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Published online before print January 22, 2004, 10.1148/radiol.2303021388
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(Radiology 2004;230:768-773.)
© RSNA, 2004

Experimental Studies

Patellar Articular Cartilage Lesions: In Vitro MR Imaging Evaluation after Placement in Gadopentetate Dimeglumine Solution1

Klaus Woertler, MD, Horst Buerger, MD, Jens Moeller and Ernst J. Rummeny, MD

1 From the Department of Radiology, Technische Universitaet Muenchen, Ismaninger Str 22, D-81675 Munich, Germany (K.W., J.M., E.J.R.); and the Gerhard Domagk Institute of Pathology, Westfaelische Wilhelms Universitaet Muenster, Germany (H.B.). Received October 24, 2002; revision requested January 7, 2003; final revision received June 3; accepted June 24. Address correspondence to K.W. (e-mail: woertler@roe.med.tu-muenchen.de).


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
PURPOSE: To evaluate T1-weighted magnetic resonance (MR) imaging after diffusion of gadopentetate dimeglumine for visualization of articular cartilage lesions.

MATERIALS AND METHODS: MR imaging was performed in eight human cadaveric patella specimens immediately and 4 hours after placement into a vessel filled with gadopentetate dimeglumine solution (2.5 mmol/L). T1-weighted spin-echo and inversion-recovery turbo spin-echo MR sequences with nulled cartilage signal (inversion time of 300 msec) were used. In a total of 128 articular cartilage areas, MR imaging findings were compared with macroscopic and histopathologic findings. Pathologic evaluation was performed by one musculoskeletal pathologist. With knowledge of pathologic observations, MR images were analyzed by one musculoskeletal radiologist with regard to intrinsic signal intensity characteristics and surface abnormalities of articular cartilage.

RESULTS: Histopathologic findings demonstrated 67 areas of normal articular cartilage and 66 cartilage lesions (grade 1, n = 19; grade 2, n = 15; grade 3, n = 26; grade 4, n = 6). All grade 3 and 4 lesions could be identified on MR images obtained immediately after submersion and after 4 hours. Ninety-four percent of grade 1 and 2 lesions were identified as areas of predominantly decreased contrast enhancement on delayed MR images obtained with both sequences. MR images obtained immediately after submersion demonstrated abnormal signal intensity in only 9% and 12% of grade 1 and 2 lesions, respectively.

CONCLUSION: T1-weighted MR images obtained in vitro after gadopentetate dimeglumine diffusion allow demonstration of articular cartilage surface lesions and early stages of cartilage degradation.

© RSNA, 2004

Index terms: Cartilage, 453.4851 • Cartilage, MR, 453.121411, 453.121413, 453.12143 • Contrast media, experimental studies • Knee, arthrography, 453.4851 • Knee, MR, 453.121411, 453.121413, 453.12143 • Patella, 453.4851


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 
With the development of new surgical techniques, such as transplantation of osteochondral auto- or allografts and autologous chondrocytes, the treatment of focal cartilage defects has become a clinical reality (1,2). Further improvement of therapeutic options for the prevention and treatment of cartilage lesions can be expected from current pharmacologic and biogenetic research.

In addition to arthroscopic exploration, magnetic resonance (MR) imaging has already developed into an important diagnostic test for the diagnosis of articular cartilage damage. However, current MR imaging techniques show substantial limitations in the detection of early stages of cartilage degradation and preclinical osteoarthritis (3–5).

The diagnosis of structural alterations of hyaline cartilage can be important for several reasons. First, chondromalacia can be symptomatic as a source of chronic pain and disability and can therefore require surgical treatment even if no surface defect is visible (1,6). Second, traumatized areas of articular cartilage may initially appear intact at arthroscopy but can later undergo degeneration with formation of defects, which may progressively enlarge with time (1,2). Third, cartilage degradation is frequently found adjacent to traumatic chondral or osteochondral defects. The definition of the true extent of the damaged area is of great importance for therapeutic decisions and the prognosis of surgical treatment (1). Fourth, with the increasing number of osteochondral transplantions, a reliable test for minimally invasive evaluation of the transplants and the donor sites is required. Further indications might result from future developments in preventative and therapeutic treatment of patients with osteoarthritis.

Results of several experimental studies indicated that T1-weighted MR imaging enhanced with gadopentetate dimeglumine by means of diffusion has the potential to demonstrate structural abnormalities of hyaline cartilage (7–10). However, this technique has not yet been evaluated sufficiently either in vitro or in vivo, in our opinion, for the visualization of naturally occurring cartilage lesions.

