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Original Research |
1 Department of Radiology, University of California at San Diego and VA
Healthcare System San Diego, 3350 La Jolla Village Dr., San Diego, CA
92161.
2 Department of Diagnostic Imaging, UNIFESP-EPM, Sao Paulo, Brazil.
3 Department of Radiology, Konyang University Hospital, Nonsan, Korea.
4 Department of Orthopaedic Surgery, University of California at San Diego and
VA Healthcare System San Diego, San Diego, CA.
Received March 21, 2008;
accepted after revision August 4, 2008.
Address correspondence to F. N. Cardoso
(fabianonassar{at}gmail.com).
Abstract
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MATERIALS AND METHODS. MR images of seven trapeziometacarpal joints of seven fresh cadaveric hands were obtained before and after arthrography. The MR appearances of the ligaments around the trapeziometacarpal joint were analyzed and correlated with corresponding anatomic sections. The imaging planes that allowed best analysis of these structures were determined.
RESULTS. Five ligaments around the trapeziometacarpal joint were generally recognized: the dorsoradial ligament; the posterior oblique ligament; the intermetacarpal ligament; the ulnar collateral ligament (UCL); and both portions of the anterior oblique ligament, the superficial anterior oblique and deep anterior oblique ligaments. The former three were attached to the dorsal aspect and the latter three to the volar aspect of the trapeziometacarpal joint. The dorsoradial ligament, posterior oblique ligament, intermetacarpal ligament, and superficial and deep anterior oblique ligaments were best visualized in the sagittal plane, whereas the UCL was best visualized in the coronal plane. MR arthrography mainly improved visualization of the intermetacarpal ligament, superficial and deep anterior oblique ligaments, and UCL.
CONCLUSION. MR arthrography improves visualization of and provides detailed information about the anatomy of the ligaments around the trapeziometacarpal joint. Knowledge of the appearance of these normal ligaments on MRI allows accurate diagnosis of lesions of the trapeziometacarpal ligaments and of the adjacent structures and aid the attending physician if and when surgery is indicated.
Keywords: hand anatomy • hand ligaments • MR arthrography • MRI • osteoarthritis • trapeziometacarpal joint • wrist anatomy
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The trapeziometacarpal joint is commonly referred to as an incongruous saddle joint. It makes possible the wide circumduction of the thumb, enabling activities such as grasping and pinching [2], that involves three arcs of motion: flexion-extension, abduction-adduction, and pronation-supination. The biconcavoconvex geometry of the trapeziometacarpal joint, which is both concave and convex on each side, however, is prone to instability and subluxation in the static resting position [3].
This joint is dependent on several ligamentous constraints to provide stability [3], and although 16 different ligaments that stabilize the trapezium or the trapeziometacarpal joint can be identified through dissection [4], only five have been directly implicated in joint stability [5]: the anterior oblique ligament, posterior oblique ligament, ulnar collateral ligament (UCL), dorsoradial ligament, and intermetacarpal ligament.
Studies in the literature have well established that ligament laxity and resultant joint hypermobility are related to the development of premature degenerative changes [6-13]. This relationship is further emphasized by the fact that ligament reconstruction has been one of the most frequently used treatments in the orthopedics armamentarium for the treatment of osteoarthritis of the CMC joint since 1973, when Eaton and Littler [7] first reported their results about a ligament reconstruction procedure in 18 patients who presented with an unstable and painful trapeziometacarpal joint.
Therefore, the noninvasive MRI evaluation of this region is crucial because of its anatomic complexity and the nonspecific nature of clinical presentations of various diseases and abnormalities.
With regard to the latter, the early symptoms of CMC joint synovitis, such as pain and joint effusion, are similar to those of synovitis of any other joint. In the region of the trapeziometacarpal joint, however, there are multiple potential sources for such symptoms. In the width of an examining finger, the orthopedic surgeon can palpate a wrist effusion, a de Quervain tenosynovitis, a trapeziometacarpal joint synovitis, a stenosing flexor tenosynovitis, or a flexor carpi radialis tendinosis, all of which may have subtle or nonspecific radiographic findings [6, 14].
Despite the high prevalence of trapeziometacarpal joint osteoarthritis, representing the most frequently operated focus in the osteoarthritic upper extremity, and severe functional impairment that this disabling condition can impose to patients [9], to our knowledge, no previous studies in the radiology literature have detailed the ligamentous anatomy of this joint. Toward that end, the purpose of our study was to compare the normal ligamentous anatomy of the trapeziometacarpal joint in cadavers on conventional MRI and MR arthrography and review the most common diseases and abnormalities that affect this articulation.
