The intrinsic ligaments of the wrist form a complex structure that is crucial to wrist stability. The two most clinically important intrinsic wrist ligaments are the lunotriquetral ligament (LTL) and the scapholunate ligament (SLL), which are vulnerable to attritional wear (1). With loss of SLL integrity, the scaphoid tends to flex, whereas the lunate and triquetrum tend to extend, imparting a dorsiflexed intercalated segment instability (DISI) orientation. Conversely, with loss of LTL integrity, the triquetrum tends to extend, whereas the scaphoid and lunate attempt to flex. However, a complete LTL tear is not sufficient to cause static carpal collapse into a volar intercalated segment instability (VISI) orientation (2). VISI-pattern lunotriquetral instability requires associated capsular damage, typically to the dorsal radiocarpal and dorsal intercarpal ligaments.

The LTL is V-shaped on sagittal section and has three separate zones: dorsal, proximal, and volar (Fig. 15.1). The dorsal and volar zones are ligamentous. The former is highly important functionally, particularly as a restraint to rotation, whereas the latter is the strongest and thickest of all three zones and transits the extension moment of the triquetrum (2, 3). The proximal zone is fibrocartilaginous and is similar histologically to the TFCC. It is thin (1–1.5 mm or less) and difficult to see reliably (3).

The radiographic appearance of wrists with LTL tears is often normal. Lunotriquetral dissociation results in disruption of the smooth arcs that are formed by the proximal and distal joint surfaces of the proximal carpal row (Gilula’s arcs 1 and 2) and the proximal joint surfaces of the distal carpal row (Gilula’s arc 3). Arthrography can be valuable in demonstrating leakage or pooling of the contrast medium at the lunotriquetral interspace. On arthrography of the normal wrist, however, age-related perforations of the LTL proximal zone, other communications between the radiocarpal and midcarpal joints, and asymptomatic LTL tears have been reported. Therefore, the results of arthrography must be correlated with clinical examination findings (2).

The dorsal and volar portions of the LTL are biomechanically more important than the proximal portion of the LTL. Therefore, the axial plane may be better for assessing LTL injuries, although many previous MR studies have discussed LTL injuries in the coronal plane. With injury of the dorsal and volar portion, a more clinically useful approach would be high-resolution MRI in the axial plane using a microscopy coil (4) (Fig. 15.2).

Complete tears of the LTL and SLL have been classified on MRI by either abnormal ligament morphology (to the point of absence of the entire ligament) or by the presence of fluid through the entire ligament on T2-weighted images (5). Partial tears of the LTL and SLL have been diagnosed by two basic criteria: the presence of fluid through a portion of the ligament and partially altered ligament morphology visualized on any or all sequences (6) (Figs. 15.3 and 15.4). However, the sensitivity for diagnosing partial intercarpal ligament tears, particularly those of the LTL, is limited.

Accurate diagnosis of LTL injury with MRI is often difficult because of low resolution and low contrast. The accuracy of MRI in making a diagnosis of LTL tear has been disappointing with sensitivities from 0% to 56% and specificities from 46% to 100% (5, 7, 8). In addition, a potential cause for false-positive MR findings of
LTL tear is lack of familiarity with the normal MR appearance at the ligament–bone interface (9). Smith and Snearly (9) reported that the proximal zone of the LTL showed a variety of shapes and signal intensities. Yoshioka et al. (10) also recently reported the shape and signal intensity of the proximal zone of the LTL with high-resolution MRI; they concluded that gaining familiarity with the normal MR appearance of the LTL proximal zone using a high-resolution technique is important to improve diagnosis of LTL injury (Fig. 15.5). The LTL proximal zone has a triangle shape in more than 85% of subjects on gradient recalled echo images. The linear intermediate or high signal intensity traversing the distal surface, or both distal and proximal surfaces, of the proximal LTL is seen in approximately two thirds of subjects (10). The amorphous shape may represent diffuse degenerative changes (9). The morphologic and signal intensity characteristics of the LTL interface with the lunate and triquetral bones vary (9).

