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Musculoskeletal Imaging |
1 From the Departments of Radiology (J.C.C., C.B.C., N.L., D.T., D.R.) and Orthopedic Surgery (R.P.), Veterans Affairs Medical Center, University of California, 3350 La Jolla Village Dr, San Diego, CA 92161; and the Department of Radiology, Ohio State University Medical Center, Columbus (J.Y.). From the 1999 RSNA scientific assembly. Received May 10, 2000; revision requested June 19; revision received August 28; accepted September 6. Supported by Veterans Affairs grant SA-360. Address correspondence to D.R. (dresnick@ucsd.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Dissection of the region of the AOB, ITT, and lateral capsular ligament was performed in three cadaveric knees, with placement of gadopentetate dimeglumine–filled tubes along their course and tibial insertions. These knees, in addition to three nondissected knees, were studied with magnetic resonance (MR) imaging by using standard and specialized oblique planes. Specimen sectioning provided anatomic correlation. Retrospective review of radiographs and MR images in 17 patients with acute Segond fractures was performed, and the relationship between the fragment and the demonstrated lateral supporting structures of the knee was noted.
RESULTS: Anatomic dissection and MR imaging of the cadaveric knees demonstrated a broad tibial insertion of the ITT, with fibers extending posterior to the Gerdy tubercle. A firm band of tissue, the AOB, extended from the fibular collateral ligament to the midportion of the lateral tibia, the typical site of a Segond fracture. The lateral capsular ligament proved to be a mere thickening of the capsule, inserting at the lateral tibia. Clinical analysis of acute Segond fractures confirmed the frequent attachment of the ITT and AOB to the avulsed fragment.
CONCLUSION: Anatomic and clinical findings suggest that fibers of the ITT and AOB are important factors in the pathogenesis of the Segond fracture.
Index terms: Knee, injuries, 452.485, 454.4191 • Knee, ligaments, menisci, and cartilage, 452.4191, 452.485, 454.92 • Knee, MR, 45.121411, 45.121415 • Iliotibial tract • Tibia, fractures, 454.4191
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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At routine radiography, the avulsed cortical fragment is constant in size and appearance, is directly lateral, and is best seen on the straight anteroposterior view of the knee. Healing of the Segond fracture is associated with a characteristic bone excrescence arising below the lateral tibial plateau (9). By using magnetic resonance (MR) imaging, marrow edema may be noted at the site of the avulsed cortical fragment, although the fragment itself may be difficult to demonstrate (10).
The anatomy of the posterolateral aspect of the knee is complex and still remains controversial (11–14). Several descriptions have been contradictory or incomplete, owing in part to the anatomic variability and perhaps to the difficulty in dissection—the structures are relatively deep and thin (15). The purpose of this study was to demonstrate the normal anatomy of the stabilizing structures of the lateral aspect of the knee with MR imaging–anatomic correlation in cadavers and to investigate the pathogenesis of the Segond fracture with MR imaging in 17 patients, with emphasis on the role of the iliotibial tract (ITT) and the anterior oblique band (AOB) of the fibular collateral ligament (FCL).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MR images of these six cadaveric knees were obtained with a 1.5-T superconducting MR imager (Signa; GE Medical Systems, Milwaukee, Wis). The specimens were positioned supine and in extension inside a receive-only knee coil. Imaging was performed in transverse, coronal, and sagittal planes. On the basis of the obliquity of each structure demonstrated with the contrast material–filled tubes, special imaging planes were also prescribed for better anatomic characterization. Coronal oblique planes (determined from sagittal images) were oriented parallel to the course of the ITT and the AOB, and sagittal oblique images (determined from transverse images) were oriented parallel to the AOB and LCL.
T1-weighted spin-echo sequences were performed with the following parameters: 600/20 (repetition time msec/echo time msec), two signals acquired, 12-cm field of view, 512 x 256 imaging matrix, 2–3-mm section thickness, with no intersection gap. Subsequently, identical MR images were obtained in the three remaining cadaveric knees, and two observers (J.C.C., D.R.) analyzed the anatomy of the lateral aspect of all six cadaveric knees by consensus, with emphasis on the course and site of the ITT, AOB, and LCL insertion.
After MR imaging, three specimens (including one with the gadopentetate dimeglumine–filled tubes) were refrozen at -40°C and subsequently sliced into 3-mm sections that corresponded to the transverse images. The anatomic sections were cleaned with running water for macroscopic evaluation. In addition, a special radiographic unit (x-ray system 43805 N; Faxitron X-ray, division of Hewlett-Packard, Palo Alto, Calif) designed to examine sections of cadaveric specimens was used.
