Slowing of radiographic joint space narrowing represents the only recommended imaging-based outcome measure to assess structural disease progression in osteoarthritis (OA) clinical trials. There are no effective disease-modifying OA drugs. The ability of magnetic resonance (MR) to image structures within the knee and to visualize cartilage morphology and composition gives MR imaging a critical role in understanding the natural history of the disease and in the search for therapies. In this article, the roles and limitations of conventional radiography and MR imaging, focusing on knee OA, and the use of other modalities in clinical practice and OA research are described.
Key points
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Radiography is still the most widely used imaging modality for clinical management of patients with osteoarthritis.
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A reduction in the loss of joint space width represents the only end point recommended by the US Food and Drug Administration for structural disease progression in clinical trials.
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Because magnetic resonance (MR) imaging visualizes many structures within the knee and directly visualizes cartilage, it has a unique role in exploring the natural history of osteoarthritis and in the search for new therapies.
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The main MR imaging-based assessment approaches for osteoarthritis are semiquantitative, quantitative, and compositional.
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Ultrasonography may be useful to evaluate synovial disease in osteoarthritis, particularly in the hand.
Radiography
This review article focuses on osteoarthritis (OA) of the knee joint to summarize the current role and limitations of each imaging modality. The first modality to be described is radiography, which is the simplest, least expensive, and most widely used. It enables detection of OA-associated bony features such as osteophytes, subchondral sclerosis, and cysts ( Fig. 1 ). Radiography can also determine joint space width (JSW), which is a surrogate for cartilage thickness and meniscal integrity in knees, but precise measurement of each of these articular structures is not possible with conventional radiograph-based methods. Despite this limitation, slowing of radiographically detected joint space narrowing (JSN) is the only structural end point approved by the US Food and Drug Administration (FDA) to show efficacy of disease-modifying OA drugs in phase 3 clinical trials. OA is radiographically defined by the presence of marginal osteophytes. Progression of JSN is the most commonly used criterion for the assessment of structural OA progression, and the total loss of JSW (bone-on-bone appearance) is one of the indicators for joint replacement.
