Septic arthritis
Septic arthritis is bacterial infection of a joint, most often Staphylococcus aureus seeding the knee hematogenously, and is a medical and surgical emergency diagnosed by expeditious arthrocentesis showing a synovial leukocyte count generally above 50,000/microliter. Treatment combines empiric intravenous antibiotics such as vancomycin plus ceftriaxone with urgent joint drainage, since delayed source control destroys cartilage within days.
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What this article covers
- Overview
A medical and surgical emergency: septic arthritis is bacterial infection within a joint space that can destroy articular cartilage within days if drainage and antibiotics are delayed.
- Epidemiology
Staphylococcus aureus causes about 40% of nongonococcal bacterial arthritis, followed by streptococci (about 30%) and gram-negative bacilli (about 20%); gram-positive cocci overall account for roughly 75% of nongonococcal cases.
- Risk factors
Preexisting arthritis or joint damage (rheumatoid arthritis or osteoarthritis).
- Pathophysiology
Hematogenous seeding is the dominant route: bacteria reach the richly vascular, non-basement-membraned synovium from a distant bacteremic source and proliferate within the closed joint space.
- Clinical features
Acute pain, swelling, warmth, and erythema of the affected joint, accompanied by fever and constitutional symptoms, in a single joint (monoarticular in the majority of native-joint cases).
- Differential diagnosis
Crystal arthropathy (gout or pseudogout): acute monoarticular pain with inflammatory synovial fluid, but crystals do not exclude concomitant infection, so aspiration is still required; see gout and pseudogout.
- Diagnosis
Septic arthritis is confirmed by arthrocentesis: synovial fluid Gram stain, culture, leukocyte count, and crystal analysis are the clinching basis for diagnosis; a synovial leukocyte count generally…
- Management
First, obtain blood and synovial fluid cultures, then start empiric intravenous antibiotics without waiting for results, because delay directly worsens cartilage destruction and outcome: vancomycin…
- Complications
Irreversible cartilage destruction and secondary osteoarthritis from delayed drainage or antibiotics, the principal driver of permanent joint dysfunction.
- Prognosis
Time to drainage and antibiotics is the dominant modifiable prognostic factor, since cartilage loss begins within days of untreated infection.
- Prevention
Arthrocentesis within 24 hours for any acute monoarticular inflammatory joint in a patient with preexisting arthritis, a prosthetic joint, or an immunocompromised state, rather than presuming a…
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