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Septic arthritis is a suppurative bacterial infection of a synovial joint. Most commonly, joint infection occurs through hematogenous seeding of the synovium. Less often, joint infection results from joint aspiration or injection, penetrating trauma, or extension into the joint space from adjacent osteomyelitis. Bacterial septic arthritis is considered a medical emergency because permanent destruction of a joint can occur from the resulting inflammatory response to infection. In particular, bacterial invasion of a joint causes activation of a potent host immune inflammatory response. This results in the production of proteolytic enzymes that destroy the extracellular cartilage matrix of the affected joint.
Populations at increased risk for septic arthritis include individuals older than 60 years of age, those with osteoarthritis or rheumatoid arthritis, and those on corticosteroids or with human immunodeficiency virus (HIV)/acquired immunodeficiency syndrome (AIDS). In particular, individuals with rheumatoid arthritis have a 10-fold greater incidence of septic arthritis than the general population. Individuals with diabetes mellitus or other chronic medical conditions such as renal disease, cirrhosis, granulomatous disease, or malignancy are also at increased risk.
Septic arthritis typically presents with erythema, swelling, tenderness and warmth about the affected joint (Figure 21.1). The patient will display decreased and painful range of motion of the affected joint (Table 21.1). Signs and symptoms of inflammation may be less pronounced in those who are immunosuppressed.