The purpose of this study was to evaluate T1-weighted MR imaging after diffusion of gadopentetate dimeglumine for visualization of articular cartilage lesions.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS
 DISCUSSION
 REFERENCES
 
Eight fresh human patella specimens from nonembalmed cadavers (age range at the time of death, 62–75 years) were obtained from the Institute of Anatomy at the Westfaelische Wilhelms Universitaet Muenster. Institutional policies were followed with regard to cadaver use. After equilibration in isotonic sodium chloride solution for a period of 24 hours, the specimens were imaged with a 1.5-T MR unit (Magnetom Vision; Siemens, Erlangen, Germany) immediately and 4 hours after placement in a vessel filled with gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany) solution (2.5 mmol/L diluted with normal saline) by using a transmit-and-receive circularly polarized knee coil (Siemens). MR images were obtained immediately and after a 4-hour delay with the following pulse sequences: transverse T1-weighted spin echo (SE) (repetition time msec/echo time msec, 630/15) with 3-mm section thickness, two signals acquired, 160-mm field of view, and 256 x 256 matrix; and transverse inversion-recovery turbo SE (7,900/90), which nulled signal from articular cartilage with an inversion time of 300 msec, echo train length of seven, 3-mm section thickness, one signal acquired, 160-mm field of view, and 256 x 256 matrix. Additionally, subtraction images were calculated from delayed images by using the corresponding images obtained immediately after submersion as an overlay.

After MR imaging, the patella specimens were sectioned with a band saw into 3-mm-thick sections parallel to the imaging plane. Six sections were obtained from each of three patella specimens (18 sections total), and five sections were obtained from each of five specimens (25 sections total). For comparison with pathologic findings, on each of these 43 sections and corresponding MR images, the patellae were subdivided into three regions: the medial facet, the central portion (or the apex of the patella), and the lateral facet. Histologic sections were obtained from all three regions of each patellar section. Since one patellar region had to be excluded because of fixation artifacts of the histologic section, comparison of MR imaging, macroscopic, and histologic findings could be performed in a total of 128 cartilage areas. Cartilage lesions were graded with the use of a modified Shahriaree classification system (11) (Table 1).


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  		TABLE 1. Shahriaree Classification System (modified) for Articular Cartilage Lesions

 
Macroscopic and histologic sections were evaluated by one experienced musculoskeletal pathologist (H.B.). A grade 1 cartilage lesion was diagnosed if the surface of articular cartilage was macro- and microscopically intact, but signs of cartilage degradation with proliferation of chondrocytes were seen at histologic examination. A grade 2 lesion was diagnosed if, in addition to the latter, superficial fissuring and/or blister formation was observed on macro- and/or microscopic sections. Surface defects of grade 3A to grade 4 were diagnosed macro- and microscopically by means of definition of the depths of the defects relative to original cartilage thickness (Table 1).

MR images were evaluated by one experienced musculoskeletal radiologist (K.W.) with knowledge of macroscopic and histologic observations. Image analysis was performed regarding the homogeneity of cartilage signal, presence of areas of increased or decreased contrast enhancement, integrity of the cartilage surface, and presence and depth of surface defects on MR images and subtraction images. Surface defects were graded according to the classification system mentioned previously.

The detectability of cartilage lesions on MR images and corresponding subtraction images was expressed in percentages of the number of pathologically confirmed lesions.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
DISCUSSION
 REFERENCES
 
The results are summarized in Table 2. Pathologic findings showed 67 areas of normal articular cartilage and 61 regions of abnormal cartilage. Five of the cartilage regions classified as abnormal included two separate cartilage lesions (eg, one grade 1 and one grade 3 lesion), and each of the other regions included only one lesion, so that a total of 66 cartilage lesions were diagnosed. Nineteen lesions were classified as grade 1, 15 as grade 2, 13 as grade 3A, 13 as grade 3B, and six as grade 4.


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  		TABLE 2. Detectability of Histologically Confirmed Articular Cartilage Lesions on MR Images and Corresponding Subtraction Images

 
Regions of normal articular cartilage showed homogeneous signal intensity and intact surfaces on 100% (67 of 67) of MR images obtained immediately after submersion and homogeneous contrast enhancement on 97% (65 of 67) of delayed MR images and subtraction images (Fig 1). Two cartilage regions considered normal at histologic examination demonstrated areas of decreased gadopentetate dimeglumine uptake on delayed MR images.



