ruptures of the lateral ligaments of the

Transcription

1 The accuracy of three-dimensional magnetic resonance imaging in the diagnosis of ruptures of the lateral ligaments of the ankle* EDDY F. C. VERHAVEN, MD, MARYAM SHAHABPOUR, MD, FRANK W. J. HANDELBERG, MD, PETER H. E. G. VAES, PhD, AND PIERRE J. E. OPDECAM, PhD From the University Hospital Vrije Universiteit Brussel, Brussels, Belgium ABSTRACT In a prospective study, the diagnostic accuracy of threedimensional magnetic resonance imaging in the evaluation of ruptures of the lateral ligaments of the ankle was determined by comparing three-dimensional magnetic resonance findings with operative findings. In a series of 18 consecutive cases of acute significant inversion trauma to the ankle, a three-dimensional fast imaging with steady-state precession pulse sequence (3D FISP) was performed. The study included only those cases in which views showed a difference in talar tilt of 15 or more, and a difference in anteroposterior drawer of 10 mm or more between the imaged and the normal ankle. All ankles were scheduled for surgical exploration. Compared with operative findings, the sensitivity, specificity, and accuracy of 3D FISP imaging were, respectively, 100%, 50%, and 94.4% for ruptures of the anterior talofibular ligament and 91.7%, 100%, and 94.4% for ruptures of the calcaneofibular ligament. We believe that 3D FISP magnetic resonance imaging is a noninvasive, fast, and very accurate diagnostic aid to operative planning for double ligament tears in younger competitive athletes. 1, ~2, ~5 Ankle injuries are very common in sporting events.2, Sprains of the lateral ankle ligaments seem to be the most *Presented at the FIMS World Congress of Sports Medicine, May 27 to June 1, 1990, Amsterdam, the Netherlands, and at the Amencan Orthopaedic Associabon, Boston, Massachusetts, June 1990 t Address correspondence and repnnt requests to Eddy F C Verhaven, MD, University Hospital Vrqe Universiteit Brussel, Laarbeeklaan 101, Brussels 1090, Belgium. 583 frequent sporting injuries and account for 10% or more of all emergency department visits. They usually result from an inversion trauma to a plantar flexed foot, mostly on an irregular surface.8, 12 The lateral ankle ligament has three main components: the anterior talofibular ligament, the strong calcaneofibular ligament, and the posterior talofibular ligament, which is 8, ~2 rarely torn, except in complete dislocation of the ankle., Despite their common incidence, lateral ligamentous injuries are frequently improperly treated due to inaccurate diagnosis.2, 15 Inadequate treatment can result in chronic ankle instability with recurrent sprains and early degenerative changes of the ankle joint, and can compromise the athlete s performance because of residual symptoms.2, 15 Knowledge of the mechanism of injury, careful physical examination, and optimal radiologic assessment will lead to the correct diagnosis and treatment. In differentiating between the various types of ankle sprains, the value and limitations of varus and anteroposterior stress views of the ankle, as well as arthrography, tenography, and computed tomography, have been reported in the literature.~~ ~~ 12 The excellent soft tissue contrast provided by magnetic resonance imaging (MRI) will offer additional information and assistance in the evaluation of ankle trauma. 2 Three-dimensional MRI is still in its early stages, and its use for visualizing the lateral ligaments of the ankle has not previously been described in the literature. All of the publications about soft tissue imaging of the ankle used standard MRI with Tl-weighted or T2-weighted spin echo multiplanar images. 2, l The purpose of this study was to determine the accuracy of three-dimensional MRI in visualizing injuries to the an-

