Measuring Disease Progression in Osteoarthritis

Radiographs are a commonly used tool to assess disease progression in osteoarthritis (OA). However, it is not the preferred method of defining and following OA progression. While it is moderately responsive to change in terms of standardised response means (SRM), it is insensitive to change in cartilage measures. MRI offers a much better assessment, and OA features are much better targeted for defining and following the disease progression. Using MRI, cartilage volume/thickness loss predicts knee replacement and has similar levels of sensitivity to discriminate treatments in clinical trials. Cartilage defect is another target which was found to also be an independent predictor of some OA outcomes. In addition to cartilage, another MRI target for diagnosis and assessment of OA progression is subchondral bone alterations, especially bone marrow lesions (BMLs). BMLs independently predict OA outcomes including knee replacement and are sensitive to progression. Targeting of BMLs by bone remodelling agents demonstrates that the natural history of the disease could be diminished. MRI-detected effusion and synovitis are also promising targets of OA progression. In addition, alterations in these tissues are promising outcome measures for clinical trials. Newer MRI methods of cartilage quality assessment, including signal intensity on T1 images and dGEMRIC, have been proposed for assessing early cartilage loss. However, the requirement for a contrast agent with dGEMRIC precludes its widespread use on safety grounds. Another promising imaging modality for OA is ultrasound. However, this approach warrants further exploration as, although it has demonstrated a wide set of advantages over other imaging modalities, there are still major limitations. Evidence for use of ultrasound indices for assessing disease progression is limited. At present, this imaging modality may be better suited as a diagnostic and an explanatory tool within clinical practice rather than large-scale studies or clinical trials.