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  		Figure 1.  A, Transverse T1-weighted SE (630/15) MR images (top) and B, transverse inversion-recovery turbo SE (7,900/90/300 [inversion time]) MR images (top) and corresponding subtraction (SUBTR) images of human patella specimens obtained immediately (t0) and 4 hours after (t4) placement in gadopentetate dimeglumine solution (2.5 mmol/L). Delayed MR and subtraction images demonstrate homogeneously increased signal intensity (arrows) of articular cartilage after gadopentetate dimeglumine diffusion. C, Corresponding macroscopic section with subdivision of patellar cartilage into three regions for pathologic correlation shows intact surface and normal height of articular cartilage. D, Photomicrographs from region 2 demonstrate normal histologic appearance of articular cartilage. (Hematoxylin-eosin stain; original magnification, x40 [left] and x100 [right].)

 
Grade 1 and 2 lesions could be identified as areas of altered gadopentetate dimeglumine diffusion on delayed MR images in 89% (17 of 19) and 100% (15 of 15) of cases, respectively. Most of these lesions corresponded to areas of decreased contrast enhancement (Fig 2); only three (one grade 1 and two grade 2 lesions) showed increased signal intensity compared with that of adjacent normal cartilage, which in two grade 2 lesions was already visible on corresponding MR images obtained immediately after submersion (Fig 3). Lesion detectability was otherwise low with MR images obtained immediately after submersion (Table 2).



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  		Figure 2.  A, Delayed transverse T1-weighted SE (630/15) MR image and B, corresponding subtraction image of human patella specimen in gadopentetate dimeglumine solution show a cartilage area of decreased signal intensity (arrows) at the lateral facet. C, Corresponding macroscopic section demonstrates intact surface and normal appearance of articular cartilage. D, Histologic sections from the lateral facet show cartilage degradation (arrows) and clusters of proliferating chondrocytes (arrowheads) consistent with a grade 1 cartilage lesion. (Hematoxylin-eosin stain; original magnification, x100.)

 


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  		Figure 3.  A, Transverse inversion-recovery turbo SE (7,900/90/300) and B, transverse T1-weighted SE (630/15) MR images of human patella specimens obtained immediately after placement into gadopentetate dimeglumine solution. C, Subtraction image from SE MR images obtained immediately and after a delay (not shown). Images demonstrate grade 3 articular cartilage lesion (arrows) at the lateral patellar facet. A small area of increased signal intensity (arrowheads) lateral to the surface lesion is visible. D, Corresponding macroscopic section of patella specimen shows surface lesion (arrow). E, Histologic sections obtained from the lateral patellar facet demonstrate surface lesion (*) and grade 2 articular cartilage lesion with fissuring (arrows) and proliferative changes (arrowheads), which correspond to signal intensity alteration on MR images. (Hematoxylin-eosin stain; original magnification, x20 [top], x40 [bottom left], x100 [bottom right].)

 
Surface defects of articular cartilage (grades 3 and 4) could always be identified on images obtained immediately and after a delay (Figs 3, 4). Radiologic and pathologic gradings of surface lesions matched in all cases (Table 2).



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  		Figure 4.  A, Transverse T1-weighted SE (630/15) delayed MR image and B, corresponding SE subtraction image of a human patella specimen in gadopentetate dimeglumine solution show diffuse thinning of articular cartilage and a deep surface defect with exposure of subchondral bone and intraosseous herniation (arrows) of cartilage. Note inhomogeneous articular cartilage enhancement. C, Corresponding macroscopic section demonstrates diffuse thinning of articular cartilage and a grade 4 defect (arrow) close to the apex of the patella. D, Histologic section obtained from the central portion of the patella shows diffuse cartilage degeneration, a focal defect (arrow), and herniation of articular cartilage (arrowheads) caused by collapse of subchondral bone. (Hematoxylin-eosin stain; original magnification, x40.)

 
Overall lesion detection rates were 53% (35 of 66) to 54% (36 of 66) with immediate MR imaging and 97% (64 of 66) with delayed MR imaging for lesions of grades 1–4. Rates were 76% (101 of 133) to 77% (102 of 133) with immediate MR imaging and 97% (129 of 133) with delayed MR imaging for lesions of grades 0–4.

