Inflammation in osteoarthritis: the latest progress and ongoing challenges

PURPOSE OF REVIEW: The understanding of inflammation in osteoarthritis is rapidly evolving. This review highlights important basic science, mechanistic, and clinical findings since 2020 that underscore the current notion of osteoarthritis as an inflammatory disease. RECENT FINDINGS: There exists a disconnect between clinical radiographic findings and patient symptoms in osteoarthritis. Inflammation, in particular synovitis, has been put forward as a potential explanation for this disconnect. New findings have shed light on the temporal dynamics and activation states of joint-resident or systemically derived immune cell populations, notably macrophages, that participate in the inflammatory response. The intricate crosstalk in which they engage may underpin disparate pain and symptoms in patients, for instance during osteoarthritis flares. The role of biological and environmental factors such as exercise, age, and diet, have been the subject of recent studies for their protective or destructive roles in osteoarthritis inflammation. Despite these advances, no disease-modifying osteoarthritis treatments targeting inflammation have emerged. SUMMARY: Osteoarthritis is a debilitating chronic disease that manifests with widely varying symptomatology. Inflammation is now appreciated as a key pathophysiological process in osteoarthritis, but there remain considerable gaps in our understanding of its role in disease progression and how best to target the inflammatory response for therapeutic interventions.