What have we learned about osteoarthritis from imaging?

Clinical and research imaging have been instrumental in shifting our understanding of osteoarthritis from a structural, cartilage-focused disorder to a whole-joint complex disease with biomechanical and inflammatory components. Initially, the only osteoarthritis imaging modality was x-ray; therefore, the focal point of diagnosis was the bone: osteophytes, sclerosis, but most importantly, the joint space narrowing. Soft-tissue visualization, dynamic imaging, and advanced image analysis techniques have shown that numerous other joint tissues and features are associated with osteoarthritis progression and symptom severity, and many of them appear before joint space narrowing is detectable. Inflammatory features like bone marrow lesions and effusion-synovitis have emerged as promising targets for intervention. The exact pathogenesis of and structure-modifying treatments for osteoarthritis remain elusive. Clinical and research imaging modalities are essential tools for monitoring the initiation and progression of the disease, identifying targets for intervention, and quantifying the impact of new treatments.