Clinical Study
A retrospective review of the radiographs and MR images of the knee in 17 patients (14 male, three female; age range, 14–43 years; mean age, 31.5 years) with a clinical history of an injury to the knee and imaging evidence of an acute Segond fracture was performed by two of the authors (J.C.C., C.B.C.), who arrived at a consensus. All patients underwent MR imaging within 7 days after the injury. Routine radiographs of the knees were available in seven patients. The radiographs were evaluated for the size, shape, orientation, and degree of the displacement of the Segond fracture fragment and for radiographic evidence of associated osseous and soft-tissue injuries. The same authors reviewed, with particular attention to the fracture fragment, the MR images and attempted to identify the structures that attached to it. In addition, marrow edema at the lateral tibial rim, joint effusion, and changes in the surrounding soft tissues were also evaluated.
All MR images were obtained with the knee in extension inside a receive-only extremity coil. The MR examinations were performed by using 1.5-T magnets (Signa; GE Medical Systems, Magnetom Vision, Siemens Medical Systems, Iselin, NJ). The sequences varied and consisted of a T1-weighted spin-echo (400–850/13–25) sequence, a T2-weighted spin-echo and fast spin-echo sequence with or without fat suppression (1,400–3,267/80–85), an intermediate-weighted spin-echo and fast spin-echo sequence (1,400– 3,267/19–32), and a gradient echo (544/18/50) sequence. The field of view was 14–16 cm, the section thickness was 3–5 mm, the intersection gap was 0–2 mm, and the image matrix was 192–515 x 192–256, with one or two signals acquired in the transverse, coronal, and sagittal planes.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MR imaging.—In three knees marked with gadopentetate dimeglumine–filled tubes, all three structures (ITT, LCL, and AOB) were identified and had an appearance similar to that seen with anatomic dissection and sectioning. The ITT fibers were seen in the coronal oblique planes inserting far laterally in the lateral tibial plateau, the typical site of the Segond fracture (Fig 3). The LCL was visualized as a thin lateral capsular structure anterior to the region where the popliteus tendon inserts in the lateral femoral condyle (Fig 4). In the sagittal and sagittal oblique planes, the biceps tendon and the FCL were found to attach together at the fibular head, and the AOB, with its anterior oblique course, inserted in the lateral aspect of the tibia (Fig 5). In the other three knees without gadopentetate dimeglumine–filled tubes, the AOB was identified in the sagittal plane in one specimen and in the transverse plane in all specimens. The broad insertion of the ITT was observed in transverse, coronal, and coronal oblique planes in all three specimens. The thin LCL was identified only in the coronal oblique plane in all three specimens.
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Clinical Study
Tears of the anterior cruciate ligament and knee effusions were present in 16 (94%) of 17 patients with acute injuries; nine (53%) had associated tears of the menisci—five (30%) in the posterior horn of the medial meniscus and four (23%) in the lateral meniscus. Bone contusions also were a frequent finding, occurring in 14 (82%) of 17 patients; most of these were in the lateral tibial plateau and femoral condyle, the typical sites associated with anterior cruciate ligament tears. Injuries to the structures of the posterolateral corner of the knee were present in six (35%) of 17 patients, four (23%) had popliteus tendon tears, and six (35%) also had tears of the medial collateral ligament.
The avulsed fracture fragments were better seen with routine radiography than MR imaging. The fragment was evident on all (seven of seven) routine radiographs in the patients who had radiographs and was evident on MR images in 13 (76%) of 17 patients. The cortical fragment was oval and was vertically oriented in all patients, measuring 0.4–1.9 x 0.1–0.4 cm (mean, 0.6 x 0.2 cm). It was either nondisplaced or displaced (up to 0.6 cm from the tibial surface). All patients had a small ill-defined area of abnormal signal intensity (high on T2-weighted images, low on T1-weighted images, following the pattern of marrow edema) at the donor site in the tibia on MR images.
The posterior fibers of the ITT were attached to the avulsed fragment in 13 (76%) of 17 patients with acute lesions and were best appreciated on the coronal images (Figs 6, 7). The LCL was identified on the coronal images, close to the fragment, in nine (53%) of 17 patients. The AOB was also attached to the avulsed fragment. This structure was identified at the level of the fracture, at a level between the lateral tibial plateau (a few millimeters below the articular surface) and the proximal tibiofibular joint (Fig 8), in seven (58%) of 12 patients in whom transverse images were available.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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The precise pathogenesis of the Segond fracture has been the subject of debate, in part related to the complexity of the lateral ligamentous anatomy (20). Segond (1) demonstrated that an internal rotation and varus stress applied to the knee causes tension on the lateral joint capsule at its midpoint; he believed that a pearly band of tissue, the LCL, produces an avulsion fracture of the lateral tibial plateau, posterior to the insertion of the ITT. Milch (21) reported this fracture in three patients and believed that the avulsed fragment occurred at the insertion site of the ITT. In 1979, Johnson (22) described the LCL as having two components: The vertical component attaches to bone, ligament, and tendon (including the ITT), and the horizontal component attaches to the lateral meniscus and ligamentous structures in the posterior and intercondylar areas of the knee. He also noted the prominent interdigitating fibers between the LCL and ITT, 2 cm proximal to their attachment in the tibial plateau. In the dynamic part of the same study, Johnson also observed that traction on the ITT proximally produces a pulling effect through the bony attachment of the LCL and Gerdy tubercle, confirming the connection between these structures.