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MRI
MRI was performed on a 1.5-T imager (Signa, GE Healthcare) with a 3-inch
(8-cm) standard flexible surface coil centered over the trapeziometacarpal
joint.
Sagittal and coronal T2-weighted fat-saturated fast spin-echo images were obtained with the following parameters: TR/TE, 2,000/80; echo-train length, 8; section thickness, 2 mm; no interslice gap; field of view, 6 x 6 cm; and data acquisition matrix, 512 x 256.
T1-weighted spin-echo MR images were acquired in the transverse, sagittal, and coronal planes centered at the level of the trapeziometa carpal joint. Sequence parameters were 500/12, a section thickness of 2 mm, no interslice gap, 2 excitations, a field of view of 6 x 6 cm, and a data acquisition matrix of 512 x 256 before and after the intraarticular injection of 1.5 mL of a solution containing a mixture of gadolinium (gadopentetate dimeglumine [Magnevist, Bayer Schering Pharma]), saline solution, and iodinated contrast agent (iohexol [Omnipaque, GE Healthcare]). This solution was obtained by adding 2 mL of gadolinium and 5 mL of iohexol to 250 mL of saline solution.
A 22-gauge needle was inserted directly through the skin from a dorsoradial approach and advanced into the trapeziometacarpal joint. The position of the tip of the needle was verified with a test injection of a small amount of iohexol.
The interval between contrast injection and MR arthrography ranged from 30 minutes to 24 hours.
Subsequently, sagittal and coronal T2-weighted fat-saturated fast spin-echo images were obtained using the same parameters used for imaging before injection.
Each cadaveric hand was placed in a prone position and the trapeziometacarpal joint was assessed in a neutral position, which was defined as 20° of flexion and adduction and 15° of pro nation using the third metacarpal as a reference point [9].
The MR appearances of ligaments around the trapeziometacarpal joint were analyzed and correlated with corresponding anatomic sections. Two musculoskeletal radiologists with 2 and 5 years of experience, respectively, reviewed all images in consensus; they compared T2-weighted fat-saturated images obtained before and after injection with T1-weighted images obtained after injection. The images were placed side by side for comparison.
The imaging planes that allowed best analysis of the trapeziometacarpal ligaments were determined by judging whether the structure in question could be visualized and whether it had a normal appearance, as defined by a linear, low-signal-intensity structure with intact attachment sites. In cases in which the ligament could be visualized, we also decided if it was poorly defined (i.e., visualized but not able to be analyzed) or well defined (i.e., excellent visualization and sharp delineation) (Table 1).
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The dorsoradial ligament is located adjacent to the dorsal side of the abductor pollicis longus tendon, which is attached distally on the lateral side of the first metacarpal [15-17]. It is best characterized in the sagittal plane and together with the posterior oblique ligament forms the dorsal ligament complex, which has recently been considered the primary restraint to dorsal dislocation of the trapeziometacarpal joint, displacing the superficial anterior oblique ligament from that point of distinction [3, 16, 18-20].
Posterior oblique ligament—The posterior oblique ligament is also a capsular ligament deep in relation to the extensor pollicis longus (EPL) tendon. It originates on the dorsal side of the trapezium, immediately adjacent and ulnar to the dorsoradial ligament, and inserts in the dorsal and ulnar aspect of the first metacarpal along with the intermetacarpal ligament (Figs. 3A, 3B, and 3C). It runs obliquely from the proximal radial to the distal ulnar aspect of the thumb.
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Intermetacarpal ligament—The intermetacarpal ligament is an extracapsular ligament that arises from the dorsoradial aspect of the second metacarpal, radial to the extensor carpi radialis longus tendon insertion, and runs toward the volar-ulnar tubercle of the first metacarpal base [15, 16] (Fig. 4).
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Volar Ligaments
UCL—The UCL, an extracapsular ligament, originates from the
distal and ulnar margin of the flexor retinaculum insertion onto the trapezial
ridge. It has a slightly oblique course from the proximoradial to the
distal-ulnar, inserting superficial and ulnar to the superficial anterior
oblique ligament on the volar-ulnar tubercle of the first metacarpal base. The
UCL typically overlaps the superficial anterior oblique ligament by 2-3 mm
[15,
16], and it is best identified
in the coronal plane (Figs. 5A,
and 5B).
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The deep anterior oblique ligament shares the function of preventing volar metacarpal subluxation with the superficial anterior oblique ligament [21] (Figs. 8, 9A, 9B, and 9C), and it is well depicted in the sagittal plane.
