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MRI in the Diagnosis of Cartilage Injury in the Wrist

¹ Department of Radiology, Yale University School of Medicine, 333 Cedar St., PO Box 208042, New Haven, CT 06520-8042.
² Department of Orthopaedics and Rehabilitation, Yale University School of Medicine, 800 Howard Ave., PO Box 208071, New Haven, CT 06520-8071.
³ Present address: United States Air Force, Yokota Air Base, Japan.
⁴ Department of Radiology, Thomas Jefferson University Hospital, 111 S 11th St., Philadelphia, PA 19107.
⁵ Department of Orthopedic Surgery, Thomas Jefferson University Hospital, Philadelphia, PA 19107.

Received September 30, 2003; accepted after revision November 17, 2003.

 
The opinions and assertions contained herein are the private views of the authors and are not to be construed as official or as representing the views of the United States Air Force or the Department of Defense.

Address correspondence to A. H. Haims (andrew.haims{at}yale.edu).

Abstract

Top Abstract Introduction Materials and Methods Results Discussion References

 
OBJECTIVE. Our purpose was to evaluate the accuracy of MRI in identifying articular cartilage abnormalities in the distal radius, scaphoid, lunate, and triquetrum of patients with wrist pain.

MATERIALS AND METHODS. Eighty-six MRI examinations of the wrist in 85 patients (41 indirect MR arthrograms and 45 unenhanced [nonarthrographic] MR images) were evaluated. The study population consisted of 47 male (54.7%) and 38 female (45.3%) patients with an average age of 37.5 years (range, 7–62 years). Three experienced musculoskeletal radiologists who were unaware of surgical findings retrospectively evaluated the MRI examinations for cartilage abnormalities in the distal radius, scaphoid, lunate, and triquetrum. All patients underwent arthroscopy of the radiocarpal joint with inspection of the articular surfaces of the distal radius, scaphoid, lunate, and triquetrum. The articular cartilage was evaluated on the basis of the 5-point scale of the Outerbridge classification system.

RESULTS. When at least two of the three radiologists had concordant interpretations, sensitivity for abnormalities in the distal radius was 27%; the scaphoid, 31%; the lunate, 41%; and the triquetrum, 18%. Specificity for the distal radius was 91%; the scaphoid, 90%; the lunate, 75%; and the triquetrum, 93%. Weighted kappa values among the three observers showed only fair agreement (0.279–0.360). High-grade more extensive cartilage lesions were no more accurately identified than low-grade lesions. Indirect MR arthrograms were not statistically more sensitive, specific, or accurate than unenhanced studies. No bone was more frequently or less frequently graded correctly or incorrectly with statistical significance. The variables of sex, age, and the presence of multiple bones with lesions did not affect accuracy.

CONCLUSION. Our findings suggest that MRI of the wrist with the techniques described is not adequately sensitive or accurate for diagnosing cartilage defects in the distal radius, scaphoid, lunate, or triquetrum.

Introduction

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MRI has been used to evaluate the wrist since the first clinical introduction of this technique into imaging practice. Despite its long-standing use, no previous study, to our knowledge, has evaluated hyaline cartilage injuries around the wrist. Conversely, the literature evaluating the cartilage around the knee joint is excellent [1–6].

Wrist pain is a common clinical problem with myriad conditions explaining the cause. In many cases, obvious clinical syndromes are excluded, and articular cartilage injury is suspected. To guide therapy, surgeons need to know whether such injury exists. Cartilage injury may result either from direct trauma or as a common end point to a host of inflammatory, endocrine, and degenerative conditions. Normal carpal kinematics depend on a complex interaction of bone anatomy, interosseous ligament integrity, the joint capsule, the triangular fibrocartilage complex, the synovium, muscle balance, and tendon positioning. Disruption of any one of these components may lead to symptomatic cartilage injury.

