RadioGraphics 2011

1. US of the Intrinsic and Extrinsic Wrist Ligaments and Triangular Fibrocartilage Complex—Normal Anatomy and Imaging Technique RadioGraphics 2011

2. DICL = dorsal intercarpalligament • DRCL = dorsal radiocarpalligament • LRLL = long radiolunateligament • LTL = lunotriquetralligament • PSTL = palmar scaphotriquetralligament • PULL = palmar ulnolunateligament • PUTL = palmar ulnotriquetralligament • RCL = radial collateral ligament • RSCL = radioscaphocapitateligament • RSLL = radioscapholunateligament • SLL = scapholunateligament • SRLL = short radiolunateligament • TFC = triangular fibrocartilage disk • TFCC = triangular fibrocartilage complex • UCL = ulnocapitate ligament

3. Introduction • During the past 2 decades, imaging has had an important role in the evaluation of the intrinsic and extrinsic wrist ligaments and the triangular fibrocartilage disk (TFC). • Arthroscopy is considered the reference standard, although the reported complication rate is as much as 2% and includes injuries to the overlying tendons, nerves, and arteries.

4. Herein we describe the US technique for evaluation of the intrinsic and extrinsic wrist ligaments and the TFCC and include a brief review of the pertinent literature related to basic anatomy and US examination of these structures. • Short video clips demonstrating real-time US examinations of these structures are included as supplemental material

5. Examination Technique • Wrist ligaments consist of type I collagen fibers with parallel orientation creating bundles that at US appear as echogenic bands and/or fibrilar structures. • The ligaments are considered torn if their fibers are not seen in the expected anatomic location or if their fibers are discontinuous.

6. All images presented here were obtained with the GE Logiq 9 ultrasound machine equipped with a 9–12-MHz linear "hockey stick" transducer. • All ligaments and the TFC are scanned primarily along the longitudinal axis according to anatomic landmarks and as needed along the short axis to confirm the imaging findings.

7. Intrinsic and Extrinsic Wrist Ligaments: Background • Taleisnik divided the carpal ligaments into two major groups: intrinsic and extrinsic. • The wrist ligaments are named for the bones from which they originate and into which they insert, proximal to distal, radial to ulnar. • Biomechanically, the intrinsic ligaments are capable of greater elongation before permanent deformation occurs, while the extrinsic ligaments are stiffer

8. The intrinsic wrist ligaments are situated entirely within the carpus, between carpal bones. • These ligaments may be divided into two major categories: interosseous, between the carpal bones; and intrinsic capsular, attaching to the carpal bones.

9. The proximal interosseous ligaments are the scapholunate ligament (SLL) and unotriquetral ligament (LTL) (Fig 1). • The distal interosseous ligaments are the trapeziotrapezoid, trapezocapitate, and capitohamate ligaments. • Palmar ligaments connecting the proximal and distal carpal rows include the scaphotrapeziotrapezoid, scaphocapitate and triquetrocapitate ligaments.

10. Of the intrinsic interosseous wrist ligaments, the two that are commonly evaluated at US are the SLL (Figs 1–3) and LTL (Figs 1, 4, ). • The extrinsic wrist ligaments are those that have an attachment on the carpus and pass out of the carpus and attach either to the distal radius or ulna and volarradioulnar ligament. They are divided into two major categories: dorsal (Fig 6) and palmar (Fig 7)

11. Distal attachment of the palmar extrinsic wrist ligaments is either on the proximal carpal row (with the lesser arc outlining the radial, distal, and ulnar aspect of the lunate) or on the capitate, forming a greater arc. • At the volar aspect of the wrist, a triangular area of weakness (called the space of Poirier) lies between the lesser and greater arcs, between the lunate and capitate, and is not covered by any ligaments. This accounts for perilunate and lunate injuries and dislocations (Fig 8)

12. Interosseous SLL and LTL • Both of these ligaments have dorsal and volar bands and structurally weaker proximal (central) membranous parts. • The thickest and functionally most important part of the SLL is the dorsal band (Fig 2a), while the thickest and functionally most important part of the LTL is the volar band (Fig 5a).

13. Disruption of the SLL and LTL may cause pain and instability. Furthermore, an SLL tear can lead to scapholunate dissociation, which together with a dorsal intercarpal ligament (DICL) tear results in dorsal intercalated segment instability. • Likewise, an LTL tear can lead to lunotriquetral dissociation, which together with a tear of the extrinsic dorsal radiocarpal ligament (DRCL) results in volar intercalated segment instability.

14. On radiographs, widening of the scapholunate interval of more than 2 mm may indicate SLL disruption; however, widening of the scapholunate interval may not occur in all cases of SLL disruption, and widening may occur as a normal variation with lunotriquetral coalition.