The SLL has three zones and appears horseshoe-shaped or C-shaped, unlike the V-shaped LTL (Fig. 15.6). The SLL is approximately 18 mm long and 2 to 3 mm thick (3). In the dorsal aspect, the SLL forms a strong ligamentous zone that appears to provide most of the ligament’s resistance to diastasis between the proximal poles of the scaphoid and lunate (11). In the proximal zone, the SLL is fibrocartilaginous like the LTL; here, the SLL proximal zone is weakest and can undergo degenerative perforation. The volar zone of the SLL is ligamentous but thinner and is separated by loose vascular connective tissue, which causes it to be less easily observed on conventional MRI. On axial images, the lig

amentous dorsal zone appears thick and homogeneous with low signal intensity, whereas the volar zone shows an inhomogeneous striated structure (Fig. 15.7). On coronal images, the dorsal zone of the SLL clearly shows a striated pattern. The striated band-like structure of the volar zone of the SLL is observed only with high-resolution imaging (Fig. 15.8). On high-resolution MRI, the shape of the SLL proximal zone varies widely from slice to slice, unlike the LTL, which keeps a relatively similar triangular shape. Totterman and Miller (12) classified the SLL’s proximal zone into three patterns: a band-like dorsal portion, a triangular or flat triangular middle portion, and a trapezoidal volar portion. The proximal zones of the SLL and LTL insert directly on the hyaline cartilage of the scaphoid, lunate, and triquetral bones,
whereas the dorsal and volar components often insert directly on the carpal bones (13).

Conventional radiography is not the appropriate imaging modality for assessing possible lesions of the SLL and can diagnose scapholunate instability only in cases with an enlarged scapholunate gap or abnormal carpal angles (DISI). Direct arthroscopy can detect ligamentous disruptions by demonstrating communication between the radiocarpal and midcarpal joints, but controversy exists concerning its ability to differentiate between asymptomatic degenerative tears and symptomatic acute or chronic lesions (14).

The possible reasons for the suboptimal diagnostic accuracy of MRI for the diagnosis of SLL tears are similar to those for LTL tears: limitations in spatial resolution, limited signal-to-noise ratios with use of available receiver coils, inherent limitations in contrast between ligamentous structures, and unfamiliarity with the normal range of SLL appearance on MRI (15).

Three-compartment MR wrist arthrography has several advantages over nonenhanced MRI of the wrist in
diagnosing SLL and LTL injuries. First, the joint cavities of the wrist can be fully expanded so that most of the ligamentous and capsular structures are stretched and can be directly visualized and evaluated (16). Second, the high signal of gadolinium–diethylene–triamine–penta-acetic acid leads to excellent delineation of all parts of these ligaments, which show low signal intensity. Third, MR arthrography can precisely localize and quantify SLL or LTL leaks, which have a significant impact on diagnosis and treatment (Fig. 15.9) (16). Limitations of MR arthrography compared with nonenhanced MRI are the additional cost and invasiveness of MR arthrography and the need to inject contrast medium into the joint. The technique is fairly complicated and time-consuming (16). Scheck et al. (16) reported that with wrist arthroscopy as the standard of reference, sensitivity and specificity values for SLL perforations were 52% and 34%, respectively, for nonenhanced MRI and 90% and 87%, respectively, for MR arthrography. They concluded MR arthrography, using three-dimensional volume acquisition with thin slices, shows the precise location and magnitude of ligamentous defects of all parts of the SLL, correlates well with wrist arthroscopy, and has potential implications for diagnosis and treatment planning (16).

To improve the diagnostic accuracy of MRI, noninvasive indirect MR arthrography has also been advocated (17). Indirect MR arthrography is predicated on the fact that intravenously injected gadolinium contrast material diffuses into the joint in such concentrations that an arthrographic effect can be obtained on T1-weighted images without decrease in the signal–to-noise ratio of long-repetition–time sequences (18). Haims et al. (18) reported that indirect MR arthrography significantly improves sensitivity in the evaluation of the SLL when compared with unenhanced MRI of the wrist but does not significantly improve the ability to evaluate the LTL. One study suggests that in the wrist, passive exercise is not significantly different from active exercise in indirect MR arthrography but produces a more predictable result (19).

The extrinsic wrist ligaments have an attachment on the carpus and pass out of the carpus, whereas the intrinsic wrist ligaments are entirely within the carpus (20). The extrinsic ligaments can be classified into volar and dorsal ligaments; the volar ligaments are important stabilizers
of the wrist, and the dorsal ligaments are less crucial for wrist stability (21). Because the distal radial articular surface is sloped, with both a volar and an ulnar incline, the axially loaded carpus tends to slide down in a volar and ulnar direction. This tendency is resisted by the obliquely oriented volar and dorsal extrinsic ligaments (22). At the volar aspect, there are three major extrinsic ligaments: the radioscaphocapitate, radiolunotriquetral, and short radiolunate ligaments (Fig. 15.10). The radioscaphocapitate (RSC) ligament is the most radial of the extrinsic ligaments, originating on the volar surface of the radial styloid process (22). It passes beneath the waist of the scaphoid to insert on the center of the capitate, creating a sling or “seat belt” for the scaphoid (21, 22

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