Conventional radiographs are limited in showing cartilage damage until the disease process has advanced to the point of joint narrowing, carpal orientation changes, or frank osseous changes. MRI has been shown to be accurate in evaluating tears of the central disk of the triangular fibrocartilage complex, scapholunate ligament, and tendon abnormalities. For further assessment of wrist pain, it is unclear whether MRI is a viable tool for the diagnosis of wrist cartilage injury. We evaluated the usefulness of MRI in the detection of articular cartilage injury in the radiocarpal articulation, inclusive of the distal radius, scaphoid, lunate, and triquetrum, compared with the gold standard of arthroscopy.

Materials and Methods

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After obtaining institutional review board approval, we retrospectively evaluated 86 MRI examinations of the wrist over a 6-year period in 85 patients who subsequently underwent arthroscopy of the same joint. The patient population consisted of 47 male (54.7%) and 38 female (45.3%) patients with an average age of 37.5 years (range, 7–62 years). Of the 86 examinations, 45 (52.3%) were unenhanced, and 41 (47.7%) were indirect MR arthrograms. The MR arthrography studies were indirectly enhanced with IV gadopentetate dimeglumine (Magnevist [0.1 mmol/kg], Berlex) given under standard technique. The selection of patients for enhanced imaging was based on the availability of a radiologist to administer the contrast material.

All MRI examinations were performed on 1.5-T superconducting magnets. Patients were imaged either in a dedicated quadrature wrist coil or in two 3-inch (7.62 cm) surface coils, depending on the study center.

The sequence and parameters for the indirect MR arthrograms were as follows: coronal fast spin-echo fat-suppressed T2-weighted (TR/TE, 6,000/70; matrix size, 256 x 256; number of excitations, 4; echo-train length, 4; field of view, 10 cm; slice thickness, 3 mm; interslice gap, 1 mm); coronal 3D gradient-echo (46/15; flip angle, 45°; matrix size, 256 x 128; number of excitations, 2; field of view, 8 cm; slice thickness, 1.2 mm; interslice gap, 0 mm); coronal T1-weighted spin-echo (500/14; matrix size, 256 x 192; number of excitations, 3; field of view, 10; slice thickness, 3 mm; interslice gap, 1 mm); and coronal and axial fat-suppressed 2D spoiled gradient-echo (220/9.3; flip angle, 90°; matrix size, 256 x 128; number of excitations, 2; field of view, 10 cm; slice thickness, 3 mm; interslice gap, 1 mm).

The sequences and parameters for the unenhanced MR images were as follows: coronal fast spin-echo fat-suppressed T2-weighted (6,000/70; matrix size, 256 x 256; number of excitations, 4; echo-train length, 4; field of view, 10 cm; slice thickness, 3 mm; interslice gap, 1 mm); coronal 3D gradient-echo (58/12; flip angle, 10°; matrix size, 256 x 128; number of excitations, 2; field of view, 8 cm; slice thickness, 1.2 mm; interslice gap, 0 mm); coronal T1-weighted spin-echo (500/14; matrix size, 256 x 192; number of excitations, 3; field of view, 10 cm; slice thickness, 3 mm; interslice gap, 1 mm); and axial fast spin-echo fat-suppressed T2-weighted (8,000/85; matrix size, 256 x 256; number of excitations, 4; echo-train length, 8; field of view, 10 cm; slice thickness, 3 mm; interslice gap, 1 mm).

Three experienced musculoskeletal radiologists who were unaware of surgical findings independently assessed the hyaline cartilage of the distal radius, scaphoid, lunate, and triquetrum. The cartilage was described as normal or abnormal on the basis of increased signal on the T2-weighted images, visualized articular defects, or subchondral marrow changes suggestive of overlying articular defects (Figs. 1 and 2).

View larger version (153K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1. —41-year-old woman with full-thickness articular cartilage defects of both radius and lunate. Coronal fat-suppressed T1-weighted MR image (TR/TE, 500/14) from indirect MR arthrogram shows subtle cartilage thinning (white arrows) and marrow enhancement (black arrows) in both distal radius and lunate.

