SAN FRANCISCO - The Centers for Disease Control has predicted that in the next 20 years nearly 60 million people in the United States will seek relief from osteoarthritis and other articular cartilage diseases. As a result, the imaging community will have the chance to become an integral part of the treatment process.
"Osteoarthritis used to be one of the most boring diseases for us as radiologists because there was no opportunity for differential diagnosis. It was just one of those things that we had to deal with as a bone or general radiologist. This is changing as we speak. I think this is going to be the most exciting area in musculoskeletal radiology in the next 10 years," said Dr. Philipp Lang in a presentation June 20 at "MR Advances in Musculoskeletal Imaging and Radiology," a conference hosted by Stanford University Medical Center.
The driving force on this new avenue of opportunity for radiology has been the advancements in treatment options, said Lang, an assistant professor of radiology at Stanford. In 1990, patients had two main choices -- pain management or total joint replacement -- for addressing their discomfort.
But the last decade has seen the advent of powerful nonsteroidal anti-inflammatory drugs such as Celebrex and Vioxx, and surgical procedures, such as ostechondral allograft transfer system (OATS) and autologous chondrocyte transplant.
When it comes to staging these diseases for surgery, as well as following up the progress of the disease, MRI will be the best bet because of its ability to detect abnormalities early, Lang said.
At Stanford, a three-fold staging system has been developed to grade cartilage lesions. Lang and his group have just completed a retrospective, longitudinal study based on that staging system. Between 1993 and 1998, the records of 43 patients who underwent MR for cartilage abnormalities were studied. Scans were performed on routine 1.5-tesla scanners using a circumferential knee coil. Knee MR scans included sagittal fast spin-echo for cartilage-sensitive sequences, with fat saturation and 4-mm slice thickness.
Nearly two years after diagnosis and treatment, the results showed osteoarthritic disease had progressed to a higher grade in around 40% of patients, Lang said. On the other hand, no particular grade of lesion showed a greater tendency toward progression.
"This is after a follow-up of 1.8 years," he added. "If you compare this to conventional radiography, it takes many years before you see this kind of progression."
What gives MRI this edge are image processing techniques for evaluating cartilage loss, such as driven equilibrium Fourier transform (DEFT), which can be used to generate a map of cartilage thickness.
"Repeated measurements of patellar cartilage have been performed using this technique and it has been reported that on average 75.1% of all test pixels could be attributed to the same cartilage thickness interval by image analysis; 14.8% deviated by one interval; 6.6% by two intervals; and 3.5% by more than two intervals, indicating that cartilage thickness can be determined with high precision in vivo," Lang wrote in the conference syllabus, summarizing earlier study findings (J Orthop Res, Nov. 1997, Vol.15:6, pp.808-813).
However, one obstacle radiologists will face is skepticism in the orthopedics community as to whether MRI is a worthwhile modality for tracking osteoarthritis. Previously published literature showed MRI to have "abysmally bad sensitivity," Lang said.
Japanese researchers at Omura Municipal Establishment Hospital tested fast spin-echo MRI for detecting articular cartilage abnormality in osteoarthrosis of the knee, and determined that the modality had a sensitivity of 60.5% (Acta Radiol, March 1998, Vol.39:2, pp.120-125).
But Lang pointed out that those images were obtained using a low-field strength of 0.5-tesla. Other studies using a 1.5-tesla scanner have produced sensitivity rates from 89% to 92%, he added.
Still, surgeons, rheumatologists and other referring physicians will take some convincing.
"You'll be shocked when talking to orthopedists about how little knowledge there is out there about how good (MRI) is," Lang said. "With this technique, we as radiologists will be able to predict much more accurately what is going to happen with patients, and treatment will be based more and more on MRI recommendations."
By Shalmali Pal
AuntMinnie.com staff writer
June 23, 2000
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