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Ligamentous restraints are necessary to stabilize the trapeziometacarpal joint and allow it to sustain extremely compressive forces that are transmitted through the length of the thumb and magnified as they cross the trapeziometacarpal joint [23]. This articulation is the second most frequent site of osteoarthritis in the hand, after the distal interphalangeal joint [1]. Because of the disabling symptoms of osteoarthritis and its profound impact on hand function, the trapeziometacarpal joint is the most common joint in the upper extremity in need of surgery as a result of osteoarthritic disease [7].
Symptomatic disease seems to be closely related to ligament laxity and joint hypermobility, which predispose the joint to incongruity, effusion, and pain and can lead to progressive cartilage erosion and metacarpal subluxation [6-13] even in the absence of radiographic signs of degenerative disease or prior injury [24].
Conversely, ligament reconstruction for stabilization of hypermobile joints has been shown to slow the apparent progression of osteoarthritis in these hands [6, 25]. When surgery is not a consideration, another treatment option is immobilization in a plaster cast for approximately 4 weeks [24].
Much less frequently than primary osteoarthritis, degenerative disease of the trapeziometacarpal joint may also occur secondary to previous trauma, such as a Bennett or Rolando fracture [3]. Radiographic evaluation allows detection of osseous abnormalities, joint space narrowing or enlargement, and subluxation [25]; however, the abnormal ligamentous structure cannot be assessed directly on conventional radiographs, which can affect treatment. For instance, a Bennett fracture that occurred less than 5 days before presentation without an associated dorsal ligament complex rupture can be reduced anatomically, whereas a Bennett fracture with an associated dorsal ligament complex rupture must be surgically repaired [3].
Despite the high frequency of trapeziometacarpal joint diseases and abnormalities requiring surgical intervention and the functional impairment that may result from injury, to our knowledge, no reports in the radiology literature describe the trapeziometacarpal joint ligaments.
Unfortunately, in addition to the highly complex anatomy of the trapeziometacarpal joint, the anatomic descriptions of these ligaments in the orthopedics literature are inconsistent. One of the inconsistencies refers to anatomic nomenclature: The beak ligament or "palmar beak" ligament, the anterior oblique ligament, the UCL, and the intermetacarpal ligament have been previously described interchangeably with the deep anterior oblique ligament [3, 12].
The most controversial topic with regard to the trapeziometacarpal joint is which ligament is the primary stabilizer of this articulation. The deep anterior oblique ligament was considered central to joint stability for almost 25 years [5, 12]. However, there now appears to be a consensus among orthopedic surgeons that the dorsal ligament complex is in fact the primary stabilizer [2, 3, 15, 16, 18] or that the dorsal ligament complex is at least as important as the deep anterior oblique ligament because the former is more important in preventing volar metacarpal subluxation, whereas the latter, dorsal metacarpal subluxation [4, 17].
Our results show that the complex of five ligaments that stabilize the trapezium and trapeziometacarpal joint can be identified using MR arthrography, with the UCL best visualized in the coronal plane and all others—that is, the superficial and deep anterior oblique ligaments, intermetacarpal ligament, posteri- or oblique ligament, and dorsoradial ligament—best identified in the sagittal plane.
In their recent study, Connell et al. [24] evaluated trapeziometacarpal joint ligamentous injuries using conventional MRI; however, they were not able to identify the superficial and deep portions of the anterior oblique ligament, whereas both portions were consistently characterized in all seven specimens in our study by means of MR arthrography.
Moreover, although no technique used for the treatment of CMC joint osteoarthritis has been proven to be superior to others, accordingly to a recent article in the Cochrane Database of Systematic Reviews [26], we might expect that, in the future, new surgical procedures will be specifically tailored to manage tears of the volar or dorsal ligament complex or, in cases of Bennett fractures, to evaluate the integrity of the ligamentous complex, which can affect treatment [3]. In this scenario, direct visualization of each ligament would be of the utmost importance, and our findings suggest that these ligaments can be easily managed through the use of MR arthrography.
Nevertheless, some limitations of our study must be acknowledged: Only a small number of specimens were evaluated; no clinical history was available; and the advanced age of the cadavers could be responsible for making visualization of attenuated ligaments more difficult through conventional MRI. Further research in specimen analysis and clinical MRI is necessary to confirm our findings.
In conclusion, MR arthrography improves visualization of and provides detailed information about the anatomy of the ligaments around the trapeziometacarpal joint. Knowledge of the appearance of these normal ligaments on MRI allows accurate diagnosis of lesions of the trapeziometacarpal ligaments and adjacent structures and will aid the attending physician if and when surgery is indicated or may have a role in avoiding unnecessary immobilization when a normal ligament is identified.
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