In an effort to simplify the understanding of the anatomy of the posterolateral aspect of the knee, Seebacher et al (23) organized it into three layers, a concept that has also been emphasized by other investigators. The first layer is the most superficial and encompasses the ITT anteriorly and the biceps femoris posteriorly. The second, or middle, layer is formed anteriorly by the retinaculum of the quadriceps and posteriorly by the patellofemoral ligaments. The third layer is the lateral joint capsule, extending from the patella to the posterior cruciate ligament. The anterior portion of the deep layer extends from the patellar tendon to the ITT. The middle portion of the joint capsule is the LCL, which is defined anteriorly by the ITT and posteriorly by the FCL. Posterior to the ITT the capsule divides into two laminae. The more superficial lamina encompasses the FCL and ends posteriorly at the fabellofibular ligament. The deeper lamina passes along the edge of the lateral meniscus forming the coronary ligament and popliteus hiatus and terminating at the arcuate ligament. The popliteus tendon passes through the hiatus in the coronary ligament to attach to the femur. Anatomic variations are observed according to whether the fabella is present or absent.
Terry et al (24) described the interrelationships of the ITT and divided it into five layers (aponeurotic, superficial, middle, deep, and capsulo-osseous). The capsulo-osseous layer is described as the deepest portion of the ITT, with fibers that insert posterior to the Gerdy tubercle in the lateral tibia. They also emphasized the interdigitating fibers extending between the different layers.
Irvine et al (25), studying typical Segond fractures and cadaveric dissections, described the FCL as having two components: a straight band that runs to the fibular head and an AOB that runs obliquely to insert into the lateral tibial rim. Their findings indicated that the Segond fracture could be a result of an avulsion of the AOB.
To our knowledge, there are no previous descriptions of the MR imaging appearance of the AOB. MR imaging–anatomic correlation allowed us to demonstrate the broad ITT insertion (extending laterally at the lateral tibial plateau), the thin appearance of the LCL (seen as an area of capsular thickening), and the presence of a relatively broad band of tissue (AOB) arising from the FCL with a strong attachment to the lateral aspect of the tibia. These structures are connected to each other and attach to the lateral tibial rim at the typical site of the Segond fracture. Findings at clinical analysis of acute Segond fractures confirmed the frequent attachment of the ITT and the AOB to the avulsed fragment, in addition to the LCL.
Our study had limitations. Although the anatomic findings were consistent in the studied specimens, the limited number of specimens and patients may not entirely take into account normal anatomic variation. Creation of lesions could not be performed, as the mechanism of injury was difficult to recreate in isolated cadaveric specimens. Visualization of an AOB or LCL as it attached to the Segond fracture fragment might have been underestimated because of massive soft-tissue edema. Although edematous LCL and AOB ligaments might also have been present, only the ITT might have been visible, attaching to the fragment when intact. Many of the clinical cases had limited information about the mechanism of injury, and surgical correlation was not available. The clinical cases, however, were included only to demonstrate the typical Segond fracture and its relationship to adjacent soft tissue structures.
In conclusion, our anatomic and clinical observations suggest that fibers of the ITT or AOB, or both, are important factors in the pathogenesis of the Segond fracture.
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FOOTNOTES |
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Author contributions: Guarantors of integrity of entire study, J.C.C., C.B.C., N.L., J.Y., D.R.; study concepts, D.R.; study design, J.C.C., D.R.; literature research, J.C.C., D.R.; clinical studies, J.C.C., C.B.C., J.Y., D.R., R.P., D.T.; data acquisition, J.C.C., R.P., C.B.C., J.Y., D.T.; data analysis/interpretation, J.C.C., C.B.C., D.R.; manuscript preparation, J.C.C.; manuscript definition of intellectual content and editing, J.C.C., D.R.; manuscript revision/review, C.B.C., N.L., D.R.; manuscript final version approval, D.R.
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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This article has been cited by other articles:
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  N. Boutry, S. Dupont, E. Glaude, X. Demondion, P. Laffargue, and A. Cotten Segond Fracture Revealed by Ultrasonography J. Ultrasound Med., October 1, 2005; 24(10): 1431 - 1435. [Full Text] [PDF]
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 G.-S. Huang, J. S. Yu, M. Munshi, W. P. Chan, C.-H. Lee, C.-Y. Chen, and D. Resnick Avulsion Fracture of the Head of the Fibula (the "Arcuate" Sign): MR Imaging Findings Predictive of Injuries to the Posterolateral Ligaments and Posterior Cruciate Ligament Am. J. Roentgenol., February 1, 2003; 180(2): 381 - 387. [Abstract] [Full Text] [PDF]
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