2 terior talofibular and the calcaneofibular ligaments in young, injured athletes. We also evaluated three-dimensional fast imaging with steady-state precession pulse sequences (3D FISP) as a diagnostic aid to operative planning and surgical repair of ligament tears by comparing the MRI findings with those found at surgery. MATERIALS AND METHODS Between October 1989 and May 1990, 18 consecutive patients (mean age, 21 years) with an acute varus trauma of the ankle were subjected to 3D FISP analysis within 6 hours following their injury. Nine patients were injured while playing soccer, eight while playing volleyball, and one while participating in judo. Patients with stress views showing a difference in talar tilt of 15 or more and an AP drawer of 10 mm or more between the injured and normal ankle were selected. Stress views were taken using an original apparatus adapted and rebuilt after Inman, with whom it was possible to reproduce a definite stress varus and anteroposterior drawer on the tibiotalar joint. 16 Patients exhibiting a difference in talar tilt of 15 or more and a difference in anteroposterior drawer of 10 mm or more, as compared to the uninjured side, were scheduled for 3D FISP analysis and surgical exploration. Three-dimensional MRI of the anterior talofibular and the calcaneofibular ligaments was taken with a 1.5 Tesla Magnetom Whole Body Imager (Siemens, Erlangen, Germany). For three-dimensional reconstruction, a multihandling station-type Kontron (Munich, Germany) was used. A series of 128 slices of contiguous 1 mm thickness were made in the coronal or sagittal plane in about 17 minutes using FISP. Surgical procedure The patient s foot was put in a neutral position with the knee held in 15 of flexion. We use the same surface coil as the one we use for the knee. Surgical exploration was performed for all 18 ankles within 24 hours of injury. We looked for a rupture of the anterior talofibular and/or the calcaneofibular ligament. Three-dimensional magnetic resonance images were compared with operative findings to confirm the accurate diagnosis of a ligamentous tear. A true-positive result was defined as a ligament that appeared ruptured on 3D MRI reconstruction that was confirmed at surgery. A true-negative result was a ligament that was shown intact on 3D images and was confirmed at surgery. The result was considered false-positive when a ruptured ligament was observed by 3D MRI and a normal ligament was found at surgery. A false-negative result was defined as a ligament that appeared normal on a 3D MRI, while surgery revealed a ruptured ligament. Sensitivity was defined as the number of true-positive results divided by the number of true-positive results plus the number of false-negative results. Specificity was defined as the number of true-negative results divided by the number of true-negative results plus the number of false-positive results. Accuracy was defined as the number of true-positive results plus the number of true-negative results divided by the number of studies.&dquo; RESULTS Preoperatively, a rupture of both the anterior talofibular ligament and the calcaneofibular ligament was found in 13 patients. In the remaining five patients, three had an isolated rupture of the anterior talofibular ligament, one had an old anterior talofibular ligament rupture, and in one there was no evidence of rupture of any ligament. Compared with operative findings, 3D FISP showed a sensitivity, specificity, and accuracy of 100%, 50%, and 94.4%, respectively, for ruptures of the anterior talofibular ligament and of 91.7%, 100%, and 94.4%, respectively, for tears of the calcaneofibular ligament. The low specificity of 50% for tears of the anterior talofibular ligament is because there was only one false-positive finding. DISCUSSION Ankle sprains are among the most common sporting injuries.15 They usually occur in the younger competitive athletes. Inadequate treatment can lead to persistent discomfort and even chronic instability., &dquo; Therefore, the severity of an ankle sprain should be adequately assessed. Radiographic views are useful in determining the type of ligament sprain and should include varus and anteroposterior stress views. There is no agreement in the literature about the real amount of talar tilt and anterior displacement of the talus in an injured , 14 and even in an Figure 1. A 3D MR image of an intact anterior talofibular ligament (white arrows), which appears as a black ribbon-like structure (low signal intensity). Inset shows the axial plane from which the reconstructions are made in an oblique plane. z

3 585 Figure 2. A 3D MR image of a ruptured anterior talofibular ligament. The low signal intensity or black color of the intact ligament is replaced by an image with a high signal intensity or white color (black arrows), obscurring the view of the ligament. Inset shows the axial plane from which the threedimensional reconstructions are taken. Figure 3. Another MR image of a ruptured anterior talofibular ligament. Fluid accumulation in the ligament, indicative of a tear, shows up as an image with intermediate signal intensity or grey-white color (black arrows). Inset shows the axial plane from which the reconstructions are made. Figure 4. A 3D MR image shows an intact calcaneofibular ligament (black arrows). The calcaneofibular ligament is seen as a grey continuous band (high signal intensity), thus less dark than an intact anterior talofibular ligament. Inset shows the axial plane at the tip of the lateral malleolus from which the three-dimensional reconstructions are made in an oblique plane through the middle of the lateral one-third of the Achilles tendon and through the medial side of the tendon of the peroneus brevis muscle. intact -, ~~ 9, 10 ankle. Therefore, a standard method that should be easily reproducible for measuring the amount of talar tilt and anterior displacement of the talus in comparison with the opposite side is absolutely necessary. There also exists no specific amount of talar tilt that distinguishes between single and double ligament tears. However, most authors agree that a difference in talar tilt of 15 or more between the injured and the opposite side is highly indicative of a rupture of both the anterior talofibular and the calcaneofibular ligaments.2,3 Similarly, a difference in anteroposterior drawer that exceeds 10 mm would also suggest a rupture of both ligaments.2, 10 According to these criteria, we obtained an accuracy of 88.9% for tears of the anterior talofibular ligament and of only 66.7% for ruptures of the calcaneofibular ligament when comparing stress views with operative findings. Another limitation of these stress views is that a local anesthetic could influence the amount of talar tilt that would then produce an incorrect radiographic reading.2> 12 When we look at the value of 3D MRI in the diagnosis of tears of the anterior talofibular ligament and the calcaneofibular ligament, we observe an accuracy of 94.4% for diagnosing tears of the anterior talofibular ligament and the calcaneofibular ligaments. The accuracy obtained for the diagnosis of a calcaneofibular ligament rupture is far superior to the same diagnosis by stress views. The anterior

