Septic arthritis: a review

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Septic arthritis is generally monoarticular and involves either the knee or hip. The hip is more commonly affected in children whereas the knee is in adults. Early intervention is imperative for preserving the affected joint.

Risk factors include age > 80, DM, RA/OA/Gout, HIV, unprotected sex, IV drug abuse, and joint replacement. Presenting symptoms may include fever (60%), pain, swelling, warmth, and erythema of the joint.

The most common pathogen is Staph Aureus. Gonorrhea should be suspected in young sexually active patients. Pseudomonas may be involved if the patient has a history of IV drug abuse. Salmonella is a common cause in patients with sickle cell disease.

Joint replacements place patients at an elevated risk for septic arthritis. < 3 months postop S. Aureus is the most common agent, 3-24 months postop Staph epidermidis, and > 24 months post replacement hematogenous infection in the most likely cause.

Radiographs, ultrasound, and MRI may aid in diagnosis, but joint aspiration is necessary to determine the offending agent and antibiotic susceptibility. Greater than 50,000 WBC is considered diagnostic for septic arthritis. ESR, CRP, and WBC may be followed to monitor tx.

The saline load test is utilized to see if a wound communicates with a joint and may be the source of the patient’s septic arthritis. 155 mL of saline is needed to achieve 95% sensitivity, 175 mL for 99% sensitivity.

Treatment: drainage, irrigation, debridement (if necessary), and IV antibiotics based on culture sensitivity. Physical therapy should be added to preserve joint function and prevent muscle atrophy.

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