MR Imaging of the Triangular Fibrocartilage Complex




MR imaging has emerged as the mainstay in imaging internal derangement of the soft tissues of the musculoskeletal system largely because of superior contrast resolution. The complex geometry and diminutive size of the triangular fibrocartilage complex (TFCC) and its constituent structures can make optimal imaging of the TFCC challenging; therefore, production of clinically useful images requires careful optimization of image acquisition parameters. This article provides a foundation for advanced TFCC imaging including factors to optimize magnetic resonance images, arthrography, detailed anatomy, and classification of injury. In addition, clinical presentations and treatments for TFCC injury are briefly considered.


Key points








  • The triangular fibrocartilage complex (TFCC) is an essential stabilizing structure of the wrist that is composed of numerous small components; an in-depth knowledge of its anatomy is essential to detect subtle pathologic conditions.



  • Injuries of the TFCC may be acute or chronic and are often classified by the Palmer classification.



  • Management of TFCC injury may include conservative, as well as surgical, treatments.



  • Modern equipment and techniques such as high-resolution 2-dimensional (2D)/3-dimensional (3D) sequences, 3 T field strength, dedicated wrist coils, and direct arthrography may improve the ability to detect TFCC injury.






Introduction


Continued improvements in MR imaging allow greater detail than ever before. Thus, MR imaging is an invaluable tool in investigating injury of small anatomy, including the TFCC of the wrist. Accurate interpretation of wrist MR imaging requires knowledge of image acquisition techniques, thorough comprehension of the intricate anatomy, and understanding of common patterns of injury. Treatment of TFCC injury is in part predicated on the specific component of the TFCC that is injured as well as the acuity. Therefore, a precise description of TFCC injuries is valuable for treatment planning.




Introduction


Continued improvements in MR imaging allow greater detail than ever before. Thus, MR imaging is an invaluable tool in investigating injury of small anatomy, including the TFCC of the wrist. Accurate interpretation of wrist MR imaging requires knowledge of image acquisition techniques, thorough comprehension of the intricate anatomy, and understanding of common patterns of injury. Treatment of TFCC injury is in part predicated on the specific component of the TFCC that is injured as well as the acuity. Therefore, a precise description of TFCC injuries is valuable for treatment planning.




Technique


Optimal imaging of the wrist requires maximizing spatial resolution, signal-to-noise ratio (SNR), and contrast resolution. These variables are interconnected and influenced by changes in field of view (FOV), matrix size, slice thickness, bandwidth, echo time, repetition time, applied magnetic field strength, and pulse sequence selection.


High-spatial-resolution sequences are necessary to evaluate the fine structures that comprise the TFCC. In theory, increasing the matrix size for a given FOV or decreasing the FOV for a fixed matrix size can increase the spatial resolution. Such alterations result in loss of signal and subsequent degradation in image quality, which can be compensated for by adjusting other parameters (such as increasing applied field strength) or using specialized coils. Signal increase is approximately linear with increases in applied field, which can allow for increased resolution or decreases in scan time (with subsequent decreased risk of motion artifact). Specialized coils can also help augment signal. For example, it may be possible to use a specialized microscopy coil at 1.5 T and generate resolution similar to that of routine 3 T examinations.


The basic pulse sequence categories commonly used for imaging the wrist include proton density (PD)-weighted imaging, T2* gradient recalled echo sequences, and fluid-sensitive sequences with fat suppression. In general, sequences are acquired with conventional 2D technique, although 3D imaging techniques specific to the wrist have recently been described. The authors’ routine wrist protocol includes coronal PD and PD fat-saturated, axial PD and PD fat-saturated, sagittal PD and PD fat-saturated, and coronal 3D PD and PD fat-saturated imaging ( Fig. 1 ).




Fig. 1


Selected coronal ( A ), sagittal ( B ), and axial ( C ) 2D PD and coronal ( D ), sagittal ( E ), and axial ( F ) 2D PD fat-saturated images of the wrist using routine sequences. Note the central disk of the TFCC ( arrows ), which is easiest to evaluate in the coronal plane.


Three-dimensional MR imaging offers several advantages over conventional 2D sequences; 3D images with isotropic voxels can be reformatted into any cross-sectional plane from a single acquisition ( Fig. 2 ). Structures can be cross-linked between planes without misregistration. Thinner slices reduce partial volume artifact because a lesion may be seen on multiple sequential slices. In addition, there is potential to decrease overall scan time because a single 3D coronal acquisition can be obtained followed by multiplanar reformats as opposed to obtaining separate orthogonal acquisitions as in conventional 2D imaging.




Fig. 2


Coronal 3D isotropic PD fat-saturated sequence ( A ). Isotropic voxels allow for reformations in any plane, including standard axial ( B ) and sagittal ( C ) reformats.


Designing a 3D imaging sequence for evaluation of the TFCC requires careful and specific optimization of multiple parameters, including scan time, echo train length (ETL), and inversion time (TI). Increased slice thickness results in decreased scan time at the cost of increased image blur. Overall, decreasing ETL improves image blur. When scan time is held constant, decreasing slice thickness with a higher ETL results in less image blur. Decreased slice thickness and higher ETL may also result in incomplete fat suppression, which can be corrected by decreasing TIs.


