Osteoarthritis (OA) pain represents a major unmet medical need. A recent American College of Rheumatology task force concluded that pain is the most common symptom of patients with rheumatic disorders, including OA, and pain is the major reason for seeking medical care . Available pharmacologic approaches include NSAIDs or analgesics, and intra-articular viscosupplementation or steroids, which can alleviate mild-to-moderate pain in OA. Treatment of severe OA pain remains inadequate and pain is a major reason for seeking surgical intervention.
Joint pain in OA is typically activity-related, often triggered by a specific activity (for instance, climbing stairs triggers knee pain) and relieved by rest. With more advanced disease, pain can also occur in rest, and is often described as not well localized, dull, and punctuated by episodes of intense pain . In addition, patients may experience symptoms that are characteristic of neuropathic pain, such as burning or “pins and needles” .
For epidemiological purposes, OA is defined as radiographic OA (joint space narrowing due to cartilage loss, subchondral bone sclerosis, and osteophytes). Population studies indicate discordance between severity of radiographic changes and severity of pain . This has been mostly studied for the knee. Other imaging techniques such as magnetic resonance imaging (MRI) have related structural changes including bone marrow lesions, sub-articular bone attrition, synovitis and effusion to knee pain, and there is ample evidence that bone marrow lesions are associated with knee pain, although the mechanism is unclear .
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