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Invited Commentary

Commonwealth Radiology, Richmond, Virginia

I am pleased to have the opportunity to provide comments related to the excellent article by Ho and colleagues in this issue of RadioGraphics (1). The authors presented a review of the basic concepts of articular cartilage imaging, the types of surgical chondral repair, and techniques used to image articular cartilage with magnetic resonance (MR) after chondral repair.

Articular cartilage lesions on MR images are very common, being found in 69% of patients undergoing arthroscopy, yet they are often overlooked (2,3). The detection of chondral lesions is important to the orthopedic surgeon because such lesions often cause symptoms. However, articular cartilage lesions may masquerade clinically as meniscal tears or other internal derangement of the joint (2). Therefore, one of the major goals in the interpretation of MR images of the knee is the detection of chondral abnormalities. MR imaging typically has high specificity but lower sensitivity for the detection of chondral lesions (4). A number of MR techniques that allow imaging with high contrast and spatial resolution thus have been developed to help improve lesion conspicuity (5,6).

As the authors imply, routine joint imaging should include sequences that provide optimal depiction of articular cartilage, particularly in light of the common occurrence of chondral lesions (2,3). Currently, routine joint imaging should include intermediate-weighted fast spin-echo sequences (7,8), three-dimensional fat-suppressed spoiled gradient-recalled echo sequences (2,9), or both. Fast spin-echo imaging with long repetition times and with an echo time of about 40 msec allows appropriate levels of T2 contrast and magnetization transfer contrast for the clear depiction of articular cartilage, while also allowing the depiction of other articular structures, including menisci, ligaments, tendons, and bone marrow (8). Three-dimensional fat-suppressed spoiled gradient-recalled echo imaging also allows high spatial resolution and high contrast resolution, depicting cartilage as a bright structure relative to other tissues and joint fluid, which have lower signal intensity (2,9).

Treatment options for chondral lesions are currently limited to surgical techniques because of the inability of articular cartilage to heal (10). However, surgically implanted repair tissue has variable clinical longevity because of the suboptimal restoration of biomechanical and biochemical function at the involved articular surface. Fortunately for the radiologist, the postsurgical assessment is limited to gross structural changes (11), because repair techniques have not advanced to the point where an assessment of biochemical or mechanical status is required. Intensive research in articular cartilage therapies is under way, because the end result of chondral derangement is osteoarthritis, which has a high prevalence in the general population and exacts enormous societal costs (12). Such research will surely bring about the development of medical and surgical strategies to restore the normal biochemical and biomechanical function of articular cartilage. The development of imaging techniques that allow biomechanical and biochemical analysis therefore will be important for determining which patients might benefit from such therapy and for assessing the outcome (13). It is for these reasons that MR imaging techniques such as diffusion imaging (13,14), magnetization transfer imaging (15), and delayed anionic contrast material–enhanced MR imaging (16) hold great promise; these techniques allow more than the assessment of morphologic changes in tissue. Since there is no need for such detailed tissue analysis, given currently used methods of therapy, these more elegant imaging techniques are not yet clinically useful. However, it is important for the radiologist to be aware that MR imaging is the only technique that enables the noninvasive assessment of the molecular content of cartilage, which has great potential value as a surrogate marker of disease, allowing the avoidance of invasive and costly postsurgical tissue sampling and analysis (17).

In summary, the authors provide a useful review of MR imaging techniques for assessing articular cartilage and thereby reinforce the need to be ever vigilant in the detection and postsurgical follow-up of chondral derangement.

	References

Top References Reference

 

