DESTIN, FLA. — While MRI applications for evaluating osteoarthritis are currently limited, methods are being developed that will eventually enable quantitative assessment of the disease, according to Charles Peterfy, M.D., who spoke at a rheumatology meeting sponsored by Virginia Commonwealth University.
Current applications of MRI including its use to noninvasively guide cartilage repair. The high-resolution delineation of cartilage defects and abnormalities that MRI provides can help guide patient selection and preoperative planning. Postoperatively, MRI can be used to monitor the integrity and durability of the repair, said Dr. Peterfy, a radiologist specializing in musculoskeletal imaging and the chief medical officer of Synarc Inc., a radiology services company.
In addition, newer applications of MRI “allow us, for the first time, to visualize all of the components of the joint simultaneously,” he said. MRI can be used to visualize menisci, ligaments, synovitis, bone abnormalities, and periarticular abnormalities.
The result is that instead of assessing in an isolated fashion any one aspect of the disease's effect, physicians can analyze the whole joint. This approach is facilitated by the development of a semiquantitative scoring system for evaluating osteoarthritis using MRI. Dr. Peterfy was one of the authors of the Whole-Organ Magnetic Resonance Imaging Score (WORMS) method for assessing the structural integrity of the knee.
The WORMS method can be used to evaluate independent articular features including: cartilage signal and morphology, subarticular bone marrow abnormality, subarticular cysts, subarticular bone attrition, marginal osteophytes, medial and lateral meniscal integrity, anterior and posterior cruciate ligament integrity, medial and lateral collateral ligament integrity, synovitis, loose bodies, and periarticular cysts/bursae.
One the most promising areas of MRI research centers around bone marrow edema-like abnormalities. These edema-like signals may represent pulsion of joint fluid through breaks in the articular surface, localized inflammation, or changes associated with trauma due to biomechanical incompetence of the articular surface.
Whatever their etiology, bone marrow edema abnormalities behave like microtrauma, said Dr. Peterfy, who is also on the advisory board for MagneVu, the maker of portable MRI units.
Using a WORMS-like evaluation method, bone marrow edema abnormalities have been shown to correlate with pain and collagen II breakdown and even to predict joint space narrowing on x-ray, and cartilage narrowing. In addition, these findings have been shown to progress very rapidly—even in as few as 3 months.
In a study of 378 patients treated at several clinical centers worldwide, 82% had bone marrow abnormalities on MRI at baseline (as scored on the bone marrow subscale of WORMS), said Dr. Peterfy. The patients were followed for 3 months, at which time, 34% of those with baseline abnormalities had progression of these abnormalities. This change correlated well with urine concentrations of collagen type II degradation product (CTXII), which results from cartilage breakdown (Arthritis Rheum. 2005 [in press]).