4 Figure 5. A 3D MR image of a ruptured calcaneofibular ligament (black arrows). The continuity of the calcaneofibular ligament is interrupted at the proximal one-third (longer arrow), where the ligament cannot be seen because of the lack of contrast, resulting from the hematoma that produces an image with a high signal intensity or white color. Inset shows axial plane. talofibular ligament can be visualized in four successive axial slices of 1 mm. A three-dimensional reconstruction in an oblique plane can be made from one of these axial planes to visualize the whole ligament. On reconstructions, the anterior talofibular ligament can be seen very clearly in contrast to its surroundings as a black ribbon-like structure (Fig. 1). A ruptured ligament produced an image with a high signal intensity or white color at the rupture site, due to the presence of a hematoma or an edema, as opposed to the low signal intensity or black color of the intact ligament (Figs. 2 and 3). The calcaneofibular ligament can also be reconstructed in an oblique plane from the axial plane. The reconstruction has to be made from an axial slice, made at the tip of the lateral malleolus in a way that the plane runs through the middle of the lateral one-third of the Achilles tendon and through the medial side of the tendon of the peroneus brevis muscle. Without 3D reconstruction, it is nearly impossible to visualize this ligament in the three traditional planes. Because the surrounding fatty structures of the calcaneofibular ligament produce a higher signal density, it appears less dark on the 3D FISP image; it shows up more as a grey cordlike structure (Fig. 4). Accordingly, the presence of a hematome, which also causes lack of contrast, cannot be shown for the calcaneofibular ligament (Figs. 5 and 6). Until now, the clinical applications of the 3D MRI have been very few. However, compared to the classical Tlweighted spin echo, 3D MRI offers many advantages. Up to Figure 6. Another image of a completely ruptured calcaneofibular ligament. The black arrows indicate the place where the ligament is ordinarily seen. Here, the ligament is obscurred because of the lack of contrast between the surrounding tissues. Only the tendon of the peroneus brevis muscle can be identified. Inset shows axial plane. now, its clinical applications have been very few. It is a fast, noninvasive diagnostic modality with a neglegible ionizing radiation exposure for the patient. Proper plane selection during reconstruction results in a higher signal intensity with images comparable to T2-weighted images. Reconstructions of selected anatomical structures can be made in all imaginable planes at whatever time. The disadvantages of this technique are the availability of the material, the cost of the examination, and the lengthy reconstruction time (about 1 hour). CONCLUSIONS We believe that 3D MRI is a very accurate technique for diagnosing ruptures of the anterior talofibular and the calcaneofibular ligament in younger athletes. When radiographic stress views give cause to suspect double ligament tears, 3D MRI will confirm the diagnosis, aiding the physician in operative planning. ACKNOWLEDGMENTS The authors thank Wilfried DePlecker and Eric Achten, MD, radiologist, for their technical assistance during the course of this study.

5 587 REFERENCES 1 Baumgardner GR Technique important in ankle X-ray studies Physician Sportsmed , Berquist TH Radiology of the Foot and Ankle New York, Raven Press, 1989, pp Cass JR, Morrey BF Ankle instability current concepts, diagnosis and treatment Mayo Clin Proc , Castaing J, Delplace J Entorses de la cheville intéret de l étude de la stabilité dans le plan sagittal pour le diagnostic de gravité. Rev Chir Orthop , Cox JS, Hewes TF: Normal talar tilt angle Clin Orthop , Duquennoy A, Lisele D, Torabi DJ: Elements radiographiques du diagnostic de gravité de l entorse Rev Chir Orthop 61 (Suppl II) , Johannsen A Radiological diagnosis of lateral ligament lesion of the ankle A comparison between talar tilt and anterior drawer sign Acta Orthop Scand , Kulund DN: The Injured Athlete Philadelphia, JB Lippincott, 1988, pp Landeros O, Frost HM, Higgins CC: Posttraumatic anterior ankle instability Clin Orthop , Lindstrand A, Mortensson W: Anterior instability in the ankle joint following acute lateral sprain Acta Radiol : , Middleton WD, Lawson TL Anatomy and MRI of the Joints A Multiplanar Atlas New York, Raven Press, 1989, pp Nicholas JA, Hershman EB The lower extremity and spine in sport medicine St Louis, CV Mosby Co, 1986, pp , Savastano AA, Lowe EB Ankle sprains Surgical treatment for recurrent sprains Am J Sports Med 8: , Sedlin ED A device for stress inversion or eversion roentgenograms of the ankle J Bone Joint Surg 42A , Smith RW, Reischi SF Treatment of ankle sprains in young athletes Am J Sports Med , Vaes P, De Boeck H, Handelberg F, et al Comparative radiologic study of the influence of ankle joint bandages on ankle joint stability. Am J Sports Med 13: 46-50, 1985