Septic arthritis is an uncommon but potentially destructive joint infection, most often caused by Staphylococcus aureus. It typically presents as acute monoarthritis, most frequently involving the knee, but can also affect other large joints or occur in a polyarticular form. Pathogenesis involves bacterial seeding of the synovium, leading to rapid inflammation, cartilage destruction, and potential systemic complications. Risk factors include rheumatoid arthritis, diabetes, immunosuppression, skin disease, prior joint pathology, and injection drug use, though cases may arise without predisposing conditions. Diagnosis relies on a high index of suspicion, supported by synovial fluid analysis, cultures, and clinical assessment. Early recognition and prompt treatment are essential to preserve joint function and reduce morbidity and mortality.