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1 Department of Radiology, University of Michigan Medical Center, 1500 E.
Medical Center Dr., Ann Arbor, MI 48109-0326.
2 Present address: Valley Radiologists, 5322 W. Northern Ave., Glendale, AZ
85301.
3 Present address: Department of Radiology, University of Missouri School of
Medicine, One Hospital Dr., Columbia, MO 65212.
4 Department of Orthopaedic Surgery, University of Michigan Medical Center, Ann
Arbor, MI 48109-0326.
Received November 19, 2001;
accepted after revision February 13, 2002.
Presented at the annual meeting of the American Roentgen Ray Society,
Seattle, April—May 2001.
Abstract
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MATERIALS AND METHODS. The dorsal aspect of the scapholunate ligament in four cadaveric wrists was evaluated on sonography without knowledge of the findings from standard arthrography, MR arthrography, and anatomic sectioning. The sonographic findings were compared with the findings from other modalities. The criteria for an abnormal scapholunate ligament included an abnormal contrast communication between the radiocarpal and midcarpal joints on arthrography and a discontinuity of the dorsal aspect of the scapholunate ligament that was documented both on MR arthrography and at anatomic sectioning.
RESULTS. Arthrography, MR arthrography, and anatomic sectioning showed the dorsal aspect of the scapholunate ligament to be normal in one specimen and abnormal in three specimens. On sonography, the normal scapholunate ligament was hyperechoic between the scaphoid and lunate bones. In the three cases of abnormality, a normal scapholunate ligament was not visualized, and an abnormal hypoechogenicity was present.
CONCLUSION. The dorsal aspect of the scapholunate ligament can be depicted on sonography; abnormality is present in patients in whom the normally hyperechoic fibrillar ligament is hypoechoic or absent.
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The development of a low-cost, noninvasive, accurate, and widely available imaging method with which to directly evaluate the scapholunate ligament would have obvious benefits. Sonography has been used to evaluate many disorders of the musculoskeletal system [9]. With regard to the wrist, the dorsal aspect of the scapholunate ligament has been shown to be at least partially visible on sonography in 78% of normal wrists [10]. However, further sonographic characterization of the abnormal scapholunate ligament is needed. We retrospectively studied the sonographic appearance of the dorsal aspect of the scapholunate ligament in four cadaveric wrists and correlated the sonographic findings with MR arthrographic and anatomic findings.
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Sonography
The eight wrist specimens were imaged with sonography (HDI 5000; ATL,
Bothell, WA) by a fellowship-trained musculoskeletal radiologist with
experience in musculoskeletal sonography using 10- and 12-MHz linear
transducers. At the time of sonography, the examiner had no information
regarding the status of the scapholunate ligament in the specimens. A liberal
amount of transmission gel was used in place of the standoff pad.
The dorsal aspect of the scapholunate articulation was imaged in the transverse plane. To identify this articulation, we began the sonographic examination in the transverse plane over the dorsal radial tubercle (Lister's tubercle). The bone cortex of the radius was identified as hyperechoic with posterior acoustic shadowing. The transducer was then advanced distally; the proximal pole of the scaphoid bone was visualized distal to the radiocarpal joint space. The transducer was then moved toward the ulnar aspect to visualize the adjacent hyperechoic cortex of the lunate bone. The dorsal scapholunate articulation is characterized by a triangular space. We obtained several images of this articulation. An effort was made to visualize any ligament fibers, which are characterized by a compact and fibrillar hyperechoic echotexture. If no ligament fibers were identified, the transducer was angled cephalad and caudally to eliminate any artifactual hypoechogenicity from anisotropy.