View larger version (128K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 2. —57-year-old woman with full-thickness articular cartilage defects in lunate. Coronal fat-suppressed fast spin-echo T2-weighted MR image (TR/TEeff, 6,000/70) shows full-thickness articular cartilage loss of ulnar side of lunate (white arrows) with associated subchondral cystic changes and edema (black arrows).

Six board-certified orthopedic surgeons with added qualifications in surgery of the hand performed all arthroscopic procedures using standard technique and equipment. These procedures were performed on all patients within 10 months of MRI examination, with a mean time of 2.5 months (range, 1 week–10 months). Cartilage damage was graded using the Outerbridge classification system [6]: grade 0, normal changes; grade 1, softening; grade 2, superficial fibrillation; grade 3, fissuring to the level of bone; and grade 4, full-thickness injury with exposed bone.

Sensitivity and specificity were reported with weighted kappa evaluations, and the McNemar test for significance was used. With regard to the weighted kappa evaluations, a value of 0.7 or greater is generally considered adequate in the clinical setting [8]. A chi-square test was used to assess the variables of age, sex, and number of bones with confirmed cartilage damage to determine whether these variables affect sensitivity, specificity, and accuracy. A chi-square test was applied to the variable or IV contrast administration for specificity and sensitivity.

Results

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Arthroscopy showed a relatively higher prevalence of cartilage injury in the distal radius and the lunate than in the scaphoid and triquetrum (Table 1). The sensitivity of the observers for identifying cartilage injury in selected bones of the wrist on MRI ranged from 9% to 62%. When at least two of the three radiologists had identical interpretations, the sensitivity for abnormalities in the distal radius was 27%; the scaphoid, 31%; the lunate, 41%; and the triquetrum, 18% (Table 2). The specificity ranged from 69% to 97%. When at least two of the three radiologists had identical interpretations, specificity for the distal radius was 91%; the scaphoid, 90%; the lunate, 75%; and the triquetrum, 93% (Table 3). Overall accuracy ranged from 59% to 86%. These numbers did not statistically improve when the criterion of two of the three observers with concordant findings was used. Weighted kappa values among the three observers showed only fair agreement (0.279–0.360).

High-grade cartilage injury at arthroscopy did not correlate with statistically improved accuracy in MRI identification by the observers (Table 4). Additional variables evaluated for impact on sensitivity, specificity, and accuracy through the use of a chi-square test were age, sex, and number of bones with confirmed cartilage damage. None of these variables was found to be statistically significant.

Sensitivity and specificity were also evaluated with regard to the absence or presence of IV contrast material. A chi-square test performed to detect differences in sensitivity between the indirect MR arthrograms and the unenhanced MR images resulted in a p value of 0.65 for the distal radius, 0.22 for the scaphoid, 0.16 for the lunate, and 1.00 for the triquetrum. Thus, with a p value of 0.05 ( = 0.1) set as a cutoff for statistical significance, no statistically significant difference was found between these two groups. IV contrast material did not improve sensitivity, specificity, or accuracy.