1. Ho YY, Stanley AJ, Hui JH, Wang SC. MR evaluation of the knee after autologous chondrocyte implantation: what radiologists need to know. RadioGraphics 2006;27:207–222.
2. Disler DG, McCauley TR, Kelman CG, et al. Fat-suppressed three-dimensional spoiled gradient-echo MR imaging of hyaline cartilage defects in the knee: comparison with standard MR imaging and arthroscopy. AJR Am J Roentgenol 1996;167: 127–132.[Abstract/Free Full Text]
3. Curl WW, Krome J, Gordon ES, Rushing J, Smith BP, Poehling CG. Cartilage injuries: a review of 31,516 knee arthroscopies. Arthroscopy 1997;13: 456–460.[Medline]
4. McCauley TR, Disler DG. State of the art: MR imaging of articular cartilage. Radiology 1998;209: 629–640.[Free Full Text]
5. Disler DG, Peters TL, Muscoreil SJ, et al. Fat-suppressed spoiled GRASS imaging of knee hyaline cartilage: technique optimization and comparison with conventional MR imaging. AJR Am J Roentgenol 1994;163:887–892.[Abstract/Free Full Text]
6. Rubenstein JD, Li JG, Majumdar S, Henkelman RM. Image resolution and signal-to-noise ratio requirements for MR imaging of degenerative cartilage. AJR Am J Roentgenol 1997;169:1089–1096.[Abstract/Free Full Text]
7. Potter HG, Linklater JM, Allen AA, Hannafin JA, Haas SB. Magnetic resonance imaging of articular cartilage in the knee: an evaluation with use of fast-spin-echo imaging. J Bone Joint Surg Am 1998;80:1276–1284.[Abstract/Free Full Text]
8. Bredella MA, Tirman PF, Peterfy CG, et al. Accuracy of T2-weighted fast spin-echo MR imaging with fat saturation in detecting cartilage defects in the knee: comparison with arthroscopy in 130 patients. AJR Am J Roentgenol 1999;172:1073–1080.[Abstract/Free Full Text]
9. Recht MP, Piraino DW, Paletta GA, Schils JP, Belhobek GH. Accuracy of fat-suppressed three-dimensional spoiled gradient-echo FLASH MR imaging in the detection of patellofemoral articular cartilage abnormalities. Radiology 1996;198:209–212.[Abstract/Free Full Text]
10. Buckwalter JA, Mow VC. Cartilage repair in osteoarthritis. In: Moskowitz RW, Howell DS, Goldberg VM, Mankin HJ, eds. Osteoarthritis. 2nd ed. Philadelphia, Pa: Saunders, 1992; 71–107.
11. Alparslan L, Winalski CS, Boutin RD, Minas T. Postoperative magnetic resonance imaging of articular cartilage repair. Semin Musculoskelet Radiol 2001;5:345–363.[CrossRef][Medline]
12. Peyron JG, Altman RD. The epidemiology of osteoarthritis. In: Moskowitz RW, Howell DS, Goldberg VM, Mankin HJ, eds. Osteoarthritis. 2nd ed. Philadelphia, Pa: Saunders, 1992; 15–37.
13. Wayne JS, Kraft KA, Shields KJ, Yin C, Owen JR, Disler DG. MR imaging of normal and matrix-depleted cartilage: correlation with biomechanical function and biochemical composition. Radiology 2003;228:493–499.[Abstract/Free Full Text]
14. Xia Y, Farquhar T, Burton WN, Ray E, Jelinski LW. Diffusion and relaxation mapping of cartilage-bone plugs and excised disks using microscopic magnetic resonance imaging. Magn Reson Med 1994;31:273–282.[Medline]
15. Gray ML, Burstein D, Lesperance LM, Gehrke L. Magnetization transfer in cartilage and its constituent macromolecules. Magn Reson Med 1995; 34:319–325.[Medline]
16. Bashir A, Gray M, Boutin RD, Burstein D. Glycosaminoglycan in articular cartilage: in vivo assessment with delayed Gd(DTPA)(2-)-enhanced MR imaging. Radiology 1997;205:551–558.[Abstract/Free Full Text]
17. Peterfy CG. Role of MR imaging in clinical research studies. Semin Musculoskelet Radiol 2001; 5:365–378.[CrossRef][Medline]

Authors’ Response

Department of Diagnostic Imaging, National University Hospital of Singapore, Singapore

We appreciate Dr Disler’s complimentary comments and we agree with his enthusiasm for MR in investigating cartilage derangement and assessing the posttherapeutic response. We concur with Dr Disler’s report that MR imaging with a three-dimensional fat-suppressed spoiled gradient-recalled echo sequence is accurate and reliable for the assessment of articular cartilage derangement (1). In our protocol, such a sequence is applied after direct arthrography, and we have found it particularly useful.

We also share in his excitement that MR has the potential to noninvasively help identify markers of cartilage diseases at the molecular level.

Thank you once again for giving us this opportunity to publish in RadioGraphics.

	Reference

Top References Reference

 

1. Disler DG. Fat-suppressed three-dimensional spoiled gradient-recalled MR imaging: assessment of articular and physeal hyaline cartilage. AJR Am J Roentgenol 1997;169:1117–1123.[Abstract/Free Full Text]

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