In general, we found almost identical detection rates with both T1-weighted SE and inversion-recovery turbo SE sequences. Both techniques enabled demonstration of homogeneous gadopentetate dimeglumine uptake in areas with intact cartilage, as well as altered contrast material behavior in regions of cartilage degradation. The low signal intensity of articular cartilage on inversion-recovery turbo SE images with an inversion time of 300 msec did not improve lesion detectability compared with that on T1-weighted SE images. Subjectively, grade 1 and 2 lesions were better visualized on T1-weighted SE images.


   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
REFERENCES
 
The ability of a substance to penetrate articular cartilage by means of diffusion is determined not only by its molecular size but also by its charge (12). The negatively charged glycosaminoglycan side chains of proteoglycans represent the main source of the negative fixed charge density of intact articular cartilage, which attracts positively charged ions and water and repels negatively charged ions (7,8,12,13). Experiments performed by Kusaka et al (14) showed that intrinsic contrast enhancement of cartilage following diffusion of Mn2+ is mirrored following diffusion of gadopentetate dimeglumine, in which Gd3+ is entrapped by a chelate complex with five negatively charged side chains, resulting in a negative net charge of the molecule (Gd-DTPA2-). As demonstrated by Bashir et al (7,9), the concentration of Gd- diethylenetriaminepentaacetic acid in articular cartilage following penetration by means of diffusion can be used as a measure of glycosaminoglycan content. In a study with human cadaveric specimens, Trattnig et al (10) observed that cartilage areas that demonstrated shorter T1 relaxation times following diffusion of gadopentetate dimeglumine corresponded to regions of proteoglycan loss at histologic examination.

The loss of proteoglycans is one of the first measurable structural changes in cartilage degradation (12,15). Therefore, contrast material–enhanced MR imaging with use of ionic substances is thought to have the potential to demonstrate abnormalities of the cartilage matrix in early osteoarthritis (5,7–10,13,16). Results of experiments performed by Bacic et al (17) showed that proteoglycan degradation induced by papain in the rabbit knee could be visualized by means of application of cationic (nitroxide) and anionic (gadopentetate dimeglumine) substances. Furthermore, in human cartilage specimens, degenerative changes accompanied by proteoglycan depletion could be demonstrated as areas of T1 shortening with the use of gadopentetate dimeglumine–enhanced MR imaging at 3 T (18).

In our study, cartilage areas with normal findings at histologic examination demonstrated a homogeneous increase of signal intensity on delayed MR images in 97% of cases. The two false-positive results observed in this study were possibly caused by alterations of the cartilage matrix, which could not be detected with the use of conventional staining techniques.

The detection of grade 1 and 2 articular cartilage lesions with MR imaging represents an unsolved problem, since SE, fast SE, and gradient-echo MR sequences have not proved sufficiently reliable in identification of structural alterations (3–5,13,19–21). T1-weighted, proton density–weighted, and T2-weighted conventional SE sequences have been reported to have low sensitivities in the detection of chondromalacia, ranging from 0% to 63% for grade 1 lesions and 0% to 68% for grade 2 lesions (19,22–24). The use of fast SE and short inversion time inversion-recovery fast SE sequences also could not significantly improve the diagnostic performance of MR imaging in early stages of cartilage degradation (25,26). Although several two- and especially three-dimensional gradient-echo techniques in combination with fat saturation have proved to be reliable in the detection of surface lesions, they showed substantial limitations in the identification of earlier stages of chondromalacia, with sensitivities of less than 50% for the diagnosis of grade 1 lesions (23,27).

Accordingly, the detection rates for histologically proved grade 1 and 2 cartilage lesions in our experimental study were low (7%–15%) on T1-weighted SE and inversion-recovery turbo SE MR images obtained immediately after positioning of the specimens in gadopentetate dimeglumine solution. Delayed MR images dramatically increased the visibility of grade 1 and 2 lesions to 89% and 100%, respectively. However, in contradiction to the previously mentioned experimental results of other authors, the contrast affinity of degraded cartilage regions was not increased in most cases. Ninety-one percent of grade 1 and 2 lesions demonstrated decreased contrast enhancement compared with areas of histologically normal cartilage; only three (9%) were visualized as regions of increased gadopentetate dimeglumine uptake. Increased signal intensity in these cases could not be attributed to magic angle effects, since it was observed on T1-weighted SE as well as inversion-recovery turbo SE images. It showed a globular rather than bandlike appearance, and it appeared not to be related to the orientation of articular cartilage relative to the main magnetic field.

