MR imaging in 26 ankles (18%) involving 23 patients. Twenty-three lesions were localized in the dome of the talus and 19, in the tibiofibular plafond. In 16 (11%) of the 146 ankles, the lesions were present in the opposing bones of the joint ("kissing" lesions). Only six of the 12 talar fractures and none of the tibial fractures involving the 26 ankles were seen on conventional radiography.
CONCLUSION. Subchondral lesions in the talus and tibia are relatively common after ankle trauma, occurring in 18% of patients in our series. Kissing lesions were present in more than half of the lesions in these patients.
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The most widely accepted classification of osteochondral talar injury, introduced by Berndt and Harty [5] and based on research on cadavers, is as follows: stage 1 is localized area of subchondral trabecular compression; stage 2 is incomplete separation of the transchondral fragment; stage 3, the fragment is completely separated but not displaced; stage 4, the fragment is displaced or inverted in its fracture bed. The first two stages are difficult to show on conventional radiography, and the lesions may go undetected when radiographs are obtained for evaluation. MR imaging shows the lesions with high sensitivity, allowing early detection and treatment of the abnormal findings [1].
In patients with traumatic osteochondral contusions of the dome of the talus, similar lesions can be seen occasionally on the opposite site of joint, the tibiofibular plafond. Lundeen [6] in 1990, using arthroscopy, was one of the first to postulate that the tibial lesions were the result of the talus impinging on the cartilage of the tibial plafond at the time of injury. Similar findings, referred to as "kissing" contusions, have also been described in the knee [7]. Bone bruises are common after severe ankle sprain. To our knowledge, no detailed studies exist on bone bruises associated with osteochondral fractures in the ankle. Canosa [8] was the first to describe the CT appearance of the kissing lesions in the ankle in a patient who had an osteochondral fracture of the talus and a mirror image fracture of the adjacent tibial plafond.
We noted in our patients undergoing MR imaging of the ankle after injury a relative high incidence of subchondral bone contusions, fractures, and kissing lesions involving the talus and tibiofibular plafond. The purpose of our study was to determine the presence and location of subchondral bone contusions, fractures, and kissing lesions of the talotibial joint after a sprain of the ankle shown on MR imaging.
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MR imaging was performed on a 0.5-T unit (Philips Medical Systems, Best, The Netherlands) with the ankle placed in a dedicated receive-only extremity coil. Conventional T1-weighted spin-echo images (TR/TE, 600/23) and T2-weighted spin-echo images (2000/100) were obtained in sagittal and coronal orientations in all patients. Short tau inversion-recovery (STIR) images (3600/20; inversion time, 150 msec) were obtained in the coronal orientation. Image section thickness ranged from 3 to 5 mm with an interslice gap of 0.0-1.5 mm. Matrix size was 256 x 256, and the field of view was 16 cm. All patients also underwent radiography of the ankle in anteroposterior, lateral, and mortise projections.
The MR images were reviewed with special attention paid to bony abnormalities suggestive of osteochondral contusions or fractures. Associated ligamentous injuries were not evaluated in this study. Two radiologists reviewed the images in consensus, and the diagnosis of a contusion was based on the criteria described by Kaplan et al. [7] and Magee and Hinson [9]: the presence of a subchondral well-defined semicircular area of decreased signal intensity on T1-weighted images and increased signal intensity on T2-weighted and STIR images. An osteochondral fracture was considered present when disruption of the subchondral bone plate extending through the cortical surface was identified on T2-weighted images. After evaluation of each MR study, the reviewers analyzed the ankle radiographs of each patient. In addition, all MR images and radiographs of the ankle obtained during the 2 years after the initial injury were reviewed.
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Of the 23 patients, arthroscopy with drilling through the subchondral bone was performed within 2 months of the injury in four patients with subchondral fractures of the talus. In 16 patients, conservative treatment was given, and in three patients the treatment was unknown.
Twenty of the 23 patients had follow-up imaging. MR imaging performed in two patients with kissing contusions showed persistence of the tibial lesions. In one of these patients, the lesion was still seen at 1-month follow-up, and in the other patient, complete resolution occurred after 10 months. MR imaging performed in two patients with kissing lesions (an osteochondral fracture of the talus and a contusion of the tibia) showed complete healing 11 months after the initial injury in one patient and minimal residual edema in the talus 17 months after the injury in the other patient. CT arthrography performed in one patient with a solitary talus fracture showed that the fracture was still visible after 7 months. Radiography in 15 patients with 12 kissing and three solitary lesions showed osteochondral fractures of the talus in three patients and no evidence of subchondral injury in the others from 1 month to 2 years after the initial injury.
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We found 42 osteochondral lesions in our series of 146 patients. Of these lesions, there were 36 bone contusions. The frequency of the findings is well within the range (6.5-39%) reported in the literature [13, 14]. However, the number of patients (11%) with kissing lesions was much higher than that reported by others. For instance, Labovitz and Schweitzer [13] found kissing lesions in only five (5%) of 109 patients. It is unclear why the number of kissing lesions was relatively high in our series. However, a large proportion of patients (17/23) with subchondral injury consisted of personnel of the military forces, individuals in whom osteochondral lesions are more likely to occur [5, 14]. In the patients with kissing lesions, we found that all osteochondral fractures were located in the talus, whereas the contusions were predominantly seen in the tibial plafond. There are several potential explanations for the higher occurrence of the subchondral fractures in the talus than in the tibiofibular plafond. First, osteochondral lesions are more commonly observed at the convex surface of a joint, whereas the concave surface is generally spared. The convex surface is believed to transmit the forces (convergence of force) toward a central focus, whereas a concave surface dissipates the forces. As a result, the concave joint surface, such as that of the talus, is likely to be more severely damaged by trauma than the tibial plafond [10]. Second, the cartilage of the tibia is stiffer than that of the talus because of differences in composition [15]. In six of the 16 kissing lesions, the abnormalities were directly opposite each other; therefore, it is likely that the lesions of the tibiofibular plafond were the result of direct impaction of the talar bone onto the opposing tibial bone. In the remaining 10 kissing lesions, the lesions were not diametrically opposed probably because rotation occurred during the injury [7].
A shortcoming of our study was the limited follow-up with MR imaging. In the one patient in whom CT was performed, no changes were noted in the osteochondral fractures after 7 months. No osteochondral lesions were seen in any of 15 patients who had radiographic followup. However, the latter technique is insensitive in detecting these lesions. Thus, the changes over time of bone contusions in the ankle remain uncertain. Nevertheless, the clinical significance of bone contusions in the ankle has not been established, and it has been suggested that these contusions do not need to be treated [9]. Osteochondral fractures, on the other hand, do need to be treated with reduced weight-bearing for an extended period of time [11]. A further shortcoming of our study was the retrospective study design. Because of the large number of military recruits, our study was subject to selection bias. This bias makes it difficult to extrapolate these findings to a general orthopedic practice.
In conclusion, we found a relatively high number of subchondral injuries (11%) involving the subchondral bone of the talus and tibia. Of these kissing lesions, bone contusions were most commonly seen in the tibial plafond, and osteochondral fractures were most often seen in the talar dome. The kissing lesions are most likely caused by impaction of the talus onto the tibia with or without torsion.
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