It is unclear which tissue should be the focus for clinical trials. Symptom-modifying trials do not require MRI, and—for structure modifying trials—the plethora of MRI OA pathology will need to be validated against meaningful clinical endpoints. Until the most important feature or features seen on MRI are defined, most studies should evaluate multiple features.
It has been difficult to accurately quantify noncartilage features of the knee, although image analysis methods are being explored. However, the need to understand the whole organ pathology has driven development of a number of semiquantitative scores.8 All divide the knee into multiple anatomical compartments and measure multiple features on variable ordinal scales within each compartment. Further development will be required in the use of all these scales, including the best ways to aggregate scores across compartments.
MRI in OA Clinical Practice
At present, the role for MRI in OA clinical practice seems small. Osteoarthritis represents a syndrome of pain, functional loss, and reduced quality of life. Currently, the most important messages from MRI studies are the concepts we have learned. The whole organ nature was emphasized above, but MRI has also given us new clues on the sources of pain and a new understanding of the structural progression in OA. The most likely sources of pain appear to be the synovium and subchondral bone; both of these tissues are innervated, which adds validity to their importance. Bone marrow lesions and cartilage defects are associated with subsequent cartilage loss. The first real clinical use of MRI may be identifying patient subsets for targeted therapies, once these are available. Using MRI to determine meniscal pathology in the OA knee does not appear warranted. The major reason for doing so is if arthroscopy and debridement are required—a decision that should be made on clinical grounds of mechanical locking of the knee, not meniscal abnormality on MRI.
Conclusions
MRI is dramatically increasing our understanding of structural pathology in arthritis. In RA, we understand the links between inflammation and damage and can understand therapeutic response. MRI has provided excellent proof-of-concept tools that may move into clinical use. In OA, we are beginning to appreciate the extent of whole-organ pathology and have better tools to quantitate pathology, but more work is required to demonstrate relevant targets with clinically meaningful endpoints. Changes in MRI technology—especially in eMRI—may improve our day-to-day management of arthritis.
Dr. Conaghan is professor of musculoskeletal medicine at the University of Leeds (U.K.) and a consultant rheumatologist at Leeds Teaching Hospitals NHS Trust.
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