Intra-articular corticosteroid injections deliver high local concentrations of anti-inflammatory agents directly to the joint space, minimizing systemic exposure. Corticosteroids inhibit phospholipase A2, blocking the arachidonic acid cascade and reducing prostaglandin, leukotriene, and cytokine production. This decreases synovial inflammation, effusion, and pain. Commonly used agents vary by solubility and duration: triamcinolone acetonide (intermediate-acting, 4-6 weeks), methylprednisolone acetate (intermediate, 4-8 weeks), and betamethasone sodium phosphate/acetate (rapid onset with sustained effect). Hyaluronic acid viscosupplementation replaces degraded synovial fluid in osteoarthritis, improving joint lubrication and shock absorption. Evidence supports corticosteroid injection for inflammatory arthropathies, adhesive capsulitis, bursitis, and tendinopathy, though repeated injections may accelerate cartilage degeneration.