15. The dorsal and volar bands of the SLL and LTL can be seen at US (Figs 2a, 3a, 4a, 5a), while the functionally less important proximal central parts of these ligaments are not accessible for US evaluation.

16. Partially torn ligaments show some irregularity of the fibers. The ligaments are considered torn if their fibers are not seen in the expected anatomic locations between the scaphoid and lunate (Fig 9) or between the lunate and triquetrum, or if discontinuity of their fibers is seen.

17. The reported sensitivity of US in depicting lesions of the dorsal band of the SLL varies from 46% to 100% , while specificity varies from 92% to 100%. • The results are less promising for LTL lesions, with sensitivity varying from 25% to 50% and specificity from 90% to 100%. • Sonoarthrography in the presence of radiocarpal joint effusion improves the visibility of the dorsal band of the LTL, with a reported sensitivity of 83% and specificity of 90%.

18. Imaging Technique • The dorsal bands of the SLL (Fig 2, Movie 1) and LTL (Fig 4, Movie 2) are scanned along their long axes at the scapholunate and lunotriquetral joints with the wrist in pronation and slight flexion. • The volar bands of the SLL (Fig 3, Movie 3) and LTL (Fig 5, Movie 4) are examined with the wrist in supination and at slight extension.

19. Triangular Fibrocartilage Complex • The TFCC lies between the distal ulna, radius, triquetrum, and lunate and consists of a TFC, dorsal and volarradioulnar ligaments, ulnar joint capsule (described earlier), and the extensor carpiulnarissubsheath (Fig 22). • Individual components of the TFCC are amenable to US evaluation (Figs 23a, 24a, 25a, 26a)

20. The anatomic location of the TFC, with the styloid process obstructing, may make this structure difficult to image with US. • The disk is evaluated from both dorsal and volar sides with dynamic imaging. The main imaging plane is coronal, but the transverse plane may also be used

21. When imaged through the extensor carpi ulnaris as an acoustic window in the dorsal coronal plane, the TFC is seen as a triangular echogenic structure at the distal aspect of the ulna (Fig 22a) • One limitation of US is the difficulty of visualizing the entire length of the disk, especially its radial attachment site, which is required for complete evaluation.

22. A few authors have reported promising results in US evaluation of the TFC, with reported sensitivities and specificities of 63% and 100% , 87.5% and 100% , and 86% and 100%. Sonoarthrography in the presence of radiocarpal joint effusion may potentially increase the diagnostic accuracy, with a reported sensitivity of 93% and specificity of 100%.

23. Imaging Technique • In our institution, the dorsal aspect of the TFC is examined with the wrist in pronation and slight radial deviation with the extensor carpi ulnaris as an acoustic window. • The volar aspect of the TFC and meniscus homologue are evaluated with the wrist in supination. In this position, the TFC frequently appears less echogenic (Fig 24, Movie 21) than the meniscus homologue, which is seen as a triangular echogenic structure distal to the TFC (Fig 24, Movie 21)

24. The dorsal and volar radioulnar ligaments are examined in their long axes in the transverse plane with respect to the distal ulna at the dorsal and volar aspects of the TFC. • The dorsal radioulnar ligament is examined with the wrist in pronation without or with slight flexion (Fig 25, Movie 22), and the volar radioulnar ligament is examined with the wrist in supination and mild extension (Fig 26, Movie 23).

25. The ulnar collateral ligament, which has been shown in many anatomic drawings in the radiology literature, is considered to be part of the ulnocarpal joint capsule rather than a true ligament. It was not visualized in several US studies. The ulnar joint capsule is examined with the wrist in a similar position as for the dorsal aspect of the TFC, in pronation and with a slight radial deviation, beneath the extensor carpi ulnaris (Fig 27, Movie 24).

26. Conclusions • US shows promising results in the evaluation of the varying normal and abnormal anatomy of the intrinsic and extrinsic wrist ligaments and the TFCC, and provides an alternative imaging method to MR imaging, MR arthrography, and CT arthrography in the evaluation of these structures.

27. Wrist ligaments consist of type I collagen fibers with parallel orientation creating bundles that at US appear as echogenic bands and/or fibrilarstructures. • The ultrasound beam must be perpendicular to the examined structure to avoid anisotropy, an artifactual decrease in echogenicity that can be misinterpreted as a tear. • The extrinsic wrist ligaments are those that have an attachment on the carpus and pass out of the carpus and attach either to the distal radius or ulna and volar radioulnar ligament. • At the volar aspect of the wrist, a triangular area of weakness (called the space of Poirier) lies between the lesser and greater arcs, between the lunate and capitate, and is not covered by any ligaments. This accounts for perilunate and lunate injuries and dislocations (Fig 8) • When imaged through the extensor carpi ulnaris as an acoustic window in the dorsal coronal plane, the TFC is seen as a triangular echogenic structure at the distal aspect of the ulna