Fluoroscopy
An initial posteroanterior fluoroscopic image was obtained before the
procedure to identify any gross abnormality of the lunate or scaphoid bones
that could potentially interfere with an imaging study, such as an osseous
fracture or destruction or the presence of a metallic foreign body. A 25-gauge
needle was inserted dorsally into the radiocarpal joint between the scaphoid
and radius bones. The placement of the intraarticular needle was confirmed by
visualizing a linear configuration of an iodinated contrast agent (iohexol
[Omnipaque]; Nycomed, Princeton, NJ) between the radius and the proximal
carpal row. A solution of 0.1 mL of gadopentetate dimeglumine (Magnevist;
Berlex Imaging, Wayne, NJ), 9 mL of iohexol, 9 mL of unflavored gelatin (Knox;
Kraft Foods, Englewood Cliffs, NJ) dissolved in water (two 8-oz packs [480 g]
of gelatin in 40 mL of boiling water), and five drops of methylene blue was
prepared, and approximately 3-5 mL of this mixture was injected into the
radiocarpal joint. If an abnormal extension of the contrast agent into the
midcarpal joint was observed, an additional 3-5 mL of contrast agent was
injected. Posteroanterior radiographs were obtained during the injection to
show the sequential extension of the contrast agent. The scapholunate joint
was profiled on radiography. If no filling of the midcarpal joint from the
radiocarpal joint occurred, the needle was removed and then dorsally inserted
into the midcarpal joint at the juncture of the hamate, capitate, triquetrum,
and lunate bones. After the placement of the intraarticular needle was
confirmed by injecting a small amount of iohexol into the joint, 3-5 mL of the
gadolinium solution was injected, and radiographs were obtained during
fluoroscopy. Any abnormal communication between the radiocarpal and midcarpal
joints was noted.
MR Imaging
The eight wrists were then imaged with MR imaging using a 1.5-T magnet
(Signa; General Electric Medical Systems, Milwaukee, WI) with a dedicated
phased array wrist coil (MRI Devices, Waukesha, WI). The imaging sequences
(matrix, 256 x 192; slice thickness, 3 mm; slice gap, 0.3 mm; and number
of excitations, 2) included axial T1-weighted MR images (TR range/TE range,
450-700/14-16) obtained with and without fat saturation.
Anatomic Sectioning
The eight cadaveric wrists were frozen and cut into 3-mm axial sections
using a band saw. The surface of each cut section was photographed.
Image Interpretation
Image interpretation was divided into two parts: first, a retrospective
review of the fluoroscopic, conventional arthrographic, MR arthrographic, and
photographic (anatomic section) images to classify the wrists as having a
normal or abnormal scapholunate ligament; and then a retrospective analysis of
the sonographic images and correlation to the findings of other imaging and
anatomic sectioning. Evaluation of the scapholunate ligament integrity on MR
and sonographic images was limited to the dorsal aspect.
To classify the wrists as having a normal or abnormal scapholunate ligament on the dorsal aspect, one orthopedic hand surgeon and two musculoskeletal radiologists with experience in wrist arthrography and MR imaging retrospectively reviewed fluoroscopic, conventional arthrographic, and MR arthrographic images as well as photographs of the anatomic sections. For a scapholunate ligament to be classified as abnormal, all of the following criteria had to be observed: an abnormal contrast communication between the radiocarpal and midcarpal joints on conventional arthrography, a discontinuity or absence of the dorsal aspect of the scapholunate ligament on MR arthrography, and a discontinuity or absence of the dorsal aspect of the scapholunate ligament in photographs of the anatomic sections. For a scapholunate ligament to be classified as normal, all of the following criteria had to be observed: no abnormal contrast communication between the radiocarpal and midcarpal joints on conventional arthrography, continuous ligament fibers extending between the dorsal aspect of the scaphoid and lunate bones on MR arthrography, and continuous ligament fibers extending between the dorsal aspect of the scaphoid and lunate bones in photographs of the anatomic sections. Agreement on classification for each wrist was reached through consensus among the three observers.
The sonographic images of the unequivocally normal and abnormal wrists (as determined by the previously mentioned criteria) were then retrospectively evaluated by two observers with experience in musculoskeletal sonography. The images were evaluated for normal hyperechoic ligamentous fibers between the scaphoid and lunate bones and for other findings. The sonographic images were then correlated with the findings of MR arthrography and anatomic sectioning.