Possible explanations for this phenomenon include that, at histologic examination, the cartilage lesions in our study (unlike those in other studies) could already be visualized by means of standard staining techniques and did not represent potential early precursor lesions of manifest cartilage degradation. Alterations consistent with the pathologic diagnosis of grade 1 and 2 lesions, in addition to loss of proteoglycans, also include alterations of the collagen network and chondrocytes (12,15). Furthermore, structural alterations occurring in the degradation process lead to an impaired diffusion capacity and an increased water content of articular cartilage (15), which might also alter contrast enhancement kinetics.

Subtle disruptions of the integrity of the cartilage surface can be invisible at macroscopic and even histologic examination with standard techniques and therefore might also be present in lesions classified as grade 1 rather than grade 2. In an experimental study with human cartilage specimens, Mlynarik and co-workers (18) observed that the expected shortening of T1 relaxation times caused by increased gadopentetate dimeglumine uptake in degraded cartilage could be reversed if fissuring of articular cartilage was already present. Therefore, as in our in vitro study, they could also identify at least two mechanisms of contrast enhancement. This, in our opinion, suggests that gadopentetate dimeglumine enhancement in articular cartilage degradation might be influenced by factors other than proteoglycan content alone.

In our study, grade 3 and 4 lesions could already be detected and graded correctly to correspond to macro- and microcopic findings on MR images obtained immediately after submersion in all cases. On delayed MR images, the visualization of surface lesions was neither improved nor impaired. Our observations correspond to the results of other authors, who investigated direct MR arthrography by using T1-weighted pulse sequences and contrast media containing gadolinium in vitro and in vivo and who reported high sensitivities (85%–100%) in the detection of grade 3 and 4 articular cartilage lesions (23,25,28).

The present study has several limitations. First, data obtained in an experimental setting with the use of cadaveric specimens cannot generally be referred to living subjects. On the other hand, the experimental character of our investigations allowed a direct correlation of imaging and histopathologic findings. Second, the fact that only patellar lesions were studied might have positively influenced the detection rates, since cartilage lesions of the patella are generally more easily identified than cartilage defects located at other anatomic sites (eg, the tibial plateau). Third, the fact that several sections were obtained from each patella specimen might also have an influence on the results, because contiguous sections might have included the same cartilage lesion. Fourth, the penetration of articular cartilage by gadopentetate dimeglumine by means of diffusion following intraarticular or intravenous administration in vivo might be less effective than it would be under experimental conditions, where a constant concentration of the contrast media can be provided. Fifth, the detection rates calculated in this study represent the percentage of articular cartilage lesions, which could be identified on MR images when they were evaluated together with macroscopic and histologic sections. Therefore, the detection rates do not equal the sensitivity of this technique as evaluated in, for instance, a multireader analysis with blinded readings.

In summary, on the basis of results of our in vitro experiments, T1-weighted MR imaging enhanced with gadopentetate dimeglumine by means of diffusion appears to have the potential to provide demonstration of articular cartilage surface defects and earlier stages of chondromalacia. Further investigations will have to be conducted to evaluate the diagnostic performance of delayed MR imaging following direct or indirect MR arthrography in vivo.

Practical applications: The results of this experimental study suggest that delayed MR imaging after application of gadopentetate dimeglumine might be used to improve the diagnostic performance of MR imaging in detection of stage 1 and 2 chondromalacia in vivo. Since our experimental model simulated a direct MR arthrography approach, however, the data can only be referred to imaging following intraarticular administration of gadopentetate dimeglumine at a concentration of 2.5 mmol/L, which appears to be acceptable for direct MR arthrography. Possible indications include imaging prior to surgical treatment of chondral defects, evaluation of donor sites for osteochondral transplants, postoperative imaging following chondral or osteochondral transplantation, and monitoring of therapeutic effects of pharmacologic treatment. Furthermore, our data suggest that delayed contrast-enhanced MR imaging of articular cartilage can be performed with the use of standard T1-weighted SE sequences instead of inversion-recovery turbo SE sequences without loss of information.


   FOOTNOTES
 
Abbreviation: SE = spin echo

Author contributions: Guarantor of integrity of entire study, K.W.; study concepts and design, K.W.; literature research, K.W.; experimental studies, K.W., H.B., J.M.; data acquisition, K.W., H.B., J.M.; data analysis/interpretation, K.W., H.B.; statistical analysis, K.W.; manuscript preparation, K.W.; manuscript definition of intellectual content, K.W., E.J.R.; manuscript editing, K.W.; manuscript revision/review and final version approval, K.W., E.J.R.


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TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS
 DISCUSSION
 REFERENCES
 

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