Discussion

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Evaluation of articular cartilage continues to be a focus of MRI. Most of this work has been done in the knee. This study is the first, to our knowledge, to specifically focus on the effectiveness of MRI for the evaluation of wrist cartilage. Different protocols have been evaluated for imaging cartilage around the knee, including fat-suppressed 3D spoiled gradient-echo sequences, fast spin-echo sequences both with and without fat suppression, 3-point Dixon chemical shift imaging, and direct MR arthrography [1–6]. The two most common sequences for the evaluation of articular cartilage are fast spin-echo and fat-suppressed 3D spoiled gradient-echo. Fast spin-echo sequences are more versatile and allow evaluation of signal abnormalities in articular cartilage and in other structures in the knee such as menisci and ligaments. With this technique, sensitivities and specificities for imaging articular cartilage in the knee have ranged from 59% to 85% and 87% to 94%, respectively. The fat-suppressed 3D spoiled gradient-echo sequence provides thin slices for evaluation of small defects and allows reconstructed images in different planes. However, signal abnormalities in articular cartilage and in other structures in the knee cannot be adequately evaluated with this sequence. With this technique, also in the knee, sensitivity and specificity for the evaluation of articular cartilage defects are 86% and 97%, respectively [1]. Accuracy in the evaluation of articular cartilage is generally the best in the patella and worst in the lateral tibial plateau [1, 3]. This difference in accuracy is thought to be related to articular cartilage thickness, with the patella being the thickest at approximately 5–6 mm [9]. Our study illustrates that MRI is relatively inaccurate for detecting and allowing description of focal articular cartilage defects in the radiocarpal joint (Fig. 3). Given the previous experience with MRI of cartilage around the knee, this finding may not be surprising. Wrist cartilage is thinner than the thinnest cartilage of the knee, where imaging has been less than optimal. Our results reflect this hypothesis, with sensitivities ranging from 18% to 41% and specificities ranging from 75% to 93%. Additionally, the wrist, more than larger joints, is prone to artifacts such as motion from difficulty in positioning the wrist and inhomogeneous fat suppression due to the inability to position the wrist at isocenter. These factors can degrade image quality, thus potentially decreasing accuracy.

View larger version (132K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 3. —46-year-old man with Outerbridge grade 3 defects of distal radius, scaphoid, lunate, and triquetrum. Coronal 3D gradient-echo MR image (TR/TE, 58/12) shows no definite abnormality to correspond to articular cartilage defects visualized on arthroscopy.

An inherent limitation to our study is the assumption that diagnostic arthroscopy of the wrist and concomitant grading of articular cartilage damage with the scale from the Outerbridge classification system are completely accurate and reproducible. They are neither. A recently published study addressed the accuracy and reproducibility of the Outerbridge classification system for chondral damage in the knee [10]. Six cadaveric knees first underwent videotaped arthroscopy and then direct arthrotomy to determine chondral damage. Those researchers found an overall accuracy rate of 68% for all observers. Predictably, low-grade lesions were diagnosed with less accuracy than high-grade lesions. The kappa value between the arthrotomy grade and the arthroscopy grade was 0.602. This kappa value correlates with fair to good agreement. The intraobserver kappa value was 0.80, which correlates with excellent agreement. The point was well made that diagnostic arthroscopy is not infallible.

Several additional limitations apply to our study. Our study was retrospective, and protocols were not specifically set up to evaluate articular cartilage. The exact type of coil that was used to image the wrist could not be determined from the retrospective examinations. In addition, an undetermined number of patients were excluded from the study because either the MRI studies or the arthroscopy reports could not be located. Exclusion of these cases could have potentially led to a population bias. As we noted earlier, the administration of IV contrast material was determined only by the availability of a radiologist to administer the contrast material. This fact also may have led to bias. Interobserver variation was examined and showed only fair agreement among the observers, but intraobserver variation was not evaluated.

The role of MRI in the diagnosis of cartilage injury in the wrist is in its infancy. Despite the limited sensitivity for the evaluation of articular cartilage defects in the wrist, MRI is still the least invasive means of evaluating wrist pain. Since the commencement of this study, better coil technology, such as the phased array wrist coil, has improved image quality. This improvement in conjunction with development of better pulse sequences and high-field-strength magnets will undoubtedly improve accuracy in imaging of articular cartilage in the wrist. In the interim, however, diagnostic arthroscopy remains the gold standard for the diagnosis of articular injury in the wrist and has the additional benefit of providing a means for treatment.

Acknowledgments
 
We thank Trace Kershaw for his statistical help on this manuscript.

References

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