Yamabe and colleagues compared high-resolution conventional 2D fast spin echo and isotropic 3D PD and PD fat saturated MR images of the wrist at 3 T. Qualitative metrics evaluated included delineation of anatomic structures, amount of artifact, quality of fat suppression, image blur, and overall quality. Quantitative metrics were also evaluated, including relative signal intensity of each structure in the wrist and relative contrast between structures of the wrist. Their qualitative analysis found that for overall image quality, delineation of anatomic structures, and amount of artifact, there was no difference between 2D and 3D MR imaging. Although the study was limited to healthy volunteers and injury was not directly assessed, they did note that there were no significant differences in relative fluid to TFCC contrast between the 2 imaging sequences, inferring that 3D and 2D imaging sequences may have similar detection rates for TFCC pathology.


Direct MR arthrography (MRA), involving intra-articular injection of dilute gadolinium contrast, is an accurate and established method for evaluating TFCC pathology. Arthrography results in distention of the joint capsule and supporting ligaments, allowing for direct visualization. In addition, there is improved contrast resolution between the high-signal gadolinium contrast and low-signal structures of the TFCC. MRA is also useful for verifying full-thickness TFCC tears, which are demonstrated by contrast extravasation into the distal radioulnar joint (DRUJ) in single-compartment radiocarpal arthrography. In addition, tear of the capsule or ulnar collateral ligament complex can be similarly visualized as contrast extravasation ( Fig. 3 ). Downsides of MRA compared with traditional MR imaging include additional cost and time, discomfort for the patient, and small risk of infection, bleeding, or contrast reaction.




Fig. 3


Sample of an MR arthrogram with coronal ( A ) FS T1-wieghted imaging (WI) and ( B ) isotropic 3D FS PD-WI sequences. Note massive contrast leak through prestyloid recess signifying tear of the ulnar collateral ligament complex of the TFCC ( thin arrows ). In addition, there is also a tear of the scapholunate ligament, allowing contrast into the midcarpal row ( thick arrows ).


Lee and colleagues recently evaluated a fast T1-weighted 3D sequence called 3D T1 high-resolution isotropic volume examination (3D-THRIVE) for the detection of central and peripheral TFCC tears. Patients in the study underwent routine 2D PD and T2-weighted MR imaging followed by arthrography and 3D-THRIVE MRA. The results of the imaging studies were compared to arthroscopy as the gold standard. Sensitivity for 3D MRA was 94.6% for central TFCC tears and 93.3% for peripheral tears compared with 2D MR imaging sensitivities of 70.3% for central TFCC tears and 60% for peripheral TFCC tears. In addition to improved sensitivity, total acquisition time for 3D MRA was shorter, averaging only 3 minutes, 40 seconds for coronal sequences.


Indirect arthrography is a technique in which a standard dose of 0.1 mmol/kg of gadolinium-based contrast is injected intravenously in lieu of direct intra-articular puncture, allowing contrast to accumulate within the synovial fluid after a brief (5–10 minute) delay. Haims and colleagues investigated the use of indirect MRA for the evaluation of TFCC central disk tears, finding no significant difference in sensitivity or specificity compared with unenhanced MR imaging.




Anatomy of the triangular fibrocartilage complex


The TFCC is an essential stabilizing structure of the DRUJ and ulnar carpus. The TFCC is centered between the distal ulna and the proximal carpal bones and is composed of a fibrocartilage disk and multiple surrounding ligaments. There is some controversy about the exact components of the TFCC, but for the purposes of this article, the complex is composed of TFC disproper, triangular ligament, ulnar collateral ligament, ulnotriquetral ligament, ulnolunate ligament, and the meniscus homologue ( Fig. 4 ).




Fig. 4


Schematic illustrating the components of the TFCC.

( From Yoshioka H, Burns JE. Magnetic resonance imaging of triangular fibrocartilage. J Magn Reson Imaging 2012;35(4):770; with permission.)


The TFC proper is composed of the dorsal and volar radioulnar ligaments and the fibrocartilage central disk. The components of the TFC proper attach to the distal radius. Typically, the fibrocartilage central disk is considered the focal point of the TFCC and is regarded as an asymmetric four-sided structure with concave facets (tetracuspid). The TFCC may be further divided into its volar and dorsal as well as radial and ulnar components.




Radial attachment


There is a broad attachment of the TFCC to the radius, with the dorsal and volar radioulnar ligaments inserting on the radius at the periphery of the central fibrocartilage disk at the level of the sigmoid notch. The radioulnar ligaments attach at bony entheses at the volar and dorsal aspects of the distal radius, while the central fibrocartilage disk transitions into the hyaline cartilage between these two ligaments. Coronal images demonstrate curvilinear intermediate signal at this transition of the central disk and the hyaline cartilage.




Ulnar attachment


The connection between the central fibrocartilage disk and the ulna occurs through the triangular ligament, which, as its name suggests, is roughly triangular (or V shaped) with the apex at the articular disk and its base occurring at the distal ulna. The triangular ligament has a striated appearance on MR imaging because of its underlying collagen fiber composition. Near its attachment on the ulna, the triangular ligament typically bifurcates into two laminae, which attach at the distal tip of the ulnar styloid and more proximally at the ulnar fovea. These two bands of the triangular ligament are often separated by relatively increased signal tissue called the ligamentum subcruentum. The more proximal fibers of the distal lamina of the triangular ligament become intimately involved with the ulnar joint capsule. In addition, the ulnotriquetral and ulnolunate ligaments lie at the volar aspect of the TFCC, while the extensor carpi ulnaris subsheath is at the dorsal ulnar aspect of the complex.

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Sep 18, 2017 | Posted by in MAGNETIC RESONANCE IMAGING | Comments Off on MR Imaging of the Triangular Fibrocartilage Complex
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