Septic arthritis

Definition and Epidemiology

• Septic arthritis is the infection of a joint, typically caused by bacteria, but can also be due to fungi or viruses.
• Commonly affects large joints like the knee and hip, but any joint can be involved.
• Higher risk in individuals with joint prostheses, rheumatoid arthritis, recent joint surgery, and immunocompromised states.

Pathophysiology

• Most commonly caused by Staphylococcus aureus, but other bacteria like Streptococci, and in sexually active individuals, Neisseria gonorrhoeae, can also cause infection.
• The infection can reach the joint through the bloodstream, from a nearby infection, or directly through trauma or surgical procedures.
• Bacterial toxins and the body’s inflammatory response lead to joint damage.

Clinical Features

• Rapid onset of severe joint pain, swelling, redness, and warmth.
• Reduced range of motion in the affected joint.
• Fever and systemic symptoms may be present.
• In gonococcal arthritis, may be associated with dermatitis and tenosynovitis.

Diagnosis

• High clinical suspicion based on symptoms and patient history.
• Joint aspiration is crucial for diagnosis, showing purulent synovial fluid, high leukocyte count, and positive culture.
• Blood cultures and other investigations to identify the source of infection.
• Imaging (X-ray, MRI, ultrasound) to assess joint damage.

Management

• Immediate empirical antibiotic therapy, later adjusted based on culture results.
• Antibiotics often given intravenously initially, followed by oral antibiotics.
• Duration of treatment varies but typically lasts for several weeks.
• Surgical drainage may be necessary in some cases, especially if there is a large effusion or if the infection is in a prosthetic joint.

Complications

• Rapid joint destruction and irreversible damage if not treated promptly.
• Potential for osteomyelitis and systemic spread of infection.
• Septic shock in severe cases.