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The remaining four wrists did not meet our criteria for a normal or abnormal dorsal aspect of the scapholunate ligament and were excluded from the study. In three of these wrists, an abnormal communication between the radiocarpal joint and midcarpal joint was observed on arthrography. Although a central perforation of the scapholunate ligament was identified on the MR images, extension of this abnormality to the dorsal aspect of the scapholunate ligament could not be excluded on the basis of the MR images and photographs of the anatomic sections. The fourth excluded specimen also was found to have an abnormal communication between the radiocarpal and midcarpal joints on arthrography, and a central perforation of the scapholunate ligament was identified on MR images. Although the dorsal aspect of the scapholunate ligament appeared intact on both MR images and photographs of the anatomic sections, this specimen was excluded on the basis of the abnormal arthrographic findings.
Retrospective review of the sonograms, as determined by the correlative imaging studies and anatomic sections, showed the normal dorsal aspect of the scapholunate ligament (Figs. 1A,1B,1C) as a hyperechoic structure, compact and fibrillar, located between and inserting into the scaphoid and lunate bones. On sonography, the abnormal dorsal scapholunate ligament (Figs. 1D,1E,1F and 2A,2B,2C) appeared as an abnormal hypoechogenicity with an absence of continuous hyperechoic ligament fibers between the scaphoid and lunate bones.
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The results of our study show that the normal dorsal aspect of the scapholunate ligament sonographically appears as a hyperechoic structure with a compact fibrillar echotexture that inserts into the scaphoid and lunate bones (Figs. 1A,1B,1C). In contrast, each of the three specimens with an abnormal dorsal aspect of the scapholunate ligament showed hypoechogenicity with no visualization of the scapholunate ligament at its expected location (Figs. 1D,1E,1F and 2A,2B,2C).
An initial anatomic landmark to use in locating the dorsal aspect of the scapholunate ligament is the dorsal tubercle of the radius (Lister's tubercle). The characteristic V-shaped articulation (Figs. 1A,1B,1C) between the scaphoid and lunate bones, where the scapholunate ligament should be identified, is distal and ulnar to Lister's tubercle. Although not specifically evaluated in our study, the dorsal radiotriquetral ligament (Figs. 1D,1E,1F) was identified as a hyperechoic and fibrillar structure superficial relative to the scaphoid bone, lunate bone, and scapholunate ligament. Care should be taken not to mistake the dorsal radiotriquetral ligament for the scapholunate ligament when evaluating the wrist on sonography. The dorsal radiotriquetral ligament is superficial relative to the scapholunate ligament and courses obliquely from the radius to the triquetrum, with other attachments to the scaphoid and lunate bones [8]. Another extrinsic ligament of the wrist, the dorsal intercarpal ligament, can also be identified on sonography immediately distal to the scapholunate ligament. The dorsal intercarpal ligament courses transversely from the scaphoid to the triquetrum bones, with attachments to the capitate and lunate bones [8]. Knowledge of these extrinsic dorsal ligaments and their characteristic courses and attachments allows differentiation between these ligaments and the intrinsic scapholunate ligament.
Among the limitations of this study is the small sample size, which was partly due to the strict criteria for normal and abnormal scapholunate ligaments as determined by correlative imaging and anatomic sections. In addition, we concentrated on only the dorsal aspect of the scapholunate ligament because of its increasingly recognized role in carpal stability as well as the easy accessibility of the dorsal aspect for sonographic evaluation [7]. Griffith et al. [10] reported that the volar aspect of the scapholunate ligament could not be visualized sonographically in 76% of normal wrists. Another limitation is our reliance on retrospective analysis of sonograms, which depends on the technique and experience of the individual acquiring the sonograms. However, the sonograms were obtained using standardized technique by one investigator with experience in musculoskeletal sonography. Last, the sensitivity and specificity of the diagnosis of scapholunate abnormalities could not be assessed in this study. This initial study establishes the sonographic appearance of normal and abnormal scapholunate ligaments. Further investigations can apply these observations to help determine the true effectiveness of sonography in assessing scapholunate ligament abnormality. Additional investigations with living patients are needed. The usefulness of dynamic imaging in the sonographic evaluation of the scapholunate ligament can then be assessed.
In conclusion, the dorsal aspect of the normal scapholunate ligament appears as a hyperechoic and fibrillar structure on sonography. Hypoechogenicity, discontinuity, or absence of such a structure indicates disruption of the dorsal aspect of the scapholunate ligament. Further studies are needed to confirm these initial